thodg/libgit2/src/midx.c

• Show log

  Commit

• Hash : fff209c4
  Author :
  Date : 2020-02-17T21:28:13
  

  midx: Add a way to write multi-pack-index files This change adds the git_midx_writer_* functions to allow to write and create `multi-pack-index` files from `.idx`/`.pack` files. Part of: #5399

Download

• src/midx.c

• /*
   * Copyright (C) the libgit2 contributors. All rights reserved.
   *
   * This file is part of libgit2, distributed under the GNU GPL v2 with
   * a Linking Exception. For full terms see the included COPYING file.
   */
  
  #include "midx.h"
  
  #include "array.h"
  #include "buffer.h"
  #include "filebuf.h"
  #include "futils.h"
  #include "hash.h"
  #include "odb.h"
  #include "pack.h"
  #include "path.h"
  #include "repository.h"
  
  #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
  #define MIDX_VERSION 1
  #define MIDX_OBJECT_ID_VERSION 1
  struct git_midx_header {
  	uint32_t signature;
  	uint8_t version;
  	uint8_t object_id_version;
  	uint8_t chunks;
  	uint8_t base_midx_files;
  	uint32_t packfiles;
  };
  
  #define MIDX_PACKFILE_NAMES_ID 0x504e414d	   /* "PNAM" */
  #define MIDX_OID_FANOUT_ID 0x4f494446	   /* "OIDF" */
  #define MIDX_OID_LOOKUP_ID 0x4f49444c	   /* "OIDL" */
  #define MIDX_OBJECT_OFFSETS_ID 0x4f4f4646	   /* "OOFF" */
  #define MIDX_OBJECT_LARGE_OFFSETS_ID 0x4c4f4646 /* "LOFF" */
  
  struct git_midx_chunk {
  	off64_t offset;
  	size_t length;
  };
  
  typedef int (*midx_write_cb)(const char *buf, size_t size, void *cb_data);
  
  static int midx_error(const char *message)
  {
  	git_error_set(GIT_ERROR_ODB, "invalid multi-pack-index file - %s", message);
  	return -1;
  }
  
  static int midx_parse_packfile_names(
  		git_midx_file *idx,
  		const unsigned char *data,
  		uint32_t packfiles,
  		struct git_midx_chunk *chunk)
  {
  	int error;
  	uint32_t i;
  	char *packfile_name = (char *)(data + chunk->offset);
  	size_t chunk_size = chunk->length, len;
  	if (chunk->offset == 0)
  		return midx_error("missing Packfile Names chunk");
  	if (chunk->length == 0)
  		return midx_error("empty Packfile Names chunk");
  	if ((error = git_vector_init(&idx->packfile_names, packfiles, git__strcmp_cb)) < 0)
  		return error;
  	for (i = 0; i < packfiles; ++i) {
  		len = p_strnlen(packfile_name, chunk_size);
  		if (len == 0)
  			return midx_error("empty packfile name");
  		if (len + 1 > chunk_size)
  			return midx_error("unterminated packfile name");
  		git_vector_insert(&idx->packfile_names, packfile_name);
  		if (i && strcmp(git_vector_get(&idx->packfile_names, i - 1), packfile_name) >= 0)
  			return midx_error("packfile names are not sorted");
  		if (strlen(packfile_name) <= strlen(".idx") || git__suffixcmp(packfile_name, ".idx") != 0)
  			return midx_error("non-.idx packfile name");
  		if (strchr(packfile_name, '/') != NULL || strchr(packfile_name, '\\') != NULL)
  			return midx_error("non-local packfile");
  		packfile_name += len + 1;
  		chunk_size -= len + 1;
  	}
  	return 0;
  }
  
  static int midx_parse_oid_fanout(
  		git_midx_file *idx,
  		const unsigned char *data,
  		struct git_midx_chunk *chunk_oid_fanout)
  {
  	uint32_t i, nr;
  	if (chunk_oid_fanout->offset == 0)
  		return midx_error("missing OID Fanout chunk");
  	if (chunk_oid_fanout->length == 0)
  		return midx_error("empty OID Fanout chunk");
  	if (chunk_oid_fanout->length != 256 * 4)
  		return midx_error("OID Fanout chunk has wrong length");
  
