Issue 37345: Add formal support for UDPLITE protocol

At the moment you can definitely use UDPLITE sockets on Linux systems, but it would be good if this support were formalized such that you can detect support at runtime easily.

At the moment, to make and use a UDPLITE socket requires something like the following code:

>>> import socket
>>> a = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, 136)
>>> b = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, 136)
>>> a.bind(('localhost', 44444))
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.setsockopt(136, 10, 16)
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.setsockopt(136, 10, 32)
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.setsockopt(136, 10, 64)
>>> b.sendto(b'test'*256, ('localhost', 44444))

If you look at this through Wireshark, you can see that the packets are different in that the checksums and checksum coverages change.

With the pull request that I am submitting momentarily, you could do the following code instead:

>>> import socket
>>> a = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDPLITE)
>>> b = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDPLITE)
>>> a.bind(('localhost', 44444))
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.set_send_checksum_coverage(16)
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.set_send_checksum_coverage(32)
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.set_send_checksum_coverage(64)
>>> b.sendto(b'test'*256, ('localhost', 44444))

One can also detect support for UDPLITE just by checking

>>> hasattr(socket, 'IPPROTO_UDPLITE')

Adding new constants like socket.IPPROTO_UDPLITE is fine.
The question is: why we need a new function?
There is no set_send_checksum_coverage() on C level IIRC

Its true that this doesnt exist at the C level, however I worry that having it purely through getsockopt() and setsockopt() would make things more confusing, so I added it as a helper function.

I can remove it in lieu of documentation if that would block merging, though I dont think that is the right move here.

On June 20, 2019 10:54:58 AM UTC, Andrew Svetlov <report@bugs.python.org> wrote:
>
>Andrew Svetlov <andrew.svetlov@gmail.com> added the comment:
>
>Adding new constants like socket.IPPROTO_UDPLITE is fine.
>The question is: why we need a new function?
>There is no set_send_checksum_coverage() on C level IIRC
>
>----------
>nosy: +asvetlov
>
>_______________________________________
>Python tracker <report@bugs.python.org>
><https://bugs.python.org/issue37345>
>_______________________________________

We have no setsockopt() shortcut helpers.
socket.setblocking() uses fcntl() internally.

I just want to be explicit so I don't mess up on protocol, since I am new to this project. Does that mean that you want me to remove the helper function and put documentation in about that sockopt, or that an exception could be made in this case?

Sorry.
Please drop helper methods but keep IPPROTO_UDPLITE, UDPLITE_SEND_CSCOV, UDPLITE_RECV_CSCOV constants.

Okay, I removed the helper functions and added some additional documentation. Does that look okay now?

3.8 is in beta stage, public API is frozen

I didn't realize that when I submitted this the first time, but I corrected that in the documentation when someone else removed it from the tags. If I re-added it it was by mistake. I notice that my browser had that auto-highlighted. Should be fixed now.

New changeset 2ac3bab2a6e1f9e17fc0c58a26e8425bb93cb0f5 by Miss Islington (bot) (Gabe Appleton) in branch 'master':
bpo-37345: Add formal UDPLITE support (GH-14258)
https://github.com/python/cpython/commit/2ac3bab2a6e1f9e17fc0c58a26e8425bb93cb0f5