thodg/got/lib/pack.c

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• Show log

  Commit

• Author : Stefan Sperling
  Date : 2018-04-22 14:51:49
  Hash : 2178c42e
  Message : read object headers with privsep

• lib/pack.c

• /*
   * Copyright (c) 2018 Stefan Sperling <stsp@openbsd.org>
   *
   * Permission to use, copy, modify, and distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
   * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   */
  
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <sys/queue.h>
  
  #include <dirent.h>
  #include <fcntl.h>
  #include <errno.h>
  #include <stdio.h>
  #include <stdint.h>
  #include <stdlib.h>
  #include <string.h>
  #include <limits.h>
  #include <sha1.h>
  #include <endian.h>
  #include <zlib.h>
  
  #include "got_error.h"
  #include "got_object.h"
  #include "got_repository.h"
  
  #include "got_lib_sha1.h"
  #include "got_lib_pack.h"
  #include "got_lib_path.h"
  #include "got_lib_delta.h"
  #include "got_lib_zbuf.h"
  #include "got_lib_object.h"
  #include "got_lib_repository.h"
  
  #ifndef nitems
  #define nitems(_a) (sizeof(_a) / sizeof((_a)[0]))
  #endif
  
  #define GOT_PACK_PREFIX		"pack-"
  #define GOT_PACKFILE_SUFFIX	".pack"
  #define GOT_PACKIDX_SUFFIX		".idx"
  #define GOT_PACKFILE_NAMELEN	(strlen(GOT_PACK_PREFIX) + \
  				SHA1_DIGEST_STRING_LENGTH - 1 + \
  				strlen(GOT_PACKFILE_SUFFIX))
  #define GOT_PACKIDX_NAMELEN	(strlen(GOT_PACK_PREFIX) + \
  				SHA1_DIGEST_STRING_LENGTH - 1 + \
  				strlen(GOT_PACKIDX_SUFFIX))
  
  #ifndef MIN
  #define	MIN(_a,_b) ((_a) < (_b) ? (_a) : (_b))
  #endif
  
  static const struct got_error *
  verify_fanout_table(uint32_t *fanout_table)
  {
  	int i;
  
  	for (i = 0; i < 0xff - 1; i++) {
  		if (be32toh(fanout_table[i]) > be32toh(fanout_table[i + 1]))
  			return got_error(GOT_ERR_BAD_PACKIDX);
  	}
  
  	return NULL;
  }
  
  static const struct got_error *
  get_packfile_size(size_t *size, const char *path)
  {
  	struct stat sb;
  	char *dot;
  
  	*size = 0;
  
  	dot = strrchr(path, '.');
  	if (dot == NULL)
  		return got_error(GOT_ERR_BAD_PATH);
  
  	/* Path must point to a pack index or to a pack file. */
  	if (strcmp(dot, ".idx") == 0) {
  		const struct got_error *err = NULL;
  		char *path_pack;
  		char base_path[PATH_MAX];
  
  		/* Convert pack index path to pack file path. */
  		if (strlcpy(base_path, path, PATH_MAX) > PATH_MAX)
  			return got_error(GOT_ERR_NO_SPACE);
  		dot = strrchr(base_path, '.');
  		if (dot == NULL)
  			return got_error(GOT_ERR_BAD_PATH);
  		*dot = '\0';
  		if (asprintf(&path_pack, "%s.pack", base_path) == -1)
  			return got_error_from_errno();
  
  		if (stat(path_pack, &sb) != 0)
  			err = got_error_from_errno();
  		free(path_pack);
  		if (err)
  			return err;
  	} else if (strcmp(dot, ".pack") == 0) {
  		if (stat(path, &sb) != 0)
  			return got_error_from_errno();
  	} else
  		return got_error(GOT_ERR_BAD_PATH);
  
  	*size = sb.st_size;
  	return 0;
  }
  
  const struct got_error *
  got_packidx_open(struct got_packidx_v2_hdr **packidx, const char *path)
  {
  	struct got_packidx_v2_hdr *p;
  	FILE *f;
  	const struct got_error *err = NULL;
  	size_t n, nobj, packfile_size;
  	SHA1_CTX ctx;
  	uint8_t sha1[SHA1_DIGEST_LENGTH];
  
  	SHA1Init(&ctx);
  
  	f = fopen(path, "rb");
  	if (f == NULL)
  		return got_error_from_errno();
  
  	err = get_packfile_size(&packfile_size, path);
  	if (err)
  		return err;
  
  	p = calloc(1, sizeof(*p));
  	if (p == NULL) {
  		err = got_error_from_errno();
  		goto done;
  	}
  
  	n = fread(&p->magic, sizeof(p->magic), 1, f);
  	if (n != 1) {
  		err = got_ferror(f, GOT_ERR_BAD_PACKIDX);
  		goto done;
  	}
  
  	if (betoh32(p->magic) != GOT_PACKIDX_V2_MAGIC) {
  		err = got_error(GOT_ERR_BAD_PACKIDX);
  		goto done;
  	}
  
  	SHA1Update(&ctx, (uint8_t *)&p->magic, sizeof(p->magic));
  
  	n = fread(&p->version, sizeof(p->version), 1, f);
  	if (n != 1) {
  		err = got_ferror(f, GOT_ERR_BAD_PACKIDX);
  		goto done;
  	}
  
  	if (betoh32(p->version) != GOT_PACKIDX_VERSION) {
  		err = got_error(GOT_ERR_BAD_PACKIDX);
  		goto done;
  	}
  
  	SHA1Update(&ctx, (uint8_t *)&p->version, sizeof(p->version));
  
  	n = fread(&p->fanout_table, sizeof(p->fanout_table), 1, f);
  	if (n != 1) {
  		err = got_ferror(f, GOT_ERR_BAD_PACKIDX);
  		goto done;
  	}
  
  	err = verify_fanout_table(p->fanout_table);
  	if (err)
  		goto done;
  
