[Webkit-unassigned] [Bug 54420] New: SharedBuffer::buffer() does not do what you think.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=54420

           Summary: SharedBuffer::buffer() does not do what you think.
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: Mac OS X 10.5
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: Page Loading
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: gavinp at chromium.org
                CC: sam at webkit.org, ggaren at apple.com, koivisto at iki.fi,
                    pkasting at google.com, gavinp at chromium.org


On the mac platform, when we build with ENABLE(PURGEABLE_MEMORY), the call SharedBuffer::buffer() can return an empty vector when the SharedBuffer contains no data, but has purgeable memory associated with it.  Some image decoders (JPEGImageDecoder & WEBPImageDecoder) rely on buffer() to get their data, and as a result are actually broken after the original image data has migrated to purgeable memory.  This migration occurs on Images in CachedImage::destroyDecodedData(), which makes JPEG and WEBP images unreconstructable by the JPEGImageDecoder after we've destroyed the decoded data, a very undesirable result, as subsequent decode attempts get a 0,0 image.

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