[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola'  added the comment:

After careful thinking I realize I'm not completely sure about how to expose 
the IPv4/6 functionality yet. I prefer to defer it for later and start landing 
a bind_socket() utility function which serves as a base for this functionality. 
See: issue17561.

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[issue17561] Add socket.create_server_sock() convenience function

[Jason R. Coombs]

Jason R. Coombs  added the comment:

In issue24209, I ended up settling on this implementation 
(https://github.com/python/cpython/blob/f289084c83190cc72db4a70c58f007ec62e75247/Lib/http/server.py#L1227-L1234),
 which seems to work well.

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[issue17561] Add socket.create_server_sock() convenience function

[STINNER Victor]

Change by STINNER Victor :


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[issue17561] Add socket.create_server_sock() convenience function

[Guido van Rossum]

Change by Guido van Rossum :


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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Change by Giampaolo Rodola' :


--
pull_requests: +10452
stage:  -> patch review

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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola'  added the comment:

Interesting. Yes, I agree this proposal is still desirable. We can reuse 
socket.create_server_sock() in smtpd, ftplib, socketserver (issue20215) and 
http.server (issue24209) modules which will inherit dual-stack IPv4/6 
capabilities for free. I should be able to provide a PR sometime during this 
month.

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assignee:  -> giampaolo.rodola

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[issue17561] Add socket.create_server_sock() convenience function

[Jason R. Coombs]

Jason R. Coombs  added the comment:

I do believe this issue is still important and relevant. See issue25667 for a 
duplicate ticket (and references to implementations) and issue24209 for another 
issue where this could have been applied.

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versions: +Python 3.8 -Python 3.4

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[issue17561] Add socket.create_server_sock() convenience function

[Cheryl Sabella]

Cheryl Sabella  added the comment:

Since Tulip/asyncio has gone through a lot of development since this issue was 
added, I wasn't sure if this has been included already or if there was still 
interest in it.  In either case, I think it might be able to be closed, but I 
wanted to make sure first.  Thanks!

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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola' added the comment:

Here's a patch for Tulip:
https://codereview.appspot.com/8307045
Will ping Tulip's ml as well.

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[issue17561] Add socket.create_server_sock() convenience function

[STINNER Victor]

Changes by STINNER Victor :


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[issue17561] Add socket.create_server_sock() convenience function

[Guido van Rossum]

Guido van Rossum added the comment:

Nikolay, you may want to check out this Python tracker issue.

Giampaolo: I didn't even know it was possible for a single socket to be
dual-stack. (It would seem problematic for UDP recvfrom() for example.) In
Tulip it does indeed make more sense to create separate sockets and just
listen on all of them (using the same protocol factory). This can be
completely transparent to the code calling start_serving() and to the
protocol implementation. So if you're brave you can just send a code review
using codereview.appspot.com to the python-tulip list!

On Mon, Apr 1, 2013 at 1:13 PM, Giampaolo Rodola' wrote:

>
> Giampaolo Rodola' added the comment:
>
> Being Tulip asynchronous I think that what it needs is an utility function
> which returns *multiple* sockets as are the addresses returned by
> getaddrinfo() and also possibly even disable the IPv4/6 dual stack in order
> to be consistent across all platforms.
>
> After the sockets are returned they can be "registered" against the event
> loop as two separate entities such as, say, ("0.0.0.0", 8000) *and* ("::",
> 8000).
> If you think this makes sense I can contribute something like this into
> Tulip, or I can bring it up on Tulip's ml and ask for other people's
> opinions.
>
> My current recipe is different in that it provides a function which
> bind()s on one socket only and tries to enable the dual stack whenever
> possible in order to support IPv4 and IPv6 with a single socket.
> In this it is similar to socket.create_connection() and clearly favors
> blocking socket usages (although it can also be used in non-blocking apps)
> which kind of represents the default for the stdlib.
>
> --
>
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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola' added the comment:

Being Tulip asynchronous I think that what it needs is an utility function 
which returns *multiple* sockets as are the addresses returned by getaddrinfo() 
and also possibly even disable the IPv4/6 dual stack in order to be consistent 
across all platforms.

