thodg/got/lib/deltify.c

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• Hash : f6027426
  Author :
  Date : 2022-02-12T21:48:46
  

  consistently match size of hash variables to that returned by murmurhash ok millert stsp

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• lib/deltify.c

• /*
   * Copyright (c) 2020 Ori Bernstein
   * Copyright (c) 2021 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/queue.h>
  
  #include <assert.h>
  #include <endian.h>
  #include <errno.h>
  #include <limits.h>
  #include <stdint.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  
  #include "got_error.h"
  
  #include "got_lib_deltify.h"
  #include "murmurhash2.h"
  
  #ifndef MIN
  #define	MIN(_a,_b) ((_a) < (_b) ? (_a) : (_b))
  #endif
  
  /*
   * The algorihm used here is FastCDC (Fast Content-Defined Chunking)
   * https://www.usenix.org/conference/atc16/technical-sessions/presentation/xia
   */
  
  static uint32_t geartab[256] = {
      0x67ed26b7, 0x32da500c, 0x53d0fee0, 0xce387dc7, 0xcd406d90, 0x2e83a4d4,
      0x9fc9a38d, 0xb67259dc, 0xca6b1722, 0x6d2ea08c, 0x235cea2e, 0x3149bb5f,
      0x1beda787, 0x2a6b77d5, 0x2f22d9ac, 0x91fc0544, 0xe413acfa, 0x5a30ff7a,
      0xad6fdde0, 0x444fd0f5, 0x7ad87864, 0x58c5ff05, 0x8d2ec336, 0x2371f853,
      0x550f8572, 0x6aa448dd, 0x7c9ddbcf, 0x95221e14, 0x2a82ec33, 0xcbec5a78,
      0xc6795a0d, 0x243995b7, 0x1c909a2f, 0x4fded51c, 0x635d334b, 0x0e2b9999,
      0x2702968d, 0x856de1d5, 0x3325d60e, 0xeb6a7502, 0xec2a9844, 0x0905835a,
      0xa1820375, 0xa4be5cab, 0x96a6c058, 0x2c2ccd70, 0xba40fce3, 0xd794c46b,
      0x8fbae83e, 0xc3aa7899, 0x3d3ff8ed, 0xa0d42b5b, 0x571c0c97, 0xd2811516,
      0xf7e7b96c, 0x4fd2fcbd, 0xe2fdec94, 0x282cc436, 0x78e8e95c, 0x80a3b613,
      0xcfbee20c, 0xd4a32d1c, 0x2a12ff13, 0x6af82936, 0xe5630258, 0x8efa6a98,
      0x294fb2d1, 0xdeb57086, 0x5f0fddb3, 0xeceda7ce, 0x4c87305f, 0x3a6d3307,
      0xe22d2942, 0x9d060217, 0x1e42ed02, 0xb6f63b52, 0x4367f39f, 0x055cf262,
      0x03a461b2, 0x5ef9e382, 0x386bc03a, 0x2a1e79c7, 0xf1a0058b, 0xd4d2dea9,
      0x56baf37d, 0x5daff6cc, 0xf03a951d, 0xaef7de45, 0xa8f4581e, 0x3960b555,
      0xffbfff6d, 0xbe702a23, 0x8f5b6d6f, 0x061739fb, 0x98696f47, 0x3fd596d4,
      0x151eac6b, 0xa9fcc4f5, 0x69181a12, 0x3ac5a107, 0xb5198fe7, 0x96bcb1da,
      0x1b5ddf8e, 0xc757d650, 0x65865c3a, 0x8fc0a41a, 0x87435536, 0x99eda6f2,
      0x41874794, 0x29cff4e8, 0xb70efd9a, 0x3103f6e7, 0x84d2453b, 0x15a450bd,
      0x74f49af1, 0x60f664b1, 0xa1c86935, 0xfdafbce1, 0xe36353e3, 0x5d9ba739,
      0xbc0559ba, 0x708b0054, 0xd41d808c, 0xb2f31723, 0x9027c41f, 0xf136d165,
      0xb5374b12, 0x9420a6ac, 0x273958b6, 0xe6c2fad0, 0xebdc1f21, 0xfb33af8b,
      0xc71c25cd, 0xe9a2d8e5, 0xbeb38a50, 0xbceb7cc2, 0x4e4e73f0, 0xcd6c251d,
      0xde4c032c, 0x4b04ac30, 0x725b8b21, 0x4eb8c33b, 0x20d07b75, 0x0567aa63,
      0xb56b2bb7, 0xc1f5fd3a, 0xcafd35ca, 0x470dd4da, 0xfe4f94cd, 0xfb8de424,
      0xe8dbcf40, 0xfe50a37a, 0x62db5b5d, 0xf32f4ab6, 0x2c4a8a51, 0x18473dc0,
      0xfe0cbb6e, 0xfe399efd, 0xdf34ecc9, 0x6ccd5055, 0x46097073, 0x139135c2,
      0x721c76f6, 0x1c6a94b4, 0x6eee014d, 0x8a508e02, 0x3da538f5, 0x280d394f,
      0x5248a0c4, 0x3ce94c6c, 0x9a71ad3a, 0x8493dd05, 0xe43f0ab6, 0x18e4ed42,
      0x6c5c0e09, 0x42b06ec9, 0x8d330343, 0xa45b6f59, 0x2a573c0c, 0xd7fd3de6,
      0xeedeab68, 0x5c84dafc, 0xbbd1b1a8, 0xa3ce1ad1, 0x85b70bed, 0xb6add07f,
      0xa531309c, 0x8f8ab852, 0x564de332, 0xeac9ed0c, 0x73da402c, 0x3ec52761,
      0x43af2f4d, 0xd6ff45c8, 0x4c367462, 0xd553bd6a, 0x44724855, 0x3b2aa728,
      0x56e5eb65, 0xeaf16173, 0x33fa42ff, 0xd714bb5d, 0xfbd0a3b9, 0xaf517134,
      0x9416c8cd, 0x534cf94f, 0x548947c2, 0x34193569, 0x32f4389a, 0xfe7028bc,
      0xed73b1ed, 0x9db95770, 0x468e3922, 0x0440c3cd, 0x60059a62, 0x33504562,
      0x2b229fbd, 0x5174dca5, 0xf7028752, 0xd63c6aa8, 0x31276f38, 0x0646721c,
      0xb0191da8, 0xe00e6de0, 0x9eac1a6e, 0x9f7628a5, 0xed6c06ea, 0x0bb8af15,
      0xf119fb12, 0x38693c1c, 0x732bc0fe, 0x84953275, 0xb82ec888, 0x33a4f1b3,
      0x3099835e, 0x028a8782, 0x5fdd51d7, 0xc6c717b3, 0xb06caf71, 0x17c8c111,
      0x61bad754, 0x9fd03061, 0xe09df1af, 0x3bc9eb73, 0x85878413, 0x9889aaf2,
      0x3f5a9e46, 0x42c9f01f, 0x9984a4f4, 0xd5de43cc, 0xd294daed, 0xbecba2d2,
      0xf1f6e72c, 0x5551128a, 0x83af87e2, 0x6f0342ba,
  };
  
