thodg/libgit2/src/delta-apply.c

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• Hash : 359fc2d2
  Author :
  Date : 2013-01-08T17:07:25
  

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• src/delta-apply.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 "common.h"
  #include "git2/odb.h"
  #include "delta-apply.h"
  
  /*
   * This file was heavily cribbed from BinaryDelta.java in JGit, which
   * itself was heavily cribbed from <code>patch-delta.c</code> in the
   * GIT project.	The original delta patching code was written by
   * Nicolas Pitre <nico@cam.org>.
   */
  
  static int hdr_sz(
  	size_t *size,
  	const unsigned char **delta,
  	const unsigned char *end)
  {
  	const unsigned char *d = *delta;
  	size_t r = 0;
  	unsigned int c, shift = 0;
  
  	do {
  		if (d == end)
  			return -1;
  		c = *d++;
  		r |= (c & 0x7f) << shift;
  		shift += 7;
  	} while (c & 0x80);
  	*delta = d;
  	*size = r;
  	return 0;
  }
  
  int git__delta_read_header(
  	const unsigned char *delta,
  	size_t delta_len,
  	size_t *base_sz,
  	size_t *res_sz)
  {
  	const unsigned char *delta_end = delta + delta_len;
  	if ((hdr_sz(base_sz, &delta, delta_end) < 0) ||
  	    (hdr_sz(res_sz, &delta, delta_end) < 0))
  		return -1;
  	return 0;
  }
  
  int git__delta_apply(
  	git_rawobj *out,
  	const unsigned char *base,
  	size_t base_len,
  	const unsigned char *delta,
  	size_t delta_len)
  {
  	const unsigned char *delta_end = delta + delta_len;
  	size_t base_sz, res_sz;
  	unsigned char *res_dp;
  
  	/* Check that the base size matches the data we were given;
  	 * if not we would underflow while accessing data from the
  	 * base object, resulting in data corruption or segfault.
  	 */
  	if ((hdr_sz(&base_sz, &delta, delta_end) < 0) || (base_sz != base_len)) {
  		giterr_set(GITERR_INVALID, "Failed to apply delta. Base size does not match given data");
  		return -1;
  	}
  
  	if (hdr_sz(&res_sz, &delta, delta_end) < 0) {
  		giterr_set(GITERR_INVALID, "Failed to apply delta. Base size does not match given data");
  		return -1;
  	}
  
  	res_dp = git__malloc(res_sz + 1);
  	GITERR_CHECK_ALLOC(res_dp);
  
  	res_dp[res_sz] = '\0';
  	out->data = res_dp;
  	out->len = res_sz;
  
  	while (delta < delta_end) {
  		unsigned char cmd = *delta++;
  		if (cmd & 0x80) {
  			/* cmd is a copy instruction; copy from the base.
  			 */
  			size_t off = 0, len = 0;
  
  			if (cmd & 0x01) off = *delta++;
  			if (cmd & 0x02) off |= *delta++ << 8;
  			if (cmd & 0x04) off |= *delta++ << 16;
  			if (cmd & 0x08) off |= *delta++ << 24;
  
  			if (cmd & 0x10) len = *delta++;
  			if (cmd & 0x20) len |= *delta++ << 8;
  			if (cmd & 0x40) len |= *delta++ << 16;
  			if (!len)		len = 0x10000;
  
  			if (base_len < off + len || res_sz < len)
  				goto fail;
  			memcpy(res_dp, base + off, len);
  			res_dp += len;
  			res_sz -= len;
  
  		} else if (cmd) {
  			/* cmd is a literal insert instruction; copy from
  			 * the delta stream itself.
  			 */
  			if (delta_end - delta < cmd || res_sz < cmd)
  				goto fail;
  			memcpy(res_dp, delta, cmd);
  			delta += cmd;
  			res_dp += cmd;
  			res_sz -= cmd;
  
  		} else {
  			/* cmd == 0 is reserved for future encodings.
  			 */
  			goto fail;
  		}
  	}
  
  	if (delta != delta_end || res_sz)
  		goto fail;
  	return 0;
  
  fail:
  	git__free(out->data);
  	out->data = NULL;
  	giterr_set(GITERR_INVALID, "Failed to apply delta");
  	return -1;
  }
  

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