pack: support SHA256 in packfilesethomson/sha256_pack

18 files changed, 348 insertions, 129 deletions

diff --git a/include/git2/odb_backend.h b/include/git2/odb_backend.h
index 092eb91ae..f68dc4e4b 100644
--- a/include/git2/odb_backend.h
+++ b/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)
@@ -90,19 +141,6 @@ GIT_EXTERN(int) git_odb_backend_loose(
 	const char *objects_dir,
 	git_odb_backend_loose_options *opts);
 
-/**
- * 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),
diff --git a/src/libgit2/commit_graph.c b/src/libgit2/commit_graph.c
index d4cb93eb4..eafcab9a8 100644
--- a/src/libgit2/commit_graph.c
+++ b/src/libgit2/commit_graph.c
@@ -524,7 +524,7 @@ 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_id(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 */
@@ -712,7 +712,8 @@ 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;
 
diff --git a/src/libgit2/indexer.c b/src/libgit2/indexer.c
index 60625b6c4..089dd34e8 100644
--- a/src/libgit2/indexer.c
+++ b/src/libgit2/indexer.c
@@ -179,7 +179,8 @@ int git_indexer_new(
 	if (fd < 0)
 		goto cleanup;
 
-	error = git_packfile_alloc(&idx->pack, git_str_cstr(&tmp_path));
+	/* TODO: SHA256 */
+	error = git_packfile_alloc(&idx->pack, git_str_cstr(&tmp_path), 0);
 	git_str_dispose(&tmp_path);
 
 	if (error < 0)
diff --git a/src/libgit2/midx.c b/src/libgit2/midx.c
index 37de58ccd..1a0bdd252 100644
--- a/src/libgit2/midx.c
+++ b/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_id(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;
diff --git a/src/libgit2/mwindow.c b/src/libgit2/mwindow.c
index ad649490a..b8295d9d1 100644
--- a/src/libgit2/mwindow.c
+++ b/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;
 	}
diff --git a/src/libgit2/mwindow.h b/src/libgit2/mwindow.h
index e32ab99d4..8e6df2613 100644
--- a/src/libgit2/mwindow.h
+++ b/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
diff --git a/src/libgit2/odb.c b/src/libgit2/odb.c
index 00d68d6f4..a91732948 100644
--- a/src/libgit2/odb.c
+++ b/src/libgit2/odb.c
@@ -632,6 +632,7 @@ 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 */
@@ -670,6 +671,7 @@ 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 ||
@@ -677,8 +679,15 @@ 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
+	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) {
diff --git a/src/libgit2/odb_pack.c b/src/libgit2/odb_pack.c
index d6243cd93..0f55c229b 100644
--- a/src/libgit2/odb_pack.c
+++ b/src/libgit2/odb_pack.c
@@ -26,6 +26,7 @@
 
 struct pack_backend {
 	git_odb_backend parent;
+	git_odb_backend_pack_options opts;
 	git_midx_file *midx;
 	git_vector midx_packs;
 	git_vector packs;
@@ -251,7 +252,7 @@ static int packfile_load__cb(void *data, git_str *path)
 	if (git_vector_search2(NULL, &backend->packs, packfile_byname_search_cmp, &index_prefix) == 0)
 		return 0;
 
-	error = git_mwindow_get_pack(&pack, path->ptr);
+	error = git_mwindow_get_pack(&pack, path->ptr, backend->opts.oid_type);
 
 	/* ignore missing .pack file as git does */
 	if (error == GIT_ENOTFOUND) {
@@ -270,10 +271,11 @@ static int pack_entry_find(struct git_pack_entry *e, struct pack_backend *backen
 {
 	struct git_pack_file *last_found = backend->last_found, *p;
 	git_midx_entry midx_entry;
+	size_t oid_hexsize = git_oid_hexsize(backend->opts.oid_type);
 	size_t i;
 
 	if (backend->midx &&
-		git_midx_entry_find(&midx_entry, backend->midx, oid, GIT_OID_SHA1_HEXSIZE) == 0 &&
+		git_midx_entry_find(&midx_entry, backend->midx, oid, oid_hexsize) == 0 &&
 		midx_entry.pack_index < git_vector_length(&backend->midx_packs)) {
 		e->offset = midx_entry.offset;
 		git_oid_cpy(&e->id, &midx_entry.sha1);
@@ -282,21 +284,21 @@ static int pack_entry_find(struct git_pack_entry *e, struct pack_backend *backen
 	}
 
 	if (last_found &&
-		git_pack_entry_find(e, last_found, oid, GIT_OID_SHA1_HEXSIZE) == 0)
+		git_pack_entry_find(e, last_found, oid, oid_hexsize) == 0)
 		return 0;
 
 	git_vector_foreach(&backend->packs, i, p) {
 		if (p == last_found)
 			continue;
 