  static uint32_t
  hashblk(const unsigned char *p, off_t n)
  {
  	return murmurhash2(p, n, 0x1d7c5ac3);
  }
  
  static const struct got_error *
  addblk(struct got_delta_table *dt, FILE *f, off_t file_offset0, off_t len,
      off_t offset, uint32_t h)
  {
  	const struct got_error *err = NULL;
  	int i;
  	uint8_t buf[GOT_DELTIFY_MAXCHUNK];
  	uint8_t buf2[GOT_DELTIFY_MAXCHUNK];
  	size_t r = 0;
  
  	if (len == 0)
  		return NULL;
  
  	i = h % dt->nalloc;
  	while (dt->blocks[i].len != 0) {
  		/*
  		 * Avoid adding duplicate blocks.
  		 * NB: A matching hash is insufficient for detecting equality.
  		 * The hash can only detect inequality.
  		 */
  		if (len == dt->blocks[i].len && h == dt->blocks[i].hash) {
  			if (r == 0) {
  				if (fseeko(f, file_offset0 + offset, SEEK_SET) == -1)
  					return got_error_from_errno("fseeko");
  				r = fread(buf, 1, len, f);
  				if (r != len) {
  					if (!ferror(f))
  						return NULL;
  					return got_ferror(f, GOT_ERR_IO);
  				}
  			}
  			if (fseeko(f, file_offset0 + dt->blocks[i].offset,
  			    SEEK_SET) == -1)
  				return got_error_from_errno("fseeko");
  			if (fread(buf2, 1, len, f) != len)
  				return got_ferror(f, GOT_ERR_IO);
  			if (memcmp(buf, buf2, len) == 0)
  				return NULL;
  		}
  
