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[libgit2.git] / src / odb_loose.c

/*
 * This file is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License, version 2,
 * as published by the Free Software Foundation.
 *
 * In addition to the permissions in the GNU General Public License,
 * the authors give you unlimited permission to link the compiled
 * version of this file into combinations with other programs,
 * and to distribute those combinations without any restriction
 * coming from the use of this file.  (The General Public License
 * restrictions do apply in other respects; for example, they cover
 * modification of the file, and distribution when not linked into
 * a combined executable.)
 *
 * This file is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; see the file COPYING.  If not, write to
 * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

#include "common.h"
#include "git2/zlib.h"
#include "git2/object.h"
#include "git2/oid.h"
#include "fileops.h"
#include "hash.h"
#include "odb.h"
#include "delta-apply.h"
#include "filebuf.h"

#include "git2/odb_backend.h"
#include "git2/types.h"

typedef struct {  /* object header data */
	git_otype type;  /* object type */
	size_t    size;  /* object size */
} obj_hdr;

typedef struct {
	git_odb_stream stream;
	git_filebuf fbuf;
	int finished;
} loose_writestream;

typedef struct loose_backend {
	git_odb_backend parent;

	int object_zlib_level; /** loose object zlib compression level. */
	int fsync_object_files; /** loose object file fsync flag. */
	char *objects_dir;
} loose_backend;

/* State structure for exploring directories,
 * in order to locate objects matching a short oid.
 */
typedef struct {
	size_t dir_len;
	unsigned char short_oid[GIT_OID_HEXSZ]; /* hex formatted oid to match */
	unsigned int short_oid_len;
	int found;				/* number of matching
						 * objects already found */
	unsigned char res_oid[GIT_OID_HEXSZ];	/* hex formatted oid of
						 * the object found */
} loose_locate_object_state;



/***********************************************************
 *
 * MISCELANEOUS HELPER FUNCTIONS
 *
 ***********************************************************/

static size_t object_file_name(char *name, size_t n, char *dir, const git_oid *id)
{
	size_t len = strlen(dir);

	/* check length: 43 = 40 hex sha1 chars + 2 * '/' + '\0' */
	if (len+43 > n)
		return len+43;

	/* the object dir: eg $GIT_DIR/objects */
	strcpy(name, dir);
	if (name[len-1] != '/')
		name[len++] = '/';

	/* loose object filename: aa/aaa... (41 bytes) */
	git_oid_pathfmt(&name[len], id);
	name[len+41] = '\0';

	return 0;
}


static size_t get_binary_object_header(obj_hdr *hdr, git_fbuffer *obj)
{
	unsigned char c;
	unsigned char *data = obj->data;
	size_t shift, size, used = 0;

	if (obj->len == 0)
		return 0;

	c = data[used++];
	hdr->type = (c >> 4) & 7;

	size = c & 15;
	shift = 4;
	while (c & 0x80) {
		if (obj->len <= used)
			return 0;
		if (sizeof(size_t) * 8 <= shift)
			return 0;
		c = data[used++];
		size += (c & 0x7f) << shift;
		shift += 7;
	}
	hdr->size = size;

	return used;
}

static size_t get_object_header(obj_hdr *hdr, unsigned char *data)
{
	char c, typename[10];
	size_t size, used = 0;

	/*
	 * type name string followed by space.
	 */
	while ((c = data[used]) != ' ') {
		typename[used++] = c;
		if (used >= sizeof(typename))
			return 0;
	}
	typename[used] = 0;
	if (used == 0)
		return 0;
	hdr->type = git_object_string2type(typename);
	used++;  /* consume the space */

	/*
	 * length follows immediately in decimal (without
	 * leading zeros).
	 */
	size = data[used++] - '0';
	if (size > 9)
		return 0;
	if (size) {
		while ((c = data[used]) != '\0') {
			size_t d = c - '0';
			if (d > 9)
				break;
			used++;
			size = size * 10 + d;
		}
	}
	hdr->size = size;

