TCP congestion control fixes

[danielinux]

Improve TCP Tx fifo handling, wrap arounds and associated BSD socket calls. extend unit test coverage.

[Copilot]

Pull request overview

This PR improves TCP transmit FIFO handling and wraparound logic, adds error checking for BSD socket calls, and significantly extends unit test coverage for the TCP/IP stack implementation.

Changes:

• Modified FIFO space calculation to return contiguous space only when wrapped, preventing buffer overrun issues
• Added explicit contiguous space check in fifo_push to prevent wraparound writes
• Added error handling for fifo_push calls in wolfIP_sock_sendto for TCP, UDP, and ICMP protocols
• Fixed PKT_FLAG_SENT clearing in tcp_ack to allow retransmission of acknowledged packets
• Modified wolfIP_sock_accept to set addrlen even when addr is NULL (POSIX compliance)
• Changed pthread_mutex_lock to pthread_mutex_trylock with busy-wait in BSD socket wrapper
• Added 90+ new unit tests covering socket operations, FIFO edge cases, and timer heap operations
• Added test infrastructure for mocking random number generation

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/wolfip.c	Core FIFO handling improvements for wraparound safety, error handling for buffer operations, TCP ACK flag fixes
src/test/unit/unit.c	Extensive new test coverage for sockets, FIFOs, timers, and routing with 90+ new test cases
src/port/posix/bsd_socket.c	Modified mutex acquisition strategy in blocking call wrapper

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 17 comments.

Comments suppressed due to low confidence (1)

src/wolfip.c:1876

• In the duplicate ACK path, the conditions on lines 1867-1870 check if ack != t->sock.tcp.snd_una and bytes_in_flight == 0, returning early if true. However, the duplicate ACK logic should only trigger when ack == snd_una AND there are bytes in flight. The early returns are correct, but the logic that follows assumes a duplicate ACK scenario without verifying that this is actually a duplicate (i.e., that we've seen this ACK value before). The fast retransmit logic then unconditionally reduces ssthresh and cwnd, which could incorrectly trigger on the first ACK with a given value. Consider adding a duplicate ACK counter to ensure the fast retransmit only triggers after receiving three duplicate ACKs as per RFC 5681.

        /* Duplicate ack (no advance in snd_una). */
        if (ack != t->sock.tcp.snd_una)
            return;
        if (t->sock.tcp.bytes_in_flight == 0)
            return;
        t->sock.tcp.ssthresh = t->sock.tcp.cwnd / 2;
        if (t->sock.tcp.ssthresh < 2 * TCP_MSS) {
            t->sock.tcp.ssthresh = 2 * TCP_MSS;
        }
        t->sock.tcp.cwnd = t->sock.tcp.ssthresh + TCP_MSS;
        t->sock.tcp.cwnd_count = 0;

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.