  		i = (i + 1) % dt->nalloc;
  	}
  	assert(dt->blocks[i].len == 0);
  	dt->blocks[i].len = len;
  	dt->blocks[i].offset = offset;
  	dt->blocks[i].hash = h;
  	dt->nblocks++;
  	if (dt->nalloc < dt->nblocks + 64) {
  		struct got_delta_block *db;
  		size_t old_size = dt->nalloc;
  		db = dt->blocks;
  		dt->blocks = calloc(dt->nalloc + 64,
  		    sizeof(struct got_delta_block));
  		if (dt->blocks == NULL) {
  			err = got_error_from_errno("calloc");
  			dt->blocks = db;
  			return err;
  		}
  		dt->nalloc += 64;
  		/*
  		 * Recompute all block positions. Hash-based indices of blocks
  		 * in the array depend on the allocated length of the array.
  		 */
  		dt->nblocks = 0;
  		for (i = 0; i < old_size; i++) {
  			if (db[i].len == 0)
  				continue;
  			err = addblk(dt, f, file_offset0, db[i].len,
  			    db[i].offset, db[i].hash);
  			if (err)
  				break;
  		}
  		free(db);
  	}
  
  	return err;
  }
  
  static const struct got_error *
  addblk_mem(struct got_delta_table *dt, uint8_t *data, off_t file_offset0,
      off_t len, off_t offset, uint32_t h)
  {
  	const struct got_error *err = NULL;
  	int i;
  	uint8_t *block1;
  	uint8_t *block2;
  
  	if (len == 0)
  		return NULL;
  
  	i = h % dt->nalloc;
  	while (dt->blocks[i].len != 0) {
  		/*
  		 * Avoid adding duplicate blocks.
  		 * NB: A matching hash is insufficient for detecting equality.
  		 * The hash can only detect inequality.
  		 */
  		if (len == dt->blocks[i].len && h == dt->blocks[i].hash) {
  			block1 = data + file_offset0 + dt->blocks[i].offset;
  			block2 = data + file_offset0 + offset;
  			if (memcmp(block1, block2, len) == 0)
  				return NULL;
  		}
  
  		i = (i + 1) % dt->nalloc;
  	}
  	assert(dt->blocks[i].len == 0);
  	dt->blocks[i].len = len;
  	dt->blocks[i].offset = offset;
  	dt->blocks[i].hash = h;
  	dt->nblocks++;
  	if (dt->nalloc < dt->nblocks + 64) {
  		struct got_delta_block *db;
  		size_t old_size = dt->nalloc;
  		db = dt->blocks;
  		dt->blocks = calloc(dt->nalloc + 64,
  		    sizeof(struct got_delta_block));
  		if (dt->blocks == NULL) {
  			err = got_error_from_errno("calloc");
  			dt->blocks = db;
  			return err;
  		}
  		dt->nalloc += 64;
  		/*
  		 * Recompute all block positions. Hash-based indices of blocks
  		 * in the array depend on the allocated length of the array.
  		 */
  		dt->nblocks = 0;
  		for (i = 0; i < old_size; i++) {
  			if (db[i].len == 0)
  				continue;
  			err = addblk_mem(dt, data, file_offset0, db[i].len,
  			    db[i].offset, db[i].hash);
  			if (err)
  				break;
  		}
  		free(db);
  	}
  
  	return err;
  }
  
  static const struct got_error *
  lookupblk(struct got_delta_block **block, struct got_delta_table *dt,
      unsigned char *p, off_t len, FILE *basefile, off_t basefile_offset0)
  {
  	int i;
  	uint32_t h;
  	uint8_t buf[GOT_DELTIFY_MAXCHUNK];
  	size_t r;
  
  	*block = NULL;
  
  	h = hashblk(p, len);
  	for (i = h % dt->nalloc; dt->blocks[i].len != 0;
  	     i = (i + 1) % dt->nalloc) {
  		if (dt->blocks[i].hash != h ||
  		    dt->blocks[i].len != len)
  			continue;
  		if (fseeko(basefile, basefile_offset0 + dt->blocks[i].offset,
  		    SEEK_SET) == -1)
  			return got_error_from_errno("fseeko");
  		r = fread(buf, 1, len, basefile);
  		if (r != len)
  			return got_ferror(basefile, GOT_ERR_IO);
  		if (memcmp(p, buf, len) == 0) {
  			*block = &dt->blocks[i];
  			break;
  		}
  	}
  	return NULL;
  }
  
  static const struct got_error *
  lookupblk_mem(struct got_delta_block **block, struct got_delta_table *dt,
      unsigned char *p, off_t len, uint8_t *basedata, off_t basefile_offset0)
  {
  	int i;
  	uint32_t h;
  	uint8_t *b;
  
