From b48ea36192617b978e3729d85c8bb148bd02c417 Mon Sep 17 00:00:00 2001
From: "Sergio R. Caprile" <scaprile@cesanta.com>
Date: Wed, 25 Feb 2026 14:14:44 -0300
Subject: [PATCH] add tests for TCP RST handling

---
 test/mip_test.c                               | 55 ++++++++++++++++++-
 .../arduino/sim800-mqtt/mongoose_config.h     |  2 +-
 2 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/test/mip_test.c b/test/mip_test.c
index 8af7f580..06ecfc63 100644
--- a/test/mip_test.c
+++ b/test/mip_test.c
@@ -378,8 +378,8 @@ static void test_tcp_basics(bool ipv6) {
 
   init_tcp_tests(&mgr, &e, &ipp, &driver, &mif, fn);
 
-  // https://datatracker.ietf.org/doc/html/rfc9293#section-3.5.2	Reset
-  // Generation non-used port. Group 1 in RFC send SYN, expect RST + ACK
+  // - https://datatracker.ietf.org/doc/html/rfc9293#section-3.5.2
+  // Reset generation, non-used port. Group 1 in RFC send SYN expect RST + ACK
   create_tcp_seg(&e, &ipp, 1234, 4321, TH_SYN, 1, 69, 0, NULL, 0);
   mg_mgr_poll(&mgr, 0);  // make sure we clean former stuff in buffer
   while (!received_response(&s_driver_data)) mg_mgr_poll(&mgr, 0);
@@ -469,7 +469,7 @@ static void test_tcp_basics(bool ipv6) {
   ASSERT(t->flags == TH_RST);
   ASSERT(t->seq == mg_htonl(4321));
 
-  // we currently don't validate checksum, no silently discarded segment test
+  // no silently discarded segment test
 
   init_tcp_handshake(&e, &ipp, &mgr);  // starts with seq_no=1000, ackno=2
 
@@ -681,6 +681,55 @@ static void test_tcp_basics(bool ipv6) {
   s_driver_data.len = 0;
   mg_mgr_free(&mgr);
 
+  // Test RST handling
+  // https://datatracker.ietf.org/doc/html/rfc9293#section-3.5.3
+  init_tcp_tests(&mgr, &e, &ipp, &driver, &mif, fn);
+  init_tcp_handshake(&e, &ipp, &mgr);  // starts with seq_no=1000, ackno=2
+
+  // RST with seq_no way out of window
+  create_tcp_seg(&e, &ipp, 1000000, 2, TH_RST, 1, 80, 0, NULL, 0);
+  mg_mgr_poll(&mgr, 0);
+  ASSERT(!received_response(&s_driver_data));
+  // make sure it is NOT closed
+  ASSERT(mgr.conns->next != NULL);  // two connections: listener + ours
+
+  {  // RST with seq_no within window but alien address
+    uint32_t ip4 = 0;
+#if MG_ENABLE_IPV6  // forge source address
+    uint64_t ip6_0 = 0;
+    if (ipp.ip6 != NULL) {
+      ip6_0 = ip6.src[0];
+      ip6.src[0] = ip6.src[0] << 1;
+    } else
+#endif
+    {
+      ip4 = ip.src;
+      ip.src = ip.src << 1;
+    }
+    create_tcp_seg(&e, &ipp, 1010, 2, TH_RST, 1, 80, 0, NULL, 0);
+    mg_mgr_poll(&mgr, 0);
+    ASSERT(!received_response(&s_driver_data));
+    // make sure it is NOT closed
+    ASSERT(mgr.conns->next != NULL);  // two connections: listener + ours
+#if MG_ENABLE_IPV6  // restore source address
+    if (ipp.ip6 != NULL) {
+      ip6.src[0] = ip6_0;
+    } else
+#endif
+    {
+      ip.src = ip4;
+    }
+  }
+  // RST with seq_no within window
+  create_tcp_seg(&e, &ipp, 1010, 2, TH_RST, 1, 80, 0, NULL, 0);
+  mg_mgr_poll(&mgr, 0);
+  ASSERT(!received_response(&s_driver_data));
+  // make sure it is closed
+  ASSERT(mgr.conns->next == NULL);  // only one connection: the listener
+
+  s_driver_data.len = 0;
+  mg_mgr_free(&mgr);
+
   // Test responses to a connecting client
   // https://datatracker.ietf.org/doc/html/rfc9293#section-3.5
   // NOTE: Mongoose ignores any data until connection is actually established
diff --git a/tutorials/mqtt/mqtt-client/arduino/sim800-mqtt/mongoose_config.h b/tutorials/mqtt/mqtt-client/arduino/sim800-mqtt/mongoose_config.h
index 803047e2..193ea6ba 100644
--- a/tutorials/mqtt/mqtt-client/arduino/sim800-mqtt/mongoose_config.h
+++ b/tutorials/mqtt/mqtt-client/arduino/sim800-mqtt/mongoose_config.h
@@ -10,7 +10,7 @@
 #define MG_ARCH MG_ARCH_CUSTOM
 #define MG_ENABLE_SOCKET 0
 #define MG_ENABLE_TCPIP 1
-#define MG_ENABLE_DRIVER_PPP 1
+#define MG_ENABLE_DRIVER_ATCMD 1
 #define MG_ENABLE_TCPIP_DRIVER_INIT 0
 #define MG_ENABLE_TCPIP_PRINT_DEBUG_STATS 0
 #define MG_ENABLE_CUSTOM_MILLIS 1