Merge pull request #6456 from libgit2/ethomson/sha256_experimental

SHA256: more SHA256 support

.github/workflows/main.yml

@@ -232,7 +232,7 @@ jobs:
           env:
             CC: clang
             CMAKE_GENERATOR: Ninja
-            CMAKE_OPTIONS: -DUSE_HTTPS=OpenSSL -DDEPRECATE_HARD=ON -DUSE_LEAK_CHECKER=valgrind -DUSE_GSSAPI=ON -DUSE_SSH=ON
+            CMAKE_OPTIONS: -DUSE_HTTPS=OpenSSL -DDEPRECATE_HARD=ON -DUSE_LEAK_CHECKER=valgrind -DUSE_GSSAPI=ON -DUSE_SSH=ON -DEXPERIMENTAL_SHA256=ON
           os: ubuntu-latest
         - name: "macOS (SHA256)"
           id: macos

.github/workflows/nightly.yml

@@ -265,10 +265,40 @@ jobs:
             RUN_INVASIVE_TESTS: true
             SKIP_PROXY_TESTS: true
           os: ubuntu-latest
+
+        # Experimental: SHA256 support
+        - name: "Linux (SHA256, Xenial, Clang, OpenSSL)"
+          id: xenial-clang-openssl
+          container:
+            name: xenial
+          env:
+            CC: clang
+            CMAKE_GENERATOR: Ninja
+            CMAKE_OPTIONS: -DUSE_HTTPS=OpenSSL -DDEPRECATE_HARD=ON -DUSE_LEAK_CHECKER=valgrind -DUSE_GSSAPI=ON -DUSE_SSH=ON
+          os: ubuntu-latest
+        - name: "macOS (SHA256)"
+          id: macos
+          os: macos-10.15
+          env:
+            CC: clang
+            CMAKE_OPTIONS: -DREGEX_BACKEND=regcomp_l -DDEPRECATE_HARD=ON -DUSE_LEAK_CHECKER=leaks -DUSE_GSSAPI=ON -DEXPERIMENTAL_SHA256=ON
+            PKG_CONFIG_PATH: /usr/local/opt/openssl/lib/pkgconfig
+            SKIP_SSH_TESTS: true
+            SKIP_NEGOTIATE_TESTS: true
+          setup-script: osx
+        - name: "Windows (SHA256, amd64, Visual Studio)"
+          id: windows-amd64-vs
+          os: windows-2019
+          env:
+            ARCH: amd64
+            CMAKE_GENERATOR: Visual Studio 16 2019
+            CMAKE_OPTIONS: -A x64 -DWIN32_LEAKCHECK=ON -DDEPRECATE_HARD=ON -DEXPERIMENTAL_SHA256=ON
+            SKIP_SSH_TESTS: true
+            SKIP_NEGOTIATE_TESTS: true
       fail-fast: false
-    name: "Build ${{ matrix.platform.name }}"
     env: ${{ matrix.platform.env }}
     runs-on: ${{ matrix.platform.os }}
+    name: "Build ${{ matrix.platform.name }}"
     steps:
     - name: Check out repository
       uses: actions/checkout@v3

ci/docker/xenial

@@ -7,11 +7,13 @@ RUN apt-get update && \
         clang \
         cmake \
         curl \
+	gettext \
         gcc \
-        git \
         krb5-user \
         libcurl4-gnutls-dev \
+	libexpat1-dev \
         libgcrypt20-dev \
+	libintl-perl \
         libkrb5-dev \
         libpcre3-dev \
         libssl-dev \
@@ -28,7 +30,17 @@ RUN apt-get update && \
         && \
     rm -rf /var/lib/apt/lists/*
 
-FROM apt AS mbedtls
+FROM apt AS git
+RUN cd /tmp && \
+    curl --location --silent --show-error https://github.com/git/git/archive/refs/tags/v2.39.1.tar.gz | \
+        tar -xz && \
+    cd git-2.39.1 && \
+    make && \
+    make prefix=/usr install && \
+    cd .. && \
+    rm -rf git-2.39.1
+
+FROM git AS mbedtls
 RUN cd /tmp && \
     curl --location --silent --show-error https://github.com/Mbed-TLS/mbedtls/archive/refs/tags/mbedtls-2.16.2.tar.gz | \
         tar -xz && \

ci/test.sh

@@ -37,6 +37,11 @@ cleanup() {
 		kill $GIT_NAMESPACE_PID
 	fi
 
+	if [ ! -z "$GIT_SHA256_PID" ]; then
+		echo "Stopping git daemon (sha256)..."
+		kill $GIT_SHA256_PID
+	fi
+
 	if [ ! -z "$PROXY_BASIC_PID" ]; then
 		echo "Stopping proxy (Basic)..."
 		kill $PROXY_BASIC_PID
@@ -145,6 +150,12 @@ if [ -z "$SKIP_GITDAEMON_TESTS" ]; then
 	cp -R "${SOURCE_DIR}/tests/resources/namespace.git" "${GIT_NAMESPACE_DIR}/namespace.git"
 	GIT_NAMESPACE="name1" git daemon --listen=localhost --port=9419 --export-all --enable=receive-pack --base-path="${GIT_NAMESPACE_DIR}" "${GIT_NAMESPACE_DIR}" &
 	GIT_NAMESPACE_PID=$!
+
+	echo "Starting git daemon (sha256)..."
+	GIT_SHA256_DIR=`mktemp -d ${TMPDIR}/git_sha256.XXXXXXXX`
+	cp -R "${SOURCE_DIR}/tests/resources/testrepo_256.git" "${GIT_SHA256_DIR}/testrepo_256.git"
+	git daemon --listen=localhost --port=9420 --export-all --enable=receive-pack --base-path="${GIT_SHA256_DIR}" "${GIT_SHA256_DIR}" &
+	GIT_SHA256_PID=$!
 fi
 
 if [ -z "$SKIP_PROXY_TESTS" ]; then
@@ -291,6 +302,14 @@ if [ -z "$SKIP_GITDAEMON_TESTS" ]; then
 	run_test gitdaemon_namespace
 	unset GITTEST_REMOTE_URL
 	unset GITTEST_REMOTE_BRANCH
+
+	echo ""
+	echo "Running gitdaemon (sha256) tests"
+	echo ""
+
+	export GITTEST_REMOTE_URL="git://localhost:9420/testrepo_256.git"
+	run_test gitdaemon_sha256
+	unset GITTEST_REMOTE_URL
 fi
 
 if [ -z "$SKIP_PROXY_TESTS" ]; then

cmake/ExperimentalFeatures.cmake

@@ -13,7 +13,7 @@ if(EXPERIMENTAL_SHA256)
 
 	set(EXPERIMENTAL 1)
 	set(GIT_EXPERIMENTAL_SHA256 1)
-	add_compile_definitions(GIT_EXPERIMENTAL_SHA256)
+	add_definitions(-DGIT_EXPERIMENTAL_SHA256=1)
 else()
 	add_feature_info("SHA256 API" OFF "experimental SHA256 APIs")
 endif()

examples/index-pack.c

@@ -28,11 +28,18 @@ int lg2_index_pack(git_repository *repo, int argc, char **argv)
 		return EXIT_FAILURE;
 	}
 
-	if (git_indexer_new(&idx, ".", 0, NULL, NULL) < 0) {
+#ifdef GIT_EXPERIMENTAL_SHA256
+	error = git_indexer_new(&idx, ".", git_repository_oid_type(repo), NULL);
+#else
+	error = git_indexer_new(&idx, ".", 0, NULL, NULL);
+#endif
+
+	if (error < 0) {
 		puts("bad idx");
 		return -1;
 	}
 
+
 	if ((fd = open(argv[1], 0)) < 0) {
 		perror("open");
 		return -1;

fuzzers/objects_fuzzer.c

@@ -39,7 +39,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 	 * to do.
 	 */
 	for (i = 0; i < ARRAY_SIZE(types); i++) {
-		if (git_object__from_raw(&object, (const char *) data, size, types[i]) < 0)
+		if (git_object__from_raw(&object, (const char *) data, size, types[i], GIT_OID_SHA1) < 0)
 			continue;
 		git_object_free(object);
 		object = NULL;

fuzzers/packfile_fuzzer.c

@@ -67,6 +67,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 	git_str path = GIT_STR_INIT;
 	git_oid oid;
 	bool append_hash = false;
+	int error;
 
 	if (size == 0)
 		return 0;
@@ -82,7 +83,13 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 		abort();
 	}
 
-	if (git_indexer_new(&indexer, ".", 0, odb, NULL) < 0) {
+#ifdef GIT_EXPERIMENTAL_SHA256
+	error = git_indexer_new(&indexer, ".", GIT_OID_SHA1, NULL);
+#else
+	error = git_indexer_new(&indexer, ".", 0, odb, NULL);
+#endif
+
+	if (error < 0) {
 		fprintf(stderr, "Failed to create the indexer: %s\n",
 			git_error_last()->message);
 		abort();

include/git2/indexer.h

@@ -62,6 +62,19 @@ typedef int GIT_CALLBACK(git_indexer_progress_cb)(const git_indexer_progress *st
 typedef struct git_indexer_options {
 	unsigned int version;
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	/** permissions to use creating packfile or 0 for defaults */
+	unsigned int mode;
+
+	/**
+	 * object database from which to read base objects when
+	 * fixing thin packs. This can be NULL if there are no thin
+	 * packs; if a thin pack is encountered, an error will be
+	 * returned if there are bases missing.
+	 */
+	git_odb *odb;
+#endif
+
 	/** progress_cb function to call with progress information */
 	git_indexer_progress_cb progress_cb;
 
@@ -87,6 +100,21 @@ GIT_EXTERN(int) git_indexer_options_init(
 	git_indexer_options *opts,
 	unsigned int version);
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+/**
+ * Create a new indexer instance
+ *
+ * @param out where to store the indexer instance
+ * @param path to the directory where the packfile should be stored
+ * @param oid_type the oid type to use for objects
+ * @return 0 or an error code.
+ */
+GIT_EXTERN(int) git_indexer_new(
+		git_indexer **out,
+		const char *path,
+		git_oid_t oid_type,
+		git_indexer_options *opts);
+#else
 /**
  * Create a new indexer instance
  *
@@ -106,6 +134,7 @@ GIT_EXTERN(int) git_indexer_new(
 		unsigned int mode,
 		git_odb *odb,
 		git_indexer_options *opts);
+#endif
 
 /**
  * Add data to the indexer

include/git2/object.h

@@ -225,6 +225,7 @@ GIT_EXTERN(int) git_object_peel(
  */
 GIT_EXTERN(int) git_object_dup(git_object **dest, git_object *source);
 
+#ifdef GIT_EXPERIMENTAL_SHA256
 /**
  * Analyzes a buffer of raw object content and determines its validity.
  * Tree, commit, and tag objects will be parsed and ensured that they
@@ -238,14 +239,39 @@ GIT_EXTERN(int) git_object_dup(git_object **dest, git_object *source);
  * @param valid Output pointer to set with validity of the object content
  * @param buf The contents to validate
  * @param len The length of the buffer
- * @param type The type of the object in the buffer
+ * @param object_type The type of the object in the buffer
+ * @param oid_type The object ID type for the OIDs in the given buffer
  * @return 0 on success or an error code
  */
 GIT_EXTERN(int) git_object_rawcontent_is_valid(
 	int *valid,
 	const char *buf,
 	size_t len,
-	git_object_t type);
+	git_object_t object_type,
+	git_oid_t oid_type);
+#else
+/**
+ * Analyzes a buffer of raw object content and determines its validity.
+ * Tree, commit, and tag objects will be parsed and ensured that they
+ * are valid, parseable content.  (Blobs are always valid by definition.)
+ * An error message will be set with an informative message if the object
+ * is not valid.
+ *
+ * @warning This function is experimental and its signature may change in
+ * the future.
+ *
+ * @param valid Output pointer to set with validity of the object content
+ * @param buf The contents to validate
+ * @param len The length of the buffer
+ * @param object_type The type of the object in the buffer
+ * @return 0 on success or an error code
+ */
+GIT_EXTERN(int) git_object_rawcontent_is_valid(
+	int *valid,
+	const char *buf,
+	size_t len,
+	git_object_t object_type);
+#endif
 
 /** @} */
 GIT_END_DECL

include/git2/odb_backend.h

@@ -24,6 +24,26 @@ GIT_BEGIN_DECL
  * Constructors for in-box ODB backends.
  */
 
+/** Options for configuring a packfile object backend. */
+typedef struct {
+	unsigned int version; /**< version for the struct */
+
+	/**
+	 * Type of object IDs to use for this object database, or
+	 * 0 for default (currently SHA1).
+	 */
+	git_oid_t oid_type;
+} git_odb_backend_pack_options;
+
+/* The current version of the diff options structure */
+#define GIT_ODB_BACKEND_PACK_OPTIONS_VERSION 1
+
+/* Stack initializer for odb pack backend options.  Alternatively use
+ * `git_odb_backend_pack_options_init` programmatic initialization.
+ */
+#define GIT_ODB_BACKEND_PACK_OPTIONS_INIT \
+	{ GIT_ODB_BACKEND_PACK_OPTIONS_VERSION }
+
 /**
  * Create a backend for the packfiles.
  *
@@ -32,7 +52,38 @@ GIT_BEGIN_DECL
  *
  * @return 0 or an error code
  */
-GIT_EXTERN(int) git_odb_backend_pack(git_odb_backend **out, const char *objects_dir);
+#ifdef GIT_EXPERIMENTAL_SHA256
+GIT_EXTERN(int) git_odb_backend_pack(
+	git_odb_backend **out,
+	const char *objects_dir,
+	const git_odb_backend_pack_options *opts);
+#else
+GIT_EXTERN(int) git_odb_backend_pack(
+	git_odb_backend **out,
+	const char *objects_dir);
+#endif
+
+/**
+ * Create a backend out of a single packfile
+ *
+ * This can be useful for inspecting the contents of a single
+ * packfile.
+ *
+ * @param out location to store the odb backend pointer
+ * @param index_file path to the packfile's .idx file
+ *
+ * @return 0 or an error code
+ */
+#ifdef GIT_EXPERIMENTAL_SHA256
+GIT_EXTERN(int) git_odb_backend_one_pack(
+	git_odb_backend **out,
+	const char *index_file,
+	const git_odb_backend_pack_options *opts);
+#else
+GIT_EXTERN(int) git_odb_backend_one_pack(
+	git_odb_backend **out,
+	const char *index_file);
+#endif
 
 typedef enum {
 	GIT_ODB_BACKEND_LOOSE_FSYNC = (1 << 0)
@@ -100,19 +151,6 @@ GIT_EXTERN(int) git_odb_backend_loose(
 	unsigned int file_mode);
 #endif
 
-/**
- * Create a backend out of a single packfile
- *
- * This can be useful for inspecting the contents of a single
- * packfile.
- *
- * @param out location to store the odb backend pointer
- * @param index_file path to the packfile's .idx file
- *
- * @return 0 or an error code
- */
-GIT_EXTERN(int) git_odb_backend_one_pack(git_odb_backend **out, const char *index_file);
-
 /** Streaming mode */
 typedef enum {
 	GIT_STREAM_RDONLY = (1 << 1),

include/git2/repository.h

@@ -351,6 +351,15 @@ typedef struct {
 	 * pointing to this URL.
 	 */
 	const char *origin_url;
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	/**
+	 *
+	 * Type of object IDs to use for this repository, or 0 for
+	 * default (currently SHA1).
+	 */
+	git_oid_t oid_type;
+#endif
 } git_repository_init_options;
 
 #define GIT_REPOSITORY_INIT_OPTIONS_VERSION 1
@@ -949,6 +958,14 @@ GIT_EXTERN(int) git_repository_ident(const char **name, const char **email, cons
  */
 GIT_EXTERN(int) git_repository_set_ident(git_repository *repo, const char *name, const char *email);
 
+/**
+ * Gets the object type used by this repository.
+ *
+ * @param repo the repository
+ * @return the object id type
+ */
+GIT_EXTERN(git_oid_t) git_repository_oid_type(git_repository *repo);
+
 /** @} */
 GIT_END_DECL
 #endif

include/git2/sys/transport.h

@@ -57,6 +57,18 @@ struct git_transport {
 		unsigned int *capabilities,
 		git_transport *transport);
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	/**
+	 * Gets the object type for the remote repository.
+	 *
+	 * This function may be called after a successful call to
+	 * `connect()`.
+	 */
+	int GIT_CALLBACK(oid_type)(
+		git_oid_t *object_type,
+		git_transport *transport);
+#endif
+
 	/**
 	 * Get the list of available references in the remote repository.
 	 *

src/cli/cmd_hash_object.c

@@ -49,26 +49,37 @@ static void print_help(void)
 	cli_opt_help_fprint(stdout, opts);
 }
 
-static int hash_buf(git_odb *odb, git_str *buf, git_object_t type)
+static int hash_buf(
+	git_odb *odb,
+	git_str *buf,
+	git_object_t object_type,
+	git_oid_t oid_type)
 {
 	git_oid oid;
 
 	if (!literally) {
 		int valid = 0;
 
-		if (git_object_rawcontent_is_valid(&valid, buf->ptr, buf->size, type) < 0 || !valid)
+#ifdef GIT_EXPERIMENTAL_SHA256
+		if (git_object_rawcontent_is_valid(&valid, buf->ptr, buf->size, object_type, oid_type) < 0 || !valid)
+			return cli_error_git();
+#else
+		GIT_UNUSED(oid_type);
+
+		if (git_object_rawcontent_is_valid(&valid, buf->ptr, buf->size, object_type) < 0 || !valid)
 			return cli_error_git();
+#endif
 	}
 
 	if (write_object) {
-		if (git_odb_write(&oid, odb, buf->ptr, buf->size, type) < 0)
+		if (git_odb_write(&oid, odb, buf->ptr, buf->size, object_type) < 0)
 			return cli_error_git();
 	} else {
 #ifdef GIT_EXPERIMENTAL_SHA256
-		if (git_odb_hash(&oid, buf->ptr, buf->size, type, GIT_OID_SHA1) < 0)
+		if (git_odb_hash(&oid, buf->ptr, buf->size, object_type, GIT_OID_SHA1) < 0)
 			return cli_error_git();
 #else
-		if (git_odb_hash(&oid, buf->ptr, buf->size, type) < 0)
+		if (git_odb_hash(&oid, buf->ptr, buf->size, object_type) < 0)
 			return cli_error_git();
 #endif
 	}
@@ -83,9 +94,10 @@ int cmd_hash_object(int argc, char **argv)
 {
 	git_repository *repo = NULL;
 	git_odb *odb = NULL;
+	git_oid_t oid_type;
 	git_str buf = GIT_STR_INIT;
 	cli_opt invalid_opt;
-	git_object_t type = GIT_OBJECT_BLOB;
+	git_object_t object_type = GIT_OBJECT_BLOB;
 	char **filename;
 	int ret = 0;
 
@@ -97,7 +109,7 @@ int cmd_hash_object(int argc, char **argv)
 		return 0;
 	}
 
-	if (type_name && (type = git_object_string2type(type_name)) == GIT_OBJECT_INVALID)
+	if (type_name && (object_type = git_object_string2type(type_name)) == GIT_OBJECT_INVALID)
 		return cli_error_usage("invalid object type '%s'", type_name);
 
 	if (write_object &&
@@ -107,6 +119,8 @@ int cmd_hash_object(int argc, char **argv)
 		goto done;
 	}
 
+	oid_type = git_repository_oid_type(repo);
+
 	/*
 	 * TODO: we're reading blobs, we shouldn't pull them all into main
 	 * memory, we should just stream them into the odb instead.
@@ -118,7 +132,7 @@ int cmd_hash_object(int argc, char **argv)
 			goto done;
 		}
 
-		if ((ret = hash_buf(odb, &buf, type)) != 0)
+		if ((ret = hash_buf(odb, &buf, object_type, oid_type)) != 0)
 			goto done;
 	} else {
 		for (filename = filenames; *filename; filename++) {
@@ -127,7 +141,7 @@ int cmd_hash_object(int argc, char **argv)
 				goto done;
 			}
 
-			if ((ret = hash_buf(odb, &buf, type)) != 0)
+			if ((ret = hash_buf(odb, &buf, object_type, oid_type)) != 0)
 				goto done;
 		}
 	}

src/libgit2/blob.c

@@ -52,11 +52,12 @@ void git_blob__free(void *_blob)
 	git__free(blob);
 }
 
-int git_blob__parse_raw(void *_blob, const char *data, size_t size)
+int git_blob__parse_raw(void *_blob, const char *data, size_t size, git_oid_t oid_type)
 {
 	git_blob *blob = (git_blob *) _blob;
 
 	GIT_ASSERT_ARG(blob);
+	GIT_UNUSED(oid_type);
 
 	blob->raw = 1;
 	blob->data.raw.data = data;
@@ -64,11 +65,12 @@ int git_blob__parse_raw(void *_blob, const char *data, size_t size)
 	return 0;
 }
 
-int git_blob__parse(void *_blob, git_odb_object *odb_obj)
+int git_blob__parse(void *_blob, git_odb_object *odb_obj, git_oid_t oid_type)
 {
 	git_blob *blob = (git_blob *) _blob;
 
 	GIT_ASSERT_ARG(blob);
+	GIT_UNUSED(oid_type);
 
 	git_cached_obj_incref((git_cached_obj *)odb_obj);
 	blob->raw = 0;

src/libgit2/blob.h

@@ -36,8 +36,8 @@ struct git_blob {
 	} while(0)
 
 void git_blob__free(void *blob);
-int git_blob__parse(void *blob, git_odb_object *obj);
-int git_blob__parse_raw(void *blob, const char *data, size_t size);
+int git_blob__parse(void *blob, git_odb_object *obj, git_oid_t oid_type);
+int git_blob__parse_raw(void *blob, const char *data, size_t size, git_oid_t oid_type);
 int git_blob__getbuf(git_str *buffer, git_blob *blob);
 
 extern int git_blob__create_from_paths(

src/libgit2/clone.c

@@ -393,12 +393,19 @@ static int checkout_branch(git_repository *repo, git_remote *remote, const git_c
 	return error;
 }
 