	/*
	 * the length must be followed by a zero byte
	 */
	if (data[used++] != '\0')
		return 0;

	return used;
}



/***********************************************************
 *
 * ZLIB RELATED FUNCTIONS
 *
 ***********************************************************/

static void init_stream(z_stream *s, void *out, size_t len)
{
	memset(s, 0, sizeof(*s));
	s->next_out  = out;
	s->avail_out = (uInt)len;
}

static void set_stream_input(z_stream *s, void *in, size_t len)
{
	s->next_in  = in;
	s->avail_in = (uInt)len;
}

static void set_stream_output(z_stream *s, void *out, size_t len)
{
	s->next_out  = out;
	s->avail_out = (uInt)len;
}


static int start_inflate(z_stream *s, git_fbuffer *obj, void *out, size_t len)
{
	int status;

	init_stream(s, out, len);
	set_stream_input(s, obj->data, obj->len);

	if ((status = inflateInit(s)) < Z_OK)
		return status;

	return inflate(s, 0);
}

static int finish_inflate(z_stream *s)
{
	int status = Z_OK;

	while (status == Z_OK)
		status = inflate(s, Z_FINISH);

	inflateEnd(s);

	if ((status != Z_STREAM_END) || (s->avail_in != 0))
		return git__throw(GIT_ERROR, "Failed to finish inflation. Stream aborted prematurely");

	return GIT_SUCCESS;
}

static int is_zlib_compressed_data(unsigned char *data)
{
	unsigned int w;

	w = ((unsigned int)(data[0]) << 8) + data[1];
	return data[0] == 0x78 && !(w % 31);
}

static int inflate_buffer(void *in, size_t inlen, void *out, size_t outlen)
{
	z_stream zs;
	int status = Z_OK;

	memset(&zs, 0x0, sizeof(zs));

	zs.next_out  = out;
	zs.avail_out = (uInt)outlen;

	zs.next_in  = in;
	zs.avail_in = (uInt)inlen;

	if (inflateInit(&zs) < Z_OK)
		return git__throw(GIT_ERROR, "Failed to inflate buffer");

	while (status == Z_OK)
		status = inflate(&zs, Z_FINISH);

	inflateEnd(&zs);

	if ((status != Z_STREAM_END) /*|| (zs.avail_in != 0) */)
		return git__throw(GIT_ERROR, "Failed to inflate buffer. Stream aborted prematurely");

	if (zs.total_out != outlen)
		return git__throw(GIT_ERROR, "Failed to inflate buffer. Stream aborted prematurely");

	return GIT_SUCCESS;
}

static void *inflate_tail(z_stream *s, void *hb, size_t used, obj_hdr *hdr)
{
	unsigned char *buf, *head = hb;
	size_t tail;

	/*
	 * allocate a buffer to hold the inflated data and copy the
	 * initial sequence of inflated data from the tail of the
	 * head buffer, if any.
	 */
	if ((buf = git__malloc(hdr->size + 1)) == NULL) {
		inflateEnd(s);
		return NULL;
	}
	tail = s->total_out - used;
	if (used > 0 && tail > 0) {
		if (tail > hdr->size)
			tail = hdr->size;
		memcpy(buf, head + used, tail);
	}
	used = tail;

	/*
	 * inflate the remainder of the object data, if any
	 */
	if (hdr->size < used)
		inflateEnd(s);
	else {
		set_stream_output(s, buf + used, hdr->size - used);
		if (finish_inflate(s)) {
			free(buf);
			return NULL;
		}
	}

	return buf;
}

/*
 * At one point, there was a loose object format that was intended to
 * mimic the format used in pack-files. This was to allow easy copying
 * of loose object data into packs. This format is no longer used, but
 * we must still read it.
 */
static int inflate_packlike_loose_disk_obj(git_rawobj *out, git_fbuffer *obj)
{
	unsigned char *in, *buf;
	obj_hdr hdr;
	size_t len, used;

	/*
	 * read the object header, which is an (uncompressed)
	 * binary encoding of the object type and size.
	 */
	if ((used = get_binary_object_header(&hdr, obj)) == 0)
		return git__throw(GIT_ERROR, "Failed to inflate loose object. Object has no header");

	if (!git_object_typeisloose(hdr.type))
		return git__throw(GIT_ERROR, "Failed to inflate loose object. Wrong object type");

