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

From: Andy Wingo
Subject: bug#30066: 'get-bytevector-some' returns only 1 byte from unbuffered ports
Date: Fri, 12 Jan 2018 11:33:32 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux)

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.

Using buffered ports has two additional advantages: you get to specify
the read size, and returned bytevectors can be allocated to precisely
the right size (no need to overallocate then truncate).


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