[Openexr-devel] Memory-Mapped files and DWA compression

[darby johnston]

Hi all,
I was implementing memory-mapped loading of OpenEXR images for my viewer and noticed a crash when loading DWA compressed files. Taking a look at the code it seems that DwaCompressor::uncompress() is writing to the const char * data that is passed to it:
int
DwaCompressor::uncompress
    (const char *inPtr,
     int inSize,
     IMATH_NAMESPACE::Box2i range,
     const char *&outPtr)
{    ...
        Int64      *dst =  (((Int64 *)inPtr) + i);
        const char *src = (char *)(((Int64 *)inPtr) + i);

        Xdr::read<CharPtrIO> (src, *dst);    ...
}
When the passed data is memory-mapped as read-only this causes a memory access violation on Windows. Copying the data to a temporary buffer and then doing the Xdr conversion fixes the issue; the performance difference should be negligible since this is only for some header data, probably less than 100 bytes. If this seems like an OK change I've attached a patch or can also submit a git pull request.

Thanks, Darby