  	idx->oid_fanout = (const uint32_t *)(data + chunk_oid_fanout->offset);
  	nr = 0;
  	for (i = 0; i < 256; ++i) {
  		uint32_t n = ntohl(idx->oid_fanout[i]);
  		if (n < nr)
  			return midx_error("index is non-monotonic");
  		nr = n;
  	}
  	idx->num_objects = nr;
  	return 0;
  }
  
  static int midx_parse_oid_lookup(
  		git_midx_file *idx,
  		const unsigned char *data,
  		struct git_midx_chunk *chunk_oid_lookup)
  {
  	uint32_t i;
  	git_oid *oid, *prev_oid, zero_oid = {{0}};
  
  	if (chunk_oid_lookup->offset == 0)
  		return midx_error("missing OID Lookup chunk");
  	if (chunk_oid_lookup->length == 0)
  		return midx_error("empty OID Lookup chunk");
  	if (chunk_oid_lookup->length != idx->num_objects * GIT_OID_RAWSZ)
  		return midx_error("OID Lookup chunk has wrong length");
  
  	idx->oid_lookup = oid = (git_oid *)(data + chunk_oid_lookup->offset);
  	prev_oid = &zero_oid;
  	for (i = 0; i < idx->num_objects; ++i, ++oid) {
  		if (git_oid_cmp(prev_oid, oid) >= 0)
  			return midx_error("OID Lookup index is non-monotonic");
  		prev_oid = oid;
  	}
  
  	return 0;
  }
  
  static int midx_parse_object_offsets(
  		git_midx_file *idx,
  		const unsigned char *data,
  		struct git_midx_chunk *chunk_object_offsets)
  {
  	if (chunk_object_offsets->offset == 0)
  		return midx_error("missing Object Offsets chunk");
  	if (chunk_object_offsets->length == 0)
  		return midx_error("empty Object Offsets chunk");
  	if (chunk_object_offsets->length != idx->num_objects * 8)
  		return midx_error("Object Offsets chunk has wrong length");
  
  	idx->object_offsets = data + chunk_object_offsets->offset;
  
  	return 0;
  }
  
  static int midx_parse_object_large_offsets(
  		git_midx_file *idx,
  		const unsigned char *data,
  		struct git_midx_chunk *chunk_object_large_offsets)
  {
  	if (chunk_object_large_offsets->length == 0)
  		return 0;
  	if (chunk_object_large_offsets->length % 8 != 0)
  		return midx_error("malformed Object Large Offsets chunk");
  
  	idx->object_large_offsets = data + chunk_object_large_offsets->offset;
  	idx->num_object_large_offsets = chunk_object_large_offsets->length / 8;
  
  	return 0;
  }
  
  int git_midx_parse(
  		git_midx_file *idx,
  		const unsigned char *data,
  		size_t size)
  {
  	struct git_midx_header *hdr;
  	const unsigned char *chunk_hdr;
  	struct git_midx_chunk *last_chunk;
  	uint32_t i;
  	off64_t last_chunk_offset, chunk_offset, trailer_offset;
  	git_oid idx_checksum = {{0}};
  	int error;
  	struct git_midx_chunk chunk_packfile_names = {0},
  					 chunk_oid_fanout = {0},
  					 chunk_oid_lookup = {0},
  					 chunk_object_offsets = {0},
  					 chunk_object_large_offsets = {0};
  
  	GIT_ASSERT_ARG(idx);
  
  	if (size < sizeof(struct git_midx_header) + GIT_OID_RAWSZ)
  		return midx_error("multi-pack index is too short");
  
  	hdr = ((struct git_midx_header *)data);
  
  	if (hdr->signature != htonl(MIDX_SIGNATURE) ||
  	    hdr->version != MIDX_VERSION ||
  	    hdr->object_id_version != MIDX_OBJECT_ID_VERSION) {
  		return midx_error("unsupported multi-pack index version");
  	}
  	if (hdr->chunks == 0)
  		return midx_error("no chunks in multi-pack index");
  
