Hello,
Mark H Weaver <m...@netris.org> skribis:
> l...@gnu.org (Ludovic Courtès) writes:
[...]
>> + if (SCM_UNBUFFEREDP (port) && (avail < max_buffer_size))
>> + {
>> + /* PORT is unbuffered. Read as much as possible from PORT. */
>> + size_t read;
>> +
>> + bv = scm_c_make_bytevector (max_buffer_size);
>> + scm_port_buffer_take (buf, (scm_t_uint8 *) SCM_BYTEVECTOR_CONTENTS
>> (bv),
>> + avail, cur, avail);
>> +
>> + read = scm_i_read_bytes (port, bv, avail,
>> + SCM_BYTEVECTOR_LENGTH (bv) - avail);
>
> Here's the R6RS specification for 'get-bytevector-some':
>
> "Reads from BINARY-INPUT-PORT, blocking as necessary, until bytes are
> available from BINARY-INPUT-PORT or until an end of file is reached.
> If bytes become available, 'get-bytevector-some' returns a freshly
> allocated bytevector containing the initial available bytes (at least
> one), and it updates BINARY-INPUT-PORT to point just past these
> bytes. If no input bytes are seen before an end of file is reached,
> the end-of-file object is returned."
>
> By my reading of this, we should block only if necessary to ensure that
> we return at least one byte (or EOF). In other words, if we can return
> at least one byte (or EOF), then we must not block, which means that we
> must not initiate another 'read'.
Indeed. So perhaps the condition above should be changed to:
if (SCM_UNBUFFEREDP (port) && (avail == 0))
?
> 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
Thanks,
Ludo’.
