[Webkit-unassigned] [Bug 15971] New: Public GIF image decoder erroneously fails if no new data has come in

[bugzilla-daemon at webkit.org]

http://bugs.webkit.org/show_bug.cgi?id=15971

           Summary: Public GIF image decoder erroneously fails if no new
                    data has come in
           Product: WebKit
           Version: 525+ (Nightly build)
          Platform: PC
        OS/Version: All
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: Images
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: zerodpx at gmail.com


GIFImageReader.cpp (not used by Safari, but used by the Cairo/Qt ports)
erroneously marks GIF decoding as having failed if we ask it to decode when no
new data has come in since the last request to decode.  Instead, this should
just result in doing nothing.

This looks like an artifact of the process of porting from the Mozilla
codebase.  I think in Mozilla's codebase, this function is never called unless
new data has come in, whereas in WebKit, the wrapper code does not guarantee
that.  Therefore, I could fix this by putting a check in the wrapper that
doesn't try to decode when there isn't new data.  But I think making the
underlying decoder fail in this case is wrong, since there's nothing dangerous
about such a call (in fact, if the check in the decoder is removed entirely,
we'd run all the way through the function without doing anything, and return
successfully).  So instead I'm planning to fix this by just changing the
"return false" to "return true" in the beginning of GIFImageReader.cpp:read().

Patch coming in a bit.


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