-		if (git_pack_entry_find(e, p, oid, GIT_OID_SHA1_HEXSIZE) == 0) {
+		if (git_pack_entry_find(e, p, oid, oid_hexsize) == 0) {
 			backend->last_found = p;
 			return 0;
 		}
 	}
 
 	return git_odb__error_notfound(
-		"failed to find pack entry", oid, GIT_OID_SHA1_HEXSIZE);
+		"failed to find pack entry", oid, oid_hexsize);
 }
 
 static int pack_entry_find_prefix(
@@ -307,7 +309,7 @@ static int pack_entry_find_prefix(
 {
 	int error;
 	size_t i;
-	git_oid found_full_oid = GIT_OID_SHA1_ZERO;
+	git_oid found_full_oid = { 0 };
 	bool found = false;
 	struct git_pack_file *last_found = backend->last_found, *p;
 	git_midx_entry midx_entry;
@@ -425,7 +427,10 @@ static int process_multi_pack_index_pack(
 	}
 
 	/* Pack was not found. Allocate a new one. */
-	error = git_mwindow_get_pack(&pack, git_str_cstr(&pack_path));
+	error = git_mwindow_get_pack(
+		&pack,
+		git_str_cstr(&pack_path),
+		backend->opts.oid_type);
 	git_str_dispose(&pack_path);
 	if (error < 0)
 		return error;
@@ -596,27 +601,28 @@ static int pack_backend__read_prefix(
 	void **buffer_p,
 	size_t *len_p,
 	git_object_t *type_p,
-	git_odb_backend *backend,
+	git_odb_backend *_backend,
 	const git_oid *short_oid,
 	size_t len)
 {
+	struct pack_backend *backend = (struct pack_backend *)_backend;
 	int error = 0;
 
 	if (len < GIT_OID_MINPREFIXLEN)
 		error = git_odb__error_ambiguous("prefix length too short");
 
-	else if (len >= GIT_OID_SHA1_HEXSIZE) {
+	else if (len >= git_oid_hexsize(backend->opts.oid_type)) {
 		/* We can fall back to regular read method */
-		error = pack_backend__read(buffer_p, len_p, type_p, backend, short_oid);
+		error = pack_backend__read(buffer_p, len_p, type_p, _backend, short_oid);
 		if (!error)
 			git_oid_cpy(out_oid, short_oid);
 	} else {
 		struct git_pack_entry e;
 		git_rawobj raw = {NULL};
 
-		if ((error = pack_entry_find_prefix(
-				&e, (struct pack_backend *)backend, short_oid, len)) == 0 &&
-			(error = git_packfile_unpack(&raw, e.p, &e.offset)) == 0)
+		if ((error = pack_entry_find_prefix(&e,
+				backend, short_oid, len)) == 0 &&
+		    (error = git_packfile_unpack(&raw, e.p, &e.offset)) == 0)
 		{
 			*buffer_p = raw.data;
 			*len_p = raw.len;
@@ -840,7 +846,10 @@ static void pack_backend__free(git_odb_backend *_backend)
 	git__free(backend);
 }
 
-static int pack_backend__alloc(struct pack_backend **out, size_t initial_size)
+static int pack_backend__alloc(
+	struct pack_backend **out,
+	size_t initial_size,
+	const git_odb_backend_pack_options *opts)
 {
 	struct pack_backend *backend = git__calloc(1, sizeof(struct pack_backend));
 	GIT_ERROR_CHECK_ALLOC(backend);
@@ -849,12 +858,19 @@ static int pack_backend__alloc(struct pack_backend **out, size_t initial_size)
 		git__free(backend);
 		return -1;
 	}
+
 	if (git_vector_init(&backend->packs, initial_size, packfile_sort__cb) < 0) {
 		git_vector_free(&backend->midx_packs);
 		git__free(backend);
 		return -1;
 	}
 
+	if (opts)
+		memcpy(&backend->opts, opts, sizeof(git_odb_backend_pack_options));
+
+	if (!backend->opts.oid_type)
+		backend->opts.oid_type = GIT_OID_DEFAULT;
+
 	backend->parent.version = GIT_ODB_BACKEND_VERSION;
 
 	backend->parent.read = &pack_backend__read;
@@ -873,17 +889,31 @@ static int pack_backend__alloc(struct pack_backend **out, size_t initial_size)
 	return 0;
 }
 