  	SHA1Update(&ctx, (uint8_t *)p->fanout_table, sizeof(p->fanout_table));
  
  	nobj = betoh32(p->fanout_table[0xff]);
  
  	p->sorted_ids = calloc(nobj, sizeof(*p->sorted_ids));
  	if (p->sorted_ids == NULL) {
  		err = got_error_from_errno();
  		goto done;
  	}
  
  	n = fread(p->sorted_ids, sizeof(*p->sorted_ids), nobj, f);
  	if (n != nobj) {
  		err = got_ferror(f, GOT_ERR_BAD_PACKIDX);
  		goto done;
  	}
  
  	SHA1Update(&ctx, (uint8_t *)p->sorted_ids,
  	    nobj * sizeof(*p->sorted_ids));
  
  	p->crc32 = calloc(nobj, sizeof(*p->crc32));
  	if (p->crc32 == NULL) {
  		err = got_error_from_errno();
  		goto done;
  	}
  
  	n = fread(p->crc32, sizeof(*p->crc32), nobj, f);
  	if (n != nobj) {
  		err = got_ferror(f, GOT_ERR_BAD_PACKIDX);
  		goto done;
  	}
  
  	SHA1Update(&ctx, (uint8_t *)p->crc32, nobj * sizeof(*p->crc32));
  
  	p->offsets = calloc(nobj, sizeof(*p->offsets));
  	if (p->offsets == NULL) {
  		err = got_error_from_errno();
  		goto done;
  	}
  
  	n = fread(p->offsets, sizeof(*p->offsets), nobj, f);
  	if (n != nobj) {
  		err = got_ferror(f, GOT_ERR_BAD_PACKIDX);
  		goto done;
  	}
  
  	SHA1Update(&ctx, (uint8_t *)p->offsets, nobj * sizeof(*p->offsets));
  
  	/* Large file offsets are contained only in files > 2GB. */
  	if (packfile_size <= 0x80000000)
  		goto checksum;
  
  	p->large_offsets = calloc(nobj, sizeof(*p->large_offsets));
  	if (p->large_offsets == NULL) {
  		err = got_error_from_errno();
  		goto done;
  	}
  
  	n = fread(p->large_offsets, sizeof(*p->large_offsets), nobj, f);
  	if (n != nobj) {
  		err = got_ferror(f, GOT_ERR_BAD_PACKIDX);
  		goto done;
  	}
  
  	SHA1Update(&ctx, (uint8_t*)p->large_offsets,
  	    nobj * sizeof(*p->large_offsets));
  
  checksum:
  	n = fread(&p->trailer, sizeof(p->trailer), 1, f);
  	if (n != 1) {
  		err = got_ferror(f, GOT_ERR_BAD_PACKIDX);
  		goto done;
  	}
  
  	SHA1Update(&ctx, p->trailer.packfile_sha1, SHA1_DIGEST_LENGTH);
  	SHA1Final(sha1, &ctx);
  	if (memcmp(p->trailer.packidx_sha1, sha1, SHA1_DIGEST_LENGTH) != 0)
  		err = got_error(GOT_ERR_PACKIDX_CSUM);
  done:
  	fclose(f);
  	if (err)
  		got_packidx_close(p);
  	else
  		*packidx = p;
  	return err;
  }
  
  void
  got_packidx_close(struct got_packidx_v2_hdr *packidx)
  {
  	free(packidx->sorted_ids);
  	free(packidx->offsets);
  	free(packidx->crc32);
  	free(packidx->large_offsets);
  	free(packidx);
  }
  
  static int
  is_packidx_filename(const char *name, size_t len)
  {
  	if (len != GOT_PACKIDX_NAMELEN)
  		return 0;
  
  	if (strncmp(name, GOT_PACK_PREFIX, strlen(GOT_PACK_PREFIX)) != 0)
  		return 0;
  
  	if (strcmp(name + strlen(GOT_PACK_PREFIX) +
  	    SHA1_DIGEST_STRING_LENGTH - 1, GOT_PACKIDX_SUFFIX) != 0)
  		return 0;
  
  	return 1;
  }
  
  static off_t
  get_object_offset(struct got_packidx_v2_hdr *packidx, int idx)
  {
  	uint32_t totobj = betoh32(packidx->fanout_table[0xff]);
  	uint32_t offset = betoh32(packidx->offsets[idx]);
  	if (offset & GOT_PACKIDX_OFFSET_VAL_IS_LARGE_IDX) {
  		uint64_t loffset;
  		idx = offset & GOT_PACKIDX_OFFSET_VAL_MASK;
  		if (idx < 0 || idx > totobj || packidx->large_offsets == NULL)
  			return -1;
  		loffset = betoh64(packidx->large_offsets[idx]);
  		return (loffset > INT64_MAX ? -1 : (off_t)loffset);
  	}
  	return (off_t)(offset & GOT_PACKIDX_OFFSET_VAL_MASK);
  }
  
  static const struct got_error *
  get_packfile_path(char **path_packfile, struct got_repository *repo,
      struct got_packidx_v2_hdr *packidx);
  
  static int
  get_object_idx(struct got_packidx_v2_hdr *packidx, struct got_object_id *id, struct got_repository *repo)
  {
  	u_int8_t id0 = id->sha1[0];
  	uint32_t totobj = betoh32(packidx->fanout_table[0xff]);
  	int i = 0;
  
  	if (id0 > 0)
  		i = betoh32(packidx->fanout_table[id0 - 1]);
  
  	while (i < totobj) {
  		struct got_object_id *oid = &packidx->sorted_ids[i];
  		int cmp = got_object_id_cmp(id, oid);
  
