[IronPython] fepy socket seek

Christopher Baus christopher at baus.net
Wed Nov 15 20:09:53 CET 2006

> When you write to file,
> 1. writer is checked for null. If it is, stream is not writable. Raise
> exception.
> 2. string is passed to the writer.
> 3. The writer does appropriate newline translation and write it.
> 4. The number of bytes written, after newline translation, is returned.
> 5. reader is checked for null. If it is, some steps are skipped.
> 6. reader's position is read.
> 7. The number of bytes written is added to the current position.
> 8. reader's position is set to the sum in 7 in order to syncrhonise.
> 6 will cause seek error if stream is not seekable. This doesn't
> happen, because reader implementations maintain position by themselves
> instead of reading underlying stream's position. It does read
> underlying stream's position in the constructor, but only if it's
> seekable. Bah, except PythonBinaryReader, that is.
> So seek error is inevitable, whenever all of following conditions are met:
> 1. write() is called
> 2. underlying stream is writable
> 3. underlying stream is readable
> 4. binary reader is used
> 5. underlying stream is not seekable

Great analysis Seo.  What I don't understand is why this happens only in
binary mode, and when the write flag is set.  Why is there a
PythonBinaryReader created at all?

I'm setting up my development environment to trace the IP code.


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