workbench/libs/png/contrib/tools/png-fix-itxt.c

   1
   2 /* png-fix-itxt version 1.0.0
   3  *
   4  * Copyright 2015 Glenn Randers-Pehrson
   5  * Last changed in libpng 1.6.18 [July 23, 2015]
   6  *
   7  * This code is released under the libpng license.
   8  * For conditions of distribution and use, see the disclaimer
   9  * and license in png.h
  10  *
  11  * Usage:
  12  *
  13  *     png-fix-itxt.exe < bad.png > good.png
  14  *
  15  * Fixes a PNG file written with libpng-1.6.0 or 1.6.1 that has one or more
  16  * uncompressed iTXt chunks.  Assumes that the actual length is greater
  17  * than or equal to the value in the length byte, and that the CRC is
  18  * correct for the actual length.  This program hunts for the CRC and
  19  * adjusts the length byte accordingly.  It is not an error to process a
  20  * PNG file that has no iTXt chunks or one that has valid iTXt chunks;
  21  * such files will simply be copied.
  22  *
  23  * Requires zlib (for crc32 and Z_NULL); build with
  24  *
  25  *     gcc -O -o png-fix-itxt png-fix-itxt.c -lz
  26  *
  27  * If you need to handle iTXt chunks larger than 500000 kbytes you must
  28  * rebuild png-fix-itxt with a larger values of MAX_LENGTH (or a smaller value
  29  * if you know you will never encounter such huge iTXt chunks).
  30  */
  31
  32 #include <stdio.h>
  33 #include <zlib.h>
  34
  35 #define MAX_LENGTH 500000
  36
  37 /* Read one character (inchar), also return octet (c), break if EOF */
  38 #define GETBREAK inchar=getchar(); \
  39                  c=(inchar & 0xffU);\
  40                  if (inchar != c) break
  41 int
  42 main(void)
  43 {
  44    unsigned int i;
  45    unsigned char buf[MAX_LENGTH];
  46    unsigned long crc;
  47    unsigned char c;
  48    int inchar;
  49
  50 /* Skip 8-byte signature */
  51    for (i=8; i; i--)
  52    {
  53       GETBREAK;
  54       putchar(c);
  55    }
  56
  57 if (inchar == c) /* !EOF */
  58 for (;;)
  59  {
  60    /* Read the length */
  61    unsigned long length; /* must be 32 bits! */
  62    GETBREAK; buf[0] = c; length  = c; length <<= 8;
  63    GETBREAK; buf[1] = c; length += c; length <<= 8;
  64    GETBREAK; buf[2] = c; length += c; length <<= 8;
  65    GETBREAK; buf[3] = c; length += c;
  66
  67    /* Read the chunkname */
  68    GETBREAK; buf[4] = c;
  69    GETBREAK; buf[5] = c;
  70    GETBREAK; buf[6] = c;
  71    GETBREAK; buf[7] = c;
  72
  73
  74    /* The iTXt chunk type expressed as integers is (105, 84, 88, 116) */
  75    if (buf[4] == 105 && buf[5] == 84 && buf[6] == 88 && buf[7] == 116)
  76    {
  77       if (length >= MAX_LENGTH-12)
  78          break;  /* To do: handle this more gracefully */
  79
  80       /* Initialize the CRC */
  81       crc = crc32(0, Z_NULL, 0);
  82
  83       /* Copy the data bytes */
  84       for (i=8; i < length + 12; i++)
  85       {
  86          GETBREAK; buf[i] = c;
  87       }
  88
  89       if (inchar != c) /* EOF */
  90          break;
  91
  92       /* Calculate the CRC */
  93       crc = crc32(crc, buf+4, (uInt)length+4);
  94
  95       for (;;)
  96       {
  97         /* Check the CRC */
  98         if (((crc >> 24) & 0xffU) == buf[length+8] &&
  99             ((crc >> 16) & 0xffU) == buf[length+9] &&
 100             ((crc >>  8) & 0xffU) == buf[length+10] &&
 101             ((crc      ) & 0xffU) == buf[length+11])
 102            break;
 103
 104         length++;
 105
 106         if (length >= MAX_LENGTH-12)
 107            break;
 108
 109         GETBREAK;
 110         buf[length+11] = c;
 111
 112         /* Update the CRC */
 113         crc = crc32(crc, buf+7+length, 1);
 114       }
 115
 116       if (inchar != c) /* EOF */
 117          break;
 118
 119       /* Update length bytes */
 120       buf[0] = (unsigned char)((length >> 24) & 0xffU);
 121       buf[1] = (unsigned char)((length >> 16) & 0xffU);
 122       buf[2] = (unsigned char)((length >>  8) & 0xffU);
 123       buf[3] = (unsigned char)((length      ) & 0xffU);
 124
 125       /* Write the fixed iTXt chunk (length, name, data, crc) */
 126       for (i=0; i<length+12; i++)
 127          putchar(buf[i]);
 128    }
 129
 130    else
 131    {
 132       if (inchar != c) /* EOF */
 133          break;
 134
 135       /* Copy bytes that were already read (length and chunk name) */
 136       for (i=0; i<8; i++)
 137          putchar(buf[i]);
 138
 139       /* Copy data bytes and CRC */
 140       for (i=8; i< length+12; i++)
 141       {
 142          GETBREAK;
 143          putchar(c);
 144       }
 145
 146       if (inchar != c) /* EOF */
 147       {
 148          break;
 149       }
 150
 151    /* The IEND chunk type expressed as integers is (73, 69, 78, 68) */
 152       if (buf[4] == 73 && buf[5] == 69 && buf[6] == 78 && buf[7] == 68)
 153          break;
 154    }
 155
 156    if (inchar != c) /* EOF */
 157       break;
 158
 159    if (buf[4] == 73 && buf[5] == 69 && buf[6] == 78 && buf[7] == 68)
 160      break;
 161  }
 162
 163  return 0;
 164 }