[Python-ideas] PEP 3156: Transport.sendfile

[Guido van Rossum]

On Fri, Jan 25, 2013 at 12:25 PM, Nikolay Kim <fafhrd91 at gmail.com> wrote:

>
> On Jan 25, 2013, at 12:04 PM, Guido van Rossum <guido at python.org> wrote:
>
> On Fri, Jan 25, 2013 at 10:11 AM, Nikolay Kim <fafhrd91 at gmail.com> wrote:
>
>>
>> On Jan 25, 2013, at 10:08 AM, Guido van Rossum <guido at python.org> wrote:
>>
>> On Fri, Jan 25, 2013 at 10:03 AM, Nikolay Kim <fafhrd91 at gmail.com> wrote:
>>
>>>
>>> I think Transport needs 'sendfile' api, something like:
>>>
>>>    @tasks.coroutine
>>>    def sendfile(self, fd, offset, nbytes):
>>>       ….
>>>
>>> otherwise it is impossible to implement sendfile without breaking
>>> transport encapsulation
>>
>>
>> Really? Can't the user write this themselves? What's wrong with this:
>>
>> while True:
>>   data = os.read(fd, 16*1024)
>>   if not data: break
>>   transport.write(data)
>>
>> (Perhaps augmented with a way to respond to pause() requests.)
>>
>>
>> i mean 'os.sendfile()', zero-copy sendfile.
>>
>
> I see (http://docs.python.org/dev/library/os.html#os.sendfile).
>
> Hm, that function is so platform-specific that we might as well force
> users to do it this way:
>
> sock = transport.get_extra_info("socket")
> if sock is not None:
>   os.sendfile(sock.fileno(), ......)
> else:
>   <use write() like I suggested above>
>
>
> there should some kind of way to flush write buffer or write callbacks.
>
> sock = transport.get_extra_info("socket")
> if sock is not None:
>    os.sendfile(sock.fileno(), ......)
> else:
>    yield from transport.write_buffer_flush()
>    <use of write() method>
>

Oh, that's an interesting idea in its own right. But I'm not sure Twisted
could implement this given that their flow control works differently.

However, I think you've convinced me that offering sendfile() is actually
better. But should it take a file descriptor or a stream (file) object?

-- 
--Guido van Rossum (python.org/~guido)
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