-int git_odb_backend_one_pack(git_odb_backend **backend_out, const char *idx)
+#ifdef GIT_EXPERIMENTAL_SHA256
+int git_odb_backend_one_pack(
+	git_odb_backend **backend_out,
+	const char *idx,
+	const git_odb_backend_pack_options *opts)
+#else
+int git_odb_backend_one_pack(
+	git_odb_backend **backend_out,
+	const char *idx)
+#endif
 {
 	struct pack_backend *backend = NULL;
 	struct git_pack_file *packfile = NULL;
 
-	if (pack_backend__alloc(&backend, 1) < 0)
+#ifndef GIT_EXPERIMENTAL_SHA256
+	git_odb_backend_pack_options *opts = NULL;
+#endif
+
+	git_oid_t oid_type = opts ? opts->oid_type : 0;
+
+	if (pack_backend__alloc(&backend, 1, opts) < 0)
 		return -1;
 
-	if (git_mwindow_get_pack(&packfile, idx) < 0 ||
-		git_vector_insert(&backend->packs, packfile) < 0)
-	{
+	if (git_mwindow_get_pack(&packfile, idx, oid_type) < 0 ||
+	    git_vector_insert(&backend->packs, packfile) < 0) {
 		pack_backend__free((git_odb_backend *)backend);
 		return -1;
 	}
@@ -892,18 +922,30 @@ int git_odb_backend_one_pack(git_odb_backend **backend_out, const char *idx)
 	return 0;
 }
 
-int git_odb_backend_pack(git_odb_backend **backend_out, const char *objects_dir)
+#ifdef GIT_EXPERIMENTAL_SHA256
+int git_odb_backend_pack(
+	git_odb_backend **backend_out,
+	const char *objects_dir,
+	const git_odb_backend_pack_options *opts)
+#else
+int git_odb_backend_pack(
+	git_odb_backend **backend_out,
+	const char *objects_dir)
+#endif
 {
 	int error = 0;
 	struct pack_backend *backend = NULL;
 	git_str path = GIT_STR_INIT;
 
-	if (pack_backend__alloc(&backend, 8) < 0)
+#ifndef GIT_EXPERIMENTAL_SHA256
+	git_odb_backend_pack_options *opts = NULL;
+#endif
+
+	if (pack_backend__alloc(&backend, 8, opts) < 0)
 		return -1;
 
 	if (!(error = git_str_joinpath(&path, objects_dir, "pack")) &&
-		git_fs_path_isdir(git_str_cstr(&path)))
-	{
+	    git_fs_path_isdir(git_str_cstr(&path))) {
 		backend->pack_folder = git_str_detach(&path);
 		error = pack_backend__refresh((git_odb_backend *)backend);
 	}
diff --git a/src/libgit2/pack.c b/src/libgit2/pack.c
index 4ea6b5909..513f31c03 100644
--- a/src/libgit2/pack.c
+++ b/src/libgit2/pack.c
@@ -32,7 +32,7 @@ static int packfile_unpack_compressed(
  * Throws GIT_EAMBIGUOUSOIDPREFIX if short oid
  * is ambiguous within the pack.
  * This method assumes that len is between
- * GIT_OID_MINPREFIXLEN and GIT_OID_SHA1_HEXSIZE.
+ * GIT_OID_MINPREFIXLEN and the oid type's hexsize.
  */
 static int pack_entry_find_offset(
 		off64_t *offset_out,
@@ -205,6 +205,7 @@ static int pack_index_check_locked(const char *path, struct git_pack_file *p)
 	size_t idx_size;
 	struct stat st;
 	int error;
+
 	/* TODO: properly open the file without access time using O_NOATIME */
 	git_file fd = git_futils_open_ro(path);
 	if (fd < 0)
@@ -218,8 +219,7 @@ static int pack_index_check_locked(const char *path, struct git_pack_file *p)
 
 	if (!S_ISREG(st.st_mode) ||
 		!git__is_sizet(st.st_size) ||
-		(idx_size = (size_t)st.st_size) < 4 * 256 + 20 + 20)
-	{
+		(idx_size = (size_t)st.st_size) < (4 * 256) + (p->oid_size * 2)) {
 		p_close(fd);
 		git_error_set(GIT_ERROR_ODB, "invalid pack index '%s'", path);
 		return -1;
@@ -242,8 +242,9 @@ static int pack_index_check_locked(const char *path, struct git_pack_file *p)
 			return packfile_error("unsupported index version");
 		}
 