  		if (cmp == 0)
  			return i;
  		i++;
  	}
  
  	return -1;
  }
  
  static struct got_packidx_v2_hdr *
  dup_packidx(struct got_packidx_v2_hdr *packidx)
  {
  	struct got_packidx_v2_hdr *p;
  	size_t nobj;
  
  	p = calloc(1, sizeof(*p));
  	if (p == NULL)
  		return NULL;
  
  	memcpy(p, packidx, sizeof(*p));
  	p->sorted_ids = NULL;
  	p->crc32 = NULL;
  	p->offsets = NULL;
  	p->large_offsets = NULL;
  
  	nobj = betoh32(p->fanout_table[0xff]);
  
  	p->sorted_ids = calloc(nobj, sizeof(*p->sorted_ids));
  	if (p->sorted_ids == NULL)
  		goto err;
  	memcpy(p->sorted_ids, packidx->sorted_ids,
  	    nobj * sizeof(*p->sorted_ids));
  
  	p->crc32 = calloc(nobj, sizeof(*p->crc32));
  	if (p->crc32 == NULL)
  		goto err;
  	memcpy(p->crc32, packidx->crc32, nobj * sizeof(*p->crc32));
  
  	p->offsets = calloc(nobj, sizeof(*p->offsets));
  	if (p->offsets == NULL)
  		goto err;
  	memcpy(p->offsets, packidx->offsets, nobj * sizeof(*p->offsets));
  
  	if (p->large_offsets) {
  		p->large_offsets = calloc(nobj, sizeof(*p->large_offsets));
  		if (p->large_offsets == NULL)
  			goto err;
  		memcpy(p->large_offsets, packidx->large_offsets,
  		    nobj * sizeof(*p->large_offsets));
  	}
  
  	return p;
  
  err:
  	free(p->large_offsets);
  	free(p->offsets);
  	free(p->crc32);
  	free(p->sorted_ids);
  	free(p);
  	return NULL;
  }
  
  static void
  cache_packidx(struct got_packidx_v2_hdr *packidx, struct got_repository *repo)
  {
  	int i;
  
  	for (i = 0; i < nitems(repo->packidx_cache); i++) {
  		if (repo->packidx_cache[i] == NULL)
  			break;
  	}
  
  	if (i == nitems(repo->packidx_cache)) {
  		got_packidx_close(repo->packidx_cache[i - 1]);
  		memmove(&repo->packidx_cache[1], &repo->packidx_cache[0],
  		    sizeof(repo->packidx_cache) -
  		    sizeof(repo->packidx_cache[0]));
  		i = 0;
  	}
  
  	repo->packidx_cache[i] = dup_packidx(packidx);
  }
  
  static const struct got_error *
  search_packidx(struct got_packidx_v2_hdr **packidx, int *idx,
      struct got_repository *repo, struct got_object_id *id)
  {
  	const struct got_error *err;
  	char *path_packdir;
  	DIR *packdir;
  	struct dirent *dent;
  	char *path_packidx;
  	int i;
  
  	/* Search pack index cache. */
  	for (i = 0; i < nitems(repo->packidx_cache); i++) {
  		if (repo->packidx_cache[i] == NULL)
  			break;
  		*idx = get_object_idx(repo->packidx_cache[i], id, repo);
  		if (*idx != -1) {
  			*packidx = repo->packidx_cache[i];
  			return NULL;
  		}
  	}
  	/* No luck. Search the filesystem. */
  
  	path_packdir = got_repo_get_path_objects_pack(repo);
  	if (path_packdir == NULL)
  		return got_error_from_errno();
  
  	packdir = opendir(path_packdir);
  	if (packdir == NULL) {
  		err = got_error_from_errno();
  		goto done;
  	}
  
  	while ((dent = readdir(packdir)) != NULL) {
  		if (!is_packidx_filename(dent->d_name, dent->d_namlen))
  			continue;
  
  		if (asprintf(&path_packidx, "%s/%s", path_packdir,
  		    dent->d_name) == -1) {
  			err = got_error_from_errno();
  			goto done;
  		}
  
  		err = got_packidx_open(packidx, path_packidx);
  		free(path_packidx);
  		if (err)
  			goto done;
  
  		*idx = get_object_idx(*packidx, id, repo);
  		if (*idx != -1) {
  			err = NULL; /* found the object */
  			cache_packidx(*packidx, repo);
  			goto done;
  		}
  
  		got_packidx_close(*packidx);
  		*packidx = NULL;
  	}
  
  	err = got_error(GOT_ERR_NO_OBJ);
  done:
  	free(path_packdir);
  	if (packdir && closedir(packdir) != 0 && err == 0)
  		err = got_error_from_errno();
  	return err;
  }
  
  static const struct got_error *
  get_packfile_path(char **path_packfile, struct got_repository *repo,
      struct got_packidx_v2_hdr *packidx)
  {
  	char *path_packdir;
  	char hex[SHA1_DIGEST_STRING_LENGTH];
  	char *sha1str;
  
  	path_packdir = got_repo_get_path_objects_pack(repo);
  	if (path_packdir == NULL)
  		return got_error_from_errno();
  
  	sha1str = got_sha1_digest_to_str(packidx->trailer.packfile_sha1,
  	    hex, sizeof(hex));
  	if (sha1str == NULL)
  		return got_error(GOT_ERR_PACKIDX_CSUM);
  
  	if (asprintf(path_packfile, "%s/%s%s%s", path_packdir,
  	    GOT_PACK_PREFIX, sha1str, GOT_PACKFILE_SUFFIX) == -1) {
  		*path_packfile = NULL;
  		return got_error_from_errno();
  	}
  
  	return NULL;
  }
  
  const struct got_error *
  read_packfile_hdr(FILE *f, struct got_packidx_v2_hdr *packidx)
  {
  	const struct got_error *err = NULL;
  	uint32_t totobj = betoh32(packidx->fanout_table[0xff]);
  	struct got_packfile_hdr hdr;
  	size_t n;
  
  	n = fread(&hdr, sizeof(hdr), 1, f);
  	if (n != 1)
  		return got_ferror(f, GOT_ERR_BAD_PACKIDX);
  
  	if (betoh32(hdr.signature) != GOT_PACKFILE_SIGNATURE ||
  	    betoh32(hdr.version) != GOT_PACKFILE_VERSION ||
  	    betoh32(hdr.nobjects) != totobj)
  		err = got_error(GOT_ERR_BAD_PACKFILE);
  
  	return err;
  }
  
  static const struct got_error *
  open_packfile(FILE **packfile, const char *path_packfile,
      struct got_repository *repo, struct got_packidx_v2_hdr *packidx)
  {
  	const struct got_error *err = NULL;
  
