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c23841c833
The git__delta_apply() function can be used to apply a Git style delta, such as those used in pack files or in git patch files, to recover the original object stream. Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
105 lines
2.3 KiB
C
105 lines
2.3 KiB
C
#include "common.h"
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#include "git/odb.h"
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/*
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* This file was heavily cribbed from BinaryDelta.java in JGit, which
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* itself was heavily cribbed from <code>patch-delta.c</code> in the
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* GIT project. The original delta patching code was written by
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* Nicolas Pitre <nico@cam.org>.
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*/
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static size_t hdr_sz(
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const unsigned char **delta,
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const unsigned char *end)
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{
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const unsigned char *d = *delta;
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size_t r = 0;
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unsigned int c, shift = 0;
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do {
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if (d == end)
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return -1;
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c = *d++;
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r |= (c & 0x7f) << shift;
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shift += 7;
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} while (c & 0x80);
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*delta = d;
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return r;
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}
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int git__delta_apply(
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git_obj *out,
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const unsigned char *base,
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size_t base_len,
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const unsigned char *delta,
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size_t delta_len)
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{
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const unsigned char *delta_end = delta + delta_len;
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size_t res_sz;
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unsigned char *res_dp;
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/* Check that the base size matches the data we were given;
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* if not we would underflow while accessing data from the
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* base object, resulting in data corruption or segfault.
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*/
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if (base_len != hdr_sz(&delta, delta_end))
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return GIT_ERROR;
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res_sz = hdr_sz(&delta, delta_end);
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if (!(res_dp = git__malloc(res_sz + 1)))
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return GIT_ERROR;
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res_dp[res_sz] = '\0';
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out->data = res_dp;
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out->len = res_sz;
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while (delta < delta_end) {
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unsigned char cmd = *delta++;
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if (cmd & 0x80) {
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/* cmd is a copy instruction; copy from the base.
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*/
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size_t off = 0, len = 0;
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if (cmd & 0x01) off = *delta++;
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if (cmd & 0x02) off |= *delta++ << 8;
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if (cmd & 0x04) off |= *delta++ << 16;
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if (cmd & 0x08) off |= *delta++ << 24;
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if (cmd & 0x10) len = *delta++;
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if (cmd & 0x20) len |= *delta++ << 8;
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if (cmd & 0x40) len |= *delta++ << 16;
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if (!len) len = 0x10000;
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if (base_len < off + len || res_sz < len)
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goto fail;
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memcpy(res_dp, base + off, len);
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res_dp += len;
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res_sz -= len;
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} else if (cmd) {
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/* cmd is a literal insert instruction; copy from
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* the delta stream itself.
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*/
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if (delta_end - delta < cmd || res_sz < cmd)
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goto fail;
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memcpy(res_dp, delta, cmd);
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delta += cmd;
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res_dp += cmd;
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res_sz -= cmd;
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} else {
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/* cmd == 0 is reserved for future encodings.
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*/
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goto fail;
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}
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}
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if (delta != delta_end || res_sz)
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goto fail;
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return GIT_SUCCESS;
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fail:
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free(out->data);
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out->data = NULL;
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return GIT_ERROR;
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}
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