-	} else
+	} else {
 		version = 1;
+	}
 
 	nr = 0;
 	index = idx_map;
@@ -264,11 +265,11 @@ static int pack_index_check_locked(const char *path, struct git_pack_file *p)
 		/*
 		 * Total size:
 		 * - 256 index entries 4 bytes each
-		 * - 24-byte entries * nr (20-byte sha1 + 4-byte offset)
-		 * - 20-byte SHA1 of the packfile
-		 * - 20-byte SHA1 file checksum
+		 * - 24/36-byte entries * nr (20/32 byte SHA + 4-byte offset)
+		 * - 20/32-byte SHA of the packfile
+		 * - 20/32-byte SHA file checksum
 		 */
-		if (idx_size != 4*256 + nr * 24 + 20 + 20) {
+		if (idx_size != (4 * 256 + (nr * (p->oid_size + 4)) + (p->oid_size * 2))) {
 			git_futils_mmap_free(&p->index_map);
 			return packfile_error("index is corrupted");
 		}
@@ -277,16 +278,16 @@ static int pack_index_check_locked(const char *path, struct git_pack_file *p)
 		 * Minimum size:
 		 * - 8 bytes of header
 		 * - 256 index entries 4 bytes each
-		 * - 20-byte sha1 entry * nr
+		 * - 20/32-byte SHA entry * nr
 		 * - 4-byte crc entry * nr
 		 * - 4-byte offset entry * nr
-		 * - 20-byte SHA1 of the packfile
-		 * - 20-byte SHA1 file checksum
+		 * - 20/32-byte SHA of the packfile
+		 * - 20/32-byte SHA file checksum
 		 * And after the 4-byte offset table might be a
 		 * variable sized table containing 8-byte entries
 		 * for offsets larger than 2^31.
 		 */
-		unsigned long min_size = 8 + 4*256 + nr*(20 + 4 + 4) + 20 + 20;
+		unsigned long min_size = 8 + (4 * 256) + (nr * (p->oid_size + 4 + 4)) + (p->oid_size * 2);
 		unsigned long max_size = min_size;
 
 		if (nr)
@@ -365,12 +366,12 @@ static unsigned char *pack_window_open(
 	 * Don't allow a negative offset, as that means we've wrapped
 	 * around.
 	 */
-	if (offset > (p->mwf.size - 20))
+	if (offset > (p->mwf.size - p->oid_size))
 		goto cleanup;
 	if (offset < 0)
 		goto cleanup;
 
-	pack_data = git_mwindow_open(&p->mwf, w_cursor, offset, 20, left);
+	pack_data = git_mwindow_open(&p->mwf, w_cursor, offset, p->oid_size, left);
 
 cleanup:
 	git_mutex_unlock(&p->mwf.lock);
@@ -473,13 +474,13 @@ int git_packfile_unpack_header(
 		return error;
 	}
 
-	/* pack_window_open() assures us we have [base, base + 20) available
-	 * as a range that we can look at at. (Its actually the hash
-	 * size that is assured.) With our object header encoding
-	 * the maximum deflated object size is 2^137, which is just
-	 * insane, so we know won't exceed what we have been given.
+	/* pack_window_open() assures us we have [base, base + oid_size)
+	 * available as a range that we can look at at. (It's actually
+	 * the hash size that is assured.) With our object header
+	 * encoding the maximum deflated object size is 2^137, which is
+	 * just insane, so we know won't exceed what we have been given.
 	 */
-	base = git_mwindow_open(&p->mwf, w_curs, *curpos, 20, &left);
+	base = git_mwindow_open(&p->mwf, w_curs, *curpos, p->oid_size, &left);
 	git_mutex_unlock(&p->lock);
 	git_mutex_unlock(&p->mwf.lock);
 	if (base == NULL)
@@ -977,11 +978,12 @@ int get_delta_base(
 	/* Assumption: the only reason this would fail is because the file is too small */
 	if (base_info == NULL)
 		return GIT_EBUFS;
-	/* pack_window_open() assured us we have [base_info, base_info + 20)
-	 * as a range that we can look at without walking off the
-	 * end of the mapped window. Its actually the hash size
-	 * that is assured. An OFS_DELTA longer than the hash size
-	 * is stupid, as then a REF_DELTA would be smaller to store.
+	/* pack_window_open() assured us we have
+	 * [base_info, base_info + oid_size) as a range that we can look
+	 * at without walking off the end of the mapped window. Its
+	 * actually the hash size that is assured. An OFS_DELTA longer
+	 * than the hash size is stupid, as then a REF_DELTA would be
+	 * smaller to store.
 	 */
 	if (type == GIT_OBJECT_OFS_DELTA) {
 		unsigned used = 0;
@@ -1002,7 +1004,7 @@ int get_delta_base(
 		*curpos += used;
 	} else if (type == GIT_OBJECT_REF_DELTA) {
 		git_oid base_oid;
-		git_oid_fromraw(&base_oid, base_info, GIT_OID_SHA1);
+		git_oid_fromraw(&base_oid, base_info, p->oid_type);
 
