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 <stdlib.h>
  13 #include <string.h>
  14 #include "delta.h"
  15
  16 void *patch_delta(void *src_buf, unsigned long src_size,
  17                   void *delta_buf, unsigned long delta_size,
  18                   unsigned long *dst_size)
  19 {
  20         const unsigned char *data, *top;
  21         unsigned char *dst_buf, *out, cmd;
  22         unsigned long size;
  23
  24         if (delta_size < DELTA_SIZE_MIN)
  25                 return NULL;
  26
  27         data = delta_buf;
  28         top = delta_buf + delta_size;
  29
  30         /* make sure the orig file size matches what we expect */
  31         size = get_delta_hdr_size(&data, top);
  32         if (size != src_size)
  33                 return NULL;
  34
  35         /* now the result size */
  36         size = get_delta_hdr_size(&data, top);
  37         dst_buf = malloc(size + 1);
  38         if (!dst_buf)
  39                 return NULL;
  40         dst_buf[size] = 0;
  41
  42         out = dst_buf;
  43         while (data < top) {
  44                 cmd = *data++;
  45                 if (cmd & 0x80) {
  46                         unsigned long cp_off = 0, cp_size = 0;
  47                         if (cmd & 0x01) cp_off = *data++;
  48                         if (cmd & 0x02) cp_off |= (*data++ << 8);
  49                         if (cmd & 0x04) cp_off |= (*data++ << 16);
  50                         if (cmd & 0x08) cp_off |= (*data++ << 24);
  51                         if (cmd & 0x10) cp_size = *data++;
  52                         if (cmd & 0x20) cp_size |= (*data++ << 8);
  53                         if (cmd & 0x40) cp_size |= (*data++ << 16);
  54                         if (cp_size == 0) cp_size = 0x10000;
  55                         if (cp_off + cp_size < cp_size ||
  56                             cp_off + cp_size > src_size ||
  57                             cp_size > size)
  58                                 goto bad;
  59                         memcpy(out, src_buf + cp_off, cp_size);
  60                         out += cp_size;
  61                         size -= cp_size;
  62                 } else if (cmd) {
  63                         if (cmd > size)
  64                                 goto bad;
  65                         memcpy(out, data, cmd);
  66                         out += cmd;
  67                         data += cmd;
  68                         size -= cmd;
  69                 } else {
  70                         /*
  71                          * cmd == 0 is reserved for future encoding
  72                          * extensions. In the mean time we must fail when
  73                          * encountering them (might be data corruption).
  74                          */
  75                         goto bad;
  76                 }
  77         }
  78
  79         /* sanity check */
  80         if (data != top || size != 0) {
  81                 bad:
  82                 free(dst_buf);
  83                 return NULL;
  84         }
  85
  86         *dst_size = out - dst_buf;
  87         return dst_buf;
  88 }