transport: teach transports about oid types and SHA256

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/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;
 

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/indexer.c

@@ -56,8 +56,8 @@ struct git_indexer {
 	git_vector deltas;
 	unsigned int fanout[256];
 	git_hash_ctx hash_ctx;
-	unsigned char checksum[GIT_HASH_SHA1_SIZE];
-	char name[(GIT_HASH_SHA1_SIZE * 2) + 1];
+	unsigned char checksum[GIT_HASH_MAX_SIZE];
+	char name[(GIT_HASH_MAX_SIZE * 2) + 1];
 	git_indexer_progress_cb progress_cb;
 	void *progress_payload;
 	char objbuf[8*1024];
@@ -69,7 +69,7 @@ struct git_indexer {
 	git_odb *odb;
 
 	/* Fields for calculating the packfile trailer (hash of everything before it) */
-	char inbuf[GIT_OID_MAX_SIZE];
+	char inbuf[GIT_HASH_MAX_SIZE];
 	size_t inbuf_len;
 	git_hash_ctx trailer;
 };
@@ -137,6 +137,20 @@ int git_indexer_init_options(git_indexer_options *opts, unsigned int version)
 }
 #endif
 
+GIT_INLINE(git_hash_algorithm_t) indexer_hash_algorithm(git_indexer *idx)
+{
+	switch (idx->oid_type) {
+		case GIT_OID_SHA1:
+			return GIT_HASH_ALGORITHM_SHA1;
+#ifdef GIT_EXPERIMENTAL_SHA256
+		case GIT_OID_SHA256:
+			return GIT_HASH_ALGORITHM_SHA256;
+#endif
+	}
+
+	return GIT_HASH_ALGORITHM_NONE;
+}
+
 static int indexer_new(
 	git_indexer **out,
 	const char *prefix,
@@ -149,6 +163,7 @@ static int indexer_new(
 	git_indexer *idx;
 	git_str path = GIT_STR_INIT, tmp_path = GIT_STR_INIT;
 	static const char suff[] = "/pack";
+	git_hash_algorithm_t checksum_type;
 	int error, fd = -1;
 
 	if (in_opts)
@@ -163,8 +178,10 @@ static int indexer_new(
 	idx->mode = mode ? mode : GIT_PACK_FILE_MODE;
 	git_str_init(&idx->entry_data, 0);
 
-	if ((error = git_hash_ctx_init(&idx->hash_ctx, GIT_HASH_ALGORITHM_SHA1)) < 0 ||
-	    (error = git_hash_ctx_init(&idx->trailer, GIT_HASH_ALGORITHM_SHA1)) < 0 ||
+	checksum_type = indexer_hash_algorithm(idx);
+
+	if ((error = git_hash_ctx_init(&idx->hash_ctx, checksum_type)) < 0 ||
+	    (error = git_hash_ctx_init(&idx->trailer, checksum_type)) < 0 ||
 	    (error = git_oidmap_new(&idx->expected_oids)) < 0)
 		goto cleanup;
 
@@ -182,8 +199,7 @@ static int indexer_new(
 	if (fd < 0)
 		goto cleanup;
 
-	/* TODO: SHA256 */
-	error = git_packfile_alloc(&idx->pack, git_str_cstr(&tmp_path), 0);
+	error = git_packfile_alloc(&idx->pack, git_str_cstr(&tmp_path), oid_type);
 	git_str_dispose(&tmp_path);
 
 	if (error < 0)
@@ -614,7 +630,7 @@ static int do_progress_callback(git_indexer *idx, git_indexer_progress *stats)
 	return 0;
 }
 
-/* Hash everything but the last 20B of input */
+/* Hash everything but the checksum trailer */
 static void hash_partially(git_indexer *idx, const uint8_t *data, size_t size)
 {
 	size_t to_expell, to_keep;
@@ -623,7 +639,10 @@ static void hash_partially(git_indexer *idx, const uint8_t *data, size_t size)
 	if (size == 0)
 		return;
 
-	/* Easy case, dump the buffer and the data minus the last 20 bytes */
+	/*
+	 * Easy case, dump the buffer and the data minus the trailing
+	 * checksum (SHA1 or SHA256).
+	 */
 	if (size >= oid_size) {
 		git_hash_update(&idx->trailer, idx->inbuf, idx->inbuf_len);
 		git_hash_update(&idx->trailer, data, size - oid_size);
@@ -761,12 +780,14 @@ static int read_stream_object(git_indexer *idx, git_indexer_progress *stats)
 {
 	git_packfile_stream *stream = &idx->stream;
 	off64_t entry_start = idx->off;
-	size_t entry_size;
+	size_t oid_size, entry_size;
 	git_object_t type;
 	git_mwindow *w = NULL;
 	int error;
 
