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

   1
   2 /* png-fix-itxt version 1.0.0
   3  *
   4  * Copyright 2013 Glenn Randers-Pehrson
   5  * Last changed in libpng 1.6.3 [July 18, 2013]
   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 #define GETBREAK ((unsigned char)(inchar=getchar())); if (inchar == EOF) break
  38
  39 int
  40 main(void)
  41 {
  42    unsigned int i;
  43    unsigned char buf[MAX_LENGTH];
  44    unsigned long crc;
  45    unsigned char c;
  46    int inchar;
  47
  48 /* Skip 8-byte signature */
  49    for (i=8; i; i--)
  50    {
  51       c=GETBREAK;
  52       putchar(c);
  53    }
  54
  55 if (inchar != EOF)
  56 for (;;)
  57  {
  58    /* Read the length */
  59    unsigned long length; /* must be 32 bits! */
  60    c=GETBREAK; buf[0] = c; length  = c; length <<= 8;
  61    c=GETBREAK; buf[1] = c; length += c; length <<= 8;
  62    c=GETBREAK; buf[2] = c; length += c; length <<= 8;
  63    c=GETBREAK; buf[3] = c; length += c;
  64
  65    /* Read the chunkname */
  66    c=GETBREAK; buf[4] = c;
  67    c=GETBREAK; buf[5] = c;
  68    c=GETBREAK; buf[6] = c;
  69    c=GETBREAK; buf[7] = c;
  70
  71
  72    /* The iTXt chunk type expressed as integers is (105, 84, 88, 116) */
  73    if (buf[4] == 105 && buf[5] == 84 && buf[6] == 88 && buf[7] == 116)
  74    {
  75       if (length >= MAX_LENGTH-12)
  76          break;  /* To do: handle this more gracefully */
  77
  78       /* Initialize the CRC */
  79       crc = crc32(0, Z_NULL, 0);
  80
  81       /* Copy the data bytes */
  82       for (i=8; i < length + 12; i++)
  83       {
  84          c=GETBREAK; buf[i] = c;
  85       }
  86
  87       /* Calculate the CRC */
  88       crc = crc32(crc, buf+4, (uInt)length+4);
  89
  90       for (;;)
  91       {
  92         /* Check the CRC */
  93         if (((crc >> 24) & 0xff) == buf[length+8] &&
  94             ((crc >> 16) & 0xff) == buf[length+9] &&
  95             ((crc >>  8) & 0xff) == buf[length+10] &&
  96             ((crc      ) & 0xff) == buf[length+11])
  97            break;
  98
  99         length++;
 100
 101         if (length >= MAX_LENGTH-12)
 102            break;
 103
 104         c=GETBREAK;
 105         buf[length+11]=c;
 106
 107         /* Update the CRC */
 108         crc = crc32(crc, buf+7+length, 1);
 109       }
 110
 111       /* Update length bytes */
 112       buf[0] = (unsigned char)((length << 24) & 0xff);
 113       buf[1] = (unsigned char)((length << 16) & 0xff);
 114       buf[2] = (unsigned char)((length <<  8) & 0xff);
 115       buf[3] = (unsigned char)((length      ) & 0xff);
 116
 117       /* Write the fixed iTXt chunk (length, name, data, crc) */
 118       for (i=0; i<length+12; i++)
 119          putchar(buf[i]);
 120    }
 121
 122    else
 123    {
 124       /* Copy bytes that were already read (length and chunk name) */
 125       for (i=0; i<8; i++)
 126          putchar(buf[i]);
 127
 128       /* Copy data bytes and CRC */
 129       for (i=8; i< length+12; i++)
 130       {
 131          c=GETBREAK;
 132          putchar(c);
 133       }
 134
 135       if (inchar == EOF)
 136       {
 137          break;
 138       }
 139
 140    /* The IEND chunk type expressed as integers is (73, 69, 78, 68) */
 141       if (buf[4] == 73 && buf[5] == 69 && buf[6] == 78 && buf[7] == 68)
 142          break;
 143    }
 144
 145    if (inchar == EOF)
 146       break;
 147
 148    if (buf[4] == 73 && buf[5] == 69 && buf[6] == 78 && buf[7] == 68)
 149      break;
 150  }
 151
 152  return 0;
 153 }