TCP_FASTOPEN option for Socket

[zonyitoo]

• Supported platforms: Linux-like, FreeBSD, macOS, Windows
• ref Support TCP Fast Open #49

[Thomasdezeeuw]

Can you add a smoke test for this?

If I call this with the value 5, does this work on non-Linux? I.e. enable it, or would it error and would users have to do if linux { 5 } else { 1 }? Depending on the answer can you also add a test for this?

[zonyitoo]

thread 'tcp_fastopen' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 22, kind: InvalidInput, message: "Invalid argument" }', tests/socket.rs:1302:32

We have the answer, value must be 0 and 1 excepts Linux.

[zonyitoo]

thread 'tcp_fastopen' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 1, kind: PermissionDenied, message: "Operation not permitted" }', tests/socket.rs:1306:36

Test failed on FreeBSD CI.

https://github.com/freebsd/freebsd-src/blob/e7d02be19d40063783d6b8f1ff2bc4c7170fd434/sys/netinet/tcp_usrreq.c#L2458-L2507

It seems that TFO is not enabled on CI's OS.

[zonyitoo]

@Thomasdezeeuw Should I remove FreeBSD support?

[Thomasdezeeuw]

Can you change the method so that 0 means disable, and >= 1 means enable, mapping anything bigger than 1 to 1 on non-Linux systems? And update the docs accordingly.

For FreeBSD can you try add a new step to .cirrus.yml? With the following:

  enable_tcp_fastopen:
    - sysctl net.inet.tcp.fastopen.client_enabled=1
    - sysctl net.inet.tcp.fastopen.server_enabled=1

After build_script should work. This should enable it on FreeBSD.

[zonyitoo]

Still not working on FreeBSD's CI test.

[Thomasdezeeuw]

@zonyitoo I'll work on FreeBSD

[Thomasdezeeuw]

@zonyitoo the sysctl names I gave you are incorrect. These should fix them:

-    - sysctl net.inet.tcp.fastopen.client_enabled=1
-    - sysctl net.inet.tcp.fastopen.server_enabled=1
+    - sudo sysctl net.inet.tcp.fastopen.client_enable=1
+    - sudo sysctl net.inet.tcp.fastopen.server_enable=1

However that doesn't seem to fix the problem (see my next comment).

[Thomasdezeeuw]

@asomers maybe you can help here. I got this to work on FreeBSD (the sysctl names are incorrect). But when retrieving the value of TCP_FASTOPEN isn't 1, but 2147483648, is this expected? I think the value comes from https://github.com/freebsd/freebsd-src/blob/e7d02be19d40063783d6b8f1ff2bc4c7170fd434/sys/netinet/tcp_usrreq.c#L2693-L2697, but I could be wrong here.

[asomers]

@Thomasdezeeuw this socket option is a flag, so you should only interpret it as either zero or non-zero. TCP_NODELAY is similar, and I see that socket2 interprets it correctly. I suggest you change the Socket::tcp_fastopen signature to match Socket::nodelay.

[Thomasdezeeuw]

@Thomasdezeeuw this socket option is a flag, so you should only interpret it as either zero or non-zero. TCP_NODELAY is similar, and I see that socket2 interprets it correctly. I suggest you change the Socket::tcp_fastopen signature to match Socket::nodelay.

Thanks. That makes the API a little awkward as the value on Linux is the accept queue length, so we'll need to rethink the API.