tcp,udp: set TOS (TCLASS) for IPv6 sockets

[maximilianfridrich]

No description provided.

[sreimers]

Unsure if IPV6_TCLASS is available on windows.

https://learn.microsoft.com/en-us/windows/win32/winsock/ipproto-ipv6-socket-options

I think some other systems also does not support this, so something like this Check should be added:

#if defined(IPV6_TCLASS)
...

[maximilianfridrich]

Good point. Thank you @sreimers. Done.

[alfredh]

Would it be possible to add a small testcase for TOS ?

it would be enough with a simple testcase with UDP/TCP socket, set the TOS fields,
sends a couple of packets in a loop.

[maximilianfridrich]

I will look into it.

[maximilianfridrich]

@alfredh I managed to create a working test with a custom UDP listener which uses recvmsg and struct cmsghdr to obtain information from the incoming IP packets. However, it turns out that this low-level socket stuff (< layer 4) is very platform dependent and I did not manage to write a test which works on all supported platforms (Windows, MAC).

I don't think it is worth putting a ton of time into this, since this new IPv6 addition is very simple and unlikely to break things (in part thanks to the #ifdefs.).

I hope this is okay. Attached is a patch with my working test (works on Linux).
test-udp-Add-TOS-test.patch.txt

[sreimers]

However, it turns out that this low-level socket stuff

It's enough to ensure tos functions are executed, no need for real low level packet checks.

[maximilianfridrich]

It's enough to ensure tos functions are executed, no need for real low level packet checks.

Thank you, I just realized that there could be value in that too and I have just added tests for that. Done.

[maximilianfridrich]

Seems like the setsockopt call fails on some Windows systems. Do you have any idea @sreimers ?

Probably the

#if defined(IPV6_TCLASS) && !defined(WIN32)

is not restrictive enough.

[sreimers]

Seems like the setsockopt call fails on some Windows systems. Do you have any idea @sreimers ?

Will try to reproduce.

[alfredh]

A simple test sending some packets with TOS set is better than nothing ...
No need to inspect incoming IP-packets ...

[alfredh]

why is TOS set on the same tcp server two times ?

is the TOS field working for TCP server or connection ?

[maximilianfridrich]

why is TOS set on the same tcp server two times ?

Mistake, removed.

is the TOS field working for TCP server or connection ?

In this test, it is set for all incoming connections on the listening (server) TCP socket. With tcp_conn_settos we could also set it per connection.

[maximilianfridrich]

Probably the #if defined(IPV6_TCLASS) && !defined(WIN32) is not restrictive enough.

Actually, the test fails already in the IPv4 case, so I guess the TOS setting functions have never worked reliably on Windows systems. It turns out that per default, Windows does not allow applications to set the TOS value (if I understand this resource correctly).

Should I simply skip the test for Windows systems, since the outcome is dependent on the Windows registry settings? Or does anyone have a better idea how to proceed?

[alfredh]

It should be fine to skip that test for Windows...

[maximilianfridrich]

It should be fine to skip that test for Windows...

Done. Let me know if it's okay the way I did it.

[alfredh]

looks good to me ... should we merge it ?

[maximilianfridrich]

Yes, I'm all for it.