  	*block = NULL;
  
  	h = hashblk(p, len);
  	for (i = h % dt->nalloc; dt->blocks[i].len != 0;
  	     i = (i + 1) % dt->nalloc) {
  		if (dt->blocks[i].hash != h ||
  		    dt->blocks[i].len != len)
  			continue;
  		b = basedata + basefile_offset0 + dt->blocks[i].offset;
  		if (memcmp(p, b, len) == 0) {
  			*block = &dt->blocks[i];
  			break;
  		}
  	}
  	return NULL;
  }
  
  static const struct got_error *
  nextblk(uint8_t *buf, off_t *blocklen, FILE *f)
  {
  	uint32_t gh;
  	const unsigned char *p;
  	size_t r;
  	off_t pos = ftello(f);
  
  	*blocklen = 0;
  
  	r = fread(buf, 1, GOT_DELTIFY_MAXCHUNK, f);
  	if (r == 0 && ferror(f))
  		return got_ferror(f, GOT_ERR_IO);
  	if (r < GOT_DELTIFY_MINCHUNK)
  		return NULL; /* no more delta-worthy blocks left */
  
  	/* Got a deltifiable block. Find the split-point where it ends. */
  	p = buf + GOT_DELTIFY_MINCHUNK;
  	gh = 0;
  	while (p != buf + r) {
  		gh = (gh << 1) + geartab[*p++];
  		if ((gh & GOT_DELTIFY_SPLITMASK) == 0)
  			break;
  	}
  
  	*blocklen = (p - buf);
  	if (fseeko(f, pos + *blocklen, SEEK_SET) == -1)
  		return got_error_from_errno("fseeko");
  
  	return NULL;
  }
  
  static const struct got_error *
  nextblk_mem(off_t *blocklen, uint8_t *data, off_t fileoffset, off_t filesize)
  {
  	uint32_t gh;
  	const unsigned char *p;
  
  	*blocklen = 0;
  
  	if (fileoffset >= filesize ||
  	    filesize - fileoffset < GOT_DELTIFY_MINCHUNK)
  		return NULL; /* no more delta-worthy blocks left */
  
  	/* Got a deltifiable block. Find the split-point where it ends. */
  	p = data + fileoffset + GOT_DELTIFY_MINCHUNK;
  	gh = 0;
  	while (p != data + MIN(fileoffset + GOT_DELTIFY_MAXCHUNK, filesize)) {
  		gh = (gh << 1) + geartab[*p++];
  		if ((gh & GOT_DELTIFY_SPLITMASK) == 0)
  			break;
  	}
  
  	*blocklen = (p - (data + fileoffset));
  	return NULL;
  }
  
  const struct got_error *
  got_deltify_init(struct got_delta_table **dt, FILE *f, off_t fileoffset,
      off_t filesize)
  {
  	const struct got_error *err = NULL;
  	uint32_t h;
  	const off_t offset0 = fileoffset;
  
  	*dt = calloc(1, sizeof(**dt));
  	if (*dt == NULL)
  		return got_error_from_errno("calloc");
  
  	(*dt)->nblocks = 0;
  	(*dt)->nalloc = 128;
  	(*dt)->blocks = calloc((*dt)->nalloc, sizeof(struct got_delta_block));
  	if ((*dt)->blocks == NULL) {
  		err = got_error_from_errno("calloc");
  		goto done;
  	}
  
  	if (fseeko(f, fileoffset, SEEK_SET) == -1)
  		return got_error_from_errno("fseeko");
  
  	while (fileoffset < filesize) {
  		uint8_t buf[GOT_DELTIFY_MAXCHUNK];
  		off_t blocklen;
  		err = nextblk(buf, &blocklen, f);
  		if (err)
  			goto done;
  		if (blocklen == 0)
  			break;
  		h = hashblk(buf, blocklen);
  		err = addblk(*dt, f, offset0, blocklen,
  		    fileoffset - offset0, h);
  		if (err)
  			goto done;
  		fileoffset += blocklen;
  		if (fseeko(f, fileoffset, SEEK_SET) == -1)
  			return got_error_from_errno("fseeko");
  	}
  done:
  	if (err) {
  		free((*dt)->blocks);
  		free(*dt);
  		*dt = NULL;
  	}
  
  	return err;
  }
  
  const struct got_error *
  got_deltify_init_mem(struct got_delta_table **dt, uint8_t *data,
      off_t fileoffset, off_t filesize)
  {
  	const struct got_error *err = NULL;
  	uint32_t h;
  	const off_t offset0 = fileoffset;
  