-static int clone_into(git_repository *repo, git_remote *_remote, const git_fetch_options *opts, const git_checkout_options *co_opts, const char *branch)
+static int clone_into(
+	git_repository *repo,
+	git_remote *_remote,
+	const git_fetch_options *opts,
+	const git_checkout_options *co_opts,
+	const char *branch)
 {
 	int error;
 	git_str reflog_message = GIT_STR_INIT;
+	git_remote_connect_options connect_opts = GIT_REMOTE_CONNECT_OPTIONS_INIT;
 	git_fetch_options fetch_opts;
 	git_remote *remote;
+	git_oid_t oid_type;
 
 	GIT_ASSERT_ARG(repo);
 	GIT_ASSERT_ARG(_remote);
@@ -414,8 +421,25 @@ static int clone_into(git_repository *repo, git_remote *_remote, const git_fetch
 	memcpy(&fetch_opts, opts, sizeof(git_fetch_options));
 	fetch_opts.update_fetchhead = 0;
 	fetch_opts.download_tags = GIT_REMOTE_DOWNLOAD_TAGS_ALL;
+
+	if ((error = git_remote_connect_options__from_fetch_opts(&connect_opts, remote, &fetch_opts)) < 0)
+		return error;
+
 	git_str_printf(&reflog_message, "clone: from %s", git_remote_url(remote));
 
+	/*
+	 * Connect to the server so that we can identify the remote
+	 * object format.
+	 */
+
+	if ((error = git_remote_connect_ext(remote, GIT_DIRECTION_FETCH,
+			&connect_opts)) < 0)
+		goto cleanup;
+
+	if ((error = git_remote_oid_type(&oid_type, remote)) < 0 ||
+	    (error = git_repository__set_objectformat(repo, oid_type)) < 0)
+		goto cleanup;
+
 	if ((error = git_remote_fetch(remote, NULL, &fetch_opts, git_str_cstr(&reflog_message))) != 0)
 		goto cleanup;
 
@@ -423,6 +447,7 @@ static int clone_into(git_repository *repo, git_remote *_remote, const git_fetch
 
 cleanup:
 	git_remote_free(remote);
+	git_remote_connect_options_dispose(&connect_opts);
 	git_str_dispose(&reflog_message);
 
 	return error;

src/libgit2/commit.c

@@ -390,7 +390,11 @@ int git_commit_amend(
 	return error;
 }
 
-static int commit_parse(git_commit *commit, const char *data, size_t size, unsigned int flags)
+static int commit_parse(
+	git_commit *commit,
+	const char *data,
+	size_t size,
+	git_commit__parse_options *opts)
 {
 	const char *buffer_start = data, *buffer;
 	const char *buffer_end = buffer_start + size;
@@ -401,6 +405,7 @@ static int commit_parse(git_commit *commit, const char *data, size_t size, unsig
 
 	GIT_ASSERT_ARG(commit);
 	GIT_ASSERT_ARG(data);
+	GIT_ASSERT_ARG(opts);
 
 	buffer = buffer_start;
 
@@ -409,13 +414,14 @@ static int commit_parse(git_commit *commit, const char *data, size_t size, unsig
 	GIT_ERROR_CHECK_ARRAY(commit->parent_ids);
 
 	/* The tree is always the first field */
-	if (!(flags & GIT_COMMIT_PARSE_QUICK)) {
+	if (!(opts->flags & GIT_COMMIT_PARSE_QUICK)) {
 		if (git_object__parse_oid_header(&commit->tree_id,
 				&buffer, buffer_end, "tree ",
-				GIT_OID_SHA1) < 0)
+				opts->oid_type) < 0)
 			goto bad_buffer;
 	} else {
-		size_t tree_len = strlen("tree ") + GIT_OID_SHA1_HEXSIZE + 1;
+		size_t tree_len = strlen("tree ") + git_oid_hexsize(opts->oid_type) + 1;
+
 		if (buffer + tree_len > buffer_end)
 			goto bad_buffer;
 		buffer += tree_len;
@@ -427,14 +433,14 @@ static int commit_parse(git_commit *commit, const char *data, size_t size, unsig
 
 	while (git_object__parse_oid_header(&parent_id,
 			&buffer, buffer_end, "parent ",
-			GIT_OID_SHA1) == 0) {
+			opts->oid_type) == 0) {
 		git_oid *new_id = git_array_alloc(commit->parent_ids);
 		GIT_ERROR_CHECK_ALLOC(new_id);
 
 		git_oid_cpy(new_id, &parent_id);
 	}
 
-	if (!(flags & GIT_COMMIT_PARSE_QUICK)) {
+	if (!opts || !(opts->flags & GIT_COMMIT_PARSE_QUICK)) {
 		commit->author = git__malloc(sizeof(git_signature));
 		GIT_ERROR_CHECK_ALLOC(commit->author);
 
@@ -458,7 +464,7 @@ static int commit_parse(git_commit *commit, const char *data, size_t size, unsig
 	if ((error = git_signature__parse(commit->committer, &buffer, buffer_end, "committer ", '\n')) < 0)
 		return error;
 
-	if (flags & GIT_COMMIT_PARSE_QUICK)
+	if (opts && opts->flags & GIT_COMMIT_PARSE_QUICK)
 		return 0;
 
 	/* Parse add'l header entries */
@@ -503,19 +509,39 @@ bad_buffer:
 	return GIT_EINVALID;
 }
 
-int git_commit__parse_raw(void *commit, const char *data, size_t size)
+int git_commit__parse(
+	void *commit,
+	git_odb_object *odb_obj,
+	git_oid_t oid_type)
 {
-	return commit_parse(commit, data, size, 0);
+	git_commit__parse_options parse_options = {0};
+	parse_options.oid_type = oid_type;
+
+	return git_commit__parse_ext(commit, odb_obj, &parse_options);
 }
 
-int git_commit__parse_ext(git_commit *commit, git_odb_object *odb_obj, unsigned int flags)
+int git_commit__parse_raw(
+	void *commit,
+	const char *data,
+	size_t size,
+	git_oid_t oid_type)
 {
-	return commit_parse(commit, git_odb_object_data(odb_obj), git_odb_object_size(odb_obj), flags);
+	git_commit__parse_options parse_options = {0};
+	parse_options.oid_type = oid_type;
+
+	return commit_parse(commit, data, size, &parse_options);
 }
 
-int git_commit__parse(void *_commit, git_odb_object *odb_obj)
+int git_commit__parse_ext(
+	git_commit *commit,
+	git_odb_object *odb_obj,
+	git_commit__parse_options *parse_opts)
 {
-	return git_commit__parse_ext(_commit, odb_obj, 0);
+	return commit_parse(
+		commit,
+		git_odb_object_data(odb_obj),
+		git_odb_object_size(odb_obj),
+		parse_opts);
 }
 
 #define GIT_COMMIT_GETTER(_rvalue, _name, _return, _invalid) \
@@ -985,11 +1011,14 @@ int git_commit_create_with_signature(
 	git_str commit = GIT_STR_INIT;
 	git_commit *parsed;
 	git_array_oid_t parents = GIT_ARRAY_INIT;
+	git_commit__parse_options parse_opts = {0};
+
+	parse_opts.oid_type = repo->oid_type;
 
 	/* The first step is to verify that all the tree and parents exist */
 	parsed = git__calloc(1, sizeof(git_commit));
 	GIT_ERROR_CHECK_ALLOC(parsed);
-	if (commit_parse(parsed, commit_content, strlen(commit_content), 0) < 0) {
+	if (commit_parse(parsed, commit_content, strlen(commit_content), &parse_opts) < 0) {
 		error = -1;
 		goto cleanup;
 	}

src/libgit2/commit.h

@@ -33,6 +33,16 @@ struct git_commit {
 	char *body;
 };
 
+typedef struct {
+	git_oid_t oid_type;
+	unsigned int flags;
+} git_commit__parse_options;
+
+typedef enum {
+	/** Only parse parents and committer info */
+	GIT_COMMIT_PARSE_QUICK = (1 << 0)
+} git_commit__parse_flags;
+
 int git_commit__header_field(
 	git_str *out,
 	const git_commit *commit,
@@ -56,14 +66,22 @@ int git_commit__create_buffer(
 	size_t parent_count,
 	const git_commit *parents[]);
 
-void git_commit__free(void *commit);
-int git_commit__parse(void *commit, git_odb_object *obj);
-int git_commit__parse_raw(void *commit, const char *data, size_t size);
+int git_commit__parse(
+	void *commit,
+	git_odb_object *obj,
+	git_oid_t oid_type);
 
-typedef enum {
-	GIT_COMMIT_PARSE_QUICK = (1 << 0) /**< Only parse parents and committer info */
-} git_commit__parse_flags;
+int git_commit__parse_raw(
+	void *commit,
+	const char *data,
+	size_t size,
+	git_oid_t oid_type);
 
-int git_commit__parse_ext(git_commit *commit, git_odb_object *odb_obj, unsigned int flags);
+int git_commit__parse_ext(
+	git_commit *commit,
+	git_odb_object *odb_obj,
+	git_commit__parse_options *parse_opts);
+
+void git_commit__free(void *commit);
 
 #endif

src/libgit2/commit_graph.c

@@ -538,7 +538,7 @@ int git_commit_graph_entry_find(
 	hi = ntohl(file->oid_fanout[(int)short_oid->id[0]]);
 	lo = ((short_oid->id[0] == 0x0) ? 0 : ntohl(file->oid_fanout[(int)short_oid->id[0] - 1]));
 
-	pos = git_pack__lookup_sha1(file->oid_lookup, GIT_OID_SHA1_SIZE, lo, hi, short_oid->id);
+	pos = git_pack__lookup_id(file->oid_lookup, GIT_OID_SHA1_SIZE, lo, hi, short_oid->id, GIT_OID_SHA1);
 
 	if (pos >= 0) {
 		/* An object matching exactly the oid was found */
@@ -726,7 +726,8 @@ int git_commit_graph_writer_add_index_file(
 	if (error < 0)
 		goto cleanup;
 
-	error = git_mwindow_get_pack(&p, idx_path);
+	/* TODO: SHA256 */
+	error = git_mwindow_get_pack(&p, idx_path, 0);
 	if (error < 0)
 		goto cleanup;
 

src/libgit2/commit_list.c

@@ -124,13 +124,17 @@ static int commit_quick_parse(
 {
 	git_oid *parent_oid;
 	git_commit *commit;
+	git_commit__parse_options parse_opts = {
+		GIT_OID_SHA1,
+		GIT_COMMIT_PARSE_QUICK
+	};
 	size_t i;
 
 	commit = git__calloc(1, sizeof(*commit));
 	GIT_ERROR_CHECK_ALLOC(commit);
 	commit->object.repo = walk->repo;
 
-	if (git_commit__parse_ext(commit, obj, GIT_COMMIT_PARSE_QUICK) < 0) {
+	if (git_commit__parse_ext(commit, obj, &parse_opts) < 0) {
 		git__free(commit);
 		return -1;
 	}

src/libgit2/fetch.c

@@ -95,7 +95,6 @@ static int filter_wants(git_remote *remote, const git_fetch_options *opts)
 	git_remote_head **heads;
 	git_refspec tagspec, head, *spec;
 	int error = 0;
-	git_odb *odb;
 	size_t i, heads_len;
 	unsigned int remote_caps;
 	unsigned int oid_mask = GIT_REMOTE_CAPABILITY_TIP_OID |
@@ -126,9 +125,6 @@ static int filter_wants(git_remote *remote, const git_fetch_options *opts)
 			goto cleanup;
 	}
 
-	if ((error = git_repository_odb__weakptr(&odb, remote->repo)) < 0)
-		goto cleanup;
-
 	if ((error = git_remote_ls((const git_remote_head ***)&heads, &heads_len, remote)) < 0 ||
 	    (error = git_remote_capabilities(&remote_caps, remote)) < 0)
 		goto cleanup;

src/libgit2/midx.c

@@ -392,7 +392,7 @@ int git_midx_entry_find(
 	hi = ntohl(idx->oid_fanout[(int)short_oid->id[0]]);
 	lo = ((short_oid->id[0] == 0x0) ? 0 : ntohl(idx->oid_fanout[(int)short_oid->id[0] - 1]));
 
-	pos = git_pack__lookup_sha1(idx->oid_lookup, GIT_OID_SHA1_SIZE, lo, hi, short_oid->id);
+	pos = git_pack__lookup_id(idx->oid_lookup, GIT_OID_SHA1_SIZE, lo, hi, short_oid->id, GIT_OID_SHA1);
 
 	if (pos >= 0) {
 		/* An object matching exactly the oid was found */
@@ -549,7 +549,8 @@ int git_midx_writer_add(
 	if (error < 0)
 		return error;
 
-	error = git_mwindow_get_pack(&p, git_str_cstr(&idx_path_buf));
+	/* TODO: SHA256 */
+	error = git_mwindow_get_pack(&p, git_str_cstr(&idx_path_buf), 0);
 	git_str_dispose(&idx_path_buf);
 	if (error < 0)
 		return error;

src/libgit2/mwindow.c

@@ -61,7 +61,10 @@ int git_mwindow_global_init(void)
 	return git_runtime_shutdown_register(git_mwindow_global_shutdown);
 }
 
-int git_mwindow_get_pack(struct git_pack_file **out, const char *path)
+int git_mwindow_get_pack(
+	struct git_pack_file **out,
+	const char *path,
+	git_oid_t oid_type)
 {
 	struct git_pack_file *pack;
 	char *packname;
@@ -86,7 +89,7 @@ int git_mwindow_get_pack(struct git_pack_file **out, const char *path)
 	}
 
 	/* If we didn't find it, we need to create it */
-	if ((error = git_packfile_alloc(&pack, path)) < 0) {
+	if ((error = git_packfile_alloc(&pack, path, oid_type)) < 0) {
 		git_mutex_unlock(&git__mwindow_mutex);
 		return error;
 	}

src/libgit2/mwindow.h

@@ -48,7 +48,10 @@ void git_mwindow_close(git_mwindow **w_cursor);
 extern int git_mwindow_global_init(void);
 
 struct git_pack_file; /* just declaration to avoid cyclical includes */
-int git_mwindow_get_pack(struct git_pack_file **out, const char *path);
+int git_mwindow_get_pack(
+	struct git_pack_file **out,
+	const char *path,
+	git_oid_t oid_type);
 int git_mwindow_put_pack(struct git_pack_file *pack);
 
 #endif

src/libgit2/object.c

@@ -27,8 +27,8 @@ typedef struct {
 	const char	*str;	/* type name string */
 	size_t		size;	/* size in bytes of the object structure */
 
-	int  (*parse)(void *self, git_odb_object *obj);
-	int  (*parse_raw)(void *self, const char *data, size_t size);
+	int  (*parse)(void *self, git_odb_object *obj, git_oid_t oid_type);
+	int  (*parse_raw)(void *self, const char *data, size_t size, git_oid_t oid_type);
 	void (*free)(void *self);
 } git_object_def;
 
@@ -60,7 +60,8 @@ int git_object__from_raw(
 	git_object **object_out,
 	const char *data,
 	size_t size,
-	git_object_t type)
+	git_object_t object_type,
+	git_oid_t oid_type)
 {
 	git_object_def *def;
 	git_object *object;
@@ -71,12 +72,15 @@ int git_object__from_raw(
 	*object_out = NULL;
 
 	/* Validate type match */
-	if (type != GIT_OBJECT_BLOB && type != GIT_OBJECT_TREE && type != GIT_OBJECT_COMMIT && type != GIT_OBJECT_TAG) {
+	if (object_type != GIT_OBJECT_BLOB &&
+	    object_type != GIT_OBJECT_TREE &&
+	    object_type != GIT_OBJECT_COMMIT &&
+	    object_type != GIT_OBJECT_TAG) {
 		git_error_set(GIT_ERROR_INVALID, "the requested type is invalid");
 		return GIT_ENOTFOUND;
 	}
 
-	if ((object_size = git_object__size(type)) == 0) {
+	if ((object_size = git_object__size(object_type)) == 0) {
 		git_error_set(GIT_ERROR_INVALID, "the requested type is invalid");
 		return GIT_ENOTFOUND;
 	}
@@ -85,15 +89,15 @@ int git_object__from_raw(
 	object = git__calloc(1, object_size);
 	GIT_ERROR_CHECK_ALLOC(object);
 	object->cached.flags = GIT_CACHE_STORE_PARSED;
-	object->cached.type = type;
-	if ((error = git_odb__hash(&object->cached.oid, data, size, type, GIT_OID_SHA1)) < 0)
+	object->cached.type = object_type;
+	if ((error = git_odb__hash(&object->cached.oid, data, size, object_type, oid_type)) < 0)
 		return error;
 
 	/* Parse raw object data */
-	def = &git_objects_table[type];
+	def = &git_objects_table[object_type];
 	GIT_ASSERT(def->free && def->parse_raw);
 
-	if ((error = def->parse_raw(object, data, size)) < 0) {
+	if ((error = def->parse_raw(object, data, size, oid_type)) < 0) {
 		def->free(object);
 		return error;
 	}
@@ -143,7 +147,7 @@ int git_object__from_odb_object(
 	def = &git_objects_table[odb_obj->cached.type];
 	GIT_ASSERT(def->free && def->parse);
 
-	if ((error = def->parse(object, odb_obj)) < 0) {
+	if ((error = def->parse(object, odb_obj, repo->oid_type)) < 0) {
 		/*
 		 * parse returns EINVALID on invalid data; downgrade
 		 * that to a normal -1 error code.
@@ -357,12 +361,11 @@ static int dereference_object(git_object **dereferenced, git_object *obj)
 static int peel_error(int error, const git_oid *oid, git_object_t type)
 {
 	const char *type_name;
-	char hex_oid[GIT_OID_SHA1_HEXSIZE + 1];
+	char hex_oid[GIT_OID_MAX_HEXSIZE + 1];
 
 	type_name = git_object_type2string(type);
 
-	git_oid_fmt(hex_oid, oid);
-	hex_oid[GIT_OID_SHA1_HEXSIZE] = '\0';
+	git_oid_nfmt(hex_oid, GIT_OID_MAX_HEXSIZE + 1, oid);
 
 	git_error_set(GIT_ERROR_OBJECT, "the git_object of id '%s' can not be "
 		"successfully peeled into a %s (git_object_t=%i).", hex_oid, type_name, type);
@@ -576,21 +579,29 @@ int git_object_rawcontent_is_valid(
 	int *valid,
 	const char *buf,
 	size_t len,
-	git_object_t type)
+	git_object_t object_type
+#ifdef GIT_EXPERIMENTAL_SHA256
+	, git_oid_t oid_type
+#endif
+	)
 {
 	git_object *obj = NULL;
 	int error;
 
+#ifndef GIT_EXPERIMENTAL_SHA256
+	git_oid_t oid_type = GIT_OID_SHA1;
+#endif
+
 	GIT_ASSERT_ARG(valid);
 	GIT_ASSERT_ARG(buf);
 
 	/* Blobs are always valid; don't bother parsing. */
-	if (type == GIT_OBJECT_BLOB) {
+	if (object_type == GIT_OBJECT_BLOB) {
 		*valid = 1;
 		return 0;
 	}
 
-	error = git_object__from_raw(&obj, buf, len, type);
+	error = git_object__from_raw(&obj, buf, len, object_type, oid_type);
 	git_object_free(obj);
 
 	if (error == 0) {
@@ -611,7 +622,7 @@ int git_object__parse_oid_header(
 	const char *header,
 	git_oid_t oid_type)
 {
-	const size_t sha_len = GIT_OID_SHA1_HEXSIZE;
+	const size_t sha_len = git_oid_hexsize(oid_type);
 	const size_t header_len = strlen(header);
 
 	const char *buffer = *buffer_out;

src/libgit2/object.h

@@ -33,7 +33,8 @@ int git_object__from_raw(
 	git_object **object_out,
 	const char *data,
 	size_t size,
-	git_object_t type);
+	git_object_t object_type,
+	git_oid_t oid_type);
 
 int git_object__from_odb_object(
 	git_object **object_out,

src/libgit2/odb.c

@@ -684,6 +684,7 @@ int git_odb__add_default_backends(
 	ino_t inode;
 	git_odb_backend *loose, *packed;
 	git_odb_backend_loose_options loose_opts = GIT_ODB_BACKEND_LOOSE_OPTIONS_INIT;
+	git_odb_backend_pack_options pack_opts = GIT_ODB_BACKEND_PACK_OPTIONS_INIT;
 
 	/* TODO: inodes are not really relevant on Win32, so we need to find
 	 * a cross-platform workaround for this */
@@ -722,6 +723,7 @@ int git_odb__add_default_backends(
 		loose_opts.flags |= GIT_ODB_BACKEND_LOOSE_FSYNC;
 
 	loose_opts.oid_type = db->options.oid_type;
+	pack_opts.oid_type = db->options.oid_type;
 
 	/* add the loose object backend */
 	if (git_odb__backend_loose(&loose, objects_dir, &loose_opts) < 0 ||
@@ -729,8 +731,17 @@ int git_odb__add_default_backends(
 		return -1;
 
 	/* add the packed file backend */
-	if (git_odb_backend_pack(&packed, objects_dir) < 0 ||
-		add_backend_internal(db, packed, git_odb__packed_priority, as_alternates, inode) < 0)
+#ifdef GIT_EXPERIMENTAL_SHA256
+	if (git_odb_backend_pack(&packed, objects_dir, &pack_opts) < 0)
+		return -1;
+#else
+	GIT_UNUSED(pack_opts);
+
+	if (git_odb_backend_pack(&packed, objects_dir) < 0)
+		return -1;
+#endif
+
+	if (add_backend_internal(db, packed, git_odb__packed_priority, as_alternates, inode) < 0)
 		return -1;
 
 	if (git_mutex_lock(&db->lock) < 0) {

src/libgit2/oid.h

@@ -66,6 +66,47 @@ GIT_INLINE(size_t) git_oid_hexsize(git_oid_t type)
 	return 0;
 }
 