  	*packfile = NULL;
  
  	*packfile = fopen(path_packfile, "rb");
  	if (*packfile == NULL) {
  		err = got_error_from_errno();
  		return err;
  	}
  
  	if (packidx) {
  		err = read_packfile_hdr(*packfile, packidx);
  		if (err) {
  			fclose(*packfile);
  			*packfile = NULL;
  		}
  	}
  	return err;
  }
  
  void
  got_pack_close(struct got_pack *pack)
  {
  	fclose(pack->packfile);
  	pack->packfile = NULL;
  	free(pack->path_packfile);
  	pack->path_packfile = NULL;
  	pack->filesize = 0;
  }
  
  static const struct got_error *
  cache_pack(struct got_pack **packp, const char *path_packfile,
      struct got_packidx_v2_hdr *packidx, struct got_repository *repo)
  {
  	const struct got_error *err = NULL;
  	struct got_pack *pack = NULL;
  	int i;
  
  	if (packp)
  		*packp = NULL;
  
  	for (i = 0; i < nitems(repo->packs); i++) {
  		pack = &repo->packs[i];
  		if (pack->path_packfile == NULL)
  			break;
  		if (strcmp(pack->path_packfile, path_packfile) == 0)
  			return NULL;
  	}
  
  	if (i == nitems(repo->packs) - 1) {
  		got_pack_close(&repo->packs[i - 1]);
  		memmove(&repo->packs[1], &repo->packs[0],
  		    sizeof(repo->packs) - sizeof(repo->packs[0]));
  		i = 0;
  	}
  
  	pack = &repo->packs[i];
  
  	pack->path_packfile = strdup(path_packfile);
  	if (pack->path_packfile == NULL) {
  		err = got_error_from_errno();
  		goto done;
  	}
  
  	err = open_packfile(&pack->packfile, path_packfile, repo, packidx);
  	if (err)
  		goto done;
  
  	err = get_packfile_size(&pack->filesize, path_packfile);
  done:
  	if (err) {
  		if (pack)
  			free(pack->path_packfile);
  		free(pack);
  	} else if (packp)
  		*packp = pack;
  	return err;
  }
  
  struct got_pack *
  get_cached_pack(const char *path_packfile, struct got_repository *repo)
  {
  	struct got_pack *pack = NULL;
  	int i;
  
  	for (i = 0; i < nitems(repo->packs); i++) {
  		pack = &repo->packs[i];
  		if (pack->path_packfile == NULL)
  			break;
  		if (strcmp(pack->path_packfile, path_packfile) == 0)
  			return pack;
  	}
  
  	return NULL;
  }
  
  static const struct got_error *
  parse_object_type_and_size(uint8_t *type, uint64_t *size, size_t *len,
      FILE *packfile)
  {
  	uint8_t t = 0;
  	uint64_t s = 0;
  	uint8_t sizeN;
  	size_t n;
  	int i = 0;
  
  	do {
  		/* We do not support size values which don't fit in 64 bit. */
  		if (i > 9)
  			return got_error(GOT_ERR_NO_SPACE);
  
  		n = fread(&sizeN, sizeof(sizeN), 1, packfile);
  		if (n != 1)
  			return got_ferror(packfile, GOT_ERR_BAD_PACKIDX);
  
  		if (i == 0) {
  			t = (sizeN & GOT_PACK_OBJ_SIZE0_TYPE_MASK) >>
  			    GOT_PACK_OBJ_SIZE0_TYPE_MASK_SHIFT;
  			s = (sizeN & GOT_PACK_OBJ_SIZE0_VAL_MASK);
  		} else {
  			size_t shift = 4 + 7 * (i - 1);
  			s |= ((sizeN & GOT_PACK_OBJ_SIZE_VAL_MASK) << shift);
  		}
  		i++;
  	} while (sizeN & GOT_PACK_OBJ_SIZE_MORE);
  
  	*type = t;
  	*size = s;
  	*len = i * sizeof(sizeN);
  	return NULL;
  }
  
  static const struct got_error *
  open_plain_object(struct got_object **obj, const char *path_packfile,
      struct got_object_id *id, uint8_t type, off_t offset, size_t size)
  {
  	*obj = calloc(1, sizeof(**obj));
  	if (*obj == NULL)
  		return got_error_from_errno();
  
  	(*obj)->path_packfile = strdup(path_packfile);
  	if ((*obj)->path_packfile == NULL) {
  		const struct got_error *err = got_error_from_errno();
  		free(*obj);
  		*obj = NULL;
  		return err;
  	}
  
