debian/patches/libpng16-compat.patch

From: Maks Orlovich <morlovich@google.com>
Subject: libpng1.6 compat: don't call png_read_update_info twice.
 (From libpng docs on changes in 1.6.x:
 "The library now issues an error if the application attempts to set a
 transform after it calls png_read_update_info() or if it attempts to call
 both png_read_update_info() and png_start_read_image() or to call either
 of them more than once.")
Origin: upstream, https://github.com/pagespeed/mod_pagespeed/commit/06fb3c1604b0c89c7db9118e3dcff246cdfd8b84
--- a/src/pagespeed/kernel/image/png_optimizer.cc
+++ b/src/pagespeed/kernel/image/png_optimizer.cc
@@ -974,29 +974,25 @@
   // Set up callbacks for interlacing (progressive) image.
   png_set_interlace_handling(png_ptr);
 
+  if (color_type == PNG_COLOR_TYPE_GRAY_ALPHA ||
+      (color_type == PNG_COLOR_TYPE_GRAY &&
+       png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))) {
+    // Expand Gray_Alpha (and Gray + tRNS which will be turned into
+    // Gray_Alpaha by png_set_expand) to RGBA.
+    png_set_gray_to_rgb(png_ptr);
+  }
+
+  // Expand paletted colors into true RGB triplets.
+  if (color_type == PNG_COLOR_TYPE_PALETTE) {
+    png_set_palette_to_rgb(png_ptr);
+  }
+
   // Update the reader struct after setting the transformations.
   png_read_update_info(png_ptr, info_ptr);
 
   // Get the updated color type.
   color_type = png_get_color_type(png_ptr, info_ptr);
 
-  if (color_type == PNG_COLOR_TYPE_GRAY_ALPHA ||
-      color_type == PNG_COLOR_TYPE_PALETTE) {
-    if (color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
-      // Expand Gray_Alpha to RGBA.
-      png_set_gray_to_rgb(png_ptr);
-    } else {
-      // Expand paletted colors into true RGB triplets.
-      png_set_palette_to_rgb(png_ptr);
-    }
-
-    // Update the reader struct after modifying the transformations.
-    png_read_update_info(png_ptr, info_ptr);
-
-    // Get the updated color type.
-    color_type = png_get_color_type(png_ptr, info_ptr);
-  }
-
   // Determine the pixel format and the number of channels.
   switch (color_type) {
     case PNG_COLOR_TYPE_GRAY:
@@ -1158,7 +1154,7 @@
   }
 
   if (png_image == NULL) {
-    PS_LOG_DFATAL(message_handler_, "Ouput PNG image cannot be NULL.");
+    PS_LOG_DFATAL(message_handler_, "Output PNG image cannot be NULL.");
     return false;
   }
   return true;