+GIT_INLINE(const char *) git_oid_type_name(git_oid_t type)
+{
+	switch (type) {
+	case GIT_OID_SHA1:
+		return "sha1";
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	case GIT_OID_SHA256:
+		return "sha256";
+#endif
+	}
+
+	return "unknown";
+}
+
+GIT_INLINE(git_oid_t) git_oid_type_fromstr(const char *name)
+{
+	if (strcmp(name, "sha1") == 0)
+		return GIT_OID_SHA1;
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	if (strcmp(name, "sha256") == 0)
+		return GIT_OID_SHA256;
+#endif
+
+	return 0;
+}
+
+GIT_INLINE(git_oid_t) git_oid_type_fromstrn(const char *name, size_t len)
+{
+	if (len == CONST_STRLEN("sha1") && strncmp(name, "sha1", len) == 0)
+		return GIT_OID_SHA1;
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	if (len == CONST_STRLEN("sha256") && strncmp(name, "sha256", len) == 0)
+		return GIT_OID_SHA256;
+#endif
+
+	return 0;
+}
+
 GIT_INLINE(git_hash_algorithm_t) git_oid_algorithm(git_oid_t type)
 {
 	switch (type) {

src/libgit2/pack-objects.c

@@ -1407,7 +1407,18 @@ int git_packbuilder_write(
 	opts.progress_cb = progress_cb;
 	opts.progress_cb_payload = progress_cb_payload;
 
-	if ((error = git_indexer_new(&indexer, path, mode, pb->odb, &opts)) < 0)
+	/* TODO: SHA256 */
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	opts.mode = mode;
+	opts.odb = pb->odb;
+
+	error = git_indexer_new(&indexer, path, GIT_OID_SHA1, &opts);
+#else
+	error = git_indexer_new(&indexer, path, mode, pb->odb, &opts);
+#endif
+
+	if (error < 0)
 		goto cleanup;
 
 	if (!git_repository__configmap_lookup(&t, pb->repo, GIT_CONFIGMAP_FSYNCOBJECTFILES) && t)

src/libgit2/pack.h

@@ -99,13 +99,19 @@ struct git_pack_file {
 
 	uint32_t num_objects;
 	uint32_t num_bad_objects;
-	git_oid *bad_object_sha1; /* array of git_oid */
+	git_oid *bad_object_ids; /* array of git_oid */
+
+	git_oid_t oid_type;
+	unsigned oid_hexsize:7,
+	         oid_size:6,
+	         pack_local:1,
+	         pack_keep:1,
+		 has_cache:1;
 
 	int index_version;
 	git_time_t mtime;
-	unsigned pack_local:1, pack_keep:1, has_cache:1;
 	git_oidmap *idx_cache;
-	unsigned char **oids;
+	unsigned char **ids;
 
 	git_pack_cache bases; /* delta base cache */
 
@@ -116,21 +122,26 @@ struct git_pack_file {
 };
 
 /**
- * Return the position where an OID (or a prefix) would be inserted within the
- * OID Lookup Table of an .idx file. This performs binary search between the lo
- * and hi indices.
+ * Return the position where an OID (or a prefix) would be inserted within
+ * the OID Lookup Table of an .idx file. This performs binary search
+ * between the lo and hi indices.
  *
- * The stride parameter is provided because .idx files version 1 store the OIDs
- * interleaved with the 4-byte file offsets of the objects within the .pack
- * file (stride = 24), whereas files with version 2 store them in a contiguous
- * flat array (stride = 20).
+ * The stride parameter is provided because .idx files version 1 store the
+ * OIDs interleaved with the 4-byte file offsets of the objects within the
+ * .pack file (stride = oid_size + 4), whereas files with version 2 store
+ * them in a contiguous flat array (stride = oid_size).
  */
-int git_pack__lookup_sha1(const void *oid_lookup_table, size_t stride, unsigned lo,
-		unsigned hi, const unsigned char *oid_prefix);
+int git_pack__lookup_id(
+	const void *id_lookup_table,
+	size_t stride,
+	unsigned lo,
+	unsigned hi,
+	const unsigned char *id_prefix,
+	const git_oid_t oid_type);
 
 struct git_pack_entry {
 	off64_t offset;
-	git_oid sha1;
+	git_oid id;
 	struct git_pack_file *p;
 };
 
@@ -174,12 +185,15 @@ int get_delta_base(
 		off64_t delta_obj_offset);
 
 void git_packfile_free(struct git_pack_file *p, bool unlink_packfile);
-int git_packfile_alloc(struct git_pack_file **pack_out, const char *path);
+int git_packfile_alloc(
+	struct git_pack_file **pack_out,
+	const char *path,
+	git_oid_t oid_type);
 
 int git_pack_entry_find(
 		struct git_pack_entry *e,
 		struct git_pack_file *p,
-		const git_oid *short_oid,
+		const git_oid *short_id,
 		size_t len);
 int git_pack_foreach_entry(
 		struct git_pack_file *p,

src/libgit2/refdb_fs.c

@@ -60,15 +60,17 @@ typedef struct refdb_fs_backend {
 	/* path to common objects' directory */
 	char *commonpath;
 
-	git_sortedcache *refcache;
+	git_oid_t oid_type;
+
+	int fsync : 1,
+	    sorted : 1;
 	int peeling_mode;
 	git_iterator_flag_t iterator_flags;
 	uint32_t direach_flags;
-	int fsync;
+	git_sortedcache *refcache;
 	git_map packed_refs_map;
 	git_mutex prlock; /* protect packed_refs_map */
 	git_futils_filestamp packed_refs_stamp;
-	bool sorted;
 } refdb_fs_backend;
 
 static int refdb_reflog_fs__delete(git_refdb_backend *_backend, const char *name);
@@ -113,6 +115,7 @@ static int packed_reload(refdb_fs_backend *backend)
 {
 	int error;
 	git_str packedrefs = GIT_STR_INIT;
+	size_t oid_hexsize = git_oid_hexsize(backend->oid_type);
 	char *scan, *eof, *eol;
 
 	if (!backend->gitpath)
@@ -158,9 +161,9 @@ static int packed_reload(refdb_fs_backend *backend)
 
 		/* parse "<OID> <refname>\n" */
 
-		if (git_oid__fromstr(&oid, scan, GIT_OID_SHA1) < 0)
+		if (git_oid__fromstr(&oid, scan, backend->oid_type) < 0)
 			goto parse_failed;
-		scan += GIT_OID_SHA1_HEXSIZE;
+		scan += oid_hexsize;
 
 		if (*scan++ != ' ')
 			goto parse_failed;
@@ -179,9 +182,9 @@ static int packed_reload(refdb_fs_backend *backend)
 		/* look for optional "^<OID>\n" */
 
 		if (*scan == '^') {
-			if (git_oid__fromstr(&oid, scan + 1, GIT_OID_SHA1) < 0)
+			if (git_oid__fromstr(&oid, scan + 1, backend->oid_type) < 0)
 				goto parse_failed;
-			scan += GIT_OID_SHA1_HEXSIZE + 1;
+			scan += oid_hexsize + 1;
 
 			if (scan < eof) {
 				if (!(eol = strchr(scan, '\n')))
@@ -214,19 +217,23 @@ parse_failed:
 }
 
 static int loose_parse_oid(
-	git_oid *oid, const char *filename, git_str *file_content)
+	git_oid *oid,
+	const char *filename,
+	git_str *file_content,
+	git_oid_t oid_type)
 {
 	const char *str = git_str_cstr(file_content);
+	size_t oid_hexsize = git_oid_hexsize(oid_type);
 
-	if (git_str_len(file_content) < GIT_OID_SHA1_HEXSIZE)
+	if (git_str_len(file_content) < oid_hexsize)
 		goto corrupted;
 
 	/* we need to get 40 OID characters from the file */
-	if (git_oid__fromstr(oid, str, GIT_OID_SHA1) < 0)
+	if (git_oid__fromstr(oid, str, oid_type) < 0)
 		goto corrupted;
 
 	/* If the file is longer than 40 chars, the 41st must be a space */
-	str += GIT_OID_SHA1_HEXSIZE;
+	str += oid_hexsize;
 	if (*str == '\0' || git__isspace(*str))
 		return 0;
 
@@ -266,7 +273,7 @@ static int loose_lookup_to_packfile(refdb_fs_backend *backend, const char *name)
 		goto done;
 
 	/* parse OID from file */
-	if ((error = loose_parse_oid(&oid, name, &ref_file)) < 0)
+	if ((error = loose_parse_oid(&oid, name, &ref_file, backend->oid_type)) < 0)
 		goto done;
 
 	if ((error = git_sortedcache_wlock(backend->refcache)) < 0)
@@ -437,7 +444,7 @@ static int loose_lookup(
 	} else {
 		git_oid oid;
 
-		if (!(error = loose_parse_oid(&oid, ref_name, &ref_file)) &&
+		if (!(error = loose_parse_oid(&oid, ref_name, &ref_file, backend->oid_type)) &&
 			out != NULL)
 			*out = git_reference__alloc(ref_name, &oid, NULL);
 	}
@@ -615,19 +622,24 @@ static const char *end_of_record(const char *p, const char *end)
 	return p;
 }
 
-static int
-cmp_record_to_refname(const char *rec, size_t data_end, const char *ref_name)
+static int cmp_record_to_refname(
+	const char *rec,
+	size_t data_end,
+	const char *ref_name,
+	git_oid_t oid_type)
 {
 	const size_t ref_len = strlen(ref_name);
 	int cmp_val;
 	const char *end;
+	size_t oid_hexsize = git_oid_hexsize(oid_type);
 
-	rec += GIT_OID_SHA1_HEXSIZE + 1; /* <oid> + space */
-	if (data_end < GIT_OID_SHA1_HEXSIZE + 3) {
-		/* an incomplete (corrupt) record is treated as less than ref_name */
+	rec += oid_hexsize + 1; /* <oid> + space */
+
+	/* an incomplete (corrupt) record is treated as less than ref_name */
+	if (data_end < oid_hexsize + 3)
 		return -1;
-	}
-	data_end -= GIT_OID_SHA1_HEXSIZE + 1;
+
+	data_end -= oid_hexsize + 1;
 
 	end = memchr(rec, '\n', data_end);
 	if (end)
@@ -675,6 +687,7 @@ static int packed_lookup(
 {
 	int error = 0;
 	const char *left, *right, *data_end;
+	size_t oid_hexsize = git_oid_hexsize(backend->oid_type);
 
 	if ((error = packed_map_check(backend)) < 0)
 		return error;
@@ -698,7 +711,7 @@ static int packed_lookup(
 
 		mid = left + (right - left) / 2;
 		rec = start_of_record(left, mid);
-		compare = cmp_record_to_refname(rec, data_end - rec, ref_name);
+		compare = cmp_record_to_refname(rec, data_end - rec, ref_name, backend->oid_type);
 
 		if (compare < 0) {
 			left = end_of_record(mid, right);
@@ -708,11 +721,11 @@ static int packed_lookup(
 			const char *eol;
 			git_oid oid, peel, *peel_ptr = NULL;
 
-			if (data_end - rec < GIT_OID_SHA1_HEXSIZE ||
-			    git_oid__fromstr(&oid, rec, GIT_OID_SHA1) < 0) {
+			if (data_end - rec < (long)oid_hexsize ||
+			    git_oid__fromstr(&oid, rec, backend->oid_type) < 0) {
 				goto parse_failed;
 			}
-			rec += GIT_OID_SHA1_HEXSIZE + 1;
+			rec += oid_hexsize + 1;
 			if (!(eol = memchr(rec, '\n', data_end - rec))) {
 				goto parse_failed;
 			}
@@ -724,8 +737,8 @@ static int packed_lookup(
 
 				if (*rec == '^') {
 					rec++;
-					if (data_end - rec < GIT_OID_SHA1_HEXSIZE ||
-						git_oid__fromstr(&peel, rec, GIT_OID_SHA1) < 0) {
+					if (data_end - rec < (long)oid_hexsize ||
+					    git_oid__fromstr(&peel, rec, backend->oid_type) < 0) {
 						goto parse_failed;
 					}
 					peel_ptr = &peel;
@@ -1108,7 +1121,7 @@ static int loose_commit(git_filebuf *file, const git_reference *ref)
 	GIT_ASSERT_ARG(ref);
 
 	if (ref->type == GIT_REFERENCE_DIRECT) {
-		char oid[GIT_OID_SHA1_HEXSIZE + 1];
+		char oid[GIT_OID_MAX_HEXSIZE + 1];
 		git_oid_nfmt(oid, sizeof(oid), &ref->target.oid);
 
 		git_filebuf_printf(file, "%s\n", oid);
@@ -1224,7 +1237,7 @@ static int packed_find_peel(refdb_fs_backend *backend, struct packref *ref)
  */
 static int packed_write_ref(struct packref *ref, git_filebuf *file)
 {
-	char oid[GIT_OID_SHA1_HEXSIZE + 1];
+	char oid[GIT_OID_MAX_HEXSIZE + 1];
 	git_oid_nfmt(oid, sizeof(oid), &ref->oid);
 
 	/*
@@ -1238,7 +1251,7 @@ static int packed_write_ref(struct packref *ref, git_filebuf *file)
 	 * The required peels have already been loaded into `ref->peel_target`.
 	 */
 	if (ref->flags & PACKREF_HAS_PEEL) {
-		char peel[GIT_OID_SHA1_HEXSIZE + 1];
+		char peel[GIT_OID_MAX_HEXSIZE + 1];
 		git_oid_nfmt(peel, sizeof(peel), &ref->peel);
 
 		if (git_filebuf_printf(file, "%s %s\n^%s\n", oid, ref->name, peel) < 0)
@@ -1302,7 +1315,7 @@ static int packed_remove_loose(refdb_fs_backend *backend)
 			continue;
 
 		/* Figure out the current id; if we find a bad ref file, skip it so we can do the rest */
-		if (loose_parse_oid(&current_id, lock.path_original, &ref_content) < 0)
+		if (loose_parse_oid(&current_id, lock.path_original, &ref_content, backend->oid_type) < 0)
 			continue;
 
 		/* If the ref moved since we packed it, we must not delete it */
@@ -1891,7 +1904,10 @@ done:
 	return out;
 }
 
-static int reflog_alloc(git_reflog **reflog, const char *name)
+static int reflog_alloc(
+	git_reflog **reflog,
+	const char *name,
+	git_oid_t oid_type)
 {
 	git_reflog *log;
 
@@ -1903,6 +1919,8 @@ static int reflog_alloc(git_reflog **reflog, const char *name)
 	log->ref_name = git__strdup(name);
 	GIT_ERROR_CHECK_ALLOC(log->ref_name);
 
+	log->oid_type = oid_type;
+
 	if (git_vector_init(&log->entries, 0, NULL) < 0) {
 		git__free(log->ref_name);
 		git__free(log);
@@ -2032,7 +2050,10 @@ static int refdb_reflog_fs__has_log(git_refdb_backend *_backend, const char *nam
 	return has_reflog(backend->repo, name);
 }
 
-static int refdb_reflog_fs__read(git_reflog **out, git_refdb_backend *_backend, const char *name)
+static int refdb_reflog_fs__read(
+	git_reflog **out,
+	git_refdb_backend *_backend,
+	const char *name)
 {
 	int error = -1;
 	git_str log_path = GIT_STR_INIT;
@@ -2048,7 +2069,7 @@ static int refdb_reflog_fs__read(git_reflog **out, git_refdb_backend *_backend,
 	backend = GIT_CONTAINER_OF(_backend, refdb_fs_backend, parent);
 	repo = backend->repo;
 
-	if (reflog_alloc(&log, name) < 0)
+	if (reflog_alloc(&log, name, backend->oid_type) < 0)
 		return -1;
 
 	if (reflog_path(&log_path, repo, name) < 0)
@@ -2086,11 +2107,11 @@ static int serialize_reflog_entry(
 	const git_signature *committer,
 	const char *msg)
 {
-	char raw_old[GIT_OID_SHA1_HEXSIZE+1];
-	char raw_new[GIT_OID_SHA1_HEXSIZE+1];
+	char raw_old[GIT_OID_MAX_HEXSIZE + 1];
+	char raw_new[GIT_OID_MAX_HEXSIZE + 1];
 
-	git_oid_tostr(raw_old, GIT_OID_SHA1_HEXSIZE+1, oid_old);
-	git_oid_tostr(raw_new, GIT_OID_SHA1_HEXSIZE+1, oid_new);
+	git_oid_tostr(raw_old, GIT_OID_MAX_HEXSIZE + 1, oid_old);
+	git_oid_tostr(raw_new, GIT_OID_MAX_HEXSIZE + 1, oid_new);
 
 	git_str_clear(buf);
 
@@ -2189,10 +2210,16 @@ success:
 }
 
 /* Append to the reflog, must be called under reference lock */
-static int reflog_append(refdb_fs_backend *backend, const git_reference *ref, const git_oid *old, const git_oid *new, const git_signature *who, const char *message)
+static int reflog_append(
+	refdb_fs_backend *backend,
+	const git_reference *ref,
+	const git_oid *old,
+	const git_oid *new,
+	const git_signature *who,
+	const char *message)
 {
 	int error, is_symbolic, open_flags;
-	git_oid old_id = GIT_OID_SHA1_ZERO, new_id = GIT_OID_SHA1_ZERO;
+	git_oid old_id, new_id;
 	git_str buf = GIT_STR_INIT, path = GIT_STR_INIT;
 	git_repository *repo = backend->repo;
 
@@ -2206,6 +2233,9 @@ static int reflog_append(refdb_fs_backend *backend, const git_reference *ref, co
 
 	/* From here on is_symbolic also means that it's HEAD */
 
+	git_oid_clear(&old_id, backend->oid_type);
+	git_oid_clear(&new_id, backend->oid_type);
+
 	if (old) {
 		git_oid_cpy(&old_id, old);
 	} else {
@@ -2402,6 +2432,7 @@ int git_refdb_backend_fs(
 		goto fail;
 
 	backend->repo = repository;
+	backend->oid_type = repository->oid_type;
 
 	if (repository->gitdir) {
 		backend->gitpath = setup_namespace(repository, repository->gitdir);

src/libgit2/reflog.c

@@ -71,7 +71,11 @@ int git_reflog_write(git_reflog *reflog)
 	return db->backend->reflog_write(db->backend, reflog);
 }
 
-int git_reflog_append(git_reflog *reflog, const git_oid *new_oid, const git_signature *committer, const char *msg)
+int git_reflog_append(
+	git_reflog *reflog,
+	const git_oid *new_oid,
+	const git_signature *committer,
+	const char *msg)
 {
 	const git_reflog_entry *previous;
 	git_reflog_entry *entry;
@@ -104,7 +108,7 @@ int git_reflog_append(git_reflog *reflog, const git_oid *new_oid, const git_sign
 	previous = git_reflog_entry_byindex(reflog, 0);
 
 	if (previous == NULL)
-		git_oid__fromstr(&entry->oid_old, GIT_OID_SHA1_HEXZERO, GIT_OID_SHA1);
+		git_oid_clear(&entry->oid_old, reflog->oid_type);
 	else
 		git_oid_cpy(&entry->oid_old, &previous->oid_cur);
 
@@ -218,12 +222,8 @@ int git_reflog_drop(git_reflog *reflog, size_t idx, int rewrite_previous_entry)
 
 	/* If the oldest entry has just been removed... */
 	if (idx == entrycount - 1) {
-		git_oid zero = GIT_OID_SHA1_ZERO;
-
 		/* ...clear the oid_old member of the "new" oldest entry */
-		if (git_oid_cpy(&entry->oid_old, &zero) < 0)
-			return -1;
-
+		git_oid_clear(&entry->oid_old, reflog->oid_type);
 		return 0;
 	}
 

src/libgit2/reflog.h

@@ -16,8 +16,6 @@
 #define GIT_REFLOG_DIR_MODE 0777
 #define GIT_REFLOG_FILE_MODE 0666
 
-#define GIT_REFLOG_SIZE_MIN (2*GIT_OID_SHA1_HEXSIZE+2+17)
-
 struct git_reflog_entry {
 	git_oid oid_old;
 	git_oid oid_cur;
@@ -30,6 +28,7 @@ struct git_reflog_entry {
 struct git_reflog {
 	git_refdb *db;
 	char *ref_name;
+	git_oid_t oid_type;
 	git_vector entries;
 };
 

src/libgit2/remote.c

@@ -1026,6 +1026,24 @@ int git_remote_capabilities(unsigned int *out, git_remote *remote)
 	return remote->transport->capabilities(out, remote->transport);
 }
 
+int git_remote_oid_type(git_oid_t *out, git_remote *remote)
+{
+	GIT_ASSERT_ARG(remote);
+
+	if (!remote->transport) {
+		git_error_set(GIT_ERROR_NET, "this remote has never connected");
+		*out = 0;
+		return -1;
+	}
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	return remote->transport->oid_type(out, remote->transport);
+#else
+	*out = GIT_OID_SHA1;
+	return 0;
+#endif
+}
+
 static int lookup_config(char **out, git_config *cfg, const char *name)
 {
 	git_config_entry *ce = NULL;
@@ -1225,24 +1243,6 @@ static int ls_to_vector(git_vector *out, git_remote *remote)
 	return 0;
 }
 
-#define copy_opts(out, in) \
-	if (in) { \
-		(out)->callbacks = (in)->callbacks; \
-		(out)->proxy_opts = (in)->proxy_opts; \
-		(out)->custom_headers = (in)->custom_headers; \
-		(out)->follow_redirects = (in)->follow_redirects; \
-	}
-
-GIT_INLINE(int) connect_opts_from_fetch_opts(
-	git_remote_connect_options *out,
-	git_remote *remote,
-	const git_fetch_options *fetch_opts)
-{
-	git_remote_connect_options tmp = GIT_REMOTE_CONNECT_OPTIONS_INIT;
-	copy_opts(&tmp, fetch_opts);
-	return git_remote_connect_options_normalize(out, remote->repo, &tmp);
-}
-
 static int connect_or_reset_options(
 	git_remote *remote,
 	int direction,
@@ -1330,7 +1330,8 @@ int git_remote_download(
 		return -1;
 	}
 
