On Sun, 16 Jun 2013, Michalis Kamburelis wrote:
Michael Van Canneyt wrote:
If an implementation of Read does not return the requested data when in
fact it is available, then the implementation of Read is broken.
I guess it depends how do you interpret TStream.Read documentation...
http://www.freepascal.org/docs-html/rtl/classes/tstream.read.html does not
explicitly say that TStream.Read returns less than requested Count *only when
the stream ends*. And I saw a lot of code working under the assumption that
only when TStream.Read returned zero -> then the stream ended.
If you want to put stricter requirements on TStream.Read, I suggest to update
the docs to explicitly say this.
Your proposal is a quick and dirty hack that does not address the real
problem.
Whether it's a hack or not really depends on your definition of "correct
TStream.Read implementation".
In my opinion, if you ask Count bytes, TStream should try to get the requested number of bytes,
only failing if they really are not available.
My proposal is also a single solution that will make ReadBuffer correct for
all the eternity.
Your proposal means that we have to fix THandleStream (Read and Write), which
is definitely broken according to your requirements. Then we check
TGZFileStream (I'm not sure whether it's already correct; it is definitely
incorrect if gzRead in PasZLib is equivalent to gzRead inside C Zlib). And
then every time I use another TStream implementation I'll have to check
whether it's Read method is trying hard enough. TStream.Read that doesn't try
hard enough is a very sneaky bug, since it will often work by accident (if
reading small enough data).
Meanwhile, someone pointed out to me that at least in Delphi XE2, TStream.ReadBuffer
has been changed to do a loop anyway. I guess we'll have to follow suit, even if I
don't think it is correct :(
So please post a bugreport (with or without) patch on the bugtracker, you can
assign it to me.
Michael.
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