[libpng17] Added contrib/tools/fixitxt.c, to repair the erroneous iTXt

chunk length written by libpng-1.6.0 and 1.6.1.

ANNOUNCE

@@ -1,5 +1,5 @@
 
-Libpng 1.7.0beta08 - April 14, 2013
+Libpng 1.7.0beta08 - April 17, 2013
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -249,7 +249,9 @@ Version 1.7.0beta07 [April 14, 2013]
     (Flavio Medeiros).
   Corrected length written to uncompressed iTXt chunks (Samuli Suominen).
 
-Version 1.7.0beta08 [April 14, 2013]
+Version 1.7.0beta08 [April 17, 2013]
+  Added contrib/tools/fixitxt.c, to repair the erroneous iTXt chunk length
+    written by libpng-1.6.0 and 1.6.1.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit

CHANGES

@@ -4536,7 +4536,9 @@ Version 1.7.0beta07 [April 14, 2013]
     (Flavio Medeiros).
   Corrected length written to uncompressed iTXt chunks (Samuli Suominen).
 
-Version 1.7.0beta08 [April 14, 2013]
+Version 1.7.0beta08 [April 17, 2013]
+  Added contrib/tools/fixitxt.c, to repair the erroneous iTXt chunk length
+    written by libpng-1.6.0 and 1.6.1.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit

contrib/tools/fixitxt.c

@@ -0,0 +1,140 @@
+#include <stdio.h>
+
+/* fixitxt version 1.0.0
+ *
+ * Copyright 2013 Glenn Randers-Pehrson
+ *
+ * This code is released under the libpng license.
+ * For conditions of distribution and use, see the disclaimer
+ * and license in png.h
+ *
+ * Usage:            
+ *
+ *     fixitxt.exe < bad.png > good.png
+ *
+ * Fixes a PNG file written with libpng-1.6.0 or 1.6.1 that has one or more
+ * uncompressed iTXt chunks.  Assumes that the actual length is greater
+ * than or equal to the value in the length byte, and that the CRC is
+ * correct for the actual length.  This program hunts for the CRC and
+ * adjusts the length byte accordingly.  It is not an error to process a
+ * PNG file that has no iTXt chunks or one that has valid iTXt chunks;
+ * such files will simply be copied.
+ *
+ * Requires zlib (for crc32 and Z_NULL); build with
+ *
+ *     gcc -O -o fixitxt fixitxt.c -lz
+ */
+
+#define GETBREAK c=getchar(); if (c == EOF) break;
+#include <zlib.h>
+
+main()
+{
+   unsigned int i;
+   unsigned char buf[100000];
+   unsigned long crc;
+   unsigned int c;
+
+/* Skip 8-byte signature */
+   for (i=8; i; i--)
+   {
+      c=GETBREAK;
+      putchar(c);
+   }
+
+if (c != EOF)
+for (;;)
+ {
+   /* Read the length */
+   unsigned int length;
+   c=GETBREAK; buf[0] = c;
+   c=GETBREAK; buf[1] = c;
+   c=GETBREAK; buf[2] = c;
+   c=GETBREAK; buf[3] = c;
+
+   length=buf[0]<<24 | buf[1]<<16 | buf[2] << 8 | buf[3];
+   /* Read the chunkname */
+   c=GETBREAK; buf[4] = c;
+   c=GETBREAK; buf[5] = c;
+   c=GETBREAK; buf[6] = c;
+   c=GETBREAK; buf[7] = c;
+
+
+   /* The iTXt chunk type expressed as integers is (105, 84, 88, 116) */
+   if (buf[4] == 105 && buf[5] == 84 && buf[6] == 88 && buf[7] == 116)
+   {
+      /* Initialize the CRC */
+      crc = crc32(0, Z_NULL, 0);
+
+      /* Copy the data bytes */
+      for (i=8; i < length + 12; i++)
+      {
+         c=GETBREAK; buf[i] = c;
+      }
+
+      /* Calculate the CRC */
+      crc = crc32(crc, buf+4, (uInt)length+4);
+
+      for (;;)
+      {
+        /* Check the CRC */
+        if (((crc >> 24) & 0xff) == buf[length+8] &&
+            ((crc >> 16) & 0xff) == buf[length+9] &&
+            ((crc >>  8) & 0xff) == buf[length+10] &&
+            ((crc      ) & 0xff) == buf[length+11])
+           break;
+
+        length++;
+
+        c=GETBREAK;
+        buf[length+11]=c;
+
+        /* Update the CRC */
+        crc = crc32(crc, buf+7+length, 1);
+      }
+
+      /* Update length bytes */
+        buf[0] = (length << 24) & 0xff;
+        buf[1] = (length << 16) & 0xff;
+        buf[2] = (length <<  8) & 0xff;
+        buf[3] = (length      ) & 0xff;
+
+      /* Write the fixed iTXt chunk (length, name, data, crc) */
+      for (i=0; i<length+12; i++)
+         putchar(buf[i]);
+   }
+
+   else
+   {
+      /* Copy bytes that were already read (length and chunk name) */
+      for (i=0; i<8; i++)
+         putchar(buf[i]);
+
+      /* Copy data bytes and CRC */
+      for (i=8; i< length+12; i++)
+      {
+         c=GETBREAK;
+         putchar(c);
+         buf[i]=c;
+      }
+
+      crc = crc32(0, Z_NULL, 0);
+      crc = crc32(crc, buf+4, (uInt)length+4);
+
+      if (c == EOF)
+      {
+         break;
+      }
+
+   /* The IEND chunk type expressed as integers is (73, 69, 78, 68) */
+      if (buf[4] == 73 && buf[5] == 69 && buf[6] == 78 && buf[7] == 68)
+         break;
+   }
+
+   if (c == EOF)
+      break;
+
+   if (buf[4] == 73 && buf[5] == 69 && buf[6] == 78 && buf[7] == 68)
+     break;
+ }
+}