-	if (connect_opts_from_fetch_opts(&connect_opts, remote, opts) < 0)
+	if (git_remote_connect_options__from_fetch_opts(&connect_opts,
+			remote, opts) < 0)
 		return -1;
 
 	if ((error = connect_or_reset_options(remote, GIT_DIRECTION_FETCH, &connect_opts)) < 0)
@@ -1350,6 +1351,8 @@ int git_remote_fetch(
 	bool prune = false;
 	git_str reflog_msg_buf = GIT_STR_INIT;
 	git_remote_connect_options connect_opts = GIT_REMOTE_CONNECT_OPTIONS_INIT;
+	unsigned int capabilities;
+	git_oid_t oid_type;
 
 	GIT_ASSERT_ARG(remote);
 
@@ -1358,7 +1361,8 @@ int git_remote_fetch(
 		return -1;
 	}
 
-	if (connect_opts_from_fetch_opts(&connect_opts, remote, opts) < 0)
+	if (git_remote_connect_options__from_fetch_opts(&connect_opts,
+			remote, opts) < 0)
 		return -1;
 
 	if ((error = connect_or_reset_options(remote, GIT_DIRECTION_FETCH, &connect_opts)) < 0)
@@ -1369,6 +1373,10 @@ int git_remote_fetch(
 		tagopt = opts->download_tags;
 	}
 
+	if ((error = git_remote_capabilities(&capabilities, remote)) < 0 ||
+	    (error = git_remote_oid_type(&oid_type, remote)) < 0)
+		return error;
+
 	/* Connect and download everything */
 	error = git_remote__download(remote, refspecs, opts);
 
@@ -2896,16 +2904,6 @@ done:
 	return error;
 }
 
-GIT_INLINE(int) connect_opts_from_push_opts(
-	git_remote_connect_options *out,
-	git_remote *remote,
-	const git_push_options *push_opts)
-{
-	git_remote_connect_options tmp = GIT_REMOTE_CONNECT_OPTIONS_INIT;
-	copy_opts(&tmp, push_opts);
-	return git_remote_connect_options_normalize(out, remote->repo, &tmp);
-}
-
 int git_remote_upload(
 	git_remote *remote,
 	const git_strarray *refspecs,
@@ -2924,7 +2922,8 @@ int git_remote_upload(
 		return -1;
 	}
 
-	if ((error = connect_opts_from_push_opts(&connect_opts, remote, opts)) < 0)
+	if ((error = git_remote_connect_options__from_push_opts(
+			&connect_opts, remote, opts)) < 0)
 		goto cleanup;
 
 	if ((error = connect_or_reset_options(remote, GIT_DIRECTION_PUSH, &connect_opts)) < 0)
@@ -2985,7 +2984,8 @@ int git_remote_push(
 		return -1;
 	}
 
-	if (connect_opts_from_push_opts(&connect_opts, remote, opts) < 0)
+	if (git_remote_connect_options__from_push_opts(&connect_opts,
+			remote, opts) < 0)
 		return -1;
 
 	if ((error = git_remote_upload(remote, refspecs, opts)) < 0)

src/libgit2/remote.h

@@ -17,6 +17,7 @@
 #include "refspec.h"
 #include "vector.h"
 #include "net.h"
+#include "proxy.h"
 
 #define GIT_REMOTE_ORIGIN "origin"
 
@@ -56,5 +57,44 @@ int git_remote_connect_options_normalize(
 	const git_remote_connect_options *src);
 
 int git_remote_capabilities(unsigned int *out, git_remote *remote);
+int git_remote_oid_type(git_oid_t *out, git_remote *remote);
+
+
+#define git_remote_connect_options__copy_opts(out, in) \
+	if (in) { \
+		(out)->callbacks = (in)->callbacks; \
+		(out)->proxy_opts = (in)->proxy_opts; \
+		(out)->custom_headers = (in)->custom_headers; \
+		(out)->follow_redirects = (in)->follow_redirects; \
+	}
+
+GIT_INLINE(int) git_remote_connect_options__from_fetch_opts(
+	git_remote_connect_options *out,
+	git_remote *remote,
+	const git_fetch_options *fetch_opts)
+{
+	git_remote_connect_options tmp = GIT_REMOTE_CONNECT_OPTIONS_INIT;
+	git_remote_connect_options__copy_opts(&tmp, fetch_opts);
+	return git_remote_connect_options_normalize(out, remote->repo, &tmp);
+}
+
+GIT_INLINE(int) git_remote_connect_options__from_push_opts(
+	git_remote_connect_options *out,
+	git_remote *remote,
+	const git_push_options *push_opts)
+{
+	git_remote_connect_options tmp = GIT_REMOTE_CONNECT_OPTIONS_INIT;
+	git_remote_connect_options__copy_opts(&tmp, push_opts);
+	return git_remote_connect_options_normalize(out, remote->repo, &tmp);
+}
+
+#undef git_remote_connect_options__copy_opts
+
+GIT_INLINE(void) git_remote_connect_options__dispose(
+	git_remote_connect_options *opts)
+{
+	git_proxy_options_dispose(&opts->proxy_opts);
+	git_strarray_dispose(&opts->custom_headers);
+}
 
 #endif

src/libgit2/repository.c

@@ -67,6 +67,7 @@ static const struct {
 static int check_repositoryformatversion(int *version, git_config *config);
 static int check_extensions(git_config *config, int version);
 static int load_global_config(git_config **config);
+static int load_objectformat(git_repository *repo, git_config *config);
 
 #define GIT_COMMONDIR_FILE "commondir"
 #define GIT_GITDIR_FILE "gitdir"
@@ -75,8 +76,8 @@ static int load_global_config(git_config **config);
 
 #define GIT_BRANCH_DEFAULT "master"
 
-#define GIT_REPO_VERSION 0
-#define GIT_REPO_MAX_VERSION 1
+#define GIT_REPO_VERSION_DEFAULT 0
+#define GIT_REPO_VERSION_MAX 1
 
 git_str git_repository__reserved_names_win32[] = {
 	{ DOT_GIT, 0, CONST_STRLEN(DOT_GIT) },
@@ -240,7 +241,7 @@ GIT_INLINE(int) validate_repo_path(git_str *path)
 	 */
 	static size_t suffix_len =
 		CONST_STRLEN("objects/pack/pack-.pack.lock") +
-		GIT_OID_SHA1_HEXSIZE;
+		GIT_OID_MAX_HEXSIZE;
 
 	return git_fs_path_validate_str_length_with_suffix(
 		path, suffix_len);
@@ -1015,7 +1016,8 @@ int git_repository_open_ext(
 	if (error < 0 && error != GIT_ENOTFOUND)
 		goto cleanup;
 
-	if (config && (error = check_repositoryformatversion(&version, config)) < 0)
+	if (config &&
+	    (error = check_repositoryformatversion(&version, config)) < 0)
 		goto cleanup;
 
 	if ((error = check_extensions(config, version)) < 0)
@@ -1030,6 +1032,13 @@ int git_repository_open_ext(
 			goto cleanup;
 	}
 
+	if (version > 0) {
+		if ((error = load_objectformat(repo, config)) < 0)
+			goto cleanup;
+	} else {
+		repo->oid_type = GIT_OID_SHA1;
+	}
+
 	/*
 	 * Ensure that the git directory and worktree are
 	 * owned by the current user.
@@ -1269,11 +1278,14 @@ int git_repository_odb__weakptr(git_odb **out, git_repository *repo)
 	*out = git_atomic_load(repo->_odb);
 	if (*out == NULL) {
 		git_str odb_path = GIT_STR_INIT;
+		git_odb_options odb_opts = GIT_ODB_OPTIONS_INIT;
 		git_odb *odb;
 
+		odb_opts.oid_type = repo->oid_type;
+
 		if ((error = git_repository__item_path(&odb_path, repo,
 				GIT_REPOSITORY_ITEM_OBJECTS)) < 0 ||
-			(error = git_odb__new(&odb, NULL)) < 0)
+			(error = git_odb__new(&odb, &odb_opts)) < 0)
 			return error;
 
 		GIT_REFCOUNT_OWN(odb, repo);
@@ -1531,6 +1543,7 @@ static int check_repositoryformatversion(int *version, git_config *config)
 	int error;
 
 	error = git_config_get_int32(version, config, "core.repositoryformatversion");
+
 	/* git ignores this if the config variable isn't there */
 	if (error == GIT_ENOTFOUND)
 		return 0;
@@ -1538,10 +1551,15 @@ static int check_repositoryformatversion(int *version, git_config *config)
 	if (error < 0)
 		return -1;
 
-	if (GIT_REPO_MAX_VERSION < *version) {
+	if (*version < 0) {
+		git_error_set(GIT_ERROR_REPOSITORY,
+			"invalid repository version %d", *version);
+	}
+
+	if (GIT_REPO_VERSION_MAX < *version) {
 		git_error_set(GIT_ERROR_REPOSITORY,
 			"unsupported repository version %d; only versions up to %d are supported",
-			*version, GIT_REPO_MAX_VERSION);
+			*version, GIT_REPO_VERSION_MAX);
 		return -1;
 	}
 
@@ -1549,7 +1567,8 @@ static int check_repositoryformatversion(int *version, git_config *config)
 }
 
 static const char *builtin_extensions[] = {
-	"noop"
+	"noop",
+	"objectformat"
 };
 
 static git_vector user_extensions = GIT_VECTOR_INIT;
@@ -1613,6 +1632,79 @@ static int check_extensions(git_config *config, int version)
 	return git_config_foreach_match(config, "^extensions\\.", check_valid_extension, NULL);
 }
 
+static int load_objectformat(git_repository *repo, git_config *config)
+{
+	git_config_entry *entry = NULL;
+	int error;
+
+	if ((error = git_config_get_entry(&entry, config, "extensions.objectformat")) < 0) {
+		if (error == GIT_ENOTFOUND) {
+			repo->oid_type = GIT_OID_SHA1;
+			git_error_clear();
+			error = 0;
+		}
+
+		goto done;
+	}
+
+	if ((repo->oid_type = git_oid_type_fromstr(entry->value)) == 0) {
+		git_error_set(GIT_ERROR_REPOSITORY,
+			"unknown object format '%s'", entry->value);
+		error = GIT_EINVALID;
+	}
+
+done:
+	git_config_entry_free(entry);
+	return error;
+}
+
+int git_repository__set_objectformat(
+	git_repository *repo,
+	git_oid_t oid_type)
+{
+	git_config *cfg;
+
+	/*
+	 * Older clients do not necessarily understand the
+	 * `objectformat` extension, even when it's set to an
+	 * object format that they understand (SHA1). Do not set
+	 * the objectformat extension unless we're not using the
+	 * default object format.
+	 */
+	if (oid_type == GIT_OID_DEFAULT)
+		return 0;
+
+	if (!git_repository_is_empty(repo) && repo->oid_type != oid_type) {
+		git_error_set(GIT_ERROR_REPOSITORY,
+			"cannot change object id type of existing repository");
+		return -1;
+	}
+
+	if (git_repository_config__weakptr(&cfg, repo) < 0)
+		return -1;
+
+	if (git_config_set_int32(cfg,
+			"core.repositoryformatversion", 1) < 0 ||
+	    git_config_set_string(cfg, "extensions.objectformat",
+			git_oid_type_name(oid_type)) < 0)
+		return -1;
+
+	/*
+	 * During repo init, we may create some backends with the
+	 * default oid type. Clear them so that we create them with
+	 * the proper oid type.
+	 */
+	if (repo->oid_type != oid_type) {
+		set_index(repo, NULL);
+		set_odb(repo, NULL);
+		set_refdb(repo, NULL);
+
+		repo->oid_type = oid_type;
+	}
+
+	return 0;
+}
+
 int git_repository__extensions(char ***out, size_t *out_len)
 {
 	git_vector extensions;
@@ -1891,19 +1983,21 @@ static int repo_init_config(
 	const char *repo_dir,
 	const char *work_dir,
 	uint32_t flags,
-	uint32_t mode)
+	uint32_t mode,
+	git_oid_t oid_type)
 {
 	int error = 0;
 	git_str cfg_path = GIT_STR_INIT, worktree_path = GIT_STR_INIT;
 	git_config *config = NULL;
 	bool is_bare = ((flags & GIT_REPOSITORY_INIT_BARE) != 0);
 	bool is_reinit = ((flags & GIT_REPOSITORY_INIT__IS_REINIT) != 0);
-	int version = 0;
+	int version = GIT_REPO_VERSION_DEFAULT;
 
 	if ((error = repo_local_config(&config, &cfg_path, NULL, repo_dir)) < 0)
 		goto cleanup;
 
-	if (is_reinit && (error = check_repositoryformatversion(&version, config)) < 0)
+	if (is_reinit &&
+	    (error = check_repositoryformatversion(&version, config)) < 0)
 		goto cleanup;
 
 	if ((error = check_extensions(config, version)) < 0)
@@ -1914,7 +2008,7 @@ static int repo_init_config(
 		goto cleanup; } while (0)
 
 	SET_REPO_CONFIG(bool, "core.bare", is_bare);
-	SET_REPO_CONFIG(int32, "core.repositoryformatversion", GIT_REPO_VERSION);
+	SET_REPO_CONFIG(int32, "core.repositoryformatversion", version);
 
 	if ((error = repo_init_fs_configs(
 			config, cfg_path.ptr, repo_dir, work_dir, !is_reinit)) < 0)
@@ -1947,6 +2041,11 @@ static int repo_init_config(
 		SET_REPO_CONFIG(bool, "receive.denyNonFastforwards", true);
 	}
 
+	if (oid_type != GIT_OID_SHA1) {
+		SET_REPO_CONFIG(int32, "core.repositoryformatversion", 1);
+		SET_REPO_CONFIG(string, "extensions.objectformat", git_oid_type_name(oid_type));
+	}
+
 cleanup:
 	git_str_dispose(&cfg_path);
 	git_str_dispose(&worktree_path);
@@ -2427,6 +2526,7 @@ int git_repository_init_ext(
 		common_path = GIT_STR_INIT;
 	const char *wd;
 	bool is_valid;
+	git_oid_t oid_type = GIT_OID_DEFAULT;
 	int error;
 
 	GIT_ASSERT_ARG(out);
@@ -2435,6 +2535,11 @@ int git_repository_init_ext(
 
 	GIT_ERROR_CHECK_VERSION(opts, GIT_REPOSITORY_INIT_OPTIONS_VERSION, "git_repository_init_options");
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	if (opts->oid_type)
+		oid_type = opts->oid_type;
+#endif
+
 	if ((error = repo_init_directories(&repo_path, &wd_path, given_repo, opts)) < 0)
 		goto out;
 
@@ -2453,13 +2558,13 @@ int git_repository_init_ext(
 
 		opts->flags |= GIT_REPOSITORY_INIT__IS_REINIT;
 
-		if ((error = repo_init_config(repo_path.ptr, wd, opts->flags, opts->mode)) < 0)
+		if ((error = repo_init_config(repo_path.ptr, wd, opts->flags, opts->mode, oid_type)) < 0)
 			goto out;
 
 		/* TODO: reinitialize the templates */
 	} else {
 		if ((error = repo_init_structure(repo_path.ptr, wd, opts)) < 0 ||
-		    (error = repo_init_config(repo_path.ptr, wd, opts->flags, opts->mode)) < 0 ||
+		    (error = repo_init_config(repo_path.ptr, wd, opts->flags, opts->mode, oid_type)) < 0 ||
 		    (error = repo_init_head(repo_path.ptr, opts->initial_head)) < 0)
 			goto out;
 	}
@@ -2922,14 +3027,14 @@ int git_repository__set_orig_head(git_repository *repo, const git_oid *orig_head
 {
 	git_filebuf file = GIT_FILEBUF_INIT;
 	git_str file_path = GIT_STR_INIT;
-	char orig_head_str[GIT_OID_SHA1_HEXSIZE];
+	char orig_head_str[GIT_OID_MAX_HEXSIZE];
 	int error = 0;
 
 	git_oid_fmt(orig_head_str, orig_head);
 
 	if ((error = git_str_joinpath(&file_path, repo->gitdir, GIT_ORIG_HEAD_FILE)) == 0 &&
 		(error = git_filebuf_open(&file, file_path.ptr, GIT_FILEBUF_CREATE_LEADING_DIRS, GIT_MERGE_FILE_MODE)) == 0 &&
-		(error = git_filebuf_printf(&file, "%.*s\n", GIT_OID_SHA1_HEXSIZE, orig_head_str)) == 0)
+		(error = git_filebuf_printf(&file, "%.*s\n", (int)git_oid_hexsize(repo->oid_type), orig_head_str)) == 0)
 		error = git_filebuf_commit(&file);
 
 	if (error < 0)
@@ -3042,7 +3147,7 @@ int git_repository_hashfile(
 		goto cleanup;
 	}
 
-	error = git_odb__hashfd_filtered(out, fd, (size_t)len, type, GIT_OID_SHA1, fl);
+	error = git_odb__hashfd_filtered(out, fd, (size_t)len, type, repo->oid_type, fl);
 
 cleanup:
 	if (fd >= 0)
@@ -3389,3 +3494,8 @@ int git_repository_submodule_cache_clear(git_repository *repo)
 	repo->submodule_cache = NULL;
 	return error;
 }
+
+git_oid_t git_repository_oid_type(git_repository *repo)
+{
+	return repo ? repo->oid_type : 0;
+}

src/libgit2/repository.h

@@ -153,6 +153,7 @@ struct git_repository {
 
 	unsigned is_bare:1;
 	unsigned is_worktree:1;
+	git_oid_t oid_type;
 
 	unsigned int lru_counter;
 
@@ -256,4 +257,12 @@ int git_repository__extensions(char ***out, size_t *out_len);
 int git_repository__set_extensions(const char **extensions, size_t len);
 void git_repository__free_extensions(void);
 
+/*
+ * Set the object format (OID type) for a repository; this will set
+ * both the configuration and the internal value for the oid type.
+ */
+int git_repository__set_objectformat(
+	git_repository *repo,
+	git_oid_t oid_type);
+
 #endif

src/libgit2/revparse.c

@@ -15,21 +15,28 @@
 
 #include "git2.h"
 
-static int maybe_sha_or_abbrev(git_object **out, git_repository *repo, const char *spec, size_t speclen)
+static int maybe_sha_or_abbrev(
+	git_object **out,
+	git_repository *repo,
+	const char *spec,
+	size_t speclen)
 {
 	git_oid oid;
 
-	if (git_oid__fromstrn(&oid, spec, speclen, GIT_OID_SHA1) < 0)
+	if (git_oid__fromstrn(&oid, spec, speclen, repo->oid_type) < 0)
 		return GIT_ENOTFOUND;
 
 	return git_object_lookup_prefix(out, repo, &oid, speclen, GIT_OBJECT_ANY);
 }
 
-static int maybe_sha(git_object **out, git_repository *repo, const char *spec)
+static int maybe_sha(
+	git_object **out,
+	git_repository *repo,
+	const char *spec)
 {
 	size_t speclen = strlen(spec);
 
-	if (speclen != GIT_OID_SHA1_HEXSIZE)
+	if (speclen != git_oid_hexsize(repo->oid_type))
 		return GIT_ENOTFOUND;
 
 	return maybe_sha_or_abbrev(out, repo, spec, speclen);
@@ -110,8 +117,8 @@ static int revparse_lookup_object(
 	if (error != GIT_ENOTFOUND)
 		return error;
 
-	if ((strlen(spec) < GIT_OID_SHA1_HEXSIZE) &&
-		((error = maybe_abbrev(object_out, repo, spec)) != GIT_ENOTFOUND))
+	if ((strlen(spec) < git_oid_hexsize(repo->oid_type)) &&
+	    ((error = maybe_abbrev(object_out, repo, spec)) != GIT_ENOTFOUND))
 			return error;
 
 	if ((error = maybe_describe(object_out, repo, spec)) != GIT_ENOTFOUND)

src/libgit2/streams/socket.c

@@ -135,9 +135,11 @@ static ssize_t socket_write(git_stream *stream, const char *data, size_t len, in
 	git_socket_stream *st = (git_socket_stream *) stream;
 	ssize_t written;
 
+	assert(flags == 0);
+
 	errno = 0;
 
-	if ((written = p_send(st->s, data, len, flags)) < 0) {
+	if ((written = p_send(st->s, data, len, 0)) < 0) {
 		net_set_error("error sending data");
 		return -1;
 	}

src/libgit2/tag.c

@@ -65,7 +65,11 @@ static int tag_error(const char *str)
 	return GIT_EINVALID;
 }
 
-static int tag_parse(git_tag *tag, const char *buffer, const char *buffer_end)
+static int tag_parse(
+	git_tag *tag,
+	const char *buffer,
+	const char *buffer_end,
+	git_oid_t oid_type)
 {
 	static const char *tag_types[] = {
 		NULL, "commit\n", "tree\n", "blob\n", "tag\n"
@@ -76,7 +80,7 @@ static int tag_parse(git_tag *tag, const char *buffer, const char *buffer_end)
 	int error;
 
 	if (git_object__parse_oid_header(&tag->target,
-			&buffer, buffer_end, "object ", GIT_OID_SHA1) < 0)
+			&buffer, buffer_end, "object ", oid_type) < 0)
 		return tag_error("object field invalid");
 
 	if (buffer + 5 >= buffer_end)
@@ -161,18 +165,25 @@ static int tag_parse(git_tag *tag, const char *buffer, const char *buffer_end)
 	return 0;
 }
 