 		/* If we have the cooperative cache, search in it first */
 		if (p->has_cache) {
@@ -1012,7 +1014,7 @@ int get_delta_base(
 				if (entry->offset == 0)
 					return packfile_error("delta offset is zero");
 
-				*curpos += 20;
+				*curpos += p->oid_size;
 				*delta_base_out = entry->offset;
 				return 0;
 			} else {
@@ -1025,9 +1027,9 @@ int get_delta_base(
 		}
 
 		/* The base entry _must_ be in the same pack */
-		if (pack_entry_find_offset(&base_offset, &unused, p, &base_oid, GIT_OID_SHA1_HEXSIZE) < 0)
+		if (pack_entry_find_offset(&base_offset, &unused, p, &base_oid, p->oid_hexsize) < 0)
 			return packfile_error("base entry delta is not in the same pack");
-		*curpos += 20;
+		*curpos += p->oid_size;
 	} else
 		return packfile_error("unknown object type");
 
@@ -1083,8 +1085,8 @@ static int packfile_open_locked(struct git_pack_file *p)
 {
 	struct stat st;
 	struct git_pack_header hdr;
-	unsigned char sha1[GIT_OID_SHA1_SIZE];
-	unsigned char *idx_sha1;
+	unsigned char checksum[GIT_OID_MAX_SIZE];
+	unsigned char *idx_checksum;
 
 	if (pack_index_open_locked(p) < 0)
 		return git_odb__error_notfound("failed to open packfile", NULL, 0);
@@ -1131,12 +1133,13 @@ static int packfile_open_locked(struct git_pack_file *p)
 
 	/* Verify the pack matches its index. */
 	if (p->num_objects != ntohl(hdr.hdr_entries) ||
-	    p_pread(p->mwf.fd, sha1, GIT_OID_SHA1_SIZE, p->mwf.size - GIT_OID_SHA1_SIZE) < 0)
+	    p_pread(p->mwf.fd, checksum, p->oid_size, p->mwf.size - p->oid_size) < 0)
 		goto cleanup;
 
-	idx_sha1 = ((unsigned char *)p->index_map.data) + p->index_map.len - 40;
+	idx_checksum = ((unsigned char *)p->index_map.data) +
+	               p->index_map.len - (p->oid_size * 2);
 
-	if (git_oid_raw_cmp(sha1, idx_sha1, GIT_OID_SHA1_SIZE) != 0)
+	if (git_oid_raw_cmp(checksum, idx_checksum, p->oid_size) != 0)
 		goto cleanup;
 
 	if (git_mwindow_file_register(&p->mwf) < 0)
@@ -1171,7 +1174,10 @@ int git_packfile__name(char **out, const char *path)
 	return 0;
 }
 
-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)
 {
 	struct stat st;
 	struct git_pack_file *p;
@@ -1219,6 +1225,9 @@ int git_packfile_alloc(struct git_pack_file **pack_out, const char *path)
 	p->pack_local = 1;
 	p->mtime = (git_time_t)st.st_mtime;
 	p->index_version = -1;
+	p->oid_type = oid_type ? oid_type : GIT_OID_DEFAULT;
+	p->oid_size = git_oid_size(p->oid_type);
+	p->oid_hexsize = git_oid_hexsize(p->oid_type);
 
 	if (git_mutex_init(&p->lock) < 0) {
 		git_error_set(GIT_ERROR_OS, "failed to initialize packfile mutex");
@@ -1260,9 +1269,9 @@ static off64_t nth_packed_object_offset_locked(struct git_pack_file *p, uint32_t
 	end = index + p->index_map.len;
 	index += 4 * 256;
 	if (p->index_version == 1)
-		return ntohl(*((uint32_t *)(index + 24 * n)));
+		return ntohl(*((uint32_t *)(index + (p->oid_size + 4) * n)));
 
-	index += 8 + p->num_objects * (20 + 4);
+	index += 8 + p->num_objects * (p->oid_size + 4);
 	off32 = ntohl(*((uint32_t *)(index + 4 * n)));
 	if (!(off32 & 0x80000000))
 		return off32;
@@ -1273,7 +1282,7 @@ static off64_t nth_packed_object_offset_locked(struct git_pack_file *p, uint32_t
 		return -1;
 
 	return (((uint64_t)ntohl(*((uint32_t *)(index + 0)))) << 32) |
-				ntohl(*((uint32_t *)(index + 4)));
+	       ntohl(*((uint32_t *)(index + 4)));
 }
 
 static int git__memcmp4(const void *a, const void *b) {
@@ -1326,15 +1335,18 @@ int git_pack_foreach_entry(
 		}
 
