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net: tcp: Fix handling of keep-alive probes #93431

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781c591
net: tcp: Fix handling of keep-alive probes
rlubos Jul 21, 2025
9c12c0e
tests: net: socket: tcp: Add test for keepalive connection upkeep
rlubos Jul 21, 2025
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4 changes: 3 additions & 1 deletion subsys/net/ip/tcp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2859,7 +2859,9 @@ static enum net_verdict tcp_in(struct tcp *conn, struct net_pkt *pkt)
/* send ACK for non-RST packet */
if (FL(&fl, &, RST)) {
net_stats_update_tcp_seg_rsterr(net_pkt_iface(pkt));
} else if ((len > 0) || FL(&fl, &, FIN)) {
} else if ((len > 0) || FL(&fl, &, FIN) ||
/* Keep-alive probe */
((len == 0) && FL(&fl, &, ACK))) {
tcp_out(conn, ACK);
}
k_mutex_unlock(&conn->lock);
Expand Down
73 changes: 55 additions & 18 deletions tests/net/socket/tcp/src/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2349,7 +2349,7 @@ ZTEST(net_socket_tcp, test_connect_and_wait_for_v4_poll)
zassert_equal(ret, 0, "close failed, %d", errno);
}

ZTEST(net_socket_tcp, test_so_keepalive)
ZTEST(net_socket_tcp, test_so_keepalive_opt)
{
struct sockaddr_in bind_addr4;
int sock, ret;
Expand Down Expand Up @@ -2430,55 +2430,92 @@ ZTEST(net_socket_tcp, test_so_keepalive)
test_context_cleanup();
}

ZTEST(net_socket_tcp, test_keepalive_timeout)
static void test_prepare_keepalive_socks(int *c_sock, int *s_sock, int *new_sock)
{
struct sockaddr_in c_saddr, s_saddr;
int c_sock, s_sock, new_sock;
uint8_t rx_buf;
int optval;
int ret;

prepare_sock_tcp_v4(MY_IPV4_ADDR, ANY_PORT, &c_sock, &c_saddr);
prepare_sock_tcp_v4(MY_IPV4_ADDR, SERVER_PORT, &s_sock, &s_saddr);
prepare_sock_tcp_v4(MY_IPV4_ADDR, ANY_PORT, c_sock, &c_saddr);
prepare_sock_tcp_v4(MY_IPV4_ADDR, SERVER_PORT, s_sock, &s_saddr);

/* Enable keep-alive on both ends and set timeouts/retries to minimum */
optval = 1;
ret = zsock_setsockopt(c_sock, SOL_SOCKET, SO_KEEPALIVE,
ret = zsock_setsockopt(*c_sock, SOL_SOCKET, SO_KEEPALIVE,
&optval, sizeof(optval));
zassert_equal(ret, 0, "setsockopt failed (%d)", errno);
ret = zsock_setsockopt(s_sock, SOL_SOCKET, SO_KEEPALIVE,
ret = zsock_setsockopt(*s_sock, SOL_SOCKET, SO_KEEPALIVE,
&optval, sizeof(optval));
zassert_equal(ret, 0, "setsockopt failed (%d)", errno);

optval = 1;
ret = zsock_setsockopt(c_sock, IPPROTO_TCP, TCP_KEEPIDLE,
ret = zsock_setsockopt(*c_sock, IPPROTO_TCP, TCP_KEEPIDLE,
&optval, sizeof(optval));
zassert_equal(ret, 0, "setsockopt failed (%d)", errno);
ret = zsock_setsockopt(s_sock, IPPROTO_TCP, TCP_KEEPIDLE,
ret = zsock_setsockopt(*s_sock, IPPROTO_TCP, TCP_KEEPIDLE,
&optval, sizeof(optval));
zassert_equal(ret, 0, "setsockopt failed (%d)", errno);

optval = 1;
ret = zsock_setsockopt(c_sock, IPPROTO_TCP, TCP_KEEPINTVL,
ret = zsock_setsockopt(*c_sock, IPPROTO_TCP, TCP_KEEPINTVL,
&optval, sizeof(optval));
zassert_equal(ret, 0, "setsockopt failed (%d)", errno);
ret = zsock_setsockopt(s_sock, IPPROTO_TCP, TCP_KEEPINTVL,
ret = zsock_setsockopt(*s_sock, IPPROTO_TCP, TCP_KEEPINTVL,
&optval, sizeof(optval));
zassert_equal(ret, 0, "setsockopt failed (%d)", errno);

optval = 1;
ret = zsock_setsockopt(c_sock, IPPROTO_TCP, TCP_KEEPCNT,
ret = zsock_setsockopt(*c_sock, IPPROTO_TCP, TCP_KEEPCNT,
&optval, sizeof(optval));
zassert_equal(ret, 0, "setsockopt failed (%d)", errno);
ret = zsock_setsockopt(s_sock, IPPROTO_TCP, TCP_KEEPCNT,
ret = zsock_setsockopt(*s_sock, IPPROTO_TCP, TCP_KEEPCNT,
&optval, sizeof(optval));
zassert_equal(ret, 0, "setsockopt failed (%d)", errno);

/* Establish connection */
test_bind(s_sock, (struct sockaddr *)&s_saddr, sizeof(s_saddr));
test_listen(s_sock);
test_connect(c_sock, (struct sockaddr *)&s_saddr, sizeof(s_saddr));
test_accept(s_sock, &new_sock, NULL, NULL);
test_bind(*s_sock, (struct sockaddr *)&s_saddr, sizeof(s_saddr));
test_listen(*s_sock);
test_connect(*c_sock, (struct sockaddr *)&s_saddr, sizeof(s_saddr));
test_accept(*s_sock, new_sock, NULL, NULL);
}

ZTEST(net_socket_tcp, test_keepalive)
{
int c_sock, s_sock, new_sock;
struct timeval optval = {
.tv_sec = 2,
.tv_usec = 500000,
};
uint8_t rx_buf;
int ret;

test_prepare_keepalive_socks(&c_sock, &s_sock, &new_sock);

ret = zsock_setsockopt(c_sock, SOL_SOCKET, SO_RCVTIMEO, &optval,
sizeof(optval));
zassert_equal(ret, 0, "setsockopt failed (%d)", errno);

/* recv() should fail, but due to receive timeout (no data), not
* connection timeout (keepalive).
*/
ret = zsock_recv(c_sock, &rx_buf, sizeof(rx_buf), 0);
zassert_equal(ret, -1, "recv() should've failed");
zassert_equal(errno, EAGAIN, "wrong errno value, %d", errno);

test_close(c_sock);
test_close(new_sock);
test_close(s_sock);

test_context_cleanup();
}

ZTEST(net_socket_tcp, test_keepalive_timeout)
{
int c_sock, s_sock, new_sock;
uint8_t rx_buf;
int ret;

test_prepare_keepalive_socks(&c_sock, &s_sock, &new_sock);

/* Kill communication - expect that connection will be closed after
* a timeout period.
Expand Down