-int git_tag__parse_raw(void *_tag, const char *data, size_t size)
+int git_tag__parse_raw(
+	void *_tag,
+	const char *data,
+	size_t size,
+	git_oid_t oid_type)
 {
-	return tag_parse(_tag, data, data + size);
+	return tag_parse(_tag, data, data + size, oid_type);
 }
 
-int git_tag__parse(void *_tag, git_odb_object *odb_obj)
+int git_tag__parse(
+	void *_tag,
+	git_odb_object *odb_obj,
+	git_oid_t oid_type)
 {
 	git_tag *tag = _tag;
 	const char *buffer = git_odb_object_data(odb_obj);
 	const char *buffer_end = buffer + git_odb_object_size(odb_obj);
 
-	return tag_parse(tag, buffer, buffer_end);
+	return tag_parse(tag, buffer, buffer_end, oid_type);
 }
 
 static int retrieve_tag_reference(
@@ -374,7 +385,7 @@ int git_tag_create_from_buffer(git_oid *oid, git_repository *repo, const char *b
 		return -1;
 
 	/* validate the buffer */
-	if (tag_parse(&tag, buffer, buffer + strlen(buffer)) < 0)
+	if (tag_parse(&tag, buffer, buffer + strlen(buffer), repo->oid_type) < 0)
 		return -1;
 
 	/* validate the target */

src/libgit2/tag.h

@@ -25,7 +25,7 @@ struct git_tag {
 };
 
 void git_tag__free(void *tag);
-int git_tag__parse(void *tag, git_odb_object *obj);
-int git_tag__parse_raw(void *tag, const char *data, size_t size);
+int git_tag__parse(void *tag, git_odb_object *obj, git_oid_t oid_type);
+int git_tag__parse_raw(void *tag, const char *data, size_t size, git_oid_t oid_type);
 
 #endif

src/libgit2/transports/local.c

@@ -266,6 +266,17 @@ static int local_capabilities(unsigned int *capabilities, git_transport *transpo
 	return 0;
 }
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+static int local_oid_type(git_oid_t *out, git_transport *transport)
+{
+	transport_local *t = (transport_local *)transport;
+
+	*out = t->repo->oid_type;
+
+	return 0;
+}
+#endif
+
 static int local_ls(const git_remote_head ***out, size_t *size, git_transport *transport)
 {
 	transport_local *t = (transport_local *)transport;
@@ -732,6 +743,9 @@ int git_transport_local(git_transport **out, git_remote *owner, void *param)
 	t->parent.connect = local_connect;
 	t->parent.set_connect_opts = local_set_connect_opts;
 	t->parent.capabilities = local_capabilities;
+#ifdef GIT_EXPERIMENTAL_SHA256
+	t->parent.oid_type = local_oid_type;
+#endif
 	t->parent.negotiate_fetch = local_negotiate_fetch;
 	t->parent.download_pack = local_download_pack;
 	t->parent.push = local_push;

src/libgit2/transports/smart.c

@@ -54,6 +54,12 @@ GIT_INLINE(int) git_smart__reset_stream(transport_smart *t, bool close_subtransp
 			return -1;
 	}
 
+	git__free(t->caps.object_format);
+	t->caps.object_format = NULL;
+
+	git__free(t->caps.agent);
+	t->caps.agent = NULL;
+
 	return 0;
 }
 
@@ -242,6 +248,30 @@ static int git_smart__capabilities(unsigned int *capabilities, git_transport *tr
 	return 0;
 }
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+static int git_smart__oid_type(git_oid_t *out, git_transport *transport)
+{
+	transport_smart *t = GIT_CONTAINER_OF(transport, transport_smart, parent);
+
+	*out = 0;
+
+	if (t->caps.object_format == NULL) {
+		*out = GIT_OID_DEFAULT;
+	} else {
+		*out = git_oid_type_fromstr(t->caps.object_format);
+
+		if (!*out) {
+			git_error_set(GIT_ERROR_INVALID,
+				"unknown object format '%s'",
+				t->caps.object_format);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+#endif
+
 static int git_smart__ls(const git_remote_head ***out, size_t *size, git_transport *transport)
 {
 	transport_smart *t = GIT_CONTAINER_OF(transport, transport_smart, parent);
@@ -386,6 +416,8 @@ static void git_smart__free(git_transport *transport)
 
 	git_remote_connect_options_dispose(&t->connect_opts);
 
+	git__free(t->caps.object_format);
+	git__free(t->caps.agent);
 	git__free(t);
 }
 
@@ -452,6 +484,9 @@ int git_transport_smart(git_transport **out, git_remote *owner, void *param)
 	t->parent.connect = git_smart__connect;
 	t->parent.set_connect_opts = git_smart__set_connect_opts;
 	t->parent.capabilities = git_smart__capabilities;
+#ifdef GIT_EXPERIMENTAL_SHA256
+	t->parent.oid_type = git_smart__oid_type;
+#endif
 	t->parent.close = git_smart__close;
 	t->parent.free = git_smart__free;
 	t->parent.negotiate_fetch = git_smart__negotiate_fetch;

src/libgit2/transports/smart.h

@@ -32,6 +32,8 @@
 #define GIT_CAP_SYMREF "symref"
 #define GIT_CAP_WANT_TIP_SHA1 "allow-tip-sha1-in-want"
 #define GIT_CAP_WANT_REACHABLE_SHA1 "allow-reachable-sha1-in-want"
+#define GIT_CAP_OBJECT_FORMAT "object-format="
+#define GIT_CAP_AGENT "agent="
 
 extern bool git_smart__ofs_delta_enabled;
 
@@ -133,6 +135,8 @@ typedef struct transport_smart_caps {
 	             thin_pack:1,
 	             want_tip_sha1:1,
 	             want_reachable_sha1:1;
+	char *object_format;
+	char *agent;
 } transport_smart_caps;
 
 typedef int (*packetsize_cb)(size_t received, void *payload);
@@ -182,7 +186,12 @@ int git_smart__get_push_stream(transport_smart *t, git_smart_subtransport_stream
 int git_smart__update_heads(transport_smart *t, git_vector *symrefs);
 
 /* smart_pkt.c */
-int git_pkt_parse_line(git_pkt **head, const char **endptr, const char *line, size_t linelen);
+typedef struct {
+	git_oid_t oid_type;
+	int seen_capabilities: 1;
+} git_pkt_parse_data;
+
+int git_pkt_parse_line(git_pkt **head, const char **endptr, const char *line, size_t linelen, git_pkt_parse_data *data);
 int git_pkt_buffer_flush(git_str *buf);
 int git_pkt_send_flush(GIT_SOCKET s);
 int git_pkt_buffer_done(git_str *buf);

src/libgit2/transports/smart_pkt.c

@@ -21,11 +21,14 @@
 
 #include <ctype.h>
 
-#define PKT_LEN_SIZE 4
-static const char pkt_done_str[] = "0009done\n";
-static const char pkt_flush_str[] = "0000";
-static const char pkt_have_prefix[] = "0032have ";
-static const char pkt_want_prefix[] = "0032want ";
+#define PKT_DONE_STR    "0009done\n"
+#define PKT_FLUSH_STR   "0000"
+#define PKT_HAVE_PREFIX "have "
+#define PKT_WANT_PREFIX "want "
+
+#define PKT_LEN_SIZE    4
+#define PKT_MAX_SIZE    0xffff
+#define PKT_MAX_WANTLEN (PKT_LEN_SIZE + CONST_STRLEN(PKT_WANT_PREFIX) + GIT_OID_MAX_HEXSIZE + 1)
 
 static int flush_pkt(git_pkt **out)
 {
@@ -212,26 +215,87 @@ static int sideband_error_pkt(git_pkt **out, const char *line, size_t len)
 	return 0;
 }
 
+static int set_data(
+	git_pkt_parse_data *data,
+	const char *line,
+	size_t len)
+{
+	const char *caps, *format_str = NULL, *eos;
+	size_t format_len;
+	git_oid_t remote_oid_type;
+
+	GIT_ASSERT_ARG(data);
+
+	if ((caps = memchr(line, '\0', len)) != NULL) {
+		caps++;
+
+		if (strncmp(caps, "object-format=", CONST_STRLEN("object-format=")) == 0)
+			format_str = caps + CONST_STRLEN("object-format=");
+		else if ((format_str = strstr(caps, " object-format=")) != NULL)
+			format_str += CONST_STRLEN(" object-format=");
+	}
+
+	if (format_str) {
+		if ((eos = strchr(format_str, ' ')) == NULL)
+			eos = strchr(format_str, '\0');
+
+		GIT_ASSERT(eos);
+
+		format_len = eos - format_str;
+
+		if ((remote_oid_type = git_oid_type_fromstrn(format_str, format_len)) == 0) {
+			git_error_set(GIT_ERROR_INVALID, "unknown remote object format '%.*s'", (int)format_len, format_str);
+			return -1;
+		}
+	} else {
+		remote_oid_type = GIT_OID_SHA1;
+	}
+
+	if (!data->oid_type) {
+		data->oid_type = remote_oid_type;
+	} else if (data->oid_type != remote_oid_type) {
+		git_error_set(GIT_ERROR_INVALID,
+		              "the local object format '%s' does not match the remote object format '%s'",
+		              git_oid_type_name(data->oid_type),
+		              git_oid_type_name(remote_oid_type));
+		return -1;
+	}
+
+	return 0;
+}
+
 /*
  * Parse an other-ref line.
  */
-static int ref_pkt(git_pkt **out, const char *line, size_t len)
+static int ref_pkt(
+	git_pkt **out,
+	const char *line,
+	size_t len,
+	git_pkt_parse_data *data)
 {
 	git_pkt_ref *pkt;
-	size_t alloclen;
+	size_t alloclen, oid_hexsize;
 
 	pkt = git__calloc(1, sizeof(git_pkt_ref));
 	GIT_ERROR_CHECK_ALLOC(pkt);
 	pkt->type = GIT_PKT_REF;
 
-	if (len < GIT_OID_SHA1_HEXSIZE ||
-	    git_oid__fromstr(&pkt->head.oid, line, GIT_OID_SHA1) < 0)
+	/* Determine OID type from capabilities */
+	if (!data->seen_capabilities && set_data(data, line, len) < 0)
+		return -1;
+
+	GIT_ASSERT(data->oid_type);
+	oid_hexsize = git_oid_hexsize(data->oid_type);
+
+	if (len < oid_hexsize ||
+	    git_oid__fromstr(&pkt->head.oid, line, data->oid_type) < 0)
 		goto out_err;
-	line += GIT_OID_SHA1_HEXSIZE;
-	len -= GIT_OID_SHA1_HEXSIZE;
+	line += oid_hexsize;
+	len -= oid_hexsize;
 
 	if (git__prefixncmp(line, len, " "))
 		goto out_err;
+
 	line++;
 	len--;
 
@@ -248,8 +312,14 @@ static int ref_pkt(git_pkt **out, const char *line, size_t len)
 	memcpy(pkt->head.name, line, len);
 	pkt->head.name[len] = '\0';
 
-	if (strlen(pkt->head.name) < len)
-		pkt->capabilities = strchr(pkt->head.name, '\0') + 1;
+	if (strlen(pkt->head.name) < len) {
+		if (!data->seen_capabilities)
+			pkt->capabilities = strchr(pkt->head.name, '\0') + 1;
+		else
+			goto out_err;
+	}
+
+	data->seen_capabilities = 1;
 
 	*out = (git_pkt *)pkt;
 	return 0;
@@ -418,7 +488,11 @@ static int parse_len(size_t *out, const char *line, size_t linelen)
  */
 
 int git_pkt_parse_line(
-	git_pkt **pkt, const char **endptr, const char *line, size_t linelen)
+	git_pkt **pkt,
+	const char **endptr,
+	const char *line,
+	size_t linelen,
+	git_pkt_parse_data *data)
 {
 	int error;
 	size_t len;
@@ -493,7 +567,7 @@ int git_pkt_parse_line(
 	else if (!git__prefixncmp(line, len, "unpack"))
 		error = unpack_pkt(pkt, line, len);
 	else
-		error = ref_pkt(pkt, line, len);
+		error = ref_pkt(pkt, line, len, data);
 
 	*endptr = line + len;
 
@@ -527,14 +601,21 @@ void git_pkt_free(git_pkt *pkt)
 
 int git_pkt_buffer_flush(git_str *buf)
 {
-	return git_str_put(buf, pkt_flush_str, strlen(pkt_flush_str));
+	return git_str_put(buf, PKT_FLUSH_STR, CONST_STRLEN(PKT_FLUSH_STR));
 }
 
-static int buffer_want_with_caps(const git_remote_head *head, transport_smart_caps *caps, git_str *buf)
+static int buffer_want_with_caps(
+	const git_remote_head *head,
+	transport_smart_caps *caps,
+	git_oid_t oid_type,
+	git_str *buf)
 {
 	git_str str = GIT_STR_INIT;
-	char oid[GIT_OID_SHA1_HEXSIZE +1] = {0};
-	size_t len;
+	char oid[GIT_OID_MAX_HEXSIZE];
+	size_t oid_hexsize, len;
+
+	oid_hexsize = git_oid_hexsize(oid_type);
+	git_oid_fmt(oid, &head->oid);
 
 	/* Prefer multi_ack_detailed */
 	if (caps->multi_ack_detailed)
@@ -560,19 +641,20 @@ static int buffer_want_with_caps(const git_remote_head *head, transport_smart_ca
 	if (git_str_oom(&str))
 		return -1;
 
-	len = strlen("XXXXwant ") + GIT_OID_SHA1_HEXSIZE + 1 /* NUL */ +
-		 git_str_len(&str) + 1 /* LF */;
-
-	if (len > 0xffff) {
+	if (str.size > (PKT_MAX_SIZE - (PKT_MAX_WANTLEN + 1))) {
 		git_error_set(GIT_ERROR_NET,
-			"tried to produce packet with invalid length %" PRIuZ, len);
+			"tried to produce packet with invalid caps length %" PRIuZ, str.size);
 		return -1;
 	}
 
+	len = PKT_LEN_SIZE + CONST_STRLEN(PKT_WANT_PREFIX) +
+	      oid_hexsize + 1 /* NUL */ +
+	      git_str_len(&str) + 1 /* LF */;
+
 	git_str_grow_by(buf, len);
-	git_oid_fmt(oid, &head->oid);
 	git_str_printf(buf,
-		"%04xwant %s %s\n", (unsigned int)len, oid, git_str_cstr(&str));
+		"%04x%s%.*s %s\n", (unsigned int)len, PKT_WANT_PREFIX,
+		(int)oid_hexsize, oid, git_str_cstr(&str));
 	git_str_dispose(&str);
 
 	GIT_ERROR_CHECK_ALLOC_STR(buf);
@@ -591,8 +673,21 @@ int git_pkt_buffer_wants(
 	transport_smart_caps *caps,
 	git_str *buf)
 {
-	size_t i = 0;
 	const git_remote_head *head;
+	char oid[GIT_OID_MAX_HEXSIZE];
+	git_oid_t oid_type;
+	size_t oid_hexsize, want_len, i = 0;
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	oid_type = count > 0 ? refs[0]->oid.type : GIT_OID_SHA1;
+#else
+	oid_type = GIT_OID_SHA1;
+#endif
+
+	oid_hexsize = git_oid_hexsize(oid_type);
+
+	want_len = PKT_LEN_SIZE + CONST_STRLEN(PKT_WANT_PREFIX) +
+	      oid_hexsize + 1 /* LF */;
 
 	if (caps->common) {
 		for (; i < count; ++i) {
@@ -601,23 +696,24 @@ int git_pkt_buffer_wants(
 				break;
 		}
 
-		if (buffer_want_with_caps(refs[i], caps, buf) < 0)
+		if (buffer_want_with_caps(refs[i], caps, oid_type, buf) < 0)
 			return -1;
 
 		i++;
 	}
 
 	for (; i < count; ++i) {
-		char oid[GIT_OID_SHA1_HEXSIZE];
-
 		head = refs[i];
+
 		if (head->local)
 			continue;
 
 		git_oid_fmt(oid, &head->oid);
-		git_str_put(buf, pkt_want_prefix, strlen(pkt_want_prefix));
-		git_str_put(buf, oid, GIT_OID_SHA1_HEXSIZE);
-		git_str_putc(buf, '\n');
+
+		git_str_printf(buf, "%04x%s%.*s\n",
+			(unsigned int)want_len, PKT_WANT_PREFIX,
+			(int)oid_hexsize, oid);
+
 		if (git_str_oom(buf))
 			return -1;
 	}
@@ -627,14 +723,27 @@ int git_pkt_buffer_wants(
 
 int git_pkt_buffer_have(git_oid *oid, git_str *buf)
 {
-	char oidhex[GIT_OID_SHA1_HEXSIZE + 1];
-
-	memset(oidhex, 0x0, sizeof(oidhex));
-	git_oid_fmt(oidhex, oid);
-	return git_str_printf(buf, "%s%s\n", pkt_have_prefix, oidhex);
+	char oid_str[GIT_OID_MAX_HEXSIZE];
+	git_oid_t oid_type;
+	size_t oid_hexsize, have_len;
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	oid_type = oid->type;
+#else
+	oid_type = GIT_OID_SHA1;
+#endif
+
+	oid_hexsize = git_oid_hexsize(oid_type);
+	have_len = PKT_LEN_SIZE + CONST_STRLEN(PKT_HAVE_PREFIX) +
+	      oid_hexsize + 1 /* LF */;
+
+	git_oid_fmt(oid_str, oid);
+	return git_str_printf(buf, "%04x%s%.*s\n",
+		(unsigned int)have_len, PKT_HAVE_PREFIX,
+		(int)oid_hexsize, oid_str);
 }
 
 int git_pkt_buffer_done(git_str *buf)
 {
-	return git_str_puts(buf, pkt_done_str);
+	return git_str_put(buf, PKT_DONE_STR, CONST_STRLEN(PKT_DONE_STR));
 }

src/libgit2/transports/smart_protocol.c

@@ -32,6 +32,7 @@ int git_smart__store_refs(transport_smart *t, int flushes)
 	int error, flush = 0, recvd;
 	const char *line_end = NULL;
 	git_pkt *pkt = NULL;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 	size_t i;
 
 	/* Clear existing refs in case git_remote_connect() is called again
@@ -45,7 +46,7 @@ int git_smart__store_refs(transport_smart *t, int flushes)
 
 	do {
 		if (buf->offset > 0)
-			error = git_pkt_parse_line(&pkt, &line_end, buf->data, buf->offset);
+			error = git_pkt_parse_line(&pkt, &line_end, buf->data, buf->offset, &pkt_parse_data);
 		else
 			error = GIT_EBUFS;
 
@@ -133,9 +134,12 @@ on_invalid:
 	return -1;
 }
 
-int git_smart__detect_caps(git_pkt_ref *pkt, transport_smart_caps *caps, git_vector *symrefs)
+int git_smart__detect_caps(
+	git_pkt_ref *pkt,
+	transport_smart_caps *caps,
+	git_vector *symrefs)
 {
-	const char *ptr;
+	const char *ptr, *start;
 
 	/* No refs or capabilities, odd but not a problem */
 	if (pkt == NULL || pkt->capabilities == NULL)
@@ -217,6 +221,28 @@ int git_smart__detect_caps(git_pkt_ref *pkt, transport_smart_caps *caps, git_vec
 			continue;
 		}
 
+		if (!git__prefixcmp(ptr, GIT_CAP_OBJECT_FORMAT)) {
+			ptr += strlen(GIT_CAP_OBJECT_FORMAT);
+
+			start = ptr;
+			ptr = strchr(ptr, ' ');
+
+			if ((caps->object_format = git__strndup(start, (ptr - start))) == NULL)
+				return -1;
+			continue;
+		}
+
+		if (!git__prefixcmp(ptr, GIT_CAP_AGENT)) {
+			ptr += strlen(GIT_CAP_AGENT);
+
+			start = ptr;
+			ptr = strchr(ptr, ' ');
+
+			if ((caps->agent = git__strndup(start, (ptr - start))) == NULL)
+				return -1;
+			continue;
+		}
+
 		/* We don't know this capability, so skip it */
 		ptr = strchr(ptr, ' ');
 	}
@@ -228,11 +254,12 @@ static int recv_pkt(git_pkt **out_pkt, git_pkt_type *out_type, gitno_buffer *buf
 {
 	const char *ptr = buf->data, *line_end = ptr;
 	git_pkt *pkt = NULL;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 	int error = 0, ret;
 
 	do {
 		if (buf->offset > 0)
-			error = git_pkt_parse_line(&pkt, &line_end, ptr, buf->offset);
+			error = git_pkt_parse_line(&pkt, &line_end, ptr, buf->offset, &pkt_parse_data);
 		else
 			error = GIT_EBUFS;
 
