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bug#30066: 'get-bytevector-some' returns only 1 byte from unbuffered por

From: Ludovic Courtès
Subject: bug#30066: 'get-bytevector-some' returns only 1 byte from unbuffered ports
Date: Sat, 13 Jan 2018 21:53:34 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux)


Andy Wingo <address@hidden> skribis:

> On Fri 12 Jan 2018 11:15, address@hidden (Ludovic Courtès) writes:
>> Andy Wingo <address@hidden> skribis:
>>> On Thu 11 Jan 2018 22:55, Mark H Weaver <address@hidden> writes:
>> [...]
>>>>>> Out of curiosity, is there a reason why you're using an unbuffered port
>>>>>> in your use case?
>>>>> It’s to implement redirect à la socat:
>>>>> https://git.savannah.gnu.org/cgit/guix.git/commit/?id=17af5d51de7c40756a4a39d336f81681de2ba447
>>>> Why is an unbuffered port being used here?  Can we change it to a
>>>> buffered port?
>>> This was also a question I had!  If you make it a buffered port at 4096
>>> bytes (for example), then get-bytevector-some works exactly like you
>>> want it to, no?
>> It might work, but that’s more by chance no?
> No, it is reliable.  get-bytevector-some on a buffered port must either
> return all the buffered bytes or perform exactly one read (up to the
> buffer size) and either return those bytes or EOF.  As far as I
> understand, that is exactly what you want.

Indeed, that works well, thanks!  So, after all, problem solved?

I think the confusion for me comes from the fact that we don’t have a
FILE*/fd distinction like in C.  It’s as if we were always using FILE*
in the sense that I’m never sure what’s going to happen or whether a
particular behavior can be relied on.

Thank you,

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