  	/*
  	 * The very first chunk's offset should be after the header, all the chunk
  	 * headers, and a special zero chunk.
  	 */
  	last_chunk_offset =
  			sizeof(struct git_midx_header) +
  			(1 + hdr->chunks) * 12;
  	trailer_offset = size - GIT_OID_RAWSZ;
  	if (trailer_offset < last_chunk_offset)
  		return midx_error("wrong index size");
  	git_oid_cpy(&idx->checksum, (git_oid *)(data + trailer_offset));
  
  	if (git_hash_buf(&idx_checksum, data, (size_t)trailer_offset) < 0)
  		return midx_error("could not calculate signature");
  	if (!git_oid_equal(&idx_checksum, &idx->checksum))
  		return midx_error("index signature mismatch");
  
  	chunk_hdr = data + sizeof(struct git_midx_header);
  	last_chunk = NULL;
  	for (i = 0; i < hdr->chunks; ++i, chunk_hdr += 12) {
  		chunk_offset = ((off64_t)ntohl(*((uint32_t *)(chunk_hdr + 4)))) << 32 |
  				((off64_t)ntohl(*((uint32_t *)(chunk_hdr + 8))));
  		if (chunk_offset < last_chunk_offset)
  			return midx_error("chunks are non-monotonic");
  		if (chunk_offset >= trailer_offset)
  			return midx_error("chunks extend beyond the trailer");
  		if (last_chunk != NULL)
  			last_chunk->length = (size_t)(chunk_offset - last_chunk_offset);
  		last_chunk_offset = chunk_offset;
  
  		switch (ntohl(*((uint32_t *)(chunk_hdr + 0)))) {
  		case MIDX_PACKFILE_NAMES_ID:
  			chunk_packfile_names.offset = last_chunk_offset;
  			last_chunk = &chunk_packfile_names;
  			break;
  
  		case MIDX_OID_FANOUT_ID:
  			chunk_oid_fanout.offset = last_chunk_offset;
  			last_chunk = &chunk_oid_fanout;
  			break;
  
  		case MIDX_OID_LOOKUP_ID:
  			chunk_oid_lookup.offset = last_chunk_offset;
  			last_chunk = &chunk_oid_lookup;
  			break;
  
  		case MIDX_OBJECT_OFFSETS_ID:
  			chunk_object_offsets.offset = last_chunk_offset;
  			last_chunk = &chunk_object_offsets;
  			break;
  
  		case MIDX_OBJECT_LARGE_OFFSETS_ID:
  			chunk_object_large_offsets.offset = last_chunk_offset;
  			last_chunk = &chunk_object_large_offsets;
  			break;
  
  		default:
  			return midx_error("unrecognized chunk ID");
  		}
  	}
  	last_chunk->length = (size_t)(trailer_offset - last_chunk_offset);
  
  	error = midx_parse_packfile_names(
  			idx, data, ntohl(hdr->packfiles), &chunk_packfile_names);
  	if (error < 0)
  		return error;
  	error = midx_parse_oid_fanout(idx, data, &chunk_oid_fanout);
  	if (error < 0)
  		return error;
  	error = midx_parse_oid_lookup(idx, data, &chunk_oid_lookup);
  	if (error < 0)
  		return error;
  	error = midx_parse_object_offsets(idx, data, &chunk_object_offsets);
  	if (error < 0)
  		return error;
  	error = midx_parse_object_large_offsets(idx, data, &chunk_object_large_offsets);
  	if (error < 0)
  		return error;
  
  	return 0;
  }
  
  int git_midx_open(
  		git_midx_file **idx_out,
  		const char *path)
  {
  	git_midx_file *idx;
  	git_file fd = -1;
  	size_t idx_size;
  	struct stat st;
  	int error;
  