@@ -723,6 +750,7 @@ static int add_push_report_pkt(git_push *push, git_pkt *pkt)
 static int add_push_report_sideband_pkt(git_push *push, git_pkt_data *data_pkt, git_str *data_pkt_buf)
 {
 	git_pkt *pkt;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 	const char *line, *line_end = NULL;
 	size_t line_len;
 	int error;
@@ -741,7 +769,7 @@ static int add_push_report_sideband_pkt(git_push *push, git_pkt_data *data_pkt,
 	}
 
 	while (line_len > 0) {
-		error = git_pkt_parse_line(&pkt, &line_end, line, line_len);
+		error = git_pkt_parse_line(&pkt, &line_end, line, line_len, &pkt_parse_data);
 
 		if (error == GIT_EBUFS) {
 			/* Buffer the data when the inner packet is split
@@ -777,6 +805,7 @@ done:
 static int parse_report(transport_smart *transport, git_push *push)
 {
 	git_pkt *pkt = NULL;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 	const char *line_end = NULL;
 	gitno_buffer *buf = &transport->buffer;
 	int error, recvd;
@@ -785,7 +814,8 @@ static int parse_report(transport_smart *transport, git_push *push)
 	for (;;) {
 		if (buf->offset > 0)
 			error = git_pkt_parse_line(&pkt, &line_end,
-						   buf->data, buf->offset);
+						   buf->data, buf->offset,
+						   &pkt_parse_data);
 		else
 			error = GIT_EBUFS;
 

src/libgit2/tree.c

@@ -85,11 +85,17 @@ static git_tree_entry *alloc_entry(const char *filename, size_t filename_len, co
 	char *filename_ptr;
 	size_t tree_len;
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	size_t oid_size = git_oid_size(id->type);
+#else
+	size_t oid_size = GIT_OID_SHA1_SIZE;
+#endif
+
 	TREE_ENTRY_CHECK_NAMELEN(filename_len);
 
 	if (GIT_ADD_SIZET_OVERFLOW(&tree_len, sizeof(git_tree_entry), filename_len) ||
 	    GIT_ADD_SIZET_OVERFLOW(&tree_len, tree_len, 1) ||
-	    GIT_ADD_SIZET_OVERFLOW(&tree_len, tree_len, GIT_OID_SHA1_SIZE))
+	    GIT_ADD_SIZET_OVERFLOW(&tree_len, tree_len, oid_size))
 		return NULL;
 
 	entry = git__calloc(1, tree_len);
@@ -383,11 +389,12 @@ static int parse_mode(uint16_t *mode_out, const char *buffer, size_t buffer_len,
 	return 0;
 }
 
-int git_tree__parse_raw(void *_tree, const char *data, size_t size)
+int git_tree__parse_raw(void *_tree, const char *data, size_t size, git_oid_t oid_type)
 {
 	git_tree *tree = _tree;
 	const char *buffer;
 	const char *buffer_end;
+	const long oid_size = (long)git_oid_size(oid_type);
 
 	buffer = data;
 	buffer_end = buffer + size;
@@ -414,35 +421,33 @@ int git_tree__parse_raw(void *_tree, const char *data, size_t size)
 		if ((filename_len = nul - buffer) == 0 || filename_len > UINT16_MAX)
 			return tree_parse_error("failed to parse tree: can't parse filename", NULL);
 
-		if ((buffer_end - (nul + 1)) < GIT_OID_SHA1_SIZE)
+		if ((buffer_end - (nul + 1)) < (long)oid_size)
 			return tree_parse_error("failed to parse tree: can't parse OID", NULL);
 
 		/* Allocate the entry */
-		{
-			entry = git_array_alloc(tree->entries);
-			GIT_ERROR_CHECK_ALLOC(entry);
-
-			entry->attr = attr;
-			entry->filename_len = (uint16_t)filename_len;
-			entry->filename = buffer;
-			git_oid__fromraw(&entry->oid, ((unsigned char *) buffer + filename_len + 1), GIT_OID_SHA1);
-		}
+		entry = git_array_alloc(tree->entries);
+		GIT_ERROR_CHECK_ALLOC(entry);
 
+		entry->attr = attr;
+		entry->filename_len = (uint16_t)filename_len;
+		entry->filename = buffer;
 		buffer += filename_len + 1;
-		buffer += GIT_OID_SHA1_SIZE;
+
+		git_oid__fromraw(&entry->oid, (unsigned char *)buffer, oid_type);
+		buffer += oid_size;
 	}
 
 	return 0;
 }
 
-int git_tree__parse(void *_tree, git_odb_object *odb_obj)
+int git_tree__parse(void *_tree, git_odb_object *odb_obj, git_oid_t oid_type)
 {
 	git_tree *tree = _tree;
 	const char *data = git_odb_object_data(odb_obj);
 	size_t size = git_odb_object_size(odb_obj);
 	int error;
 
-	if ((error = git_tree__parse_raw(tree, data, size)) < 0 ||
+	if ((error = git_tree__parse_raw(tree, data, size, oid_type)) < 0 ||
 	    (error = git_odb_object_dup(&tree->odb_obj, odb_obj)) < 0)
 		return error;
 
@@ -506,6 +511,7 @@ static int git_treebuilder__write_with_buffer(
 	git_odb *odb;
 	git_tree_entry *entry;
 	git_vector entries = GIT_VECTOR_INIT;
+	size_t oid_size = git_oid_size(bld->repo->oid_type);
 
 	git_str_clear(buf);
 
@@ -529,7 +535,7 @@ static int git_treebuilder__write_with_buffer(
 
 		git_str_printf(buf, "%o ", entry->attr);
 		git_str_put(buf, entry->filename, entry->filename_len + 1);
-		git_str_put(buf, (char *)entry->oid.id, GIT_OID_SHA1_SIZE);
+		git_str_put(buf, (char *)entry->oid.id, oid_size);
 
 		if (git_str_oom(buf)) {
 			error = -1;

src/libgit2/tree.h

@@ -41,8 +41,8 @@ GIT_INLINE(bool) git_tree_entry__is_tree(const struct git_tree_entry *e)
 }
 
 void git_tree__free(void *tree);
-int git_tree__parse(void *tree, git_odb_object *obj);
-int git_tree__parse_raw(void *_tree, const char *data, size_t size);
+int git_tree__parse(void *tree, git_odb_object *obj, git_oid_t oid_type);
+int git_tree__parse_raw(void *_tree, const char *data, size_t size, git_oid_t oid_type);
 
 /**
  * Write a tree to the given repository

src/util/hash.h

@@ -23,6 +23,8 @@ typedef enum {
 	GIT_HASH_ALGORITHM_SHA256
 } git_hash_algorithm_t;
 
+#define GIT_HASH_MAX_SIZE GIT_HASH_SHA256_SIZE
+
 typedef struct git_hash_ctx {
 	union {
 		git_hash_sha1_ctx sha1;
@@ -45,4 +47,15 @@ int git_hash_vec(unsigned char *out, git_str_vec *vec, size_t n, git_hash_algori
 
 int git_hash_fmt(char *out, unsigned char *hash, size_t hash_len);
 
+GIT_INLINE(size_t) git_hash_size(git_hash_algorithm_t algorithm) {
+	switch (algorithm) {
+		case GIT_HASH_ALGORITHM_SHA1:
+			return GIT_HASH_SHA1_SIZE;
+		case GIT_HASH_ALGORITHM_SHA256:
+			return GIT_HASH_SHA256_SIZE;
+		default:
+			return 0;
+	}
+}
+
 #endif

tests/clar/clar_libgit2.c

@@ -477,6 +477,25 @@ int cl_repo_get_bool(git_repository *repo, const char *cfg)
 	return val;
 }
 
+void cl_repo_set_int(git_repository *repo, const char *cfg, int value)
+{
+	git_config *config;
+	cl_git_pass(git_repository_config(&config, repo));
+	cl_git_pass(git_config_set_int32(config, cfg, value));
+	git_config_free(config);
+}
+
+int cl_repo_get_int(git_repository *repo, const char *cfg)
+{
+	int val = 0;
+	git_config *config;
+	cl_git_pass(git_repository_config(&config, repo));
+	if (git_config_get_int32(&val, config, cfg) < 0)
+		git_error_clear();
+	git_config_free(config);
+	return val;
+}
+
 void cl_repo_set_string(git_repository *repo, const char *cfg, const char *value)
 {
 	git_config *config;

tests/clar/clar_libgit2.h

@@ -231,6 +231,9 @@ void cl_repo_commit_from_index(
 void cl_repo_set_bool(git_repository *repo, const char *cfg, int value);
 int cl_repo_get_bool(git_repository *repo, const char *cfg);
 
+void cl_repo_set_int(git_repository *repo, const char *cfg, int value);
+int cl_repo_get_int(git_repository *repo, const char *cfg);
+
 void cl_repo_set_string(git_repository *repo, const char *cfg, const char *value);
 
 /*

tests/libgit2/CMakeLists.txt

@@ -70,6 +70,7 @@ add_clar_test(libgit2_tests online              -v -sonline -xonline::customcert
 add_clar_test(libgit2_tests online_customcert   -v -sonline::customcert)
 add_clar_test(libgit2_tests gitdaemon           -v -sonline::push)
 add_clar_test(libgit2_tests gitdaemon_namespace -v -sonline::clone::namespace)
+add_clar_test(libgit2_tests gitdaemon_sha256    -v -sonline::clone::sha256)
 add_clar_test(libgit2_tests ssh                 -v -sonline::push -sonline::clone::ssh_cert -sonline::clone::ssh_with_paths -sonline::clone::path_whitespace_ssh -sonline::clone::ssh_auth_methods)
 add_clar_test(libgit2_tests proxy               -v -sonline::clone::proxy)
 add_clar_test(libgit2_tests auth_clone          -v -sonline::clone::cred)

tests/libgit2/commit/parse.c

@@ -287,7 +287,7 @@ static int parse_commit(git_commit **out, const char *buffer)
 	fake_odb_object.buffer = (char *)buffer;
 	fake_odb_object.cached.size = strlen(fake_odb_object.buffer);
 
-	error = git_commit__parse(commit, &fake_odb_object);
+	error = git_commit__parse(commit, &fake_odb_object, GIT_OID_SHA1);
 
 	*out = commit;
 	return error;

tests/libgit2/core/oid.c

@@ -192,3 +192,22 @@ void test_core_oid__fmt_substr_sha1(void)
 	git_oid_fmt_substr(buf, &id_sha1, 5, 6);
 	cl_assert_equal_s(buf, "12eea6");
 }
+
+void test_core_oid__type_lookup(void)
+{
+	cl_assert_equal_i(GIT_OID_SHA1, git_oid_type_fromstr("sha1"));
+	cl_assert_equal_i(GIT_OID_SHA1, git_oid_type_fromstrn("sha1...", 4));
+	cl_assert_equal_s("sha1", git_oid_type_name(GIT_OID_SHA1));
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_assert_equal_i(GIT_OID_SHA256, git_oid_type_fromstr("sha256"));
+	cl_assert_equal_i(GIT_OID_SHA256, git_oid_type_fromstrn("sha256...", 6));
+	cl_assert_equal_s("sha256", git_oid_type_name(GIT_OID_SHA256));
+#endif
+
+	cl_assert_equal_i(0, git_oid_type_fromstr("sha42"));
+	cl_assert_equal_i(0, git_oid_type_fromstrn("sha1", 3));
+	cl_assert_equal_i(0, git_oid_type_fromstrn("sha1...", 5));
+	cl_assert_equal_s("unknown", git_oid_type_name(0));
+	cl_assert_equal_s("unknown", git_oid_type_name(42));
+}

tests/libgit2/core/opts.c

@@ -34,8 +34,9 @@ void test_core_opts__extensions_query(void)
 
 	cl_git_pass(git_libgit2_opts(GIT_OPT_GET_EXTENSIONS, &out));
 
-	cl_assert_equal_sz(out.count, 1);
+	cl_assert_equal_sz(out.count, 2);
 	cl_assert_equal_s("noop", out.strings[0]);
+	cl_assert_equal_s("objectformat", out.strings[1]);
 
 	git_strarray_dispose(&out);
 }
@@ -48,9 +49,10 @@ void test_core_opts__extensions_add(void)
 	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_EXTENSIONS, in, ARRAY_SIZE(in)));
 	cl_git_pass(git_libgit2_opts(GIT_OPT_GET_EXTENSIONS, &out));
 
-	cl_assert_equal_sz(out.count, 2);
+	cl_assert_equal_sz(out.count, 3);
 	cl_assert_equal_s("noop", out.strings[0]);
-	cl_assert_equal_s("foo", out.strings[1]);
+	cl_assert_equal_s("objectformat", out.strings[1]);
+	cl_assert_equal_s("foo", out.strings[2]);
 
 	git_strarray_dispose(&out);
 }
@@ -63,9 +65,10 @@ void test_core_opts__extensions_remove(void)
 	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_EXTENSIONS, in, ARRAY_SIZE(in)));
 	cl_git_pass(git_libgit2_opts(GIT_OPT_GET_EXTENSIONS, &out));
 
-	cl_assert_equal_sz(out.count, 2);
-	cl_assert_equal_s("bar", out.strings[0]);
-	cl_assert_equal_s("baz", out.strings[1]);
+	cl_assert_equal_sz(out.count, 3);
+	cl_assert_equal_s("objectformat", out.strings[0]);
+	cl_assert_equal_s("bar", out.strings[1]);
+	cl_assert_equal_s("baz", out.strings[2]);
 
 	git_strarray_dispose(&out);
 }

tests/libgit2/object/lookup256.c

+#include "clar_libgit2.h"
+
+#include "repository.h"
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+static git_repository *g_repo;
+#endif
+
+void test_object_lookup256__initialize(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	g_repo = cl_git_sandbox_init("testrepo_256.git");
+#endif
+}
+
+void test_object_lookup256__cleanup(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_sandbox_cleanup();
+#endif
+}
+
+void test_object_lookup256__lookup_wrong_type_returns_enotfound(void)
+{
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
+	const char *commit = "4d46d9719e425ef2dfb5bfba098d0b62e21b2b92d0731892eef70db0870e3744";
+	git_oid oid;
+	git_object *object;
+
+	cl_git_pass(git_oid__fromstr(&oid, commit, GIT_OID_SHA256));
+	cl_assert_equal_i(
+		GIT_ENOTFOUND, git_object_lookup(&object, g_repo, &oid, GIT_OBJECT_TAG));
+#endif
+}
+
+void test_object_lookup256__lookup_nonexisting_returns_enotfound(void)
+{
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
+	const char *unknown = "deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef";
+	git_oid oid;
+	git_object *object;
+
+	cl_git_pass(git_oid__fromstr(&oid, unknown, GIT_OID_SHA256));
+	cl_assert_equal_i(
+		GIT_ENOTFOUND, git_object_lookup(&object, g_repo, &oid, GIT_OBJECT_ANY));
+#endif
+}
+
+void test_object_lookup256__lookup_wrong_type_by_abbreviated_id_returns_enotfound(void)
+{
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
+	const char *commit = "4d46d97";
+	git_oid oid;
+	git_object *object;
+
+	cl_git_pass(git_oid__fromstrn(&oid, commit, strlen(commit), GIT_OID_SHA256));
+	cl_assert_equal_i(
+		GIT_ENOTFOUND, git_object_lookup_prefix(&object, g_repo, &oid, strlen(commit), GIT_OBJECT_TAG));
+#endif
+}
+
+void test_object_lookup256__lookup_wrong_type_eventually_returns_enotfound(void)
+{
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
+	const char *commit = "4d46d9719e425ef2dfb5bfba098d0b62e21b2b92d0731892eef70db0870e3744";
+	git_oid oid;
+	git_object *object;
+
+	cl_git_pass(git_oid__fromstr(&oid, commit, GIT_OID_SHA256));
+
+	cl_git_pass(git_object_lookup(&object, g_repo, &oid, GIT_OBJECT_COMMIT));
+	git_object_free(object);
+
+	cl_assert_equal_i(
+		GIT_ENOTFOUND, git_object_lookup(&object, g_repo, &oid, GIT_OBJECT_TAG));
+#endif
+}
+
+void test_object_lookup256__lookup_corrupt_object_returns_error(void)
+{
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
+	const char *commit = "5ca8959deb2b8327458e0344523eb1ddeeef4bce03e35864640b452f84d26848",
+	      *file = "objects/5c/a8959deb2b8327458e0344523eb1ddeeef4bce03e35864640b452f84d26848";
+	git_str path = GIT_STR_INIT, contents = GIT_STR_INIT;
+	git_oid oid;
+	git_object *object;
+	size_t i;
+
+	cl_git_pass(git_oid__fromstr(&oid, commit, GIT_OID_SHA256));
+	cl_git_pass(git_str_joinpath(&path, git_repository_path(g_repo), file));
+	cl_git_pass(git_futils_readbuffer(&contents, path.ptr));
+
+	/* Corrupt and try to read the object */
+	for (i = 0; i < contents.size; i++) {
+		contents.ptr[i] ^= 0x1;
+		cl_git_pass(git_futils_writebuffer(&contents, path.ptr, O_RDWR, 0644));
+		cl_git_fail(git_object_lookup(&object, g_repo, &oid, GIT_OBJECT_COMMIT));
+		contents.ptr[i] ^= 0x1;
+	}
+
+	/* Restore original content and assert we can read the object */
+	cl_git_pass(git_futils_writebuffer(&contents, path.ptr, O_RDWR, 0644));
+	cl_git_pass(git_object_lookup(&object, g_repo, &oid, GIT_OBJECT_COMMIT));
+
+	git_object_free(object);
+	git_str_dispose(&path);
+	git_str_dispose(&contents);
+#endif
+}
+
+void test_object_lookup256__lookup_object_with_wrong_hash_returns_error(void)
+{
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
+	const char *oldloose = "objects/5c/a8959deb2b8327458e0344523eb1ddeeef4bce03e35864640b452f84d26848",
+	      *newloose = "objects/5c/a8959deb2b8327458e0344523eb1ddeeef4bce03e35864640b452f84d26840",
+	      *commit = "5ca8959deb2b8327458e0344523eb1ddeeef4bce03e35864640b452f84d26840";
+
+	git_str oldpath = GIT_STR_INIT, newpath = GIT_STR_INIT;
+	git_object *object;
+	git_oid oid;
+
+	cl_git_pass(git_oid__fromstr(&oid, commit, GIT_OID_SHA256));
+
+	/* Copy object to another location with wrong hash */
+	cl_git_pass(git_str_joinpath(&oldpath, git_repository_path(g_repo), oldloose));
+	cl_git_pass(git_str_joinpath(&newpath, git_repository_path(g_repo), newloose));
+	cl_git_pass(git_futils_cp(oldpath.ptr, newpath.ptr, 0644));
+
+	/* Verify that lookup fails due to a hashsum mismatch */
+	cl_git_fail_with(GIT_EMISMATCH, git_object_lookup(&object, g_repo, &oid, GIT_OBJECT_COMMIT));
+
+	/* Disable verification and try again */
+	cl_git_pass(git_libgit2_opts(GIT_OPT_ENABLE_STRICT_HASH_VERIFICATION, 0));
+	cl_git_pass(git_object_lookup(&object, g_repo, &oid, GIT_OBJECT_COMMIT));
+	cl_git_pass(git_libgit2_opts(GIT_OPT_ENABLE_STRICT_HASH_VERIFICATION, 1));
+
+	git_object_free(object);
+	git_str_dispose(&oldpath);
+	git_str_dispose(&newpath);
+#endif
+}

tests/libgit2/object/tag/parse.c

@@ -14,7 +14,7 @@ static void assert_tag_parses(const char *data, size_t datalen,
 	if (!datalen)
 		datalen = strlen(data);
 
-	cl_git_pass(git_object__from_raw((git_object **) &tag, data, datalen, GIT_OBJECT_TAG));
+	cl_git_pass(git_object__from_raw((git_object **) &tag, data, datalen, GIT_OBJECT_TAG, GIT_OID_SHA1));
 	cl_assert_equal_i(tag->type, GIT_OBJECT_TAG);
 
 	if (expected_oid) {
@@ -54,7 +54,7 @@ static void assert_tag_fails(const char *data, size_t datalen)
 	git_object *object;
 	if (!datalen)
 		datalen = strlen(data);
-	cl_git_fail(git_object__from_raw(&object, data, datalen, GIT_OBJECT_TAG));
+	cl_git_fail(git_object__from_raw(&object, data, datalen, GIT_OBJECT_TAG, GIT_OID_SHA1));
 }
 
 void test_object_tag_parse__valid_tag_parses(void)

tests/libgit2/object/tree/parse.c

@@ -26,7 +26,7 @@ static void assert_tree_parses(const char *data, size_t datalen,
 
 	if (!datalen)
 		datalen = strlen(data);
-	cl_git_pass(git_object__from_raw((git_object **) &tree, data, datalen, GIT_OBJECT_TREE));
+	cl_git_pass(git_object__from_raw((git_object **) &tree, data, datalen, GIT_OBJECT_TREE, GIT_OID_SHA1));
 
 	cl_assert_equal_i(git_tree_entrycount(tree), expected_nentries);
 
@@ -51,7 +51,7 @@ static void assert_tree_fails(const char *data, size_t datalen)
 	git_object *object;
 	if (!datalen)
 		datalen = strlen(data);
-	cl_git_fail(git_object__from_raw(&object, data, datalen, GIT_OBJECT_TREE));
+	cl_git_fail(git_object__from_raw(&object, data, datalen, GIT_OBJECT_TREE, GIT_OID_SHA1));
 }
 
 void test_object_tree_parse__single_blob_parses(void)

tests/libgit2/object/validate.c

 #include "clar_libgit2.h"
 