  	*dt = calloc(1, sizeof(**dt));
  	if (*dt == NULL)
  		return got_error_from_errno("calloc");
  
  	(*dt)->nblocks = 0;
  	(*dt)->nalloc = 128;
  	(*dt)->blocks = calloc((*dt)->nalloc, sizeof(struct got_delta_block));
  	if ((*dt)->blocks == NULL) {
  		err = got_error_from_errno("calloc");
  		goto done;
  	}
  
  	while (fileoffset < filesize) {
  		off_t blocklen;
  		err = nextblk_mem(&blocklen, data, fileoffset, filesize);
  		if (err)
  			goto done;
  		if (blocklen == 0)
  			break;
  		h = hashblk(data + fileoffset, blocklen);
  		err = addblk_mem(*dt, data, offset0, blocklen,
  		    fileoffset - offset0, h);
  		if (err)
  			goto done;
  		fileoffset += blocklen;
  	}
  done:
  	if (err) {
  		free((*dt)->blocks);
  		free(*dt);
  		*dt = NULL;
  	}
  
  	return err;
  }
  
  void
  got_deltify_free(struct got_delta_table *dt)
  {
  	if (dt == NULL)
  		return;
  	free(dt->blocks);
  	free(dt);
  }
  
  static const struct got_error *
  emitdelta(struct got_delta_instruction **deltas, size_t *nalloc, int *ndeltas,
      const size_t alloc_chunk_size, int copy, off_t offset, off_t len)
  {
  	struct got_delta_instruction *d, *p;
  
  	if (*nalloc < *ndeltas + alloc_chunk_size) {
  		p = reallocarray(*deltas, *nalloc + alloc_chunk_size,
  		    sizeof(struct got_delta_instruction));
  		if (p == NULL)
  			return got_error_from_errno("reallocarray");
  		*deltas = p;
  		*nalloc += alloc_chunk_size;
  	}
  	*ndeltas += 1;
  	d = &(*deltas)[*ndeltas - 1];
  	d->copy = copy;
  	d->offset = offset;
  	d->len = len;
  	return NULL;
  }
  
  static const struct got_error *
  stretchblk(FILE *basefile, off_t base_offset0, struct got_delta_block *block,
      FILE *f, off_t filesize, off_t *blocklen)
  {
  	uint8_t basebuf[GOT_DELTIFY_MAXCHUNK], buf[GOT_DELTIFY_MAXCHUNK];
  	size_t base_r, r, i;
  	int buf_equal = 1;
  
  	if (fseeko(basefile, base_offset0 + block->offset + *blocklen,
  	    SEEK_SET) == -1)
  		return got_error_from_errno("fseeko");
  
  	while (buf_equal && *blocklen < (1 << 24) - 1) {
  		base_r = fread(basebuf, 1, sizeof(basebuf), basefile);
  		if (base_r == 0) {
  			if (ferror(basefile))
  				return got_ferror(basefile, GOT_ERR_IO);
  			break;
  		}
  		r = fread(buf, 1, sizeof(buf), f);
  		if (r == 0) {
  			if (ferror(f))
  				return got_ferror(f, GOT_ERR_IO);
  			break;
  		}
  		for (i = 0; i < MIN(base_r, r); i++) {
  			if (buf[i] != basebuf[i]) {
  				buf_equal = 0;
  				break;
  			}
  			(*blocklen)++;
  		}
  	}
  
  	return NULL;
  }
  
  static const struct got_error *
  stretchblk_file_mem(uint8_t *basedata, off_t base_offset0, off_t basefile_size,
       struct got_delta_block *block, FILE *f, off_t filesize, off_t *blocklen)
  {
  	uint8_t buf[GOT_DELTIFY_MAXCHUNK];
  	size_t r, i;
  	int buf_equal = 1;
  	off_t base_offset = base_offset0 + block->offset + *blocklen;
  
  	if (base_offset > basefile_size) {
  		return got_error_fmt(GOT_ERR_RANGE,
  		    "read beyond the size of delta base at offset %llu",
  		    base_offset);
  	}
  
  	while (buf_equal && *blocklen < (1 << 24) - 1) {
  		if (base_offset + *blocklen >= basefile_size)
  			break;
  		r = fread(buf, 1, sizeof(buf), f);
  		if (r == 0) {
  			if (ferror(f))
  				return got_ferror(f, GOT_ERR_IO);
  			break;
  		}
  		for (i = 0; i < MIN(basefile_size - base_offset, r); i++) {
  			if (buf[i] != *(basedata + base_offset + i)) {
  				buf_equal = 0;
  				break;
  			}
  			(*blocklen)++;
  		}
  	}
  
