[Python-ideas] PEP 3156: getting the socket or peer name from the transport

[Ronald Oussoren]

On 24 Jan, 2013, at 22:50, Guido van Rossum <guido at python.org> wrote:

> On Thu, Jan 24, 2013 at 12:51 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
>> On Fri, Jan 25, 2013 at 5:12 AM, Guido van Rossum <guido at python.org> wrote:
>>> On Thu, Jan 24, 2013 at 11:05 AM, Nikolay Kim <fafhrd91 at gmail.com> wrote:
>>>> transport could have dictionary attribute where it can store optional information
>>>> like socket name, peer name or file path, etc.
>>> 
>>> Aha, that makes some sense. Though maybe it shouldn't be a dict -- it
>>> may be expensive to populate some values in some cases, so maybe there
>>> should just be a method transport.get_extra_info('key') which computes
>>> and returns (and possibly caches) certain values but returns None if
>>> the info is not supported. E.g. get_extra_info('name'),
>>> get_extra_info('peer'). This API makes it pretty clear that the caller
>>> should check the value for None before using it.
>> 
>> A "get_extra_info" API like that is also amenable to providing an
>> explicit default for the "key not present" case, and makes it clearer
>> that the calculations involved may not be cheap.
> 
> Yeah, the signature could be get_extra_info(key, default=None).
> 
>> You could even go so
>> far as to have it return a Future, allowing it to be used for info
>> that requires network activity.
> 
> I think that goes too far. It doesn't look like getpeername() goes out
> to the network -- what other use case did you have in mind? (I suppose
> it could use a Future for some keys only -- but then the caller would
> still need to be aware that it could return None instead of a Future,
> so it would be somewhat awkward to use -- you couldn't write

A transport that tunnels traffic over a SOCKS or SSH tunnel might require network access to get the sockname or peername of the proxied connection. I don't know enough about either protocol to know for sure, and the information could also be fetched during connection setup and then cached.

Ronald