-#define VALID_COMMIT "tree bdd24e358576f1baa275df98cdcaf3ac9a3f4233\n" \
-               "parent d6d956f1d66210bfcd0484166befab33b5987a39\n" \
-               "author Edward Thomson <ethomson@edwardthomson.com> 1638286404 -0500\n" \
-               "committer Edward Thomson <ethomson@edwardthomson.com> 1638324642 -0500\n" \
-               "\n" \
-               "commit go here.\n"
-#define VALID_TREE "100644 HEADER\0\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42"
-
-#define INVALID_COMMIT "tree bdd24e358576f1baa275df98cdcaf3ac9a3f4233\n" \
-               "parent d6d956f1d66210bfcd0484166befab33b5987a39\n" \
-               "committer Edward Thomson <ethomson@edwardthomson.com> 1638324642 -0500\n" \
-               "\n" \
-               "commit go here.\n"
-#define INVALID_TREE "100644 HEADER \x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42"
-
-void test_object_validate__valid(void)
+#define VALID_COMMIT_SHA1 \
+	"tree bdd24e358576f1baa275df98cdcaf3ac9a3f4233\n" \
+	"parent d6d956f1d66210bfcd0484166befab33b5987a39\n" \
+	"author Edward Thomson <ethomson@edwardthomson.com> 1638286404 -0500\n" \
+	"committer Edward Thomson <ethomson@edwardthomson.com> 1638324642 -0500\n" \
+	"\n" \
+	"commit go here.\n"
+
+#define VALID_TREE_SHA1 \
+	"100644 HEADER\0\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42"
+
+#define INVALID_COMMIT_SHA1 \
+	"tree bdd24e358576f1baa275df98cdcaf3ac9a3f4233\n" \
+	"parent d6d956f1d66210bfcd0484166befab33b5987a39\n" \
+	"committer Edward Thomson <ethomson@edwardthomson.com> 1638324642 -0500\n" \
+	"\n" \
+	"commit go here.\n"
+
+#define INVALID_TREE_SHA1 \
+	"100644 HEADER \x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42"
+
+#define VALID_COMMIT_SHA256 \
+	"tree d0fc7f52dc42358506e7f3f3be72f5271994abb104b9397ab3e19bb42361504d\n" \
+	"parent 652412419a24ba62a1d897f40aeb80eecbf873797b04a1bbb8d71918653ef65b\n" \
+	"author Edward Thomson <ethomson@edwardthomson.com> 1638286404 -0500\n" \
+	"committer Edward Thomson <ethomson@edwardthomson.com> 1638324642 -0500\n" \
+	"\n" \
+	"commit go here.\n"
+
+#define VALID_TREE_SHA256 \
+	"100644 HEADER\0\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42"
+
+#define INVALID_COMMIT_SHA256 \
+	"tree d0fc7f52dc42358506e7f3f3be72f5271994abb104b9397ab3e19bb42361504d\n" \
+	"parent 652412419a24ba62a1d897f40aeb80eecbf873797b04a1bbb8d71918653ef65b\n" \
+	"committer Edward Thomson <ethomson@edwardthomson.com> 1638324642 -0500\n" \
+	"\n" \
+	"commit go here.\n"
+
+#define INVALID_TREE_SHA256 \
+	"100644 HEADER \x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42\x42"
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+# define sha1_rawcontent_is_valid(v, c, l, t) \
+         git_object_rawcontent_is_valid(v, c, l, t, GIT_OID_SHA1)
+#else
+# define sha1_rawcontent_is_valid(v, c, l, t) \
+         git_object_rawcontent_is_valid(v, c, l, t)
+#endif
+
+void test_object_validate__valid_sha1(void)
+{
+	int valid;
+
+	cl_git_pass(sha1_rawcontent_is_valid(&valid, "", 0, GIT_OBJECT_BLOB));
+	cl_assert_equal_i(1, valid);
+
+	cl_git_pass(sha1_rawcontent_is_valid(&valid, "foobar", 0, GIT_OBJECT_BLOB));
+	cl_assert_equal_i(1, valid);
+
+	cl_git_pass(sha1_rawcontent_is_valid(&valid, VALID_COMMIT_SHA1, CONST_STRLEN(VALID_COMMIT_SHA1), GIT_OBJECT_COMMIT));
+	cl_assert_equal_i(1, valid);
+
+	cl_git_pass(sha1_rawcontent_is_valid(&valid, VALID_TREE_SHA1, CONST_STRLEN(VALID_TREE_SHA1), GIT_OBJECT_TREE));
+	cl_assert_equal_i(1, valid);
+}
+
+void test_object_validate__cannot_parse_sha256_as_sha1(void)
+{
+	int valid;
+
+	cl_git_pass(sha1_rawcontent_is_valid(&valid, VALID_COMMIT_SHA256, CONST_STRLEN(INVALID_COMMIT_SHA256), GIT_OBJECT_COMMIT));
+	cl_assert_equal_i(0, valid);
+
+	cl_git_pass(sha1_rawcontent_is_valid(&valid, INVALID_TREE_SHA256, CONST_STRLEN(INVALID_TREE_SHA256), GIT_OBJECT_TREE));
+	cl_assert_equal_i(0, valid);
+}
+
+void test_object_validate__invalid_sha1(void)
 {
 	int valid;
 
-	cl_git_pass(git_object_rawcontent_is_valid(&valid, "", 0, GIT_OBJECT_BLOB));
+	cl_git_pass(sha1_rawcontent_is_valid(&valid, "", 0, GIT_OBJECT_COMMIT));
+	cl_assert_equal_i(0, valid);
+
+	cl_git_pass(sha1_rawcontent_is_valid(&valid, "foobar", 0, GIT_OBJECT_COMMIT));
+	cl_assert_equal_i(0, valid);
+
+	cl_git_pass(sha1_rawcontent_is_valid(&valid, INVALID_COMMIT_SHA1, CONST_STRLEN(INVALID_COMMIT_SHA1), GIT_OBJECT_COMMIT));
+	cl_assert_equal_i(0, valid);
+
+	cl_git_pass(sha1_rawcontent_is_valid(&valid, INVALID_TREE_SHA1, CONST_STRLEN(INVALID_TREE_SHA1), GIT_OBJECT_TREE));
+	cl_assert_equal_i(0, valid);
+}
+
+
+void test_object_validate__valid_sha256(void)
+{
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
+	int valid;
+
+	cl_git_pass(git_object_rawcontent_is_valid(&valid, "", 0, GIT_OBJECT_BLOB, GIT_OID_SHA256));
 	cl_assert_equal_i(1, valid);
 
-	cl_git_pass(git_object_rawcontent_is_valid(&valid, "foobar", 0, GIT_OBJECT_BLOB));
+	cl_git_pass(git_object_rawcontent_is_valid(&valid, "foobar", 0, GIT_OBJECT_BLOB, GIT_OID_SHA256));
 	cl_assert_equal_i(1, valid);
 
-	cl_git_pass(git_object_rawcontent_is_valid(&valid, VALID_COMMIT, CONST_STRLEN(VALID_COMMIT), GIT_OBJECT_COMMIT));
+	cl_git_pass(git_object_rawcontent_is_valid(&valid, VALID_COMMIT_SHA256, CONST_STRLEN(VALID_COMMIT_SHA256), GIT_OBJECT_COMMIT, GIT_OID_SHA256));
 	cl_assert_equal_i(1, valid);
 
-	cl_git_pass(git_object_rawcontent_is_valid(&valid, VALID_TREE, CONST_STRLEN(VALID_TREE), GIT_OBJECT_TREE));
+	cl_git_pass(git_object_rawcontent_is_valid(&valid, VALID_TREE_SHA256, CONST_STRLEN(VALID_TREE_SHA256), GIT_OBJECT_TREE, GIT_OID_SHA256));
 	cl_assert_equal_i(1, valid);
+#endif
 }
 
-void test_object_validate__invalid(void)
+void test_object_validate__invalid_sha256(void)
 {
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
 	int valid;
 
-	cl_git_pass(git_object_rawcontent_is_valid(&valid, "", 0, GIT_OBJECT_COMMIT));
+	cl_git_pass(git_object_rawcontent_is_valid(&valid, "", 0, GIT_OBJECT_COMMIT, GIT_OID_SHA256));
+	cl_assert_equal_i(0, valid);
+
+	cl_git_pass(git_object_rawcontent_is_valid(&valid, "foobar", 0, GIT_OBJECT_COMMIT, GIT_OID_SHA256));
 	cl_assert_equal_i(0, valid);
 
-	cl_git_pass(git_object_rawcontent_is_valid(&valid, "foobar", 0, GIT_OBJECT_COMMIT));
+	cl_git_pass(git_object_rawcontent_is_valid(&valid, INVALID_COMMIT_SHA256, CONST_STRLEN(INVALID_COMMIT_SHA256), GIT_OBJECT_COMMIT, GIT_OID_SHA256));
 	cl_assert_equal_i(0, valid);
 
-	cl_git_pass(git_object_rawcontent_is_valid(&valid, INVALID_COMMIT, CONST_STRLEN(INVALID_COMMIT), GIT_OBJECT_COMMIT));
+	cl_git_pass(git_object_rawcontent_is_valid(&valid, INVALID_TREE_SHA256, CONST_STRLEN(INVALID_TREE_SHA256), GIT_OBJECT_TREE, GIT_OID_SHA256));
+	cl_assert_equal_i(0, valid);
+#endif
+}
+
+void test_object_validate__cannot_parse_sha1_as_sha256(void)
+{
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
+	int valid;
+
+	cl_git_pass(git_object_rawcontent_is_valid(&valid, VALID_COMMIT_SHA1, CONST_STRLEN(INVALID_COMMIT_SHA1), GIT_OBJECT_COMMIT, GIT_OID_SHA256));
 	cl_assert_equal_i(0, valid);
 
-	cl_git_pass(git_object_rawcontent_is_valid(&valid, INVALID_TREE, CONST_STRLEN(INVALID_TREE), GIT_OBJECT_TREE));
+	cl_git_pass(git_object_rawcontent_is_valid(&valid, INVALID_TREE_SHA1, CONST_STRLEN(INVALID_TREE_SHA1), GIT_OBJECT_TREE, GIT_OID_SHA256));
 	cl_assert_equal_i(0, valid);
+#endif
 }

tests/libgit2/odb/foreach.c

@@ -52,7 +52,16 @@ void test_odb_foreach__one_pack(void)
 	int nobj = 0;
 
 	cl_git_pass(git_odb__new(&_odb, NULL));
-	cl_git_pass(git_odb_backend_one_pack(&backend, cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx")));
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_odb_backend_one_pack(&backend,
+		cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx"),
+		NULL));
+#else
+	cl_git_pass(git_odb_backend_one_pack(&backend,
+		cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx")));
+#endif
+
 	cl_git_pass(git_odb_add_backend(_odb, backend, 1));
 	_repo = NULL;
 

tests/libgit2/odb/pack_data_one256.h

+/* Just a few to make sure it's working, the rest is tested already */
+#ifdef GIT_EXPERIMENTAL_SHA256
+static const char *packed_objects_one256[] = {
+	"ea926306b1bab6d3f25f45609907eb6dff91a1460b25e63bf4a0494c70e7a269",
+	"d048ba2ef4fafa502a44cbc1a50cd58359b9bc243b84a08f541a08ca5f621137",
+	"a66bda0109d2b3c9bc87970da81bd91076b5f871febbc860f09ae997668b6800",
+	"3609a41c0506fe19d01fb8b4729923362675f191fe5f63fab3111ef804c48fdf",
+	"22b6705b86e4aa9120eff203af24709d483698d9f78695e86e82de121784b570",
+	"6f11d93bfb269ee8c7a506178f60c430abfac5d424acfd9c0b0b27b98e6ab49b",
+	"0aefd477d9e5b3f8d708a3cf6d78be6b670dfa2e2ec41244634f3b8f115d8e04",
+	"580474d948cd2ebd2e5ce7a5b81b872d87ba4639c1ac4c0fa7a11a8eddf9827c",
+	"0636b4292bfdd7274a977cb6f8b2ded8f315ea1bcd8dbedfca37964c2ed3d085",
+	"19fb1c78b11f0f8bda658d6fa6cc63c0b573c0f6760ee5a9c2df6ce2cde00c5c",
+	"7f2f7afccb317bb3fdd28555f126846dc4eebe5d9ae7b8d8a1456e8ff85422ce",
+	"4066249c68b0d3c8b39ebe02c9188935900465acad02a49269710f56720fa58e",
+	"a560d1fa1edf114f57b402e16d662c17b1e3b7e8601ff7dcea6615ba7f1e48ef",
+	"58923faa87c7d559d308a114ec2b164e5d6046c889420ed1def6eef2d55106a2",
+	"753ddabab8ae9c1e733cda15e8e3c83dd43f5a2d939ae32cc3b30b0be1e91f96",
+	"46333d32b3801cf11d9f80b557245c9e32b0e05deca61dae968914fde159f0e5"
+};
+#endif

tests/libgit2/odb/packed256.c

+#include "clar_libgit2.h"
+#include "odb.h"
+#include "pack_data_256.h"
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+static git_odb *_odb;
+#endif
+
+void test_odb_packed256__initialize(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	git_odb_options opts = GIT_ODB_OPTIONS_INIT;
+
+	opts.oid_type = GIT_OID_SHA256;
+
+	cl_git_pass(git_odb__open(
+		&_odb,
+		cl_fixture("testrepo_256.git/objects"),
+		&opts));
+#endif
+}
+
+void test_odb_packed256__cleanup(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	git_odb_free(_odb);
+	_odb = NULL;
+#endif
+}
+
+void test_odb_packed256__mass_read(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(packed_objects_256); ++i) {
+		git_oid id;
+		git_odb_object *obj;
+
+		cl_git_pass(git_oid__fromstr(&id, packed_objects_256[i], GIT_OID_SHA256));
+		cl_assert(git_odb_exists(_odb, &id) == 1);
+		cl_git_pass(git_odb_read(&obj, _odb, &id));
+
+		git_odb_object_free(obj);
+	}
+#endif
+}
+
+void test_odb_packed256__read_header_0(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(packed_objects_256); ++i) {
+		git_oid id;
+		git_odb_object *obj;
+		size_t len;
+		git_object_t type;
+
+		cl_git_pass(git_oid__fromstr(&id, packed_objects_256[i], GIT_OID_SHA256));
+
+		cl_git_pass(git_odb_read(&obj, _odb, &id));
+		cl_git_pass(git_odb_read_header(&len, &type, _odb, &id));
+
+		cl_assert(obj->cached.size == len);
+		cl_assert(obj->cached.type == type);
+
+		git_odb_object_free(obj);
+	}
+#endif
+}
+
+void test_odb_packed256__read_header_1(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(loose_objects_256); ++i) {
+		git_oid id;
+		git_odb_object *obj;
+		size_t len;
+		git_object_t type;
+
+		cl_git_pass(git_oid__fromstr(&id, loose_objects_256[i], GIT_OID_SHA256));
+
+		cl_assert(git_odb_exists(_odb, &id) == 1);
+
+		cl_git_pass(git_odb_read(&obj, _odb, &id));
+		cl_git_pass(git_odb_read_header(&len, &type, _odb, &id));
+
+		cl_assert(obj->cached.size == len);
+		cl_assert(obj->cached.type == type);
+
+		git_odb_object_free(obj);
+	}
+#endif
+}
+

tests/libgit2/odb/packed_one.c → tests/libgit2/odb/packedone.c

@@ -6,22 +6,29 @@
 
 static git_odb *_odb;
 
-void test_odb_packed_one__initialize(void)
+void test_odb_packedone__initialize(void)
 {
 	git_odb_backend *backend = NULL;
 
 	cl_git_pass(git_odb__new(&_odb, NULL));
-	cl_git_pass(git_odb_backend_one_pack(&backend, cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx")));
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_odb_backend_one_pack(&backend,
+		cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx"),
+		NULL));
+#else
+	cl_git_pass(git_odb_backend_one_pack(&backend,
+		cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx")));
+#endif
 	cl_git_pass(git_odb_add_backend(_odb, backend, 1));
 }
 
-void test_odb_packed_one__cleanup(void)
+void test_odb_packedone__cleanup(void)
 {
 	git_odb_free(_odb);
 	_odb = NULL;
 }
 
-void test_odb_packed_one__mass_read(void)
+void test_odb_packedone__mass_read(void)
 {
 	unsigned int i;
 
@@ -37,7 +44,7 @@ void test_odb_packed_one__mass_read(void)
 	}
 }
 
-void test_odb_packed_one__read_header_0(void)
+void test_odb_packedone__read_header_0(void)
 {
 	unsigned int i;
 

tests/libgit2/odb/packedone256.c

+#include "clar_libgit2.h"
+#include "git2/odb_backend.h"
+
+#include "pack_data_one256.h"
+#include "pack.h"
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+static git_odb *_odb;
+#endif
+
+void test_odb_packedone256__initialize(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	git_odb_backend *backend = NULL;
+	git_odb_options odb_opts = GIT_ODB_OPTIONS_INIT;
+	git_odb_backend_pack_options backend_opts = GIT_ODB_BACKEND_PACK_OPTIONS_INIT;
+
+	odb_opts.oid_type = GIT_OID_SHA256;
+	backend_opts.oid_type = GIT_OID_SHA256;
+
+	cl_git_pass(git_odb__new(&_odb, &odb_opts));
+	cl_git_pass(git_odb_backend_one_pack(
+		&backend,
+		cl_fixture("testrepo_256.git/objects/pack/pack-e2f07f30db7e480ea84a0e64ee791b9b270067124b2609019b74f33f256f33fa.idx"),
+		&backend_opts));
+	cl_git_pass(git_odb_add_backend(_odb, backend, 1));
+#endif
+}
+
+void test_odb_packedone256__cleanup(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	git_odb_free(_odb);
+	_odb = NULL;
+#endif
+}
+
+void test_odb_packedone256__mass_read(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(packed_objects_one256); ++i) {
+		git_oid id;
+		git_odb_object *obj;
+
+		cl_git_pass(git_oid__fromstr(&id, packed_objects_one256[i], GIT_OID_SHA256));
+		cl_assert(git_odb_exists(_odb, &id) == 1);
+		cl_git_pass(git_odb_read(&obj, _odb, &id));
+
+		git_odb_object_free(obj);
+	}
+#endif
+}
+
+void test_odb_packedone256__read_header_0(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(packed_objects_one256); ++i) {
+		git_oid id;
+		git_odb_object *obj;
+		size_t len;
+		git_object_t type;
+
+		cl_git_pass(git_oid__fromstr(&id, packed_objects_one256[i], GIT_OID_SHA256));
+
+		cl_git_pass(git_odb_read(&obj, _odb, &id));
+		cl_git_pass(git_odb_read_header(&len, &type, _odb, &id));
+
+		cl_assert(obj->cached.size == len);
+		cl_assert(obj->cached.type == type);
+
+		git_odb_object_free(obj);
+	}
+#endif
+}

tests/libgit2/odb/sorting.c

@@ -82,7 +82,11 @@ void test_odb_sorting__override_default_backend_priority(void)
 
 	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_ODB_LOOSE_PRIORITY, 5));
 	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_ODB_PACKED_PRIORITY, 3));
-	git_odb_backend_pack(&packed, "./testrepo.git/objects");
+	git_odb_backend_pack(&packed, "./testrepo.git/objects"
+#ifdef GIT_EXPERIMENTAL_SHA256
+		, NULL
+#endif
+	);
 	git_odb__backend_loose(&loose, "./testrepo.git/objects", NULL);
 
 	cl_git_pass(git_odb__open(&new_odb, cl_fixture("testrepo.git/objects"), NULL));

tests/libgit2/online/clone.c

@@ -1177,3 +1177,22 @@ void test_online_clone__namespace_with_specified_branch(void)
 
 	git_reference_free(head);
 }
+
+void test_online_clone__sha256(void)
+{
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
+	git_clone_options options = GIT_CLONE_OPTIONS_INIT;
+	git_reference *head;
+
+	if (!_remote_url)
+		cl_skip();
+
+	cl_git_pass(git_clone(&g_repo, _remote_url, "./sha256", &options));
+	cl_git_pass(git_reference_lookup(&head, g_repo, GIT_HEAD_FILE));
+	cl_assert_equal_i(GIT_REFERENCE_SYMBOLIC, git_reference_type(head));
+
+	git_reference_free(head);
+#endif
+}

tests/libgit2/pack/indexer.c

@@ -100,7 +100,12 @@ void test_pack_indexer__out_of_order(void)
 	git_indexer *idx = 0;
 	git_indexer_progress stats = { 0 };
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, NULL));
+#else
 	cl_git_pass(git_indexer_new(&idx, ".", 0, NULL, NULL));
+#endif
+
 	cl_git_pass(git_indexer_append(
 		idx, out_of_order_pack, out_of_order_pack_len, &stats));
 	cl_git_pass(git_indexer_commit(idx, &stats));
@@ -117,7 +122,12 @@ void test_pack_indexer__missing_trailer(void)
 	git_indexer *idx = 0;
 	git_indexer_progress stats = { 0 };
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, NULL));
+#else
 	cl_git_pass(git_indexer_new(&idx, ".", 0, NULL, NULL));
+#endif
+
 	cl_git_pass(git_indexer_append(
 		idx, missing_trailer_pack, missing_trailer_pack_len, &stats));
 	cl_git_fail(git_indexer_commit(idx, &stats));
@@ -133,7 +143,12 @@ void test_pack_indexer__leaky(void)
 	git_indexer *idx = 0;
 	git_indexer_progress stats = { 0 };
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, NULL));
+#else
 	cl_git_pass(git_indexer_new(&idx, ".", 0, NULL, NULL));
+#endif
+
 	cl_git_pass(git_indexer_append(
 		idx, leaky_pack, leaky_pack_len, &stats));
 	cl_git_fail(git_indexer_commit(idx, &stats));
@@ -151,6 +166,7 @@ void test_pack_indexer__fix_thin(void)
 	git_repository *repo;
 	git_odb *odb;
 	git_oid id, should_id;
+	git_indexer_options opts = GIT_INDEXER_OPTIONS_INIT;
 
 	cl_git_pass(git_repository_init(&repo, "thin.git", true));
 	cl_git_pass(git_repository_odb(&odb, repo));
@@ -160,7 +176,13 @@ void test_pack_indexer__fix_thin(void)
 	git_oid__fromstr(&should_id, "e68fe8129b546b101aee9510c5328e7f21ca1d18", GIT_OID_SHA1);
 	cl_assert_equal_oid(&should_id, &id);
 
-	cl_git_pass(git_indexer_new(&idx, ".", 0, odb, NULL));
+#ifdef GIT_EXPERIMENTAL_SHA256
+	opts.odb = odb;
+	cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, &opts));
+#else
+	cl_git_pass(git_indexer_new(&idx, ".", 0, odb, &opts));
+#endif
+
 	cl_git_pass(git_indexer_append(idx, thin_pack, thin_pack_len, &stats));
 	cl_git_pass(git_indexer_commit(idx, &stats));
 