  	return NULL;
  }
  
  static const struct got_error *
  stretchblk_mem_file(FILE *basefile, off_t base_offset0,
      struct got_delta_block *block, uint8_t *data, off_t fileoffset,
      off_t filesize, off_t *blocklen)
  {
  	uint8_t basebuf[GOT_DELTIFY_MAXCHUNK];
  	size_t base_r, i;
  	int buf_equal = 1;
  
  	if (fileoffset > filesize) {
  		return got_error_fmt(GOT_ERR_RANGE,
  		    "read beyond the size of deltify file at offset %llu",
  		    fileoffset);
  	}
  
  	if (fseeko(basefile, base_offset0 + block->offset + *blocklen,
  	    SEEK_SET) == -1)
  		return got_error_from_errno("fseeko");
  
  	while (buf_equal && *blocklen < (1 << 24) - 1) {
  		if (fileoffset + *blocklen >= filesize)
  			break;
  		base_r = fread(basebuf, 1, sizeof(basebuf), basefile);
  		if (base_r == 0) {
  			if (ferror(basefile))
  				return got_ferror(basefile, GOT_ERR_IO);
  			break;
  		}
  		for (i = 0; i < MIN(base_r, filesize - fileoffset); i++) {
  			if (*(data + fileoffset + i) != basebuf[i]) {
  				buf_equal = 0;
  				break;
  			}
  			(*blocklen)++;
  		}
  	}
  
  	return NULL;
  }
  
  static const struct got_error *
  stretchblk_mem_mem(uint8_t *basedata, off_t base_offset0, off_t basefile_size,
      struct got_delta_block *block, uint8_t *data, off_t fileoffset,
      off_t filesize, off_t *blocklen)
  {
  	off_t i, maxlen;
  	off_t base_offset = base_offset0 + block->offset + *blocklen;
  	uint8_t *p, *q;
  
  	if (base_offset > basefile_size) {
  		return got_error_fmt(GOT_ERR_RANGE,
  		    "read beyond the size of delta base at offset %llu",
  		    base_offset);
  	}
  
  	if (fileoffset > filesize) {
  		return got_error_fmt(GOT_ERR_RANGE,
  		    "read beyond the size of deltify file at offset %llu",
  		    fileoffset);
  	}
  
  	p = data + fileoffset;
  	q = basedata + base_offset;
  	maxlen = MIN(basefile_size - base_offset, filesize - fileoffset);
  	for (i = 0; i < maxlen && *blocklen < (1 << 24) - 1; i++) {
  		if (p[i] != q[i])
  			break;
  		(*blocklen)++;
  	}
  
  	return NULL;
  }
  
  const struct got_error *
  got_deltify(struct got_delta_instruction **deltas, int *ndeltas,
      FILE *f, off_t fileoffset, off_t filesize,
      struct got_delta_table *dt, FILE *basefile,
      off_t basefile_offset0, off_t basefile_size)
  {
  	const struct got_error *err = NULL;
  	const off_t offset0 = fileoffset;
  	size_t nalloc = 0;
  	const size_t alloc_chunk_size = 64;
  
  	*deltas = NULL;
  	*ndeltas = 0;
  
  	/*
  	 * offset0 indicates where data to be deltified begins.
  	 * For example, we want to avoid deltifying a Git object header at
  	 * the beginning of the file.
  	 */
  	if (fseeko(f, offset0, SEEK_SET) == -1)
  		return got_error_from_errno("fseeko");
  
  	*deltas = reallocarray(NULL, alloc_chunk_size,
  	    sizeof(struct got_delta_instruction));
  	if (*deltas == NULL)
  		return got_error_from_errno("reallocarray");
  	nalloc = alloc_chunk_size;
  
