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gh-123832: Adjust socket.getaddrinfo docs for better POSIX compliance #126182

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Nov 14, 2024
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gh-123832: Adjust socket.getaddrinfo docs for better POSIX compliance #126182

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gh-123832: Adjust `socket.getaddrinfo` docs for better POSIX compliance
encukou Oct 28, 2024
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encukou Nov 4, 2024
a6f1e2a
Update Doc/library/socket.rst
encukou Nov 12, 2024
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Remove unacceptable whitespace
encukou Nov 13, 2024
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31 changes: 28 additions & 3 deletions Doc/library/socket.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -928,7 +928,9 @@

.. versionadded:: 3.7

.. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0)
.. function:: getaddrinfo(host, port, family=AF_UNSPEC, type=0, proto=0, flags=0)

This function wraps the C function ``getaddrinfo`` of the underlying system.

Translate the *host*/*port* argument into a sequence of 5-tuples that contain
all the necessary arguments for creating a socket connected to that service.
Expand All @@ -938,9 +940,11 @@
and *port*, you can pass ``NULL`` to the underlying C API.

The *family*, *type* and *proto* arguments can be optionally specified
in order to narrow the list of addresses returned. Passing zero as a
value for each of these arguments selects the full range of results.
in order to provide options and limit the list of addresses returned.
Pass their default values (:data:`AF_UNSPEC`, 0, and 0, respectively)
to not limit the results. See the note below for details.

The *flags* argument can be one or several of the ``AI_*`` constants,

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py:const reference target not found: AI_NUMERICHOST [ref.const]
and will influence how results are computed and returned.
For example, :const:`AI_NUMERICHOST` will disable domain name resolution
and will raise an error if *host* is a domain name.
Expand All @@ -959,6 +963,25 @@
:const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect`
method.

.. note::

If you intend to use results from :func:`!getaddrinfo` to create a socket

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py:data reference target not found: IPPROTO_TCP [ref.data]

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py:data reference target not found: IPPROTO_UDP [ref.data]
(rather than, for example, retrieve *canonname*),
consider limiting the results by *type* (e.g. :data:`SOCK_STREAM` or
:data:`SOCK_DGRAM`) and/or *proto* (e.g. :data:`IPPROTO_TCP` or
:data:`IPPROTO_UDP`) that your application can handle.

With default values of *family*, *type*, *proto* and/or *flags*,
many systems will return a sorted list of all matching addresses,
which should generally be tried in order until a connection succeeds
(possibly tried in parallel, for example, using a `Happy Eyeballs`_ algorithm).
In these cases, limiting the *type* and/or *proto* can help eliminate
unsuccessful or unusable connecton attempts.

Some systems will, however, only return a single address.
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If we know typical details for "many systems" and "some systems" we should include an possible example with each such as "(ex: most Linux configurations)" or "(ex: reported on Solaris and AIX configurations)". I'm wording those non-concretely as well, but suggest adding it just to add some context for people looking into behaviors as to when they may encounter the unexpected.

not a big deal without this, just a nice to have.

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For your reference from #123832, "many" are basically mainstream (Linux, macOS, FreeBSD) and "some" are Illumos / Solaris / AIX. I haven't had a chance to get my hands on anything more exotic recently (HP-UX and VMS come to mind...).

I would also prefer to be more specific, but I thought the details were left out to avoid "finger pointing".

On these systems, limiting the *type* and/or *proto* helps ensure that
this address is usable.
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.. audit-event:: socket.getaddrinfo host,port,family,type,protocol socket.getaddrinfo

The following example fetches address information for a hypothetical TCP
Expand All @@ -978,6 +1001,8 @@
for IPv6 multicast addresses, string representing an address will not
contain ``%scope_id`` part.

.. _Happy Eyeballs: https://en.wikipedia.org/wiki/Happy_Eyeballs

.. function:: getfqdn([name])

Return a fully qualified domain name for *name*. If *name* is omitted or empty,
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