 		if (p->index_version > 1) {
-			const unsigned char *off = index + 24 * p->num_objects;
+			const unsigned char *off = index +
+				(p->oid_size + 4) * p->num_objects;
+
 			for (i = 0; i < p->num_objects; i++)
 				git_vector_insert(&offsets, (void*)&off[4 * i]);
+
 			git_vector_sort(&offsets);
 			git_vector_foreach(&offsets, i, current)
 				git_vector_insert(&oids, (void*)&index[5 * (current - off)]);
 		} else {
 			for (i = 0; i < p->num_objects; i++)
-				git_vector_insert(&offsets, (void*)&index[24 * i]);
+				git_vector_insert(&offsets, (void*)&index[(p->oid_size + 4) * i]);
 			git_vector_sort(&offsets);
 			git_vector_foreach(&offsets, i, current)
 				git_vector_insert(&oids, (void*)&current[4]);
@@ -1362,7 +1374,7 @@ int git_pack_foreach_entry(
 			git_array_clear(oids);
 			GIT_ERROR_CHECK_ALLOC(oid);
 		}
-		git_oid_fromraw(oid, p->ids[i], GIT_OID_SHA1);
+		git_oid_fromraw(oid, p->ids[i], p->oid_type);
 	}
 
 	git_mutex_unlock(&p->lock);
@@ -1412,10 +1424,13 @@ int git_pack_foreach_entry_offset(
 
 	/* all offsets should have been validated by pack_index_check_locked */
 	if (p->index_version > 1) {
-		const unsigned char *offsets = index + 24 * p->num_objects;
+		const unsigned char *offsets = index +
+			(p->oid_size + 4) * p->num_objects;
 		const unsigned char *large_offset_ptr;
-		const unsigned char *large_offsets = index + 28 * p->num_objects;
-		const unsigned char *large_offsets_end = ((const unsigned char *)p->index_map.data) + p->index_map.len - 20;
+		const unsigned char *large_offsets = index +
+			(p->oid_size + 8) * p->num_objects;
+		const unsigned char *large_offsets_end = ((const unsigned char *)p->index_map.data) + p->index_map.len - p->oid_size;
+
 		for (i = 0; i < p->num_objects; i++) {
 			current_offset = ntohl(*(const uint32_t *)(offsets + 4 * i));
 			if (current_offset & 0x80000000) {
@@ -1428,7 +1443,7 @@ int git_pack_foreach_entry_offset(
 						ntohl(*((uint32_t *)(large_offset_ptr + 4)));
 			}
 
-			git_oid_fromraw(&current_oid, (index + 20 * i), GIT_OID_SHA1);
+			git_oid_fromraw(&current_oid, (index + p->oid_size * i), p->oid_type);
 			if ((error = cb(&current_oid, current_offset, data)) != 0) {
 				error = git_error_set_after_callback(error);
 				goto cleanup;
@@ -1436,8 +1451,8 @@ int git_pack_foreach_entry_offset(
 		}
 	} else {
 		for (i = 0; i < p->num_objects; i++) {
-			current_offset = ntohl(*(const uint32_t *)(index + 24 * i));
-			git_oid_fromraw(&current_oid, (index + 24 * i + 4), GIT_OID_SHA1);
+			current_offset = ntohl(*(const uint32_t *)(index + (p->oid_size + 4) * i));
+			git_oid_fromraw(&current_oid, (index + (p->oid_size + 4) * i + 4), p->oid_type);
 			if ((error = cb(&current_oid, current_offset, data)) != 0) {
 				error = git_error_set_after_callback(error);
 				goto cleanup;
@@ -1455,13 +1470,15 @@ int git_pack__lookup_id(
 	size_t stride,
 	unsigned lo,
 	unsigned hi,
-	const unsigned char *oid_prefix)
+	const unsigned char *oid_prefix,
+	const git_oid_t oid_type)
 {
 	const unsigned char *base = oid_lookup_table;
+	size_t oid_size = git_oid_size(oid_type);
 
 	while (lo < hi) {
 		unsigned mi = (lo + hi) / 2;
-		int cmp = git_oid_raw_cmp(base + mi * stride, oid_prefix, GIT_OID_SHA1_SIZE);
+		int cmp = git_oid_raw_cmp(base + mi * stride, oid_prefix, oid_size);
 
 		if (!cmp)
 			return mi;
@@ -1516,9 +1533,9 @@ static int pack_entry_find_offset(
 	lo = ((short_oid->id[0] == 0x0) ? 0 : ntohl(level1_ofs[(int)short_oid->id[0] - 1]));
 
 	if (p->index_version > 1) {
-		stride = 20;
+		stride = p->oid_size;
 	} else {
-		stride = 24;
+		stride = p->oid_size + 4;
 		index += 4;
 	}
 