  	while (fileoffset < filesize) {
  		uint8_t buf[GOT_DELTIFY_MAXCHUNK];
  		off_t blocklen;
  		struct got_delta_block *block;
  		err = nextblk(buf, &blocklen, f);
  		if (err)
  			break;
  		if (blocklen == 0) {
  			/* Source remainder from the file itself. */
  			if (fileoffset < filesize) {
  				err = emitdelta(deltas, &nalloc, ndeltas,
  				    alloc_chunk_size, 0, fileoffset - offset0,
  				    filesize - fileoffset);
  			}
  			break;
  		}
  		err = lookupblk(&block, dt, buf, blocklen, basefile,
  		    basefile_offset0);
  		if (err)
  			break;
  		if (block != NULL) {
  			/*
  			 * We have found a matching block in the delta base.
  			 * Attempt to stretch the block as far as possible and
  			 * generate a copy instruction.
  			 */
  			err = stretchblk(basefile, basefile_offset0, block,
  			    f, filesize, &blocklen);
  			if (err)
  				break;
  			err = emitdelta(deltas, &nalloc, ndeltas,
  			    alloc_chunk_size, 1, block->offset, blocklen);
  			if (err)
  				break;
  		} else {
  			/*
  			 * No match.
  			 * This block needs to be sourced from the file itself.
  			 */
  			err = emitdelta(deltas, &nalloc, ndeltas,
  			    alloc_chunk_size, 0, fileoffset - offset0, blocklen);
  			if (err)
  				break;
  		}
  		fileoffset += blocklen;
  		if (fseeko(f, fileoffset, SEEK_SET) == -1) {
  			err = got_error_from_errno("fseeko");
  			break;
  		}
  	}
  
  	if (err) {
  		free(*deltas);
  		*deltas = NULL;
  		*ndeltas = 0;
  	}
  	return err;
  }
  
  const struct got_error *
  got_deltify_file_mem(struct got_delta_instruction **deltas, int *ndeltas,
      FILE *f, off_t fileoffset, off_t filesize,
      struct got_delta_table *dt, uint8_t *basedata,
      off_t basefile_offset0, off_t basefile_size)
  {
  	const struct got_error *err = NULL;
  	const off_t offset0 = fileoffset;
  	size_t nalloc = 0;
  	const size_t alloc_chunk_size = 64;
  
  	*deltas = NULL;
  	*ndeltas = 0;
  
  	/*
  	 * offset0 indicates where data to be deltified begins.
  	 * For example, we want to avoid deltifying a Git object header at
  	 * the beginning of the file.
  	 */
  	if (fseeko(f, offset0, SEEK_SET) == -1)
  		return got_error_from_errno("fseeko");
  
  	*deltas = reallocarray(NULL, alloc_chunk_size,
  	    sizeof(struct got_delta_instruction));
  	if (*deltas == NULL)
  		return got_error_from_errno("reallocarray");
  	nalloc = alloc_chunk_size;
  
  	while (fileoffset < filesize) {
  		uint8_t buf[GOT_DELTIFY_MAXCHUNK];
  		off_t blocklen;
  		struct got_delta_block *block;
  		err = nextblk(buf, &blocklen, f);
  		if (err)
  			break;
  		if (blocklen == 0) {
  			/* Source remainder from the file itself. */
  			if (fileoffset < filesize) {
  				err = emitdelta(deltas, &nalloc, ndeltas,
  				    alloc_chunk_size, 0, fileoffset - offset0,
  				    filesize - fileoffset);
  			}
  			break;
  		}
  		err = lookupblk_mem(&block, dt, buf, blocklen, basedata,
  		    basefile_offset0);
  		if (err)
  			break;
  		if (block != NULL) {
  			/*
  			 * We have found a matching block in the delta base.
  			 * Attempt to stretch the block as far as possible and
  			 * generate a copy instruction.
  			 */
  			err = stretchblk_file_mem(basedata, basefile_offset0,
  			    basefile_size, block, f, filesize, &blocklen);
  			if (err)
  				break;
  			err = emitdelta(deltas, &nalloc, ndeltas,
  			    alloc_chunk_size, 1, block->offset, blocklen);
  			if (err)
  				break;
  		} else {
  			/*
  			 * No match.
  			 * This block needs to be sourced from the file itself.
  			 */
  			err = emitdelta(deltas, &nalloc, ndeltas,
  			    alloc_chunk_size, 0, fileoffset - offset0, blocklen);
  			if (err)
  				break;
  		}
  		fileoffset += blocklen;
  		if (fseeko(f, fileoffset, SEEK_SET) == -1) {
  			err = got_error_from_errno("fseeko");
  			break;
  		}
  	}
  
  	if (err) {
  		free(*deltas);
  		*deltas = NULL;
  		*ndeltas = 0;
  	}
  	return err;
  }
  
  const struct got_error *
  got_deltify_mem_file(struct got_delta_instruction **deltas, int *ndeltas,
      uint8_t *data, off_t fileoffset, off_t filesize,
      struct got_delta_table *dt, FILE *basefile,
      off_t basefile_offset0, off_t basefile_size)
  {
  	const struct got_error *err = NULL;
  	const off_t offset0 = fileoffset;
  	size_t nalloc = 0;
  	const size_t alloc_chunk_size = 64;
  