  	(*obj)->type = type;
  	(*obj)->flags = GOT_OBJ_FLAG_PACKED;
  	(*obj)->hdrlen = 0;
  	(*obj)->size = size;
  	memcpy(&(*obj)->id, id, sizeof((*obj)->id));
  	(*obj)->pack_offset = offset;
  
  	return NULL;
  }
  
  static const struct got_error *
  parse_negative_offset(int64_t *offset, size_t *len, FILE *packfile)
  {
  	int64_t o = 0;
  	uint8_t offN;
  	size_t n;
  	int i = 0;
  
  	do {
  		/* We do not support offset values which don't fit in 64 bit. */
  		if (i > 8)
  			return got_error(GOT_ERR_NO_SPACE);
  
  		n = fread(&offN, sizeof(offN), 1, packfile);
  		if (n != 1)
  			return got_ferror(packfile, GOT_ERR_BAD_PACKIDX);
  
  		if (i == 0)
  			o = (offN & GOT_PACK_OBJ_DELTA_OFF_VAL_MASK);
  		else {
  			o++;
  			o <<= 7;
  			o += (offN & GOT_PACK_OBJ_DELTA_OFF_VAL_MASK);
  		}
  		i++;
  	} while (offN & GOT_PACK_OBJ_DELTA_OFF_MORE);
  
  	*offset = o;
  	*len = i * sizeof(offN);
  	return NULL;
  }
  
  static const struct got_error *
  parse_offset_delta(off_t *base_offset, FILE *packfile, off_t offset)
  {
  	const struct got_error *err;
  	int64_t negoffset;
  	size_t negofflen;
  
  	err = parse_negative_offset(&negoffset, &negofflen, packfile);
  	if (err)
  		return err;
  
  	/* Compute the base object's offset (must be in the same pack file). */
  	*base_offset = (offset - negoffset);
  	if (*base_offset <= 0)
  		return got_error(GOT_ERR_BAD_PACKFILE);
  
  	return NULL;
  }
  
  static const struct got_error *
  resolve_delta_chain(struct got_delta_chain *, struct got_repository *,
      FILE *, const char *, off_t, size_t, int, size_t, unsigned int);
  
  static const struct got_error *
  add_delta(struct got_delta_chain *deltas, const char *path_packfile,
      off_t delta_offset, size_t tslen, int delta_type, size_t delta_size,
      size_t delta_data_offset, uint8_t *delta_buf, size_t delta_len)
  {
  	struct got_delta *delta;
  
  	delta = got_delta_open(path_packfile, delta_offset, tslen,
  	    delta_type, delta_size, delta_data_offset, delta_buf,
  	    delta_len);
  	if (delta == NULL)
  		return got_error_from_errno();
  	/* delta is freed in got_object_close() */
  	deltas->nentries++;
  	SIMPLEQ_INSERT_HEAD(&deltas->entries, delta, entry);
  	return NULL;
  }
  
  static const struct got_error *
  resolve_offset_delta(struct got_delta_chain *deltas,
      struct got_repository *repo, FILE *packfile, const char *path_packfile,
      off_t delta_offset,size_t tslen, int delta_type, size_t delta_size,
      unsigned int recursion)
  
  {
  	const struct got_error *err;
  	off_t base_offset;
  	uint8_t base_type;
  	uint64_t base_size;
  	size_t base_tslen;
  	off_t delta_data_offset;
  	uint8_t *delta_buf;
  	size_t delta_len;
  
  	err = parse_offset_delta(&base_offset, packfile, delta_offset);
  	if (err)
  		return err;
  
  	delta_data_offset = ftello(packfile);
  	if (delta_data_offset == -1)
  		return got_error_from_errno();
  
  	err = got_inflate_to_mem(&delta_buf, &delta_len, packfile);
  	if (err)
  		return err;
  
  	err = add_delta(deltas, path_packfile, delta_offset, tslen,
  	    delta_type, delta_size, delta_data_offset, delta_buf, delta_len);
  	if (err)
  		return err;
  
  	/* An offset delta must be in the same packfile. */
  	if (fseeko(packfile, base_offset, SEEK_SET) != 0)
  		return got_error_from_errno();
  
  	err = parse_object_type_and_size(&base_type, &base_size, &base_tslen,
  	    packfile);
  	if (err)
  		return err;
  
  	return resolve_delta_chain(deltas, repo, packfile, path_packfile,
  	    base_offset, base_tslen, base_type, base_size, recursion - 1);
  }
  
  static const struct got_error *
  resolve_ref_delta(struct got_delta_chain *deltas, struct got_repository *repo,
      FILE *packfile, const char *path_packfile, off_t delta_offset,
      size_t tslen, int delta_type, size_t delta_size, unsigned int recursion)
  {
  	const struct got_error *err;
  	struct got_object_id id;
  	struct got_packidx_v2_hdr *packidx;
  	int idx;
  	off_t base_offset;
  	uint8_t base_type;
  	uint64_t base_size;
  	size_t base_tslen;
  	size_t n;
  	char *path_base_packfile;
  	struct got_pack *base_pack;
  	off_t delta_data_offset;
  	uint8_t *delta_buf;
  	size_t delta_len;
  
  	n = fread(&id, sizeof(id), 1, packfile);
  	if (n != 1)
  		return got_ferror(packfile, GOT_ERR_IO);
  
  	delta_data_offset = ftello(packfile);
  	if (delta_data_offset == -1)
  		return got_error_from_errno();
  
  	err = got_inflate_to_mem(&delta_buf, &delta_len, packfile);
  	if (err)
  		return err;
  
  	err = add_delta(deltas, path_packfile, delta_offset, tslen,
  	    delta_type, delta_size, delta_data_offset, delta_buf, delta_len);
  	if (err)
  		return err;
  
  	err = search_packidx(&packidx, &idx, repo, &id);
  	if (err)
  		return err;
  
  	base_offset = get_object_offset(packidx, idx);
  	if (base_offset == (uint64_t)-1) {
  		return got_error(GOT_ERR_BAD_PACKIDX);
  	}
  
  	err = get_packfile_path(&path_base_packfile, repo, packidx);
  	if (err)
  		return err;
  
  	base_pack = get_cached_pack(path_base_packfile, repo);
  	if (base_pack == NULL) {
  		err = cache_pack(&base_pack, path_base_packfile, NULL, repo);
  		if (err)
  			goto done;
  	}
  
