From 69e8c0a92fed0c497a68e1d639ed661088f8b20c Mon Sep 17 00:00:00 2001
From: cpq <sergey.lyubka@cesanta.com>
Date: Fri, 30 Oct 2026 09:33:54 +0000
Subject: [PATCH] Fix: DHCP client stuck in REQUESTING state forever if the
 REQUEST or ACK is lost

---
 mongoose.c        | 4 ++++
 src/net_builtin.c | 4 ++++
 test/mip_test.c   | 4 ++++
 3 files changed, 12 insertions(+)

diff --git a/mongoose.c b/mongoose.c
index e06b827f..615fd9a7 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -9399,6 +9399,7 @@ static void rx_dhcp_client(struct mg_tcpip_if *ifp, struct pkt *pkt) {
                         : pkt->dhcp->siaddr ? pkt->dhcp->siaddr
                                             : pkt->ip->src);
     ifp->state = MG_TCPIP_STATE_REQ;  // REQUESTING state
+    ifp->lease_expire = ifp->now + 5000;  // No ACK by then: start over
   } else if (msgtype == 5) {          // DHCPACK
     if (ifp->state == MG_TCPIP_STATE_REQ && ip && gw && lease) {  // got an IP
       uint64_t rand;
@@ -10706,6 +10707,9 @@ static void mg_ip_poll(struct mg_tcpip_if *ifp, bool s1) {
   if (ifp->enable_dhcp_client && s1) {
     if (ifp->state == MG_TCPIP_STATE_UP) {
       tx_dhcp_discover(ifp);  // INIT (4.4.1)
+    } else if (ifp->state == MG_TCPIP_STATE_REQ &&
+               ifp->now >= ifp->lease_expire) {
+      ifp->state = MG_TCPIP_STATE_UP;  // REQUEST or ACK lost: DISCOVER again
     } else if (ifp->state == MG_TCPIP_STATE_READY &&
                ifp->lease_expire > 0) {  // BOUND / RENEWING / REBINDING
       if (ifp->now >= ifp->lease_expire) {
diff --git a/src/net_builtin.c b/src/net_builtin.c
index 95f29e93..ec9882f0 100644
--- a/src/net_builtin.c
+++ b/src/net_builtin.c
@@ -734,6 +734,7 @@ static void rx_dhcp_client(struct mg_tcpip_if *ifp, struct pkt *pkt) {
                         : pkt->dhcp->siaddr ? pkt->dhcp->siaddr
                                             : pkt->ip->src);
     ifp->state = MG_TCPIP_STATE_REQ;  // REQUESTING state
+    ifp->lease_expire = ifp->now + 5000;  // No ACK by then: start over
   } else if (msgtype == 5) {          // DHCPACK
     if (ifp->state == MG_TCPIP_STATE_REQ && ip && gw && lease) {  // got an IP
       uint64_t rand;
@@ -2041,6 +2042,9 @@ static void mg_ip_poll(struct mg_tcpip_if *ifp, bool s1) {
   if (ifp->enable_dhcp_client && s1) {
     if (ifp->state == MG_TCPIP_STATE_UP) {
       tx_dhcp_discover(ifp);  // INIT (4.4.1)
+    } else if (ifp->state == MG_TCPIP_STATE_REQ &&
+               ifp->now >= ifp->lease_expire) {
+      ifp->state = MG_TCPIP_STATE_UP;  // REQUEST or ACK lost: DISCOVER again
     } else if (ifp->state == MG_TCPIP_STATE_READY &&
                ifp->lease_expire > 0) {  // BOUND / RENEWING / REBINDING
       if (ifp->now >= ifp->lease_expire) {
diff --git a/test/mip_test.c b/test/mip_test.c
index 365650f1..75656867 100644
--- a/test/mip_test.c
+++ b/test/mip_test.c
@@ -80,6 +80,10 @@ static void test_statechange(void) {
   onstatechange(&iface);
   ASSERT(executed == true);
   executed = false;
+  iface.enable_dhcp_client = true;  // DHCP REQUEST unanswered: start over
+  iface.state = MG_TCPIP_STATE_REQ, iface.lease_expire = 0;
+  mg_ip_poll(&iface, true);
+  ASSERT(iface.state == MG_TCPIP_STATE_UP);
 }
 #if MG_ENABLE_IPV6
 static void mif6_fn(struct mg_tcpip_if *ifp, int ev, void *ev_data) {