After the sockets are returned they can be "registered" against the event loop 
as two separate entities such as, say, ("0.0.0.0", 8000) *and* ("::", 8000).
If you think this makes sense I can contribute something like this into Tulip, 
or I can bring it up on Tulip's ml and ask for other people's opinions.

My current recipe is different in that it provides a function which bind()s on 
one socket only and tries to enable the dual stack whenever possible in order 
to support IPv4 and IPv6 with a single socket.
In this it is similar to socket.create_connection() and clearly favors blocking 
socket usages (although it can also be used in non-blocking apps) which kind of 
represents the default for the stdlib.

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[issue17561] Add socket.create_server_sock() convenience function

[Guido van Rossum]

Guido van Rossum added the comment:

start_serving() in base_events.py.

On Fri, Mar 29, 2013 at 4:58 AM, Giampaolo Rodola'
wrote:

>
> Giampaolo Rodola' added the comment:
>
> >> Where should I look?
> > Tulip is at code.google.com/p/tulip
>
> I meant in the code (and what needs to be done/refactored exactly).
>
> --
>
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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola' added the comment:

>> Where should I look?
> Tulip is at code.google.com/p/tulip

I meant in the code (and what needs to be done/refactored exactly).

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[issue17561] Add socket.create_server_sock() convenience function

[Guido van Rossum]

Guido van Rossum added the comment:

Tulip is at code.google.com/p/tulip

On Thu, Mar 28, 2013 at 7:51 PM, Giampaolo Rodola'
wrote:

>
> Giampaolo Rodola' added the comment:
>
> Yep, no prob. It would also be a good chance to test it in a real-world
> app. Where should I look?
>
> --
>
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> 
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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Changes by Giampaolo Rodola' :


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nosy: +josiah.carlson, loewis

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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola' added the comment:

Yep, no prob. It would also be a good chance to test it in a real-world app. 
Where should I look?

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[issue17561] Add socket.create_server_sock() convenience function

[Guido van Rossum]

Guido van Rossum added the comment:

Perhaps you can contribute something like this to Tulip?  We've got code to run 
a server that can handle IPv4 and IPv6, but we currently don't have something 
that just creates a separate socket for each address family.  Our UDP and TCP 
paths are also quite different.

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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola' added the comment:

I managed to write a container class which listens on multiples addresses and 
uses select/poll on accept() as suggested by Charles.
FWICT it seems to work pretty well and supports non-blocking sockets and 
timeouts (tested on Linux, Windows and OSX).

It is available as a recipe here:
http://code.activestate.com/recipes/578504

IMO has_dual_stack() and create_server_sock() functions can already be included 
as-is (will adapt the recipe in order to get rid of Python 2.X support and 
submit another patch).

As for including also MultipleSocketsListener that's debatable.
It can either be added or linked/mentioned it in the doc.

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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola' added the comment:

Agreed. Then it probably makes sense to expose also a socket.has_dual_stack() 
function so that the user can pre-emptively decide whether using a custom class.
Updated draft patch is in attachment.

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Added file: http://bugs.python.org/file29600/socket2.patch

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[issue17561] Add socket.create_server_sock() convenience function

[Charles-François Natali]

Charles-François Natali added the comment:

> Providing a custom class instantiating two sockets looks like a dead end to 
> me though. To say one, what is getsockname() supposed to return? Same for 
> detach(), fileno(), 'family' and probably others I can't think of right now.

Indeed.

So we might opt for a best-effort approach: try disabling IPV6_V6ONLY
on the socket if it's set: that way it should work on most platforms.
And add a note to the documentation. IIRC that's what Java does.

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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola' added the comment:

Thanks for clarifying, I have a better understanding of the problem now.
Providing a custom class instantiating two sockets looks like a dead end to me 
though. To say one, what is getsockname() supposed to return? Same for 
detach(), fileno(), 'family' and probably others I can't think of right now.

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[issue17561] Add socket.create_server_sock() convenience function

[Charles-François Natali]

Charles-François Natali added the comment:

> What you say is right but whether the kernel supports an hybrid IPv4/6 stack
> or not there's not much we can do about it anyway.
> Exactly what are you suggesting with the ServerSocket class you mentioned?
> What do you expect it to do?