  	*deltas = NULL;
  	*ndeltas = 0;
  
  	*deltas = reallocarray(NULL, alloc_chunk_size,
  	    sizeof(struct got_delta_instruction));
  	if (*deltas == NULL)
  		return got_error_from_errno("reallocarray");
  	nalloc = alloc_chunk_size;
  
  	while (fileoffset < filesize) {
  		off_t blocklen;
  		struct got_delta_block *block;
  		err = nextblk_mem(&blocklen, data, fileoffset, filesize);
  		if (err)
  			break;
  		if (blocklen == 0) {
  			/* Source remainder from the file itself. */
  			if (fileoffset < filesize) {
  				err = emitdelta(deltas, &nalloc, ndeltas,
  				    alloc_chunk_size, 0, fileoffset - offset0,
  				    filesize - fileoffset);
  			}
  			break;
  		}
  		err = lookupblk(&block, dt, data + fileoffset, blocklen,
  		    basefile, basefile_offset0);
  		if (err)
  			break;
  		if (block != NULL) {
  			/*
  			 * We have found a matching block in the delta base.
  			 * Attempt to stretch the block as far as possible and
  			 * generate a copy instruction.
  			 */
  			err = stretchblk_mem_file(basefile, basefile_offset0,
  			    block, data, fileoffset + blocklen, filesize,
  			    &blocklen);
  			if (err)
  				break;
  			err = emitdelta(deltas, &nalloc, ndeltas,
  			    alloc_chunk_size, 1, block->offset, blocklen);
  			if (err)
  				break;
  		} else {
  			/*
  			 * No match.
  			 * This block needs to be sourced from the file itself.
  			 */
  			err = emitdelta(deltas, &nalloc, ndeltas,
  			    alloc_chunk_size, 0, fileoffset - offset0, blocklen);
  			if (err)
  				break;
  		}
  		fileoffset += blocklen;
  	}
  
  	if (err) {
  		free(*deltas);
  		*deltas = NULL;
  		*ndeltas = 0;
  	}
  	return err;
  }
  
  const struct got_error *
  got_deltify_mem_mem(struct got_delta_instruction **deltas, int *ndeltas,
      uint8_t *data, off_t fileoffset, off_t filesize,
      struct got_delta_table *dt, uint8_t *basedata,
      off_t basefile_offset0, off_t basefile_size)
  {
  	const struct got_error *err = NULL;
  	const off_t offset0 = fileoffset;
  	size_t nalloc = 0;
  	const size_t alloc_chunk_size = 64;
  
  	*deltas = NULL;
  	*ndeltas = 0;
  
  	*deltas = reallocarray(NULL, alloc_chunk_size,
  	    sizeof(struct got_delta_instruction));
  	if (*deltas == NULL)
  		return got_error_from_errno("reallocarray");
  	nalloc = alloc_chunk_size;
  
  	while (fileoffset < filesize) {
  		off_t blocklen;
  		struct got_delta_block *block;
  		err = nextblk_mem(&blocklen, data, fileoffset, filesize);
  		if (err)
  			break;
  		if (blocklen == 0) {
  			/* Source remainder from the file itself. */
  			if (fileoffset < filesize) {
  				err = emitdelta(deltas, &nalloc, ndeltas,
  				    alloc_chunk_size, 0, fileoffset - offset0,
  				    filesize - fileoffset);
  			}
  			break;
  		}
  		err = lookupblk_mem(&block, dt, data + fileoffset, blocklen,
  		    basedata, basefile_offset0);
  		if (err)
  			break;
  		if (block != NULL) {
  			/*
  			 * We have found a matching block in the delta base.
  			 * Attempt to stretch the block as far as possible and
  			 * generate a copy instruction.
  			 */
  			err = stretchblk_mem_mem(basedata, basefile_offset0,
  			    basefile_size, block, data, fileoffset + blocklen,
  			    filesize, &blocklen);
  			if (err)
  				break;
  			err = emitdelta(deltas, &nalloc, ndeltas,
  			    alloc_chunk_size, 1, block->offset, blocklen);
  			if (err)
  				break;
  		} else {
  			/*
  			 * No match.
  			 * This block needs to be sourced from the file itself.
  			 */
  			err = emitdelta(deltas, &nalloc, ndeltas,
  			    alloc_chunk_size, 0, fileoffset - offset0, blocklen);
  			if (err)
  				break;
  		}
  		fileoffset += blocklen;
  	}
  
  	if (err) {
  		free(*deltas);
  		*deltas = NULL;
  		*ndeltas = 0;
  	}
  	return err;
  }
  

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