@@ -1527,7 +1544,8 @@ static int pack_entry_find_offset(
 		short_oid->id[0], short_oid->id[1], short_oid->id[2], lo, hi, p->num_objects);
 #endif
 
-	pos = git_pack__lookup_id(index, stride, lo, hi, short_oid->id);
+	pos = git_pack__lookup_id(index, stride, lo, hi,
+		short_oid->id, p->oid_type);
 
 	if (pos >= 0) {
 		/* An object matching exactly the oid was found */
@@ -1545,7 +1563,9 @@ static int pack_entry_find_offset(
 		}
 	}
 
-	if (found && len != GIT_OID_SHA1_HEXSIZE && pos + 1 < (int)p->num_objects) {
+	if (found &&
+	    len != p->oid_hexsize &&
+	    pos + 1 < (int)p->num_objects) {
 		/* Check for ambiguousity */
 		const unsigned char *next = current + stride;
 
@@ -1570,13 +1590,13 @@ static int pack_entry_find_offset(
 	}
 
 	*offset_out = offset;
-	git_oid_fromraw(found_oid, current, GIT_OID_SHA1);
+	git_oid_fromraw(found_oid, current, p->oid_type);
 
 #ifdef INDEX_DEBUG_LOOKUP
 	{
-		unsigned char hex_sha1[GIT_OID_SHA1_HEXSIZE + 1];
+		char hex_sha1[p->oid_hexsize + 1];
 		git_oid_fmt(hex_sha1, found_oid);
-		hex_sha1[GIT_OID_SHA1_HEXSIZE] = '\0';
+		hex_sha1[p->oid_hexsize] = '\0';
 		printf("found lo=%d %s\n", lo, hex_sha1);
 	}
 #endif
@@ -1598,7 +1618,7 @@ int git_pack_entry_find(
 
 	GIT_ASSERT_ARG(p);
 
-	if (len == GIT_OID_SHA1_HEXSIZE && p->num_bad_objects) {
+	if (len == p->oid_hexsize && p->num_bad_objects) {
 		unsigned i;
 		for (i = 0; i < p->num_bad_objects; i++)
 			if (git_oid__cmp(short_oid, &p->bad_object_ids[i]) == 0)
diff --git a/src/libgit2/pack.h b/src/libgit2/pack.h
index 6c9dbf20b..1a9eb14b2 100644
--- a/src/libgit2/pack.h
+++ b/src/libgit2/pack.h
@@ -101,9 +101,15 @@ struct git_pack_file {
 	uint32_t num_bad_objects;
 	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 **ids;
 
@@ -116,21 +122,22 @@ 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_id(
 	const void *id_lookup_table,
 	size_t stride,
 	unsigned lo,
 	unsigned hi,
-	const unsigned char *id_prefix);
+	const unsigned char *id_prefix,
+	const git_oid_t oid_type);
 
 struct git_pack_entry {
 	off64_t offset;
@@ -178,7 +185,10 @@ 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,
diff --git a/tests/libgit2/odb/foreach.c b/tests/libgit2/odb/foreach.c
index 98b5d80b7..5e4dae41b 100644
--- a/tests/libgit2/odb/foreach.c
+++ b/tests/libgit2/odb/foreach.c
@@ -52,7 +52,15 @@ 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")));
+	cl_git_pass(git_odb_backend_one_pack(
+		&backend,
+		cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx")
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+, NULL
+#endif
+
+		));
 	cl_git_pass(git_odb_add_backend(_odb, backend, 1));
 	_repo = NULL;
 
diff --git a/tests/libgit2/odb/loose.c b/tests/libgit2/odb/loose.c
index 93895deb5..9651ebab6 100644
--- a/tests/libgit2/odb/loose.c
+++ b/tests/libgit2/odb/loose.c
@@ -188,18 +188,6 @@ void test_odb_loose__exists_sha256(void)
 #endif
 }
 