  	if (fseeko(base_pack->packfile, base_offset, SEEK_SET) != 0) {
  		err = got_error_from_errno();
  		goto done;
  	}
  
  	err = parse_object_type_and_size(&base_type, &base_size, &base_tslen,
  	    base_pack->packfile);
  	if (err)
  		goto done;
  
  	err = resolve_delta_chain(deltas, repo, base_pack->packfile,
  	    path_base_packfile, base_offset, base_tslen, base_type,
  	    base_size, recursion - 1);
  done:
  	free(path_base_packfile);
  	return err;
  }
  
  static const struct got_error *
  resolve_delta_chain(struct got_delta_chain *deltas, struct got_repository *repo,
      FILE *packfile, const char *path_packfile, off_t delta_offset, size_t tslen,
      int delta_type, size_t delta_size, unsigned int recursion)
  {
  	const struct got_error *err = NULL;
  
  	if (--recursion == 0)
  		return got_error(GOT_ERR_RECURSION);
  
  	switch (delta_type) {
  	case GOT_OBJ_TYPE_COMMIT:
  	case GOT_OBJ_TYPE_TREE:
  	case GOT_OBJ_TYPE_BLOB:
  	case GOT_OBJ_TYPE_TAG:
  		/* Plain types are the final delta base. Recursion ends. */
  		err = add_delta(deltas, path_packfile, delta_offset, tslen,
  		    delta_type, delta_size, 0, NULL, 0);
  		break;
  	case GOT_OBJ_TYPE_OFFSET_DELTA:
  		err = resolve_offset_delta(deltas, repo, packfile,
  		    path_packfile, delta_offset, tslen, delta_type,
  		    delta_size, recursion - 1);
  		break;
  	case GOT_OBJ_TYPE_REF_DELTA:
  		err = resolve_ref_delta(deltas, repo, packfile,
  		    path_packfile, delta_offset, tslen, delta_type,
  		    delta_size, recursion - 1);
  		break;
  	default:
  		return got_error(GOT_ERR_OBJ_TYPE);
  	}
  
  	return err;
  }
  
  static const struct got_error *
  open_delta_object(struct got_object **obj, struct got_repository *repo,
      struct got_packidx_v2_hdr *packidx, const char *path_packfile,
      FILE *packfile, struct got_object_id *id, off_t offset, size_t tslen,
      int delta_type, size_t delta_size)
  {
  	const struct got_error *err = NULL;
  	int resolved_type;
  
  	*obj = calloc(1, sizeof(**obj));
  	if (*obj == NULL)
  		return got_error_from_errno();
  
  	(*obj)->flags = 0;
  	(*obj)->hdrlen = 0;
  	(*obj)->size = 0; /* Not known because deltas aren't applied yet. */
  	memcpy(&(*obj)->id, id, sizeof((*obj)->id));
  	(*obj)->pack_offset = offset + tslen;
  
  	(*obj)->path_packfile = strdup(path_packfile);
  	if ((*obj)->path_packfile == NULL) {
  		err = got_error_from_errno();
  		goto done;
  	}
  	(*obj)->flags |= GOT_OBJ_FLAG_PACKED;
  
  	SIMPLEQ_INIT(&(*obj)->deltas.entries);
  	(*obj)->flags |= GOT_OBJ_FLAG_DELTIFIED;
  
  	err = resolve_delta_chain(&(*obj)->deltas, repo, packfile,
  	    path_packfile, offset, tslen, delta_type, delta_size,
  	    GOT_DELTA_CHAIN_RECURSION_MAX);
  	if (err)
  		goto done;
  
  	err = got_delta_chain_get_base_type(&resolved_type, &(*obj)->deltas);
  	if (err)
  		goto done;
  	(*obj)->type = resolved_type;
  
  done:
  	if (err) {
  		got_object_close(*obj);
  		*obj = NULL;
  	}
  	return err;
  }
  
  static const struct got_error *
  open_packed_object(struct got_object **obj, struct got_repository *repo,
      struct got_packidx_v2_hdr *packidx, int idx, struct got_object_id *id)
  {
  	const struct got_error *err = NULL;
  	off_t offset;
  	char *path_packfile;
  	struct got_pack *pack;
  	uint8_t type;
  	uint64_t size;
  	size_t tslen;
  
  	*obj = NULL;
  
  	offset = get_object_offset(packidx, idx);
  	if (offset == (uint64_t)-1)
  		return got_error(GOT_ERR_BAD_PACKIDX);
  
  	err = get_packfile_path(&path_packfile, repo, packidx);
  	if (err)
  		return err;
  
  	pack = get_cached_pack(path_packfile, repo);
  	if (pack == NULL) {
  		err = cache_pack(&pack, path_packfile, packidx, repo);
  		if (err)
  			goto done;
  	}
  
  	if (fseeko(pack->packfile, offset, SEEK_SET) != 0) {
  		err = got_error_from_errno();
  		goto done;
  	}
  
  	err = parse_object_type_and_size(&type, &size, &tslen, pack->packfile);
  	if (err)
  		goto done;
  
  	switch (type) {
  	case GOT_OBJ_TYPE_COMMIT:
  	case GOT_OBJ_TYPE_TREE:
  	case GOT_OBJ_TYPE_BLOB:
  	case GOT_OBJ_TYPE_TAG:
  		err = open_plain_object(obj, path_packfile, id, type,
  		    offset + tslen, size);
  		break;
  
  	case GOT_OBJ_TYPE_OFFSET_DELTA:
  	case GOT_OBJ_TYPE_REF_DELTA:
  		err = open_delta_object(obj, repo, packidx, path_packfile,
  		    pack->packfile, id, offset, tslen, type, size);
  		break;
  
