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@fluxnic.net>
   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 = xmallocz(size);
  37
  38         out = dst_buf;
  39         while (data < top) {
  40                 cmd = *data++;
  41                 if (cmd & 0x80) {
  42                         unsigned long cp_off = 0, cp_size = 0;
  43 #define PARSE_CP_PARAM(bit, var, shift) do { \
  44                         if (cmd & (bit)) { \
  45                                 if (data >= top) \
  46                                         goto bad_length; \
  47                                 var |= ((unsigned) *data++ << (shift)); \
  48                         } } while (0)
  49                         PARSE_CP_PARAM(0x01, cp_off, 0);
  50                         PARSE_CP_PARAM(0x02, cp_off, 8);
  51                         PARSE_CP_PARAM(0x04, cp_off, 16);
  52                         PARSE_CP_PARAM(0x08, cp_off, 24);
  53                         PARSE_CP_PARAM(0x10, cp_size, 0);
  54                         PARSE_CP_PARAM(0x20, cp_size, 8);
  55                         PARSE_CP_PARAM(0x40, cp_size, 16);
  56 #undef PARSE_CP_PARAM
  57                         if (cp_size == 0) cp_size = 0x10000;
  58                         if (unsigned_add_overflows(cp_off, cp_size) ||
  59                             cp_off + cp_size > src_size ||
  60                             cp_size > size)
  61                                 goto bad_length;
  62                         memcpy(out, (char *) src_buf + cp_off, cp_size);
  63                         out += cp_size;
  64                         size -= cp_size;
  65                 } else if (cmd) {
  66                         if (cmd > size || cmd > top - data)
  67                                 goto bad_length;
  68                         memcpy(out, data, cmd);
  69                         out += cmd;
  70                         data += cmd;
  71                         size -= cmd;
  72                 } else {
  73                         /*
  74                          * cmd == 0 is reserved for future encoding
  75                          * extensions. In the mean time we must fail when
  76                          * encountering them (might be data corruption).
  77                          */
  78                         error("unexpected delta opcode 0");
  79                         goto bad;
  80                 }
  81         }
  82
  83         /* sanity check */
  84         if (data != top || size != 0) {
  85                 bad_length:
  86                 error("delta replay has gone wild");
  87                 bad:
  88                 free(dst_buf);
  89                 return NULL;
  90         }
  91
  92         *dst_size = out - dst_buf;
  93         return dst_buf;
  94 }