git/patch-delta.c

   1 /*
   2  * patch-delta.c:
   3  * recreate a buffer from a source and the delta produced by diff-delta.c
   4  *
   5  * (C) 2005 Nicolas Pitre <nico@cam.org>
   6  *
   7  * This code is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include "git-compat-util.h"
  13 #include "delta.h"
  14
  15 void *patch_delta(const void *src_buf, unsigned long src_size,
  16                   const void *delta_buf, unsigned long delta_size,
  17                   unsigned long *dst_size)
  18 {
  19         const unsigned char *data, *top;
  20         unsigned char *dst_buf, *out, cmd;
  21         unsigned long size;
  22
  23         if (delta_size < DELTA_SIZE_MIN)
  24                 return NULL;
  25
  26         data = delta_buf;
  27         top = (const unsigned char *) delta_buf + delta_size;
  28
  29         /* make sure the orig file size matches what we expect */
  30         size = get_delta_hdr_size(&data, top);
  31         if (size != src_size)
  32                 return NULL;
  33
  34         /* now the result size */
  35         size = get_delta_hdr_size(&data, top);
  36         dst_buf = xmalloc(size + 1);
  37         dst_buf[size] = 0;
  38
  39         out = dst_buf;
  40         while (data < top) {
  41                 cmd = *data++;
  42                 if (cmd & 0x80) {
  43                         unsigned long cp_off = 0, cp_size = 0;
  44                         if (cmd & 0x01) cp_off = *data++;
  45                         if (cmd & 0x02) cp_off |= (*data++ << 8);
  46                         if (cmd & 0x04) cp_off |= (*data++ << 16);
  47                         if (cmd & 0x08) cp_off |= (*data++ << 24);
  48                         if (cmd & 0x10) cp_size = *data++;
  49                         if (cmd & 0x20) cp_size |= (*data++ << 8);
  50                         if (cmd & 0x40) cp_size |= (*data++ << 16);
  51                         if (cp_size == 0) cp_size = 0x10000;
  52                         if (cp_off + cp_size < cp_size ||
  53                             cp_off + cp_size > src_size ||
  54                             cp_size > size)
  55                                 break;
  56                         memcpy(out, (char *) src_buf + cp_off, cp_size);
  57                         out += cp_size;
  58                         size -= cp_size;
  59                 } else if (cmd) {
  60                         if (cmd > size)
  61                                 break;
  62                         memcpy(out, data, cmd);
  63                         out += cmd;
  64                         data += cmd;
  65                         size -= cmd;
  66                 } else {
  67                         /*
  68                          * cmd == 0 is reserved for future encoding
  69                          * extensions. In the mean time we must fail when
  70                          * encountering them (might be data corruption).
  71                          */
  72                         error("unexpected delta opcode 0");
  73                         goto bad;
  74                 }
  75         }
  76
  77         /* sanity check */
  78         if (data != top || size != 0) {
  79                 error("delta replay has gone wild");
  80                 bad:
  81                 free(dst_buf);
  82                 return NULL;
  83         }
  84
  85         *dst_size = out - dst_buf;
  86         return dst_buf;
  87 }