  	/* TODO: properly open the file without access time using O_NOATIME */
  	fd = git_futils_open_ro(path);
  	if (fd < 0)
  		return fd;
  
  	if (p_fstat(fd, &st) < 0) {
  		p_close(fd);
  		git_error_set(GIT_ERROR_ODB, "multi-pack-index file not found - '%s'", path);
  		return -1;
  	}
  
  	if (!S_ISREG(st.st_mode) || !git__is_sizet(st.st_size)) {
  		p_close(fd);
  		git_error_set(GIT_ERROR_ODB, "invalid pack index '%s'", path);
  		return -1;
  	}
  	idx_size = (size_t)st.st_size;
  
  	idx = git__calloc(1, sizeof(git_midx_file));
  	GIT_ERROR_CHECK_ALLOC(idx);
  
  	error = git_buf_sets(&idx->filename, path);
  	if (error < 0)
  		return error;
  
  	error = git_futils_mmap_ro(&idx->index_map, fd, 0, idx_size);
  	p_close(fd);
  	if (error < 0) {
  		git_midx_free(idx);
  		return error;
  	}
  
  	if ((error = git_midx_parse(idx, idx->index_map.data, idx_size)) < 0) {
  		git_midx_free(idx);
  		return error;
  	}
  
  	*idx_out = idx;
  	return 0;
  }
  
  bool git_midx_needs_refresh(
  		const git_midx_file *idx,
  		const char *path)
  {
  	git_file fd = -1;
  	struct stat st;
  	ssize_t bytes_read;
  	git_oid idx_checksum = {{0}};
  
  	/* TODO: properly open the file without access time using O_NOATIME */
  	fd = git_futils_open_ro(path);
  	if (fd < 0)
  		return true;
  
  	if (p_fstat(fd, &st) < 0) {
  		p_close(fd);
  		return true;
  	}
  
  	if (!S_ISREG(st.st_mode) ||
  	    !git__is_sizet(st.st_size) ||
  	    (size_t)st.st_size != idx->index_map.len) {
  		p_close(fd);
  		return true;
  	}
  
  	bytes_read = p_pread(fd, &idx_checksum, GIT_OID_RAWSZ, st.st_size - GIT_OID_RAWSZ);
  	p_close(fd);
  
  	if (bytes_read != GIT_OID_RAWSZ)
  		return true;
  
  	return !git_oid_equal(&idx_checksum, &idx->checksum);
  }
  
  int git_midx_entry_find(
  		git_midx_entry *e,
  		git_midx_file *idx,
  		const git_oid *short_oid,
  		size_t len)
  {
  	int pos, found = 0;
  	size_t pack_index;
  	uint32_t hi, lo;
  	const git_oid *current = NULL;
  	const unsigned char *object_offset;
  	off64_t offset;
  
  	GIT_ASSERT_ARG(idx);
  
  	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_RAWSZ, lo, hi, short_oid->id);
  
  	if (pos >= 0) {
  		/* An object matching exactly the oid was found */
  		found = 1;
  		current = idx->oid_lookup + pos;
  	} else {
  		/* No object was found */
  		/* pos refers to the object with the "closest" oid to short_oid */
  		pos = -1 - pos;
  		if (pos < (int)idx->num_objects) {
  			current = idx->oid_lookup + pos;
  
  			if (!git_oid_ncmp(short_oid, current, len))
  				found = 1;
  		}
  	}
  
  	if (found && len != GIT_OID_HEXSZ && pos + 1 < (int)idx->num_objects) {
  		/* Check for ambiguousity */
  		const git_oid *next = current + 1;
  
  		if (!git_oid_ncmp(short_oid, next, len)) {
  			found = 2;
  		}
  	}
  
  	if (!found)
  		return git_odb__error_notfound("failed to find offset for multi-pack index entry", short_oid, len);
  	if (found > 1)
  		return git_odb__error_ambiguous("found multiple offsets for multi-pack index entry");
  
  	object_offset = idx->object_offsets + pos * 8;
  	offset = ntohl(*((uint32_t *)(object_offset + 4)));
  	if (offset & 0x80000000) {
  		uint32_t object_large_offsets_pos = offset & 0x7fffffff;
  		const unsigned char *object_large_offsets_index = idx->object_large_offsets;
  