	/*
	 * allocate a buffer and inflate the data into it
	 */
	buf = git__malloc(hdr.size + 1);
	if (!buf)
		return GIT_ENOMEM;

	in  = ((unsigned char *)obj->data) + used;
	len = obj->len - used;
	if (inflate_buffer(in, len, buf, hdr.size)) {
		free(buf);
		return git__throw(GIT_ERROR, "Failed to inflate loose object. Could not inflate buffer");
	}
	buf[hdr.size] = '\0';

	out->data = buf;
	out->len  = hdr.size;
	out->type = hdr.type;

	return GIT_SUCCESS;
}

static int inflate_disk_obj(git_rawobj *out, git_fbuffer *obj)
{
	unsigned char head[64], *buf;
	z_stream zs;
	obj_hdr hdr;
	size_t used;

	/*
	 * check for a pack-like loose object
	 */
	if (!is_zlib_compressed_data(obj->data))
		return inflate_packlike_loose_disk_obj(out, obj);

	/*
	 * inflate the initial part of the io buffer in order
	 * to parse the object header (type and size).
	 */
	if (start_inflate(&zs, obj, head, sizeof(head)) < Z_OK)
		return git__throw(GIT_ERROR, "Failed to inflate disk object. Could not inflate buffer");

	if ((used = get_object_header(&hdr, head)) == 0)
		return git__throw(GIT_ERROR, "Failed to inflate disk object. Object has no header");

	if (!git_object_typeisloose(hdr.type))
		return git__throw(GIT_ERROR, "Failed to inflate disk object. Wrong object type");

	/*
	 * allocate a buffer and inflate the object data into it
	 * (including the initial sequence in the head buffer).
	 */
	if ((buf = inflate_tail(&zs, head, used, &hdr)) == NULL)
		return GIT_ENOMEM;
	buf[hdr.size] = '\0';

	out->data = buf;
	out->len  = hdr.size;
	out->type = hdr.type;

	return GIT_SUCCESS;
}






/***********************************************************
 *
 * ODB OBJECT READING & WRITING
 *
 * Backend for the public API; read headers and full objects
 * from the ODB. Write raw data to the ODB.
 *
 ***********************************************************/

static int read_loose(git_rawobj *out, const char *loc)
{
	int error;
	git_fbuffer obj = GIT_FBUFFER_INIT;

	assert(out && loc);

	out->data = NULL;
	out->len  = 0;
	out->type = GIT_OBJ_BAD;

	if (git_futils_readbuffer(&obj, loc) < 0)
		return git__throw(GIT_ENOTFOUND, "Failed to read loose object. File not found");

	error = inflate_disk_obj(out, &obj);
	git_futils_freebuffer(&obj);

	return error == GIT_SUCCESS ? GIT_SUCCESS : git__rethrow(error, "Failed to read loose object");
}

static int read_header_loose(git_rawobj *out, const char *loc)
{
	int error = GIT_SUCCESS, z_return = Z_ERRNO, read_bytes;
	git_file fd;
	z_stream zs;
	obj_hdr header_obj;
	unsigned char raw_buffer[16], inflated_buffer[64];

	assert(out && loc);

	out->data = NULL;

	if ((fd = p_open(loc, O_RDONLY)) < 0)
		return git__throw(GIT_ENOTFOUND, "Failed to read loose object header. File not found");

	init_stream(&zs, inflated_buffer, sizeof(inflated_buffer));

	if (inflateInit(&zs) < Z_OK) {
		error = GIT_EZLIB;
		goto cleanup;
	}

	do {
		if ((read_bytes = read(fd, raw_buffer, sizeof(raw_buffer))) > 0) {
			set_stream_input(&zs, raw_buffer, read_bytes);
			z_return = inflate(&zs, 0);
		} else {
			z_return = Z_STREAM_END;
			break;
		}
	} while (z_return == Z_OK);

	if ((z_return != Z_STREAM_END && z_return != Z_BUF_ERROR)
		|| get_object_header(&header_obj, inflated_buffer) == 0
		|| git_object_typeisloose(header_obj.type) == 0) {
		error = GIT_EOBJCORRUPTED;
		goto cleanup;
	}

	out->len  = header_obj.size;
	out->type = header_obj.type;

cleanup:
	finish_inflate(&zs);
	p_close(fd);

	if (error < GIT_SUCCESS)
		return git__throw(error, "Failed to read loose object header. Header is corrupted");

	return GIT_SUCCESS;
}

static int locate_object(char *object_location, loose_backend *backend, const git_oid *oid)
{
	object_file_name(object_location, GIT_PATH_MAX, backend->objects_dir, oid);
	return git_futils_exists(object_location);
}