-	if (idx->pack->mwf.size <= idx->off + 20)
+	oid_size = git_oid_size(idx->oid_type);
+
+	if (idx->pack->mwf.size <= idx->off + (long long)oid_size)
 		return GIT_EBUFS;
 
 	if (!idx->have_stream) {
@@ -963,15 +984,17 @@ static int inject_object(git_indexer *idx, git_oid *id)
 	git_odb_object *obj = NULL;
 	struct entry *entry = NULL;
 	struct git_pack_entry *pentry = NULL;
-	unsigned char empty_checksum[GIT_HASH_SHA1_SIZE] = {0};
+	unsigned char empty_checksum[GIT_HASH_MAX_SIZE] = {0};
 	unsigned char hdr[64];
 	git_str buf = GIT_STR_INIT;
 	off64_t entry_start;
 	const void *data;
 	size_t len, hdr_len;
-	size_t checksum_size = GIT_HASH_SHA1_SIZE;
+	size_t checksum_size;
 	int error;
 
+	checksum_size = git_hash_size(indexer_hash_algorithm(idx));
+
 	if ((error = seek_back_trailer(idx)) < 0)
 		goto cleanup;
 
@@ -1205,10 +1228,10 @@ int git_indexer_commit(git_indexer *idx, git_indexer_progress *stats)
 	struct git_pack_idx_header hdr;
 	git_str filename = GIT_STR_INIT;
 	struct entry *entry;
-	unsigned char checksum[GIT_HASH_SHA1_SIZE];
+	unsigned char checksum[GIT_HASH_MAX_SIZE];
 	git_filebuf index_file = {0};
 	void *packfile_trailer;
-	size_t checksum_size = GIT_HASH_SHA1_SIZE;
+	size_t checksum_size;
 	bool mismatch;
 
 	if (!idx->parsed_header) {
@@ -1216,6 +1239,9 @@ int git_indexer_commit(git_indexer *idx, git_indexer_progress *stats)
 		return -1;
 	}
 
+	checksum_size = git_hash_size(indexer_hash_algorithm(idx));
+	GIT_ASSERT(checksum_size);
+
 	/* Test for this before resolve_deltas(), as it plays with idx->off */
 	if (idx->off + (ssize_t)checksum_size < idx->pack->mwf.size) {
 		git_error_set(GIT_ERROR_INDEXER, "unexpected data at the end of the pack");

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

@@ -56,5 +56,37 @@ 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
 
 #endif

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/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);

src/libgit2/transports/smart_pkt.c

@@ -21,11 +21,14 @@
 
 #include <ctype.h>
 
+#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
-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_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)
 {
@@ -598,16 +601,20 @@ 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_MAX_HEXSIZE + 1] = {0};
+	char oid[GIT_OID_MAX_HEXSIZE];
 	size_t oid_hexsize, len;
 
-	oid_hexsize = git_oid_hexsize(head->oid.type);
+	oid_hexsize = git_oid_hexsize(oid_type);
 	git_oid_fmt(oid, &head->oid);
 
 	/* Prefer multi_ack_detailed */
@@ -634,18 +641,19 @@ static int buffer_want_with_caps(const git_remote_head *head, transport_smart_ca
 	if (git_str_oom(&str))
 		return -1;
 
-	len = strlen("XXXXwant ") + oid_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_str_printf(buf,
-		"%04xwant %.*s %s\n", (unsigned int)len,
+		"%04x%s%.*s %s\n", (unsigned int)len, PKT_WANT_PREFIX,
 		(int)oid_hexsize, oid, git_str_cstr(&str));
 	git_str_dispose(&str);
 
@@ -665,8 +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) {
@@ -675,15 +696,13 @@ 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_MAX_HEXSIZE];
-
 		head = refs[i];
 
 		if (head->local)
@@ -691,9 +710,9 @@ int git_pkt_buffer_wants(
 
 		git_oid_fmt(oid, &head->oid);
 
-		git_str_put(buf, pkt_want_prefix, strlen(pkt_want_prefix));
-		git_str_put(buf, oid, git_oid_hexsize(head->oid.type));
-		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;
@@ -704,14 +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

@@ -134,9 +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)
@@ -218,6 +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, ' ');
 	}

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