[tcp] `dead_socket_tx` Causes Unit Test Regressions to Fail

[gatoWololo]

Running test_connect currently fails with:

Failed to terminate connection: TrySendError { kind: Disconnected }
thread 'protocols::tcp::tests::test_connect' panicked at 'Failed to terminate connection: TrySendError { kind: Disconnected }', src/protocols/tcp/established/background/mod.rs:58:14
stack backtrace:
   0: rust_begin_unwind
             at /rustc/ca82264ec7556a6011b9d3f1b2fd4c7cd0bc8ae2/library/std/src/panicking.rs:493:5
   1: core::panicking::panic_fmt
             at /rustc/ca82264ec7556a6011b9d3f1b2fd4c7cd0bc8ae2/library/core/src/panicking.rs:92:14
   2: core::result::unwrap_failed
             at /rustc/ca82264ec7556a6011b9d3f1b2fd4c7cd0bc8ae2/library/core/src/result.rs:1355:5
   3: core::result::Result<T,E>::expect
             at /home/gatowololo/.rustup/toolchains/nightly-2021-05-10-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/result.rs:997:23
   4: catnip::protocols::tcp::established::background::background::{{closure}}
             at ./src/protocols/tcp/established/background/mod.rs:56:9

This line:

        dead_socket_tx
            .unbounded_send(fd)
            .expect("Failed to terminate connection");

As the error message states, the unbound_send always fails because the receiver is disconnected. So we always panic here.

Looking at the code. It seems the channel pair is created here:

impl<RT: Runtime> Peer<RT> {
    pub fn new(rt: RT, arp: arp::Peer<RT>, file_table: FileTable) -> Self {
        let (tx, _rx) = mpsc::unbounded();
        let inner = Rc::new(RefCell::new(Inner::new(rt.clone(), arp, file_table, tx)));
        Self { inner }
    }
...
}

As you can see the receiver is immediately dropped. So I don't see how this code is every supposed to not fail. Or what is the point of it since it doesn't seem to do anything?