/* Explore an entry of a directory and see if it matches a short oid */
int fn_locate_object_short_oid(void *state, char *pathbuf) {
	loose_locate_object_state *sstate = (loose_locate_object_state *)state;

	size_t pathbuf_len = strlen(pathbuf);
	if (pathbuf_len - sstate->dir_len != GIT_OID_HEXSZ - 2) {
		/* Entry cannot be an object. Continue to next entry */
		return GIT_SUCCESS;
	}

	if (!git_futils_exists(pathbuf) && git_futils_isdir(pathbuf)) {
		/* We are already in the directory matching the 2 first hex characters,
		 * compare the first ncmp characters of the oids */
		if (!memcmp(sstate->short_oid + 2,
			(unsigned char *)pathbuf + sstate->dir_len,
			sstate->short_oid_len - 2)) {

			if (!sstate->found) {
				sstate->res_oid[0] = sstate->short_oid[0];
				sstate->res_oid[1] = sstate->short_oid[1];
				memcpy(sstate->res_oid+2, pathbuf+sstate->dir_len, GIT_OID_HEXSZ-2);
			}
			sstate->found++;
		}
	}
	if (sstate->found > 1)
		return git__throw(GIT_EAMBIGUOUSOIDPREFIX, "Ambiguous sha1 prefix within loose objects");

	return GIT_SUCCESS;
}

/* Locate an object matching a given short oid */
static int locate_object_short_oid(char *object_location, git_oid *res_oid, loose_backend *backend, const git_oid *short_oid, unsigned int len)
{
	char *objects_dir = backend->objects_dir;
	size_t dir_len = strlen(objects_dir);
	loose_locate_object_state state;
	int error;

	if (dir_len+43 > GIT_PATH_MAX)
		return git__throw(GIT_ERROR, "Failed to locate object from short oid. Object path too long");

	strcpy(object_location, objects_dir);

	/* Add a separator if not already there */
	if (object_location[dir_len-1] != '/')
		object_location[dir_len++] = '/';

	/* Convert raw oid to hex formatted oid */
	git_oid_fmt((char *)state.short_oid, short_oid);
	/* Explore OBJ_DIR/xx/ where xx is the beginning of hex formatted short oid */
	sprintf(object_location+dir_len, "%.2s/", state.short_oid);

	/* Check that directory exists */
	if (git_futils_exists(object_location) || git_futils_isdir(object_location))
		return git__throw(GIT_ENOTFOUND, "Failed to locate object from short oid. Object not found");

	state.dir_len = dir_len+3;
	state.short_oid_len = len;
	state.found = 0;
	/* Explore directory to find a unique object matching short_oid */
	error = git_futils_direach(object_location, GIT_PATH_MAX, fn_locate_object_short_oid, &state);
	if (error) {
		return git__rethrow(error, "Failed to locate object from short oid");
	}
	if (!state.found) {
		return git__throw(GIT_ENOTFOUND, "Failed to locate object from short oid. Object not found");
	}

	/* Convert obtained hex formatted oid to raw */
	error = git_oid_fromstr(res_oid, (char *)state.res_oid);
	if (error) {
		return git__rethrow(error, "Failed to locate object from short oid");
	}

	/* Update the location according to the oid obtained */
	git_oid_pathfmt(object_location+dir_len, res_oid);

	return GIT_SUCCESS;
}









/***********************************************************
 *
 * LOOSE BACKEND PUBLIC API
 *
 * Implement the git_odb_backend API calls
 *
 ***********************************************************/

int loose_backend__read_header(size_t *len_p, git_otype *type_p, git_odb_backend *backend, const git_oid *oid)
{
	char object_path[GIT_PATH_MAX];
	git_rawobj raw;
	int error;

	assert(backend && oid);

	raw.len = 0;
	raw.type = GIT_OBJ_BAD;

	if (locate_object(object_path, (loose_backend *)backend, oid) < 0)
		return git__throw(GIT_ENOTFOUND, "Failed to read loose backend header. Object not found");

	if ((error = read_header_loose(&raw, object_path)) < GIT_SUCCESS)
		return error;

