odb: allow creating an ODB backend from a packfile index

git_odb_backend_one_packfile() allows us to create an ODB backend out
of an .idx file.

include/git2/odb_backend.h

@@ -100,6 +100,7 @@ struct git_odb_stream {
 
 GIT_EXTERN(int) git_odb_backend_pack(git_odb_backend **backend_out, const char *objects_dir);
 GIT_EXTERN(int) git_odb_backend_loose(git_odb_backend **backend_out, const char *objects_dir, int compression_level, int do_fsync);
+GIT_EXTERN(int) git_odb_backend_one_pack(git_odb_backend **backend_out, const char *index_file);
 
 GIT_END_DECL
 

src/odb_pack.c

@@ -458,6 +458,41 @@ static void pack_backend__free(git_odb_backend *_backend)
 	git__free(backend);
 }
 
+int git_odb_backend_one_pack(git_odb_backend **backend_out, const char *idx)
+{
+	struct pack_backend *backend = NULL;
+	struct git_pack_file *packfile = NULL;
+
+	if (git_packfile_check(&packfile, idx) < 0)
+		return -1;
+
+	backend = git__calloc(1, sizeof(struct pack_backend));
+	GITERR_CHECK_ALLOC(backend);
+
+	if (git_vector_init(&backend->packs, 1, NULL) < 0)
+		goto on_error;
+
+	if (git_vector_insert(&backend->packs, packfile) < 0)
+		goto on_error;
+
+	backend->parent.read = &pack_backend__read;
+	backend->parent.read_prefix = &pack_backend__read_prefix;
+	backend->parent.read_header = NULL;
+	backend->parent.exists = &pack_backend__exists;
+	backend->parent.foreach = &pack_backend__foreach;
+	backend->parent.free = &pack_backend__free;
+
+	*backend_out = (git_odb_backend *)backend;
+
+	return 0;
+
+on_error:
+	git_vector_free(&backend->packs);
+	git__free(backend);
+	git__free(packfile);
+	return -1;
+}
+
 int git_odb_backend_pack(git_odb_backend **backend_out, const char *objects_dir)
 {
 	struct pack_backend *backend = NULL;

tests-clar/odb/foreach.c

@@ -7,12 +7,6 @@ static git_odb *_odb;
 static git_repository *_repo;
 static int nobj;
 
-void test_odb_foreach__initialize(void)
-{
-	cl_git_pass(git_repository_open(&_repo, cl_fixture("testrepo.git")));
-	git_repository_odb(&_odb, _repo);
-}
-
 void test_odb_foreach__cleanup(void)
 {
 	git_odb_free(_odb);
@@ -31,6 +25,23 @@ static int foreach_cb(git_oid *oid, void *data)
 
 void test_odb_foreach__foreach(void)
 {
+	cl_git_pass(git_repository_open(&_repo, cl_fixture("testrepo.git")));
+	git_repository_odb(&_odb, _repo);
+
 	cl_git_pass(git_odb_foreach(_odb, foreach_cb, NULL));
 	cl_assert(nobj == 1683);
 }
+
+void test_odb_foreach__one_pack(void)
+{
+	git_odb_backend *backend = NULL;
+
+	cl_git_pass(git_odb_new(&_odb));
+	cl_git_pass(git_odb_backend_one_pack(&backend, cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx")));
+	cl_git_pass(git_odb_add_backend(_odb, backend, 1));
+	_repo = NULL;
+
+	nobj = 0;
+	cl_git_pass(git_odb_foreach(_odb, foreach_cb, NULL));
+	cl_assert(nobj == 1628);
+}

tests-clar/odb/pack_data_one.h

+/* Just a few to make sure it's working, the rest is tested already */
+static const char *packed_objects_one[] = {
+	"9fcf811e00fa469688943a9152c16d4ee90fb9a9",
+	"a93f42a5b5e9de40fa645a9ff1e276a021c9542b",
+	"12bf5f3e3470d90db177ccf1b5e8126409377fc6",
+	"ed1ea164cdbe3c4b200fb4fa19861ea90eaee222",
+	"dfae6ed8f6dd8acc3b40a31811ea316239223559",
+	"aefe66d192771201e369fde830530f4475beec30",
+	"775e4b4c1296e9e3104f2a36ca9cf9356a130959",
+	"412ec4e4a6a7419bc1be00561fe474e54cb499fe",
+	"236e7579fed7763be77209efb8708960982f3cb3",
+	"09fe9364461cf60dd1c46b0e9545b1e47bb1a297",
+	"d76d8a6390d1cf32138d98a91b1eb7e0275a12f5",
+	"d0fdf2dcff2f548952eec536ccc6d266550041bc",
+	"a20d733a9fa79fa5b4cbb9639864f93325ec27a6",
+	"785d3fe8e7db5ade2c2242fecd46c32a7f4dc59f",
+	"4d8d0fd9cb6045075385701c3f933ec13345e9c4",
+	"0cfd861bd547b6520d1fc2e190e8359e0a9c9b90"
+};

tests-clar/odb/packed_one.c

+#include "clar_libgit2.h"
+#include "odb.h"
+#include "pack_data_one.h"
+#include "pack.h"
+
+static git_odb *_odb;
+
+void test_odb_packed_one__initialize(void)
+{
+	git_odb_backend *backend = NULL;
+
+	cl_git_pass(git_odb_new(&_odb));
+	cl_git_pass(git_odb_backend_one_pack(&backend, cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx")));
+	cl_git_pass(git_odb_add_backend(_odb, backend, 1));
+}
+
+void test_odb_packed_one__cleanup(void)
+{
+	git_odb_free(_odb);
+}
+
+void test_odb_packed_one__mass_read(void)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(packed_objects_one); ++i) {
+		git_oid id;
+		git_odb_object *obj;
+
+		cl_git_pass(git_oid_fromstr(&id, packed_objects_one[i]));
+		cl_assert(git_odb_exists(_odb, &id) == 1);
+		cl_git_pass(git_odb_read(&obj, _odb, &id));
+
+		git_odb_object_free(obj);
+	}
+}
+
+void test_odb_packed_one__read_header_0(void)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(packed_objects_one); ++i) {
+		git_oid id;
+		git_odb_object *obj;
+		size_t len;
+		git_otype type;
+
+		cl_git_pass(git_oid_fromstr(&id, packed_objects_one[i]));
+
+		cl_git_pass(git_odb_read(&obj, _odb, &id));
+		cl_git_pass(git_odb_read_header(&len, &type, _odb, &id));
+
+		cl_assert(obj->raw.len == len);
+		cl_assert(obj->raw.type == type);
+
+		git_odb_object_free(obj);
+	}
+}