There's a confusion.
Dual-stack merely means that the host supports both IPv4 and IPv6 natively.
The IPV6_V6ONLY tunable is just a way to enable or not IPv4-mapped
addresses (i.e. ::::) so that an IPv4 client can
connect to this socket. It can be set system-wide, or on a socket
basis.

> Note that platforms supporting the dual-stack are already supported. This:
>
 socket.create_server_socket(("::", 0))
>
> ...on Linux will create a socket which is reachable both as "::1" and
> "127.0.0.1".

Try the same thing after:
# echo 1 > /proc/sys/net/ipv6/bindv6only

It won't accept IPv4 connections anymore.

And that's the default on many (most) platforms, e.g. FreeBSD and
OpenBSD (I think it's also true for Windows).

So the bottom line is that with the current code, on some - most -
platforms, we'll only accept IPv6 connections (and since you iterate
over getaddrinfo() in an unspecified order you may very well bind to
IPv4 only first, in which case you'll only accept IPv4 clients).

The proper way to procedd, on platforms which don't support unsetting
IPV6_V6ONLY, is to use two sockets, one in IPv4, and one IPv6, and use
select() to accept connections.

This would propably belong to an overriden accept() method in a
ServerSocket class, since it's far from trivial.

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[issue17561] Add socket.create_server_sock() convenience function

[Guido van Rossum]

Guido van Rossum added the comment:

Tulip has something similar.  Someone should compare the two and make sure they 
are equivalent or similar.

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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola' added the comment:

Side note: this is how in pyftpdlib I determine whether a platform supports the 
dual stack:

def support_hybrid_ip_v4_v6():
# Note: IPPROTO_IPV6 constant is broken on Windows, see:
# http://bugs.python.org/issue6926
sock = None
try:
if not socket.has_ipv6:
return False
sock = socket.socket(socket.AF_INET6)
return not sock.getsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY)
except (socket.error, AttributeError):
return False
finally:
if sock is not None:
sock.close()

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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

Giampaolo Rodola' added the comment:

What you say is right but whether the kernel supports an hybrid IPv4/6 stack or 
not there's not much we can do about it anyway.
Exactly what are you suggesting with the ServerSocket class you mentioned? What 
do you expect it to do?
Note that platforms supporting the dual-stack are already supported. This:

>>> socket.create_server_socket(("::", 0))

...on Linux will create a socket which is reachable both as "::1" and 
"127.0.0.1".
So if I'm not mistaken the alias for specifying "listen on all interfaces for 
both IPv4 and IPv6 addresses" would be "::" instead of "" / None.
We can document that.

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[issue17561] Add socket.create_server_sock() convenience function

[Charles-François Natali]

Charles-François Natali added the comment:

I think that's a good idea.

However, there's a problem with the implementation: if one passes "" or None as 
address on a dual-stack node, the resulting socket will be either IPv4 bound to 
INADDR_ANY, or IPv6 bound to IN6ADDR_ANY, whereas one would expect to be bound 
both in IPv4 and IPv6. In the later case, some platforms (like Linux) use 
IPv4-mapped addresses by default, some others (e.g. some versions of FreeBSD) 
don't. So, depending on IPV6_V6ONLY setting, binding to IPV6 any won't accept 
IPv4 connections. Also, some platforms don't support mapped addresses at all, 
so the only portable solution is to bind both to 0.0.0.0 and ::, whith two 
different sockets, and use select() to accept both.

So it would maybe make sense to expose a ServerSocket class, with an accept 
method which would do the right thing (as an added bonus, it could expose 
set_reuse_addr(bool), since SO_REUSEADDR have subtle semantic differences 
between Unix and Windows).

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[issue17561] Add socket.create_server_sock() convenience function

[Antoine Pitrou]

Changes by Antoine Pitrou :


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[issue17561] Add socket.create_server_sock() convenience function

[Giampaolo Rodola']

New submission from Giampaolo Rodola':

Here's a function similar to socket.create_connection() which addresses all the 
repetitive tasks needed to order to create an IPv4/IPv6 agnostic server socket.

--
components: Library (Lib)
files: socket.patch
keywords: easy, needs review, patch
messages: 185348
nosy: giampaolo.rodola, pitrou
priority: normal
severity: normal
status: open
title: Add socket.create_server_sock() convenience function
type: enhancement
versions: Python 3.4
Added file: http://bugs.python.org/file29596/socket.patch

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