  		/* Make sure we're not being sent out of bounds */
  		if (object_large_offsets_pos >= idx->num_object_large_offsets)
  			return git_odb__error_notfound("invalid index into the object large offsets table", short_oid, len);
  
  		object_large_offsets_index += 8 * object_large_offsets_pos;
  
  		offset = (((uint64_t)ntohl(*((uint32_t *)(object_large_offsets_index + 0)))) << 32) |
  				ntohl(*((uint32_t *)(object_large_offsets_index + 4)));
  	}
  	pack_index = ntohl(*((uint32_t *)(object_offset + 0)));
  	if (pack_index >= git_vector_length(&idx->packfile_names))
  		return midx_error("invalid index into the packfile names table");
  	e->pack_index = pack_index;
  	e->offset = offset;
  	git_oid_cpy(&e->sha1, current);
  	return 0;
  }
  
  int git_midx_foreach_entry(
  		git_midx_file *idx,
  		git_odb_foreach_cb cb,
  		void *data)
  {
  	size_t i;
  	int error;
  
  	GIT_ASSERT_ARG(idx);
  
  	for (i = 0; i < idx->num_objects; ++i) {
  		if ((error = cb(&idx->oid_lookup[i], data)) != 0)
  			return git_error_set_after_callback(error);
  	}
  
  	return error;
  }
  
  int git_midx_close(git_midx_file *idx)
  {
  	GIT_ASSERT_ARG(idx);
  
  	if (idx->index_map.data)
  		git_futils_mmap_free(&idx->index_map);
  
  	git_vector_free(&idx->packfile_names);
  
  	return 0;
  }
  
  void git_midx_free(git_midx_file *idx)
  {
  	if (!idx)
  		return;
  
  	git_buf_dispose(&idx->filename);
  	git_midx_close(idx);
  	git__free(idx);
  }
  
  static int packfile__cmp(const void *a_, const void *b_)
  {
  	const struct git_pack_file *a = a_;
  	const struct git_pack_file *b = b_;
  
  	return strcmp(a->pack_name, b->pack_name);
  }
  
  int git_midx_writer_new(
  		git_midx_writer **out,
  		const char *pack_dir)
  {
  	git_midx_writer *w = git__calloc(1, sizeof(git_midx_writer));
  	GIT_ERROR_CHECK_ALLOC(w);
  
  	if (git_buf_sets(&w->pack_dir, pack_dir) < 0) {
  		git__free(w);
  		return -1;
  	}
  	git_path_squash_slashes(&w->pack_dir);
  
  	if (git_vector_init(&w->packs, 0, packfile__cmp) < 0) {
  		git_buf_dispose(&w->pack_dir);
  		git__free(w);
  		return -1;
  	}
  
  	*out = w;
  	return 0;
  }
  
  void git_midx_writer_free(git_midx_writer *w)
  {
  	struct git_pack_file *p;
  	size_t i;
  
  	if (!w)
  		return;
  
  	git_vector_foreach (&w->packs, i, p)
  		git_mwindow_put_pack(p);
  	git_vector_free(&w->packs);
  	git_buf_dispose(&w->pack_dir);
  	git__free(w);
  }
  
  int git_midx_writer_add(
  		git_midx_writer *w,
  		const char *idx_path)
  {
  	git_buf idx_path_buf = GIT_BUF_INIT;
  	int error;
  	struct git_pack_file *p;
  
  	error = git_path_prettify(&idx_path_buf, idx_path, git_buf_cstr(&w->pack_dir));
  	if (error < 0)
  		return error;
  
  	error = git_mwindow_get_pack(&p, git_buf_cstr(&idx_path_buf));
  	git_buf_dispose(&idx_path_buf);
  	if (error < 0)
  		return error;
  
  	error = git_vector_insert(&w->packs, p);
  	if (error < 0) {
  		git_mwindow_put_pack(p);
  		return error;
  	}
  
  	return 0;
  }
  
  typedef git_array_t(git_midx_entry) object_entry_array_t;
  
  struct object_entry_cb_state {
  	uint32_t pack_index;
  	object_entry_array_t *object_entries_array;
  };
  
