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/*
* Copyright (C) 2009-2011 the libgit2 contributors
*
* 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_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))
return git__throw(GIT_ERROR, "Failed to apply delta. Base size does not match given data");
if (hdr_sz(&res_sz, &delta, delta_end) < 0)
return git__throw(GIT_ERROR, "Failed to apply delta. Base size does not match given data");
if ((res_dp = git__malloc(res_sz + 1)) == NULL)
return GIT_ENOMEM;
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 GIT_SUCCESS;
fail:
free(out->data);
out->data = NULL;
return git__throw(GIT_ERROR, "Failed to apply delta");
}
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