-void test_odb_loose__zzz(void)
-{
-	write_object_files(&one_sha256);
-	write_object_files(&commit_sha256);
-	write_object_files(&tree_sha256);
-	write_object_files(&tag_sha256);
-	write_object_files(&zero_sha256);
-	write_object_files(&two_sha256);
-	write_object_files(&some_sha256);
-	abort();
-}
-
 void test_odb_loose__simple_reads_sha1(void)
 {
 	test_read_object(&commit);
diff --git a/tests/libgit2/odb/pack_data_one_sha256.h b/tests/libgit2/odb/pack_data_one_sha256.h
new file mode 100644
index 000000000..4b9282a40
--- /dev/null
+++ b/tests/libgit2/odb/pack_data_one_sha256.h
@@ -0,0 +1,10 @@
+/* Just a few to make sure it's working, the rest is tested already */
+static const char *packed_objects_one_sha256[] = {
+	"083c2b8b445640d171e7aa667b0b32007006f786711032ebb82931cca69cc15b",
+	"34a4854b5426f92460b4ae35e6d79746be66c38bffd6ef3bc4f053ed78a36ba4",
+	"473a0f4c3be8a93681a267e3b1e9a7dcda1185436fe141f7749120a303721813",
+	"4c0d52d180c61d01ce1a91dec5ee58f0cbe65fd59433aea803ab927965493fd7",
+	"a2a430fb63b294f868af4ef6ccc9c3e8256e370859ce578a23837ac85337f562",
+	"f535d7595d5d0e5e530b5deb34542c96491fea300a1318036b605306548cb225",
+	"f8625e43f9e04f24291f77cdbe4c71b3c2a3b0003f60419b3ed06a058d766c8b"
+};
diff --git a/tests/libgit2/odb/packed_one.c b/tests/libgit2/odb/packed_one.c
index 777b54b98..8822585c6 100644
--- a/tests/libgit2/odb/packed_one.c
+++ b/tests/libgit2/odb/packed_one.c
@@ -11,7 +11,13 @@ void test_odb_packed_one__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")));
+	cl_git_pass(git_odb_backend_one_pack(
+		&backend,
+		cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx")
+#ifdef GIT_EXPERIMENTAL_SHA256
+		, NULL
+#endif
+		));
 	cl_git_pass(git_odb_add_backend(_odb, backend, 1));
 }
 
diff --git a/tests/libgit2/odb/packed_one_sha256.c b/tests/libgit2/odb/packed_one_sha256.c
new file mode 100644
index 000000000..6cebc321b
--- /dev/null
+++ b/tests/libgit2/odb/packed_one_sha256.c
@@ -0,0 +1,75 @@
+#include "clar_libgit2.h"
+#include "git2/odb_backend.h"
+
+#include "pack_data_one_sha256.h"
+#include "pack.h"
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+static git_odb *_odb;
+#endif
+
+void test_odb_packed_one_sha256__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("packfile-sha256/pack-b4a043c0ec5e079e8ac67d823776d752efc71661592db317474a0cf292915f31.idx"), &backend_opts));
+	cl_git_pass(git_odb_add_backend(_odb, backend, 1));
+#endif
+}
+
+void test_odb_packed_one_sha256__cleanup(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	git_odb_free(_odb);
+	_odb = NULL;
+#endif
+}
+
+void test_odb_packed_one_sha256__mass_read(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(packed_objects_one_sha256); ++i) {
+		git_oid id;
+		git_odb_object *obj;
+
+		cl_git_pass(git_oid_fromstr(&id, packed_objects_one_sha256[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_packed_one_sha256__read_header_0(void)
+{
+#ifdef GIT_EXPERIMENTAL_SHA256
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(packed_objects_one_sha256); ++i) {
+		git_oid id;
+		git_odb_object *obj;
+		size_t len;
+		git_object_t type;
+
+		cl_git_pass(git_oid_fromstr(&id, packed_objects_one_sha256[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
+}
diff --git a/tests/libgit2/odb/sorting.c b/tests/libgit2/odb/sorting.c
index 33ce289b5..dc4d615c7 100644
--- a/tests/libgit2/odb/sorting.c
+++ b/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));
diff --git a/tests/resources/packfile-sha256/pack-b4a043c0ec5e079e8ac67d823776d752efc71661592db317474a0cf292915f31.idx b/tests/resources/packfile-sha256/pack-b4a043c0ec5e079e8ac67d823776d752efc71661592db317474a0cf292915f31.idx
new file mode 100644
index 000000000..7aa472cea
--- /dev/null
+++ b/tests/resources/packfile-sha256/pack-b4a043c0ec5e079e8ac67d823776d752efc71661592db317474a0cf292915f31.idx
diff --git a/tests/resources/packfile-sha256/pack-b4a043c0ec5e079e8ac67d823776d752efc71661592db317474a0cf292915f31.pack b/tests/resources/packfile-sha256/pack-b4a043c0ec5e079e8ac67d823776d752efc71661592db317474a0cf292915f31.pack
new file mode 100644
index 000000000..adbe70ad3
--- /dev/null
+++ b/tests/resources/packfile-sha256/pack-b4a043c0ec5e079e8ac67d823776d752efc71661592db317474a0cf292915f31.pack