	*len_p = raw.len;
	*type_p = raw.type;
	return GIT_SUCCESS;
}

int loose_backend__read(void **buffer_p, size_t *len_p, git_otype *type_p, git_odb_backend *backend, const git_oid *oid)
{
	char object_path[GIT_PATH_MAX];
	git_rawobj raw;
	int error;

	assert(backend && oid);

	if (locate_object(object_path, (loose_backend *)backend, oid) < 0)
		return git__throw(GIT_ENOTFOUND, "Failed to read loose backend. Object not found");

	if ((error = read_loose(&raw, object_path)) < GIT_SUCCESS)
		return git__rethrow(error, "Failed to read loose backend");

	*buffer_p = raw.data;
	*len_p = raw.len;
	*type_p = raw.type;

	return GIT_SUCCESS;
}

int loose_backend__read_prefix(
	git_oid *out_oid,
	void **buffer_p,
	size_t *len_p,
	git_otype *type_p,
	git_odb_backend *backend,
	const git_oid *short_oid,
	unsigned int len)
{
	if (len < GIT_OID_MINPREFIXLEN)
		return git__throw(GIT_EAMBIGUOUSOIDPREFIX, "Failed to read loose backend. Prefix length is lower than %d.", GIT_OID_MINPREFIXLEN);

	if (len >= GIT_OID_HEXSZ) {
		/* We can fall back to regular read method */
		int error = loose_backend__read(buffer_p, len_p, type_p, backend, short_oid);
		if (error == GIT_SUCCESS)
			git_oid_cpy(out_oid, short_oid);

		return error;
	} else {
		char object_path[GIT_PATH_MAX];
		git_rawobj raw;
		int error;

		assert(backend && short_oid);

		if ((error = locate_object_short_oid(object_path, out_oid, (loose_backend *)backend, short_oid, len)) < 0) {
			return git__rethrow(error, "Failed to read loose backend");
		}

		if ((error = read_loose(&raw, object_path)) < GIT_SUCCESS)
			return git__rethrow(error, "Failed to read loose backend");

		*buffer_p = raw.data;
		*len_p = raw.len;
		*type_p = raw.type;
	}

	return GIT_SUCCESS;
}

int loose_backend__exists(git_odb_backend *backend, const git_oid *oid)
{
	char object_path[GIT_PATH_MAX];

	assert(backend && oid);

	return locate_object(object_path, (loose_backend *)backend, oid) == GIT_SUCCESS;
}

int loose_backend__stream_fwrite(git_oid *oid, git_odb_stream *_stream)
{
	loose_writestream *stream = (loose_writestream *)_stream;
	loose_backend *backend = (loose_backend *)_stream->backend;

	int error;
	char final_path[GIT_PATH_MAX];

	if ((error = git_filebuf_hash(oid, &stream->fbuf)) < GIT_SUCCESS)
		return git__rethrow(error, "Failed to write loose backend");

	if (object_file_name(final_path, sizeof(final_path), backend->objects_dir, oid))
		return GIT_ENOMEM;

	if ((error = git_futils_mkpath2file(final_path)) < GIT_SUCCESS)
		return git__rethrow(error, "Failed to write loose backend");

	stream->finished = 1;
	return git_filebuf_commit_at(&stream->fbuf, final_path);
}

int loose_backend__stream_write(git_odb_stream *_stream, const char *data, size_t len)
{
	loose_writestream *stream = (loose_writestream *)_stream;
	return git_filebuf_write(&stream->fbuf, data, len);
}

void loose_backend__stream_free(git_odb_stream *_stream)
{
	loose_writestream *stream = (loose_writestream *)_stream;

	if (!stream->finished)
		git_filebuf_cleanup(&stream->fbuf);

	free(stream);
}

static int format_object_header(char *hdr, size_t n, size_t obj_len, git_otype obj_type)
{
	const char *type_str = git_object_type2string(obj_type);
	int len = snprintf(hdr, n, "%s %"PRIuZ, type_str, obj_len);

	assert(len > 0);             /* otherwise snprintf() is broken  */
	assert(((size_t) len) < n);  /* otherwise the caller is broken! */

	if (len < 0 || ((size_t) len) >= n)
		return git__throw(GIT_ERROR, "Failed to format object header. Length is out of bounds");
	return len+1;
}

int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_backend, size_t length, git_otype type)
{
	loose_backend *backend;
	loose_writestream *stream;

	char hdr[64], tmp_path[GIT_PATH_MAX];
	int  hdrlen;
	int error;

