Fixed TCP connection close.

If TCP FSM is in ESTABLISHED state,  waits  for TCP close handshaking until TIME_WAIT
The purpose is to prevent eth/wifi driver stop and  FIN ACK corrupt.
This may happend if network interface disconnect follows immediately after socket_close.

features/lwipstack/LWIPStack.cpp

@@ -16,6 +16,7 @@
 #include "nsapi.h"
 #include "mbed_interface.h"
 #include "mbed_assert.h"
+#include "rtos/ThisThread.h"
 #include <stdio.h>
 #include <stdbool.h>
 #include <string.h>
@@ -50,9 +51,12 @@ void LWIP::socket_callback(struct netconn *nc, enum netconn_evt eh, u16_t len)
     }
 
     LWIP &lwip = LWIP::get_instance();
-
     lwip.adaptation.lock();
 
+    if (eh == NETCONN_EVT_RCVPLUS && nc->state == NETCONN_NONE) {
+        lwip._event_flag.set(TCP_CLOSED_FLAG);
+    }
+
     for (int i = 0; i < MEMP_NUM_NETCONN; i++) {
         if (lwip.arena[i].in_use
                 && lwip.arena[i].conn == nc
@@ -292,7 +296,17 @@ nsapi_error_t LWIP::socket_open(nsapi_socket_t *handle, nsapi_protocol_t proto)
 nsapi_error_t LWIP::socket_close(nsapi_socket_t handle)
 {
     struct mbed_lwip_socket *s = (struct mbed_lwip_socket *)handle;
-
+#if LWIP_TCP
+    /* Check if TCP FSM is in ESTABLISHED state.
+     * Then give extra time for connection close handshaking  until TIME_WAIT state.
+     * The purpose is to prevent eth/wifi driver stop and  FIN ACK corrupt.
+     * This may happend if network interface disconnect follows immediately after socket_close.*/
+    if (NETCONNTYPE_GROUP(s->conn->type) == NETCONN_TCP && s->conn->pcb.tcp->state == ESTABLISHED) {
+        _event_flag.clear(TCP_CLOSED_FLAG);
+        netconn_shutdown(s->conn, false, true);
+        _event_flag.wait_any(TCP_CLOSED_FLAG, TCP_CLOSE_TIMEOUT);
+    }
+#endif
     netbuf_delete(s->buf);
     err_t err = netconn_delete(s->conn);
     arena_dealloc(s);

features/lwipstack/LWIPStack.h

@@ -587,6 +587,8 @@ class LWIP : public OnboardNetworkStack, private mbed::NonCopyable<LWIP> {
     LWIPMemoryManager memory_manager;
     osThreadId tcpip_thread_id;
     rtos::Mutex adaptation;
+    rtos::EventFlags _event_flag;
+    static const int TCP_CLOSED_FLAG = 0x4u;
 };
 
 #endif /* LWIPSTACK_H_ */

features/lwipstack/lwipopts.h

@@ -244,6 +244,11 @@
 #define LWIP_TCP                    1
 #define TCP_OVERSIZE                0
 #define LWIP_TCP_KEEPALIVE          1
+#ifdef MBED_CONF_TCP_CLOSE_TIMEOUT
+#define TCP_CLOSE_TIMEOUT            MBED_CONF_TCP_CLOSE_TIMEOUT
+#else
+#define TCP_CLOSE_TIMEOUT            1000
+#endif
 #else
 #define LWIP_TCP                    0
 #endif

features/lwipstack/mbed_lib.json

@@ -100,6 +100,10 @@
             "help": "Maximum number of retransmissions of SYN segments. Current default (used if null here) is set to 6 in opt.h",
             "value": null
         },
+        "tcp-close-timeout": {
+            "help": "Maximum number of 1ms intervals for TCP close handshaking timeout",
+            "value": 1000
+        },
         "pbuf-pool-size": {
             "help": "Number of pbufs in pool - usually used for received packets, so this determines how much data can be buffered between reception and the application reading. If a driver uses PBUF_RAM for reception, less pool may be needed. Current default (used if null here) is set to 5 in lwipopts.h, unless overridden by target Ethernet drivers.",
             "value": null