  static int object_entry__cb(const git_oid *oid, off64_t offset, void *data)
  {
  	struct object_entry_cb_state *state = (struct object_entry_cb_state *)data;
  
  	git_midx_entry *entry = git_array_alloc(*state->object_entries_array);
  	GIT_ERROR_CHECK_ALLOC(entry);
  
  	git_oid_cpy(&entry->sha1, oid);
  	entry->offset = offset;
  	entry->pack_index = state->pack_index;
  
  	return 0;
  }
  
  static int object_entry__cmp(const void *a_, const void *b_)
  {
  	const git_midx_entry *a = (const git_midx_entry *)a_;
  	const git_midx_entry *b = (const git_midx_entry *)b_;
  
  	return git_oid_cmp(&a->sha1, &b->sha1);
  }
  
  static int write_offset(off64_t offset, midx_write_cb write_cb, void *cb_data)
  {
  	int error;
  	uint32_t word;
  
  	word = htonl((uint32_t)((offset >> 32) & 0xffffffffu));
  	error = write_cb((const char *)&word, sizeof(word), cb_data);
  	if (error < 0)
  		return error;
  	word = htonl((uint32_t)((offset >> 0) & 0xffffffffu));
  	error = write_cb((const char *)&word, sizeof(word), cb_data);
  	if (error < 0)
  		return error;
  
  	return 0;
  }
  
  static int write_chunk_header(int chunk_id, off64_t offset, midx_write_cb write_cb, void *cb_data)
  {
  	uint32_t word = htonl(chunk_id);
  	int error = write_cb((const char *)&word, sizeof(word), cb_data);
  	if (error < 0)
  		return error;
  	return write_offset(offset, write_cb, cb_data);
  
  	return 0;
  }
  
  static int midx_write_buf(const char *buf, size_t size, void *data)
  {
  	git_buf *b = (git_buf *)data;
  	return git_buf_put(b, buf, size);
  }
  
  struct midx_write_hash_context {
  	midx_write_cb write_cb;
  	void *cb_data;
  	git_hash_ctx *ctx;
  };
  
  static int midx_write_hash(const char *buf, size_t size, void *data)
  {
  	struct midx_write_hash_context *ctx = (struct midx_write_hash_context *)data;
  	int error;
  
  	error = git_hash_update(ctx->ctx, buf, size);
  	if (error < 0)
  		return error;
  
  	return ctx->write_cb(buf, size, ctx->cb_data);
  }
  
  static int midx_write(
  		git_midx_writer *w,
  		midx_write_cb write_cb,
  		void *cb_data)
  {
  	int error = 0;
  	size_t i;
  	struct git_pack_file *p;
  	struct git_midx_header hdr = {
  			.signature = htonl(MIDX_SIGNATURE),
  			.version = MIDX_VERSION,
  			.object_id_version = MIDX_OBJECT_ID_VERSION,
  			.base_midx_files = 0,
  	};
  	uint32_t oid_fanout_count;
  	uint32_t object_large_offsets_count;
  	uint32_t oid_fanout[256];
  	off64_t offset;
  	git_buf packfile_names = GIT_BUF_INIT,
  		oid_lookup = GIT_BUF_INIT,
  		object_offsets = GIT_BUF_INIT,
  		object_large_offsets = GIT_BUF_INIT;
  	git_oid idx_checksum = {{0}};
  	git_midx_entry *entry;
  	object_entry_array_t object_entries_array = GIT_ARRAY_INIT;
  	git_vector object_entries = GIT_VECTOR_INIT;
  	git_hash_ctx ctx;
  	struct midx_write_hash_context hash_cb_data = {
  		.write_cb = write_cb,
  		.cb_data = cb_data,
  		.ctx = &ctx,
  	};
  
  	error = git_hash_ctx_init(&ctx);
  	if (error < 0)
  		return error;
  	cb_data = &hash_cb_data;
  	write_cb = midx_write_hash;
  
  	git_vector_sort(&w->packs);
  	git_vector_foreach (&w->packs, i, p) {
  		git_buf relative_index = GIT_BUF_INIT;
  		struct object_entry_cb_state state = {
  				.pack_index = (uint32_t)i,
  				.object_entries_array = &object_entries_array,
  		};
  		size_t path_len;
  
