Long timeouts, not topic, session breaks, with fix #23

Suggested PR title

fix(espidf): apply Z_CONFIG_SOCKET_TIMEOUT in the ESP-IDF TCP port

Suggested PR body

The ESP-IDF TCP link never applies the receive timeout it is given, so
recv() blocks indefinitely.

src/link/unicast/tcp.c passes Z_CONFIG_SOCKET_TIMEOUT into the platform
open function, and every other port applies it. tcp_lwip.c:

tv.tv_sec = tout / (uint32_t)1000;
tv.tv_usec = (tout % (uint32_t)1000) * (uint32_t)1000;
setsockopt(..., SOL_SOCKET, SO_RCVTIMEO, (char *)&tv, sizeof(tv));

tcp_esp32.c discards it on the first line of the function:

static z_result_t _z_tcp_esp32_open(..., uint32_t tout) {
    _ZP_UNUSED(tout);

Why it matters beyond the read itself

Since 1.9.0 the read task runs as a future on a shared executor. A task parked
in a recv() that never returns holds that executor, so everything queued
behind it is delayed by however long the peer stays silent.

Observed on an ESP32-P4 talking to a rmw_zenohd router, with
ZENOH_DEBUG=3:

02:36:11 _z_open_connect_locator    Successfully opened connect locator [0]
02:36:11 _z_keep_alive_encode       Encoding _Z_MID_T_KEEP_ALIVE
02:36:41 _z_keep_alive_decode       Decoding _Z_MID_T_KEEP_ALIVE

Thirty seconds between a completed handshake and a usable session, spent
waiting for the peer's first byte because nothing else could run. With an idle
router that byte is its keep-alive, at lease/2.

The same blockage starved the lease task, which both sends keep-alives and
performs the expiry check, so sessions were torn down once a minute with
Closing session because it has expired after 60000ms even though the router
was answering promptly.

Why a timeout is safe here

By the library's existing design rather than by luck. A short read returns
SIZE_MAX, _z_link_socket_recv_zbuf leaves the buffer position untouched,
and _z_unicast_client_read reports "nothing to read" — the ordinary
non-fatal path, which is what Z_CONFIG_SOCKET_TIMEOUT exists to produce.

The change

_z_tcp_esp32_open now honours its tout parameter, and
_z_tcp_esp32_accept sets Z_CONFIG_SOCKET_TIMEOUT the way tcp_lwip.c's
accept path does. Both follow the ordering and error handling already used in
the surrounding code.

Testing

ESP-IDF 5.5.5 on ESP32-P4, against ROS 2 Jazzy with rmw_zenoh. With the
patch the session becomes usable immediately after the handshake, and the
minute-by-minute session drops stop. Verified against a build with the fix

--- a/src/link/transport/tcp/tcp_esp32.c
+++ b/src/link/transport/tcp/tcp_esp32.c
@@ -54,11 +54,19 @@
}

static z_result_t _z_tcp_esp32_open(_z_sys_net_socket_t *sock, const _z_sys_net_endpoint_t endpoint, uint32_t tout) {

• _ZP_UNUSED(tout);
  z_result_t ret = _Z_RES_OK;

  sock->_fd = socket(endpoint._iptcp->ai_family, endpoint._iptcp->ai_socktype, endpoint._iptcp->ai_protocol);
  if (sock->_fd != -1) {

•    z_time_t tv;
  

•    tv.tv_sec = tout / (uint32_t)1000;
  

•    tv.tv_usec = (tout % (uint32_t)1000) * (uint32_t)1000;
  

•    if ((ret == _Z_RES_OK) &&
  

•        (setsockopt(sock->_fd, SOL_SOCKET, SO_RCVTIMEO, (char *)&tv, sizeof(tv)) < 0)) {
  

•        _Z_ERROR_LOG(_Z_ERR_GENERIC);
  

•        ret = _Z_ERR_GENERIC;
  

•    }
  

•    int optflag = 1;
     if ((ret == _Z_RES_OK) &&
         (setsockopt(sock->_fd, SOL_SOCKET, SO_KEEPALIVE, (void *)&optflag, sizeof(optflag)) < 0)) {
  

@@ -165,6 +173,14 @@
_Z_ERROR_RETURN(_Z_ERR_GENERIC);
}

• z_time_t tv;
• tv.tv_sec = Z_CONFIG_SOCKET_TIMEOUT / (uint32_t)1000;
• tv.tv_usec = (Z_CONFIG_SOCKET_TIMEOUT % (uint32_t)1000) * (uint32_t)1000;
• if (setsockopt(con_socket, SOL_SOCKET, SO_RCVTIMEO, (char *)&tv, sizeof(tv)) < 0) {

•    close(con_socket);
  

•    _Z_ERROR_RETURN(_Z_ERR_GENERIC);
  

• }
• int optflag = 1;
  if (setsockopt(con_socket, SOL_SOCKET, SO_KEEPALIVE, (void *)&optflag, sizeof(optflag)) < 0) {
  close(con_socket);

applied and no other workaround in place.