Implemented socket state capturing

[antoncxx]

Add socket state to Listener

Exposes the TCP connection state (e.g. LISTEN, ESTABLISHED, TIME_WAIT) as a new state: SocketState field on the Listener struct, available on all supported platforms.

What changed

• New SocketState enum with 12 variants covering the full TCP state machine, plus Unknown for UDP and unrecognized values
• Display impl renders standard names (ESTABLISHED, SYN_SENT, CLOSE_WAIT, etc.)
• Listener::new and its Display impl updated to include the state field
• Platform-specific state parsing on all four targets:
  • Linux — hex value from /proc/net/tcp parsed via from_linux(u8)
  • macOS — tcpsi_state from proc_pidfdinfo socket info via from_bsd(i32)
  • FreeBSD / NetBSD / OpenBSD — t_state / ki_tstate from native C layer, UDP gets -1 → Unknown
  • Windows — MIB_TCP_STATE row field via from_windows(u32), UDP gets Unknown

Breaking change

Listener gains a new state field — callers constructing Listener directly (e.g. in tests) must now supply a SocketState. Integration test updated
accordingly.

[GyulyVGC]

Thanks so much Anton, this is a nice addition.

I'd love to have comprehensive tests about some, if not all, the possible states.
But I'm not sure TCP states are something that can be easily replicated in a programmatic way in a test suite.

[antoncxx]

Thanks so much Anton, this is a nice addition.

I'd love to have comprehensive tests about some, if not all, the possible states. But I'm not sure TCP states are something that can be easily replicated in a programmatic way in a test suite.

I added the following integration tests for the SocketState field:

• test_tcp_listen_state — binds a TCP listener on IPv4 and asserts the state is Listen
• test_tcp_established_state — connects a TCP stream to a local server, accepts it, and asserts the accepted socket has state Established
• test_udp_state_is_unknown — binds a UDP socket and asserts the state is Unknown; even though the Linux kernel reports 0x07 (CLOSED) for UDP sockets in /proc/net/udp, we override it to Unknown since UDP is connectionless and the value is meaningless
• test_tcp_listen_state_ipv6 — same as the listen test but on IPv6
• test_tcp_established_state_ipv6 — same as the established test but on IPv6
• test_tcp_close_wait_state — drops the client side of a connection to send a FIN, reads until EOF on the accepted socket to confirm the kernel received it, then asserts the state is CloseWait

I couldn't come up with a reliable way to test the remaining states (SynSent, SynReceived, FinWait1, FinWait2, TimeWait, LastAck, Closing) as they are transient and require precise timing to observe before the kernel advances past them.

[Jamba777]

@GyulyVGC Hey! Just wondering if you have an ETA for merging this PR 🙂

[GyulyVGC]

Hey @Jamba777 thanks for your interest in this feature

I'm pretty busy this period but I'll try my best to merge this and publish a new version in June