	assert(_backend);

	backend = (loose_backend *)_backend;
	*stream_out = NULL;

	hdrlen = format_object_header(hdr, sizeof(hdr), length, type);
	if (hdrlen < GIT_SUCCESS)
		return git__throw(GIT_EOBJCORRUPTED, "Failed to create loose backend stream. Object is corrupted");

	stream = git__calloc(1, sizeof(loose_writestream));
	if (stream == NULL)
		return GIT_ENOMEM;

	stream->stream.backend = _backend;
	stream->stream.read = NULL; /* read only */
	stream->stream.write = &loose_backend__stream_write;
	stream->stream.finalize_write = &loose_backend__stream_fwrite;
	stream->stream.free = &loose_backend__stream_free;
	stream->stream.mode = GIT_STREAM_WRONLY;

	git_path_join(tmp_path, backend->objects_dir, "tmp_object");

	error = git_filebuf_open(&stream->fbuf, tmp_path,
		GIT_FILEBUF_HASH_CONTENTS |
		GIT_FILEBUF_DEFLATE_CONTENTS |
		GIT_FILEBUF_TEMPORARY);

	if (error < GIT_SUCCESS) {
		free(stream);
		return git__rethrow(error, "Failed to create loose backend stream");
	}

	error = stream->stream.write((git_odb_stream *)stream, hdr, hdrlen);
	if (error < GIT_SUCCESS) {
		git_filebuf_cleanup(&stream->fbuf);
		free(stream);
		return git__rethrow(error, "Failed to create loose backend stream");
	}

	*stream_out = (git_odb_stream *)stream;
	return GIT_SUCCESS;
}

int loose_backend__write(git_oid *oid, git_odb_backend *_backend, const void *data, size_t len, git_otype type)
{
	int error, header_len;
	char final_path[GIT_PATH_MAX], header[64];
	git_filebuf fbuf;
	loose_backend *backend;

	backend = (loose_backend *)_backend;

	/* prepare the header for the file */
	{
		header_len = format_object_header(header, sizeof(header), len, type);
		if (header_len < GIT_SUCCESS)
			return GIT_EOBJCORRUPTED;
	}

	git_path_join(final_path, backend->objects_dir, "tmp_object");

	error = git_filebuf_open(&fbuf, final_path,
		GIT_FILEBUF_HASH_CONTENTS |
		GIT_FILEBUF_DEFLATE_CONTENTS |
		GIT_FILEBUF_TEMPORARY);

	if (error < GIT_SUCCESS)
		return error;

	git_filebuf_write(&fbuf, header, header_len);
	git_filebuf_write(&fbuf, data, len);
	git_filebuf_hash(oid, &fbuf);

	if ((error = object_file_name(final_path, sizeof(final_path), backend->objects_dir, oid)) < GIT_SUCCESS)
		goto cleanup;

	if ((error = git_futils_mkpath2file(final_path)) < GIT_SUCCESS)
		goto cleanup;

	return git_filebuf_commit_at(&fbuf, final_path);

cleanup:
	git_filebuf_cleanup(&fbuf);
	return error;
}

void loose_backend__free(git_odb_backend *_backend)
{
	loose_backend *backend;
	assert(_backend);
	backend = (loose_backend *)_backend;

	free(backend->objects_dir);
	free(backend);
}

int git_odb_backend_loose(git_odb_backend **backend_out, const char *objects_dir)
{
	loose_backend *backend;

	backend = git__calloc(1, sizeof(loose_backend));
	if (backend == NULL)
		return GIT_ENOMEM;

	backend->objects_dir = git__strdup(objects_dir);
	if (backend->objects_dir == NULL) {
		free(backend);
		return GIT_ENOMEM;
	}

	backend->object_zlib_level = Z_BEST_SPEED;
	backend->fsync_object_files = 0;

	backend->parent.read = &loose_backend__read;
	backend->parent.write = &loose_backend__write;
	backend->parent.read_prefix = &loose_backend__read_prefix;
	backend->parent.read_header = &loose_backend__read_header;
	backend->parent.writestream = &loose_backend__stream;
	backend->parent.exists = &loose_backend__exists;
	backend->parent.free = &loose_backend__free;

	*backend_out = (git_odb_backend *)backend;
	return GIT_SUCCESS;
}