  		error = git_buf_sets(&relative_index, p->pack_name);
  		if (error < 0)
  			goto cleanup;
  		error = git_path_make_relative(&relative_index, git_buf_cstr(&w->pack_dir));
  		if (error < 0) {
  			git_buf_dispose(&relative_index);
  			goto cleanup;
  		}
  		path_len = git_buf_len(&relative_index);
  		if (path_len <= strlen(".pack") || git__suffixcmp(git_buf_cstr(&relative_index), ".pack") != 0) {
  			git_buf_dispose(&relative_index);
  			goto cleanup;
  		}
  		path_len -= strlen(".pack");
  
  		git_buf_put(&packfile_names, git_buf_cstr(&relative_index), path_len);
  		git_buf_puts(&packfile_names, ".idx");
  		git_buf_putc(&packfile_names, '\0');
  		git_buf_dispose(&relative_index);
  
  		error = git_pack_foreach_entry_offset(p, object_entry__cb, &state);
  		if (error < 0)
  			goto cleanup;
  	}
  
  	/* Sort the object entries. */
  	error = git_vector_init(&object_entries, git_array_size(object_entries_array), object_entry__cmp);
  	if (error < 0)
  		goto cleanup;
  	git_array_foreach (object_entries_array, i, entry)
  		error = git_vector_set(NULL, &object_entries, i, entry);
  	git_vector_set_sorted(&object_entries, 0);
  	git_vector_sort(&object_entries);
  	git_vector_uniq(&object_entries, NULL);
  
  	/* Pad the packfile names so it is a multiple of four. */
  	while (git_buf_len(&packfile_names) & 3)
  		git_buf_putc(&packfile_names, '\0');
  
  	/* Fill the OID Fanout table. */
  	oid_fanout_count = 0;
  	for (i = 0; i < 256; i++) {
  		while (oid_fanout_count < git_vector_length(&object_entries) &&
  		       ((const git_midx_entry *)git_vector_get(&object_entries, oid_fanout_count))->sha1.id[0] <= i)
  			++oid_fanout_count;
  		oid_fanout[i] = htonl(oid_fanout_count);
  	}
  
  	/* Fill the OID Lookup table. */
  	git_vector_foreach (&object_entries, i, entry) {
  		error = git_buf_put(&oid_lookup, (const char *)&entry->sha1, sizeof(entry->sha1));
  		if (error < 0)
  			goto cleanup;
  	}
  
  	/* Fill the Object Offsets and Object Large Offsets tables. */
  	object_large_offsets_count = 0;
  	git_vector_foreach (&object_entries, i, entry) {
  		uint32_t word;
  
  		word = htonl((uint32_t)entry->pack_index);
  		error = git_buf_put(&object_offsets, (const char *)&word, sizeof(word));
  		if (error < 0)
  			goto cleanup;
  		if (entry->offset >= 0x80000000l) {
  			word = htonl(0x80000000u | object_large_offsets_count++);
  			error = write_offset(entry->offset, midx_write_buf, &object_large_offsets);
  		} else {
  			word = htonl((uint32_t)entry->offset & 0x7fffffffu);
  		}
  		error = git_buf_put(&object_offsets, (const char *)&word, sizeof(word));
  		if (error < 0)
  			goto cleanup;
  	}
  
  	/* Write the header. */
  	hdr.packfiles = htonl((uint32_t)git_vector_length(&w->packs));
  	hdr.chunks = 4;
  	if (git_buf_len(&object_large_offsets) > 0)
  		hdr.chunks++;
  	error = write_cb((const char *)&hdr, sizeof(hdr), cb_data);
  	if (error < 0)
  		goto cleanup;
  