  	default:
  		err = got_error(GOT_ERR_OBJ_TYPE);
  		goto done;
  	}
  done:
  	free(path_packfile);
  	return err;
  }
  
  const struct got_error *
  got_packfile_open_object(struct got_object **obj, struct got_object_id *id,
      struct got_repository *repo)
  {
  	const struct got_error *err = NULL;
  	struct got_packidx_v2_hdr *packidx = NULL;
  	int idx;
  
  	err = search_packidx(&packidx, &idx, repo, id);
  	if (err)
  		return err;
  
  	err = open_packed_object(obj, repo, packidx, idx, id);
  	if (err)
  		return err;
  
  	err = cache_pack(NULL, (*obj)->path_packfile, packidx, repo);
  	return err;
  }
  
  static const struct got_error *
  get_delta_chain_max_size(uint64_t *max_size, struct got_delta_chain *deltas)
  {
  	struct got_delta *delta;
  	uint64_t base_size = 0, result_size = 0;
  
  	*max_size = 0;
  	SIMPLEQ_FOREACH(delta, &deltas->entries, entry) {
  		/* Plain object types are the delta base. */
  		if (delta->type != GOT_OBJ_TYPE_COMMIT &&
  		    delta->type != GOT_OBJ_TYPE_TREE &&
  		    delta->type != GOT_OBJ_TYPE_BLOB &&
  		    delta->type != GOT_OBJ_TYPE_TAG) {
  			const struct got_error *err;
  			err = got_delta_get_sizes(&base_size, &result_size,
  			    delta->delta_buf, delta->delta_len);
  			if (err)
  				return err;
  		} else
  			base_size = delta->size;
  		if (base_size > *max_size)
  			*max_size = base_size;
  		if (result_size > *max_size)
  			*max_size = result_size;
  	}
  
  	return NULL;
  }
  
  static const struct got_error *
  dump_delta_chain_to_file(size_t *result_size, struct got_delta_chain *deltas,
      FILE *outfile, struct got_repository *repo)
  {
  	const struct got_error *err = NULL;
  	struct got_delta *delta;
  	FILE *base_file = NULL, *accum_file = NULL;
  	uint8_t *base_buf = NULL, *accum_buf = NULL;
  	size_t accum_size = 0;
  	uint64_t max_size;
  	int n = 0;
  
  	*result_size = 0;
  
  	if (SIMPLEQ_EMPTY(&deltas->entries))
  		return got_error(GOT_ERR_BAD_DELTA_CHAIN);
  
  	/* We process small enough files entirely in memory for speed. */
  	err = get_delta_chain_max_size(&max_size, deltas);
  	if (err)
  		return err;
  	if (max_size < GOT_DELTA_RESULT_SIZE_CACHED_MAX) {
  		accum_buf = malloc(max_size);
  		if (accum_buf == NULL)
  			return got_error_from_errno();
  	} else {
  		base_file = got_opentemp();
  		if (base_file == NULL)
  			return got_error_from_errno();
  
  		accum_file = got_opentemp();
  		if (accum_file == NULL) {
  			err = got_error_from_errno();
  			fclose(base_file);
  			return err;
  		}
  	}
  
  	/* Deltas are ordered in ascending order. */
  	SIMPLEQ_FOREACH(delta, &deltas->entries, entry) {
  		if (n == 0) {
  			struct got_pack *pack;
  			size_t base_len;
  
  			/* Plain object types are the delta base. */
  			if (delta->type != GOT_OBJ_TYPE_COMMIT &&
  			    delta->type != GOT_OBJ_TYPE_TREE &&
  			    delta->type != GOT_OBJ_TYPE_BLOB &&
  			    delta->type != GOT_OBJ_TYPE_TAG) {
  				err = got_error(GOT_ERR_BAD_DELTA_CHAIN);
  				goto done;
  			}
  
  			pack = get_cached_pack(delta->path_packfile, repo);
  			if (pack == NULL) {
  				err = got_error(GOT_ERR_BAD_DELTA_CHAIN);
  				goto done;
  			}
  
  			if (fseeko(pack->packfile, delta->offset + delta->tslen,
  			    SEEK_SET) != 0) {
  				err = got_error_from_errno();
  				goto done;
  			}
  			if (base_file)
  				err = got_inflate_to_file(&base_len,
  				    pack->packfile, base_file);
  			else {
  				err = got_inflate_to_mem(&base_buf, &base_len,
  				    pack->packfile);
  				if (base_len < max_size) {
  					uint8_t *p;
  					p = reallocarray(base_buf, 1, max_size);
  					if (p == NULL) {
  						err = got_error_from_errno();
  						goto done;
  					}
  					base_buf = p;
  				}
  			}
  			if (err)
  				goto done;
  			n++;
  			if (base_file)
  				rewind(base_file);
  			continue;
  		}
  
  		if (base_buf) {
  			err = got_delta_apply_in_mem(base_buf, delta->delta_buf,
  			    delta->delta_len, accum_buf, &accum_size);
  			n++;
  		} else {
  			err = got_delta_apply(base_file, delta->delta_buf,
  			    delta->delta_len,
  			    /* Final delta application writes to output file. */
  			    ++n < deltas->nentries ? accum_file : outfile,
  			    &accum_size);
  		}
  		if (err)
  			goto done;
  
  		if (n < deltas->nentries) {
  			/* Accumulated delta becomes the new base. */
  			if (base_buf) {
  				uint8_t *tmp = accum_buf;
  				accum_buf = base_buf;
  				base_buf = tmp;
  			} else {
  				FILE *tmp = accum_file;
  				accum_file = base_file;
  				base_file = tmp;
  				rewind(base_file);
  				rewind(accum_file);
  			}
  		}
  	}
  
  done:
  	free(base_buf);
  	if (accum_buf) {
  		size_t len = fwrite(accum_buf, 1, accum_size, outfile);
  		free(accum_buf);
  		if (len != accum_size)
  			return got_ferror(outfile, GOT_ERR_IO);
  	}
  	if (base_file)
  		fclose(base_file);
  	if (accum_file)
  		fclose(accum_file);
  	rewind(outfile);
  	if (err == NULL)
  		*result_size = accum_size;
  	return err;
  }
  
  static const struct got_error *
  dump_delta_chain_to_mem(uint8_t **outbuf, size_t *outlen,
      struct got_delta_chain *deltas, struct got_repository *repo)
  {
  	const struct got_error *err = NULL;
  	struct got_delta *delta;
  	uint8_t *base_buf = NULL, *accum_buf = NULL;
  	size_t accum_size;
  	uint64_t max_size;
  	int n = 0;
  
