Prototype of RAW decoding in Skia.

src/codec/SkCodec.cpp

Index: src/codec/SkCodec.cpp
diff --git a/src/codec/SkCodec.cpp b/src/codec/SkCodec.cpp
index 87a7ded7dd6bd2e0c0a6da19de1d9782a50553c3..73c2165fe3311268194928439c6764d782804b1f 100644
--- a/src/codec/SkCodec.cpp
+++ b/src/codec/SkCodec.cpp
@@ -16,6 +16,9 @@
 #if !defined(GOOGLE3)
 #include "SkJpegCodec.h"
 #endif
+#ifdef SK_CODEC_DECODES_RAW
+#include "SkRawCodec.h"
+#endif
 #include "SkStream.h"
 #include "SkWebpCodec.h"
 
@@ -85,6 +88,13 @@ SkCodec* SkCodec::NewFromStream(SkStream* stream,
                 break;
             }
         }
+
+        // Try to treat the input as RAW if all the other checks failed.
+        if (!codec && streamDeleter) {

[msarett, 2016/01/07 16:39:11]

We check streamDeleter here because one of the other codecs may take ownership,
fail to create a codec (return NULL), and then delete the stream?

I think this is correct, just want to make sure I understand.

[scroggo, 2016/01/07 20:57:42]

I think this is redundant.

If codec is NULL, streamDeleter should not be NULL. Maybe this should
SkASSERT(streamDeleter) instead?

[yujieqin, 2016/01/08 14:00:12]

msarett@, yes, we run into once this issue that other codec.NewFromStream()
already took the ownership but failed to create the codec. In this case, the
(codec == nullptr) and (streamDeleter == nullptr).

scroggo@, do you think the case mentioned above is actually an assert? Just
asking because I think the current skia does not treat this case as an
assertion.

[scroggo, 2016/01/08 17:12:25]

My mistake. It is possible that the first few bytes told us it was a BMP (for
example), so we try to create a BMP codec. But the stream fails shortly
thereafter. BMP still deletes the stream (since we don't need to check if it's
something else), so both are NULL.

But I think you can make it the other way around:

if (streamDeleter) {
    SkASSERT(!codec);
    codec.reset(...);
}

If there is still a stream, to use, there should not be a codec already created.
If there was, we should already have a problem of use after free (streamDeleter
deletes it before codec keeps reading it).

+#ifdef SK_CODEC_DECODES_RAW

[msarett, 2016/01/07 16:39:11]

nit: Can we surround the entire if statement with the #ifdef?

[yujieqin, 2016/01/08 14:00:12]

Done.

+            codec.reset(SkRawCodec::NewFromStream(streamDeleter.detach()));
+#endif
+        }
     }
 
     // Set the max size at 128 megapixels (512 MB for kN32).