Handle PNG warnings as non-fatal

The libpng library may emit warnings when decoding a PNG image, which
are non-fatal. So far we were handling them as errors and stopping the
decoding process, which prevents Dillo from decoding some images. In
particular, images that emit the warning:

> iCCP: known incorrect sRGB profile

Fixes: https://github.com/dillo-browser/dillo/issues/179
Authored-by: dogma

2 files changed, 12 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index f073f389..f2a25047 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -16,6 +16,8 @@ dillo-3.1.1 [not released yet]
    Patches: Rodrigo Arias Mallo <rodarima@gmail.com>
 +- Add HTML tests to the distributed tarball.
    Patches: Matt Jolly
++- Gracefully handle warnings from PNG images.
+   Patches: dogma
 
 dillo-3.1.0 [May 4, 2024]
 
diff --git a/src/png.c b/src/png.c
index fdee20cc..ae3d9f82 100644
--- a/src/png.c
+++ b/src/png.c
@@ -114,6 +114,15 @@ void Png_error_handling(png_structp png_ptr, png_const_charp msg)
    longjmp(png->jmpbuf, 1);
 }
 
+static
+void Png_warning_handler(png_structp png_ptr, png_const_charp msg)
+{
+   DilloPng *png;
+
+   png = png_get_error_ptr(png_ptr);
+   MSG_WARN("Png warning: %s in %s\n", msg, URL_STR(png->url));
+}
+
 static void
 Png_datainfo_callback(png_structp png_ptr, png_infop info_ptr)
 {
@@ -354,7 +363,7 @@ static void Png_write(DilloPng *png, void *Buf, uint_t BufSize)
                            PNG_LIBPNG_VER_STRING,
                            png,
                            (png_error_ptr)Png_error_handling,
-                           (png_error_ptr)Png_error_handling);
+                           (png_error_ptr)Png_warning_handler);
          dReturn_if_fail (png->png_ptr != NULL);
          png->info_ptr = png_create_info_struct(png->png_ptr);
          dReturn_if_fail (png->info_ptr != NULL);