@@ -192,7 +214,12 @@ void test_pack_indexer__fix_thin(void)
 
 		cl_git_pass(p_stat(name, &st));
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+		cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, NULL));
+#else
 		cl_git_pass(git_indexer_new(&idx, ".", 0, NULL, NULL));
+#endif
+
 		read = p_read(fd, buffer, sizeof(buffer));
 		cl_assert(read != -1);
 		p_close(fd);
@@ -216,6 +243,7 @@ void test_pack_indexer__corrupt_length(void)
 	git_repository *repo;
 	git_odb *odb;
 	git_oid id, should_id;
+	git_indexer_options opts = GIT_INDEXER_OPTIONS_INIT;
 
 	cl_git_pass(git_repository_init(&repo, "thin.git", true));
 	cl_git_pass(git_repository_odb(&odb, repo));
@@ -225,7 +253,13 @@ void test_pack_indexer__corrupt_length(void)
 	git_oid__fromstr(&should_id, "e68fe8129b546b101aee9510c5328e7f21ca1d18", GIT_OID_SHA1);
 	cl_assert_equal_oid(&should_id, &id);
 
-	cl_git_pass(git_indexer_new(&idx, ".", 0, odb, NULL));
+#ifdef GIT_EXPERIMENTAL_SHA256
+	opts.odb = odb;
+	cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, &opts));
+#else
+	cl_git_pass(git_indexer_new(&idx, ".", 0, odb, &opts));
+#endif
+
 	cl_git_pass(git_indexer_append(
 		idx, corrupt_thin_pack, corrupt_thin_pack_len, &stats));
 	cl_git_fail(git_indexer_commit(idx, &stats));
@@ -246,7 +280,12 @@ void test_pack_indexer__incomplete_pack_fails_with_strict(void)
 
 	opts.verify = 1;
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, &opts));
+#else
 	cl_git_pass(git_indexer_new(&idx, ".", 0, NULL, &opts));
+#endif
+
 	cl_git_pass(git_indexer_append(
 		idx, incomplete_pack, incomplete_pack_len, &stats));
 	cl_git_fail(git_indexer_commit(idx, &stats));
@@ -266,7 +305,12 @@ void test_pack_indexer__out_of_order_with_connectivity_checks(void)
 
 	opts.verify = 1;
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, &opts));
+#else
 	cl_git_pass(git_indexer_new(&idx, ".", 0, NULL, &opts));
+#endif
+
 	cl_git_pass(git_indexer_append(
 		idx, out_of_order_pack, out_of_order_pack_len, &stats));
 	cl_git_pass(git_indexer_commit(idx, &stats));
@@ -309,7 +353,12 @@ void test_pack_indexer__no_tmp_files(void)
 	git_str_dispose(&path);
 	cl_assert(git_str_len(&first_tmp_file) == 0);
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, NULL));
+#else
 	cl_git_pass(git_indexer_new(&idx, ".", 0, NULL, NULL));
+#endif
+
 	git_indexer_free(idx);
 
 	cl_git_pass(git_str_sets(&path, clar_sandbox_path()));

tests/libgit2/pack/packbuilder.c

@@ -104,7 +104,12 @@ void test_pack_packbuilder__create_pack(void)
 
 	seed_packbuilder();
 
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_indexer_new(&_indexer, ".", GIT_OID_SHA1, NULL));
+#else
 	cl_git_pass(git_indexer_new(&_indexer, ".", 0, NULL, NULL));
+#endif
+
 	cl_git_pass(git_packbuilder_foreach(_packbuilder, feed_indexer, &stats));
 	cl_git_pass(git_indexer_commit(_indexer, &stats));
 
@@ -244,7 +249,13 @@ void test_pack_packbuilder__foreach(void)
 	git_indexer *idx;
 
 	seed_packbuilder();
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, NULL));
+#else
 	cl_git_pass(git_indexer_new(&idx, ".", 0, NULL, NULL));
+#endif
+
 	cl_git_pass(git_packbuilder_foreach(_packbuilder, foreach_cb, idx));
 	cl_git_pass(git_indexer_commit(idx, &_stats));
 	git_indexer_free(idx);
@@ -262,7 +273,13 @@ void test_pack_packbuilder__foreach_with_cancel(void)
 	git_indexer *idx;
 
 	seed_packbuilder();
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_git_pass(git_indexer_new(&idx, ".", GIT_OID_SHA1, NULL));
+#else
 	cl_git_pass(git_indexer_new(&idx, ".", 0, NULL, NULL));
+#endif
+
 	cl_git_fail_with(
 		git_packbuilder_foreach(_packbuilder, foreach_cancel_cb, idx), -1111);
 	git_indexer_free(idx);

tests/libgit2/repo/init.c

@@ -142,27 +142,46 @@ void test_repo_init__reinit_bare_repo(void)
 	cl_git_pass(git_repository_init(&g_repo, "reinit.git", 1));
 }
 
-void test_repo_init__reinit_too_recent_bare_repo(void)
+void test_repo_init__reinit_nondefault_version(void)
 {
 	git_config *config;
 
+	cl_set_cleanup(&cleanup_repository, "reinit.git");
+
 	/* Initialize the repository */
 	cl_git_pass(git_repository_init(&g_repo, "reinit.git", 1));
 	git_repository_config(&config, g_repo);
 
+	/* Set the config to a supported but not default version */
+	cl_repo_set_string(g_repo, "core.repositoryformatversion", "1");
+	git_config_free(config);
+	git_repository_free(g_repo);
+	g_repo = NULL;
+
+	/* Try to reinitialize the repository */
+	cl_git_pass(git_repository_init(&g_repo, "reinit.git", 1));
+	cl_assert_equal_i(1, cl_repo_get_int(g_repo, "core.repositoryformatversion"));
+
+	cl_fixture_cleanup("reinit.git");
+}
+
+void test_repo_init__reinit_unsupported_version(void)
+{
+	cl_set_cleanup(&cleanup_repository, "reinit.git");
+
+	/* Initialize the repository */
+	cl_git_pass(git_repository_init(&g_repo, "reinit.git", 1));
+
 	/*
 	 * Hack the config of the repository to make it look like it has
-	 * been created by a recenter version of git/libgit2
+	 * been created by a too new and unsupported version of git/libgit2
 	 */
-	cl_git_pass(git_config_set_int32(config, "core.repositoryformatversion", 42));
-
-	git_config_free(config);
+	cl_repo_set_string(g_repo, "core.repositoryformatversion", "42");
 	git_repository_free(g_repo);
 	g_repo = NULL;
 
-	/* Try to reinitialize the repository */
+	/* Try and fail to reinitialize the repository */
 	cl_git_fail(git_repository_init(&g_repo, "reinit.git", 1));
-
 	cl_fixture_cleanup("reinit.git");
 }
 
@@ -708,7 +727,7 @@ void test_repo_init__defaultbranch_config_empty(void)
 void test_repo_init__longpath(void)
 {
 #ifdef GIT_WIN32
-	size_t padding = CONST_STRLEN("objects/pack/pack-.pack.lock") + GIT_OID_SHA1_HEXSIZE;
+	size_t padding = CONST_STRLEN("objects/pack/pack-.pack.lock") + GIT_OID_MAX_HEXSIZE;
 	size_t max, i;
 	git_str path = GIT_STR_INIT;
 	git_repository *one = NULL, *two = NULL;

tests/libgit2/repo/objectformat.c

+#include "clar_libgit2.h"
+#include "futils.h"
+#include "sysdir.h"
+#include "repository.h"
+#include <ctype.h>
+
+git_repository *repo;
+git_config *config;
+
+void test_repo_objectformat__initialize(void)
+{
+	repo = cl_git_sandbox_init("empty_bare.git");
+
+	cl_git_pass(git_repository_config(&config, repo));
+	cl_git_pass(git_config_set_int32(config, "core.repositoryformatversion", 1));
+}
+
+void test_repo_objectformat__cleanup(void)
+{
+	git_config_free(config);
+	cl_git_sandbox_cleanup();
+}
+
+void test_repo_objectformat__unspecified(void)
+{
+	git_repository *other;
+
+	cl_git_pass(git_repository_open(&other, "empty_bare.git"));
+	cl_assert_equal_i(GIT_OID_SHA1, git_repository_oid_type(other));
+	git_repository_free(other);
+}
+
+void test_repo_objectformat__sha1(void)
+{
+	git_repository *other;
+
+	cl_git_pass(git_config_set_string(config, "extensions.objectformat", "sha1"));
+
+	cl_git_pass(git_repository_open(&other, "empty_bare.git"));
+	cl_assert_equal_i(GIT_OID_SHA1, git_repository_oid_type(other));
+	git_repository_free(other);
+}
+
+void test_repo_objectformat__sha256(void)
+{
+#ifndef GIT_EXPERIMENTAL_SHA256
+	cl_skip();
+#else
+	git_repository *other;
+
+	cl_git_pass(git_config_set_string(config, "extensions.objectformat", "sha256"));
+
+	cl_git_pass(git_repository_open(&other, "empty_bare.git"));
+	cl_assert_equal_i(GIT_OID_SHA256, git_repository_oid_type(other));
+	git_repository_free(other);
+#endif
+}
+
+void test_repo_objectformat__invalid(void)
+{
+	git_repository *other;
+
+	cl_git_pass(git_config_set_string(config, "extensions.objectformat", "bogus"));
+
+	cl_git_fail_with(GIT_EINVALID, git_repository_open(&other, "empty_bare.git"));
+	cl_assert_equal_s("unknown object format 'bogus'", git_error_last()->message);
+	git_repository_free(other);
+}
+

tests/libgit2/transports/smart/packet.c

@@ -11,8 +11,9 @@ static void assert_flush_parses(const char *line)
 	size_t linelen = strlen(line) + 1;
 	const char *endptr;
 	git_pkt *pkt;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_FLUSH);
 	cl_assert_equal_strn(endptr, line + 4, linelen - 4);
 
@@ -24,8 +25,9 @@ static void assert_data_pkt_parses(const char *line, const char *expected_data,
 	size_t linelen = strlen(line) + 1;
 	const char *endptr;
 	git_pkt_data *pkt;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_DATA);
 	cl_assert_equal_i(pkt->len, expected_len);
 	cl_assert_equal_strn(pkt->data, expected_data, expected_len);
@@ -38,8 +40,9 @@ static void assert_sideband_progress_parses(const char *line, const char *expect
 	size_t linelen = strlen(line) + 1;
 	const char *endptr;
 	git_pkt_progress *pkt;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_PROGRESS);
 	cl_assert_equal_i(pkt->len, expected_len);
 	cl_assert_equal_strn(pkt->data, expected_data, expected_len);
@@ -52,8 +55,9 @@ static void assert_error_parses(const char *line, const char *expected_error, si
 	size_t linelen = strlen(line) + 1;
 	const char *endptr;
 	git_pkt_err *pkt;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_ERR);
 	cl_assert_equal_i(pkt->len, expected_len);
 	cl_assert_equal_strn(pkt->error, expected_error, expected_len);
@@ -67,10 +71,11 @@ static void assert_ack_parses(const char *line, const char *expected_oid, enum g
 	const char *endptr;
 	git_pkt_ack *pkt;
 	git_oid oid;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
 	cl_git_pass(git_oid__fromstr(&oid, expected_oid, GIT_OID_SHA1));
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_ACK);
 	cl_assert_equal_oid(&pkt->oid, &oid);
 	cl_assert_equal_i(pkt->status, expected_status);
@@ -83,8 +88,9 @@ static void assert_nak_parses(const char *line)
 	size_t linelen = strlen(line) + 1;
 	const char *endptr;
 	git_pkt *pkt;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_NAK);
 	cl_assert_equal_strn(endptr, line + 7, linelen - 7);
 
@@ -96,8 +102,9 @@ static void assert_comment_parses(const char *line, const char *expected_comment
 	size_t linelen = strlen(line) + 1;
 	const char *endptr;
 	git_pkt_comment *pkt;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_COMMENT);
 	cl_assert_equal_strn(pkt->comment, expected_comment, strlen(expected_comment));
 
@@ -109,8 +116,9 @@ static void assert_ok_parses(const char *line, const char *expected_ref)
 	size_t linelen = strlen(line) + 1;
 	const char *endptr;
 	git_pkt_ok *pkt;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_OK);
 	cl_assert_equal_strn(pkt->ref, expected_ref, strlen(expected_ref));
 
@@ -122,8 +130,9 @@ static void assert_unpack_parses(const char *line, bool ok)
 	size_t linelen = strlen(line) + 1;
 	const char *endptr;
 	git_pkt_unpack *pkt;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_UNPACK);
 	cl_assert_equal_i(pkt->unpack_ok, ok);
 
@@ -135,8 +144,9 @@ static void assert_ng_parses(const char *line, const char *expected_ref, const c
 	size_t linelen = strlen(line) + 1;
 	const char *endptr;
 	git_pkt_ng *pkt;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_NG);
 	cl_assert_equal_strn(pkt->ref, expected_ref, strlen(expected_ref));
 	cl_assert_equal_strn(pkt->msg, expected_msg, strlen(expected_msg));
@@ -153,10 +163,11 @@ static void assert_ref_parses_(const char *line, size_t linelen, const char *exp
 	const char *endptr;
 	git_pkt_ref *pkt;
 	git_oid oid;
+	git_pkt_parse_data pkt_parse_data = { 0 };
 
 	cl_git_pass(git_oid__fromstr(&oid, expected_oid, GIT_OID_SHA1));
 
-	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen));
+	cl_git_pass(git_pkt_parse_line((git_pkt **) &pkt, &endptr, line, linelen, &pkt_parse_data));
 	cl_assert_equal_i(pkt->type, GIT_PKT_REF);
 	cl_assert_equal_oid(&pkt->head.oid, &oid);
 	cl_assert_equal_strn(pkt->head.name, expected_ref, strlen(expected_ref));
@@ -171,8 +182,10 @@ static void assert_ref_parses_(const char *line, size_t linelen, const char *exp
 static void assert_pkt_fails(const char *line)
 {
 	const char *endptr;
+	git_pkt_parse_data pkt_parse_data = { 0 };
+
 	git_pkt *pkt;
-	cl_git_fail(git_pkt_parse_line(&pkt, &endptr, line, strlen(line) + 1));
+	cl_git_fail(git_pkt_parse_line(&pkt, &endptr, line, strlen(line) + 1, &pkt_parse_data));
 }
 
 void test_transports_smart_packet__parsing_garbage_fails(void)

tests/resources/testrepo_256.git/FETCH_HEAD

+decaff3051968d1f3a2defd3d4a80ced03101555e1fd8913b3544026c0717d4f		branch 'master' of git://example.com/git/testrepo.git
+7e9424c06052ca33bfc599bccadee60065d8664a9af7648a1455100c4f772e1c	not-for-merge  branch 'haacked' of git://example.com/git/testrepo.git

tests/resources/testrepo_256.git/HEAD

+ref: refs/heads/master

tests/resources/testrepo_256.git/HEAD_TRACKER

+ref: HEAD

tests/resources/testrepo_256.git/config

+[core]
+	repositoryFormatVersion = 1
+	filemode = true
+	bare = true
+	ignorecase = true
+	precomposeunicode = true
+[extensions]
+	objectFormat = sha256

tests/resources/testrepo_256.git/description

+Unnamed repository; edit this file 'description' to name the repository.

tests/resources/testrepo_256.git/hooks/applypatch-msg.sample

+#!/bin/sh
+#
+# An example hook script to check the commit log message taken by
+# applypatch from an e-mail message.
+#
+# The hook should exit with non-zero status after issuing an
+# appropriate message if it wants to stop the commit.  The hook is
+# allowed to edit the commit message file.
+#
+# To enable this hook, rename this file to "applypatch-msg".
+
+. git-sh-setup
+commitmsg="$(git rev-parse --git-path hooks/commit-msg)"
+test -x "$commitmsg" && exec "$commitmsg" ${1+"$@"}
+:

tests/resources/testrepo_256.git/hooks/commit-msg.sample

+#!/bin/sh
+#
+# An example hook script to check the commit log message.
+# Called by "git commit" with one argument, the name of the file
+# that has the commit message.  The hook should exit with non-zero
+# status after issuing an appropriate message if it wants to stop the
+# commit.  The hook is allowed to edit the commit message file.
+#
+# To enable this hook, rename this file to "commit-msg".
+
+# Uncomment the below to add a Signed-off-by line to the message.
+# Doing this in a hook is a bad idea in general, but the prepare-commit-msg
+# hook is more suited to it.
+#
+# SOB=$(git var GIT_AUTHOR_IDENT | sed -n 's/^\(.*>\).*$/Signed-off-by: \1/p')
+# grep -qs "^$SOB" "$1" || echo "$SOB" >> "$1"
+
+# This example catches duplicate Signed-off-by lines.
+
+test "" = "$(grep '^Signed-off-by: ' "$1" |
+	 sort | uniq -c | sed -e '/^[ 	]*1[ 	]/d')" || {
+	echo >&2 Duplicate Signed-off-by lines.
+	exit 1
+}

tests/resources/testrepo_256.git/hooks/fsmonitor-watchman.sample

+#!/usr/bin/perl
+
+use strict;
+use warnings;
+use IPC::Open2;
+
+# An example hook script to integrate Watchman
+# (https://facebook.github.io/watchman/) with git to speed up detecting
+# new and modified files.
+#
+# The hook is passed a version (currently 2) and last update token
+# formatted as a string and outputs to stdout a new update token and
+# all files that have been modified since the update token. Paths must
+# be relative to the root of the working tree and separated by a single NUL.
+#
+# To enable this hook, rename this file to "query-watchman" and set
+# 'git config core.fsmonitor .git/hooks/query-watchman'
+#
+my ($version, $last_update_token) = @ARGV;
+
+# Uncomment for debugging
+# print STDERR "$0 $version $last_update_token\n";
+
+# Check the hook interface version
+if ($version ne 2) {
+	die "Unsupported query-fsmonitor hook version '$version'.\n" .
+	    "Falling back to scanning...\n";
+}
+
+my $git_work_tree = get_working_dir();
+
+my $retry = 1;
+
+my $json_pkg;
+eval {
+	require JSON::XS;
+	$json_pkg = "JSON::XS";
+	1;
+} or do {
+	require JSON::PP;
+	$json_pkg = "JSON::PP";
+};
+
+launch_watchman();
+
+sub launch_watchman {
+	my $o = watchman_query();
+	if (is_work_tree_watched($o)) {
+		output_result($o->{clock}, @{$o->{files}});
+	}
+}
+
+sub output_result {
+	my ($clockid, @files) = @_;
+
+	# Uncomment for debugging watchman output
+	# open (my $fh, ">", ".git/watchman-output.out");
+	# binmode $fh, ":utf8";
+	# print $fh "$clockid\n@files\n";
+	# close $fh;
+
+	binmode STDOUT, ":utf8";
+	print $clockid;
+	print "\0";
+	local $, = "\0";
+	print @files;
+}
+
+sub watchman_clock {
+	my $response = qx/watchman clock "$git_work_tree"/;
+	die "Failed to get clock id on '$git_work_tree'.\n" .
+		"Falling back to scanning...\n" if $? != 0;
+
+	return $json_pkg->new->utf8->decode($response);
+}
+
+sub watchman_query {
+	my $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'watchman -j --no-pretty')
+	or die "open2() failed: $!\n" .
+	"Falling back to scanning...\n";
+
+	# In the query expression below we're asking for names of files that
+	# changed since $last_update_token but not from the .git folder.
+	#
+	# To accomplish this, we're using the "since" generator to use the
+	# recency index to select candidate nodes and "fields" to limit the
+	# output to file names only. Then we're using the "expression" term to
+	# further constrain the results.
+	if (substr($last_update_token, 0, 1) eq "c") {
+		$last_update_token = "\"$last_update_token\"";
+	}
+	my $query = <<"	END";
+		["query", "$git_work_tree", {
+			"since": $last_update_token,
+			"fields": ["name"],
+			"expression": ["not", ["dirname", ".git"]]
+		}]
+	END
+
+	# Uncomment for debugging the watchman query
+	# open (my $fh, ">", ".git/watchman-query.json");
+	# print $fh $query;
+	# close $fh;
+
+	print CHLD_IN $query;
+	close CHLD_IN;
+	my $response = do {local $/; <CHLD_OUT>};
+
+	# Uncomment for debugging the watch response
+	# open ($fh, ">", ".git/watchman-response.json");
+	# print $fh $response;
+	# close $fh;
+
+	die "Watchman: command returned no output.\n" .
+	"Falling back to scanning...\n" if $response eq "";
+	die "Watchman: command returned invalid output: $response\n" .
+	"Falling back to scanning...\n" unless $response =~ /^\{/;
+
+	return $json_pkg->new->utf8->decode($response);
+}
+
+sub is_work_tree_watched {
+	my ($output) = @_;
+	my $error = $output->{error};
+	if ($retry > 0 and $error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {
+		$retry--;
+		my $response = qx/watchman watch "$git_work_tree"/;
+		die "Failed to make watchman watch '$git_work_tree'.\n" .
+		    "Falling back to scanning...\n" if $? != 0;
+		$output = $json_pkg->new->utf8->decode($response);
+		$error = $output->{error};
+		die "Watchman: $error.\n" .
+		"Falling back to scanning...\n" if $error;
+
+		# Uncomment for debugging watchman output
+		# open (my $fh, ">", ".git/watchman-output.out");
+		# close $fh;
+
+		# Watchman will always return all files on the first query so
+		# return the fast "everything is dirty" flag to git and do the
+		# Watchman query just to get it over with now so we won't pay
+		# the cost in git to look up each individual file.
+		my $o = watchman_clock();
+		$error = $output->{error};
+
+		die "Watchman: $error.\n" .
+		"Falling back to scanning...\n" if $error;
+
+		output_result($o->{clock}, ("/"));
+		$last_update_token = $o->{clock};
+
+		eval { launch_watchman() };
+		return 0;
+	}
+
+	die "Watchman: $error.\n" .
+	"Falling back to scanning...\n" if $error;
+
+	return 1;
+}
+
+sub get_working_dir {
+	my $working_dir;
+	if ($^O =~ 'msys' || $^O =~ 'cygwin') {
+		$working_dir = Win32::GetCwd();
+		$working_dir =~ tr/\\/\//;
+	} else {
+		require Cwd;
+		$working_dir = Cwd::cwd();
+	}
+
+	return $working_dir;
+}