> Anyway, this is stuff from highly esteemed Squeakers, and it seems to
> have been tested a bit by other people too. And if we can't trust them
> then... :)

Trust or not - it ain't working correctly ;-( Turns out that the CRC
validation is broken since a) #pastEndRead may return nil so that the crc
update is incorrectly applied to the "same bytes" multiple times and b) some
internal methods quite deliberately set the #position explicitly. What then
happens is that perfectly valid PNGs will raise crc errors.

So CRC checking needs to be added at a lower level - namely right at the
place where the data is decoded. The attached CS (which should go after V7)
addresses these issues.

"Change Set:  ZipCrcTests
Date:   29 February 2004
Author:   Andreas Raab

Integrates CRC validation at the level of InflateStream thereby avoiding
some of the problems when dealing with it in subclasses. With these changes
CRC validation is implicit - when we hit the end of a stream (such as upon
#contents, #upToEnd or similar) the CRC will be validated automatically. If
a missing or wrong crc is encountered a CRCError will be raised. Some tests
are provided to show what is expected if a missing/wrong CRC is encountered.
"

Cheers,
  - Andreas
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