  	*outbuf = NULL;
  	*outlen = 0;
  
  	if (SIMPLEQ_EMPTY(&deltas->entries))
  		return got_error(GOT_ERR_BAD_DELTA_CHAIN);
  
  	err = get_delta_chain_max_size(&max_size, deltas);
  	if (err)
  		return err;
  	accum_buf = malloc(max_size);
  	if (accum_buf == NULL)
  		return got_error_from_errno();
  
  	/* Deltas are ordered in ascending order. */
  	SIMPLEQ_FOREACH(delta, &deltas->entries, entry) {
  		if (n == 0) {
  			struct got_pack *pack;
  			size_t base_len;
  
  			/* Plain object types are the delta base. */
  			if (delta->type != GOT_OBJ_TYPE_COMMIT &&
  			    delta->type != GOT_OBJ_TYPE_TREE &&
  			    delta->type != GOT_OBJ_TYPE_BLOB &&
  			    delta->type != GOT_OBJ_TYPE_TAG) {
  				err = got_error(GOT_ERR_BAD_DELTA_CHAIN);
  				goto done;
  			}
  
  			pack = get_cached_pack(delta->path_packfile, repo);
  			if (pack == NULL) {
  				err = got_error(GOT_ERR_BAD_DELTA_CHAIN);
  				goto done;
  			}
  
  			if (fseeko(pack->packfile, delta->offset + delta->tslen,
  			    SEEK_SET) != 0) {
  				err = got_error_from_errno();
  				goto done;
  			}
  			err = got_inflate_to_mem(&base_buf, &base_len,
  			    pack->packfile);
  			if (base_len < max_size) {
  				uint8_t *p;
  				p = reallocarray(base_buf, 1, max_size);
  				if (p == NULL) {
  					err = got_error_from_errno();
  					goto done;
  				}
  				base_buf = p;
  			}
  			if (err)
  				goto done;
  			n++;
  			continue;
  		}
  
  		err = got_delta_apply_in_mem(base_buf, delta->delta_buf,
  		    delta->delta_len, accum_buf, &accum_size);
  		n++;
  		if (err)
  			goto done;
  
  		if (n < deltas->nentries) {
  			/* Accumulated delta becomes the new base. */
  			uint8_t *tmp = accum_buf;
  			accum_buf = base_buf;
  			base_buf = tmp;
  		}
  	}
  
  done:
  	free(base_buf);
  	if (err) {
  		free(accum_buf);
  		*outbuf = NULL;
  		*outlen = 0;
  	} else {
  		*outbuf = accum_buf;
  		*outlen = accum_size;
  	}
  	return err;
  }
  
  const struct got_error *
  got_packfile_extract_object(FILE **f, struct got_object *obj,
      struct got_repository *repo)
  {
  	const struct got_error *err = NULL;
  
  	if ((obj->flags & GOT_OBJ_FLAG_PACKED) == 0)
  		return got_error(GOT_ERR_OBJ_NOT_PACKED);
  
  	*f = got_opentemp();
  	if (*f == NULL) {
  		err = got_error(GOT_ERR_FILE_OPEN);
  		goto done;
  	}
  
  	if ((obj->flags & GOT_OBJ_FLAG_DELTIFIED) == 0) {
  		struct got_pack *pack;
  
  		pack = get_cached_pack(obj->path_packfile, repo);
  		if (pack == NULL) {
  			err = cache_pack(&pack, obj->path_packfile, NULL, repo);
  			if (err)
  				goto done;
  		}
  
  		if (fseeko(pack->packfile, obj->pack_offset, SEEK_SET) != 0) {
  			err = got_error_from_errno();
  			goto done;
  		}
  
  		err = got_inflate_to_file(&obj->size, pack->packfile, *f);
  	} else
  		err = dump_delta_chain_to_file(&obj->size, &obj->deltas, *f,
  		    repo);
  done:
  	if (err && *f) {
  		fclose(*f);
  		*f = NULL;
  	}
  	return err;
  }
  
  const struct got_error *
  got_packfile_extract_object_to_mem(uint8_t **buf, size_t *len,
      struct got_object *obj, struct got_repository *repo)
  {
  	const struct got_error *err = NULL;
  
  	if ((obj->flags & GOT_OBJ_FLAG_PACKED) == 0)
  		return got_error(GOT_ERR_OBJ_NOT_PACKED);
  
  	if ((obj->flags & GOT_OBJ_FLAG_DELTIFIED) == 0) {
  		struct got_pack *pack;
  
  		pack = get_cached_pack(obj->path_packfile, repo);
  		if (pack == NULL) {
  			err = cache_pack(&pack, obj->path_packfile, NULL, repo);
  			if (err)
  				goto done;
  		}
  
  		if (fseeko(pack->packfile, obj->pack_offset, SEEK_SET) != 0) {
  			err = got_error_from_errno();
  			goto done;
  		}
  
  		err = got_inflate_to_mem(buf, len, pack->packfile);
  	} else
  		err = dump_delta_chain_to_mem(buf, len, &obj->deltas, repo);
  done:
  	return err;
  }