  	/* Write the chunk headers. */
  	offset = sizeof(hdr) + (hdr.chunks + 1) * 12;
  	error = write_chunk_header(MIDX_PACKFILE_NAMES_ID, offset, write_cb, cb_data);
  	if (error < 0)
  		goto cleanup;
  	offset += git_buf_len(&packfile_names);
  	error = write_chunk_header(MIDX_OID_FANOUT_ID, offset, write_cb, cb_data);
  	if (error < 0)
  		goto cleanup;
  	offset += sizeof(oid_fanout);
  	error = write_chunk_header(MIDX_OID_LOOKUP_ID, offset, write_cb, cb_data);
  	if (error < 0)
  		goto cleanup;
  	offset += git_buf_len(&oid_lookup);
  	error = write_chunk_header(MIDX_OBJECT_OFFSETS_ID, offset, write_cb, cb_data);
  	if (error < 0)
  		goto cleanup;
  	offset += git_buf_len(&object_offsets);
  	if (git_buf_len(&object_large_offsets) > 0) {
  		error = write_chunk_header(MIDX_OBJECT_LARGE_OFFSETS_ID, offset, write_cb, cb_data);
  		if (error < 0)
  			goto cleanup;
  		offset += git_buf_len(&object_large_offsets);
  	}
  	error = write_chunk_header(0, offset, write_cb, cb_data);
  	if (error < 0)
  		goto cleanup;
  
  	/* Write all the chunks. */
  	error = write_cb(git_buf_cstr(&packfile_names), git_buf_len(&packfile_names), cb_data);
  	if (error < 0)
  		goto cleanup;
  	error = write_cb((const char *)oid_fanout, sizeof(oid_fanout), cb_data);
  	if (error < 0)
  		goto cleanup;
  	error = write_cb(git_buf_cstr(&oid_lookup), git_buf_len(&oid_lookup), cb_data);
  	if (error < 0)
  		goto cleanup;
  	error = write_cb(git_buf_cstr(&object_offsets), git_buf_len(&object_offsets), cb_data);
  	if (error < 0)
  		goto cleanup;
  	error = write_cb(git_buf_cstr(&object_large_offsets), git_buf_len(&object_large_offsets), cb_data);
  	if (error < 0)
  		goto cleanup;
  
  	/* Finalize the checksum and write the trailer. */
  	error = git_hash_final(&idx_checksum, &ctx);
  	if (error < 0)
  		goto cleanup;
  	error = write_cb((const char *)&idx_checksum, sizeof(idx_checksum), cb_data);
  	if (error < 0)
  		goto cleanup;
  
  cleanup:
  	git_array_clear(object_entries_array);
  	git_vector_free(&object_entries);
  	git_buf_dispose(&packfile_names);
  	git_buf_dispose(&oid_lookup);
  	git_buf_dispose(&object_offsets);
  	git_buf_dispose(&object_large_offsets);
  	git_hash_ctx_cleanup(&ctx);
  	return error;
  }
  
  static int midx_write_filebuf(const char *buf, size_t size, void *data)
  {
  	git_filebuf *f = (git_filebuf *)data;
  	return git_filebuf_write(f, buf, size);
  }
  
  int git_midx_writer_commit(
  		git_midx_writer *w)
  {
  	int error;
  	int filebuf_flags = GIT_FILEBUF_DO_NOT_BUFFER;
  	git_buf midx_path = GIT_BUF_INIT;
  	git_filebuf output = GIT_FILEBUF_INIT;
  
  	error = git_buf_joinpath(&midx_path, git_buf_cstr(&w->pack_dir), "multi-pack-index");
  	if (error < 0)
  		return error;
  
  	if (git_repository__fsync_gitdir)
  		filebuf_flags |= GIT_FILEBUF_FSYNC;
  	error = git_filebuf_open(&output, git_buf_cstr(&midx_path), filebuf_flags, 0644);
  	git_buf_dispose(&midx_path);
  	if (error < 0)
  		return error;
  
  	error = midx_write(w, midx_write_filebuf, &output);
  	if (error < 0) {
  		git_filebuf_cleanup(&output);
  		return error;
  	}
  
  	return git_filebuf_commit(&output);
  }
  
  int git_midx_writer_dump(
  		git_buf *midx,
  		git_midx_writer *w)
  {
  	return midx_write(w, midx_write_buf, midx);
  }
  

Download