Make Jpeg decoding more fault resistant.

src/images/SkImageDecoder_libpng.cpp

Index: src/images/SkImageDecoder_libpng.cpp
diff --git a/src/images/SkImageDecoder_libpng.cpp b/src/images/SkImageDecoder_libpng.cpp
index e942f21c787c5e01f6d11ea392309ca6aad562b7..1d37a8c73419d91e67087fea8a551176b911f604 100644
--- a/src/images/SkImageDecoder_libpng.cpp
+++ b/src/images/SkImageDecoder_libpng.cpp
@@ -199,6 +199,9 @@ static bool hasTransparencyInPalette(png_structp png_ptr, png_infop info_ptr) {
     return false;
 }
 
+void do_nothing(png_structp, png_const_charp) { /* do nothing */ }

[scroggo, 2013/10/01 22:04:14]

More specific name?

+
+
 bool SkPNGImageDecoder::onDecodeInit(SkStream* sk_stream, png_structp *png_ptrp,
                                      png_infop *info_ptrp) {
     /* Create and initialize the png_struct with the desired error handler
@@ -212,6 +215,12 @@ bool SkPNGImageDecoder::onDecodeInit(SkStream* sk_stream, png_structp *png_ptrp,
     if (png_ptr == NULL) {
         return false;
     }
+
+    png_error_ptr warning_fn = &do_nothing;

[scroggo, 2013/10/01 22:04:14]

Again, this stuff should only be done

#if !defined(SK_DEBUG)

so that we can still see errors in debug mode (unless you think these are never
errors?).

Also, these statements overwrite the functions set by png_create_read_struct,
above.

+    png_voidp error_ptr = png_get_error_ptr(png_ptr);
+    png_error_ptr error_fn = NULL;  // leave as default
+    png_set_error_fn(png_ptr, error_ptr, error_fn, warning_fn);
+
     *png_ptrp = png_ptr;
 
     /* Allocate/initialize the memory for image information. */
@@ -495,9 +504,13 @@ bool SkPNGImageDecoder::getBitmapConfig(png_structp png_ptr, png_infop info_ptr,
                                                     transpColor->green >> 8,
                                                     transpColor->blue >> 8);
                 } else {
-                    *theTranspColorp = SkPackARGB32(0xFF, transpColor->red,
-                                                    transpColor->green,
-                                                    transpColor->blue);
+                    *theTranspColorp = SkPackARGB32(0xFF,
+                                                    0xFF & (transpColor->red),
+                                                    0xFF & (transpColor->green),
+                                                    0xFF & (transpColor->blue));
+                    /* We apply the mask because in a very small

[scroggo, 2013/10/01 22:04:14]

Shouldn't this go above the code it applies to?

+                       number of corrupt PNGs, (transpColor->red > 255)
+                       and (bitDepth == 8), for certain versions of libpng. */
                 }
             } else {    // gray
                 if (16 == bitDepth) {
@@ -505,9 +518,10 @@ bool SkPNGImageDecoder::getBitmapConfig(png_structp png_ptr, png_infop info_ptr,
                                                     transpColor->gray >> 8,
                                                     transpColor->gray >> 8);
                 } else {
-                    *theTranspColorp = SkPackARGB32(0xFF, transpColor->gray,
-                                                    transpColor->gray,
-                                                    transpColor->gray);
+                    *theTranspColorp = SkPackARGB32(0xFF,

[scroggo, 2013/10/01 22:04:14]

Similar comment explaining the mask?

+                                                    0xFF & (transpColor->gray),
+                                                    0xFF & (transpColor->gray),
+                                                    0xFF & (transpColor->gray));
                 }
             }
         }