TCP server now sends/handles ping packets.

docs/TCP_Network.txt

@@ -101,9 +101,9 @@ special ids and packets:
 3 - Disconnect notification:
 [uint8_t id (3)][uint8_t (packet id of connection that got disconnected)]
 4 - ping packet
-[uint8_t id (4)][uint64_t ping_id]
+[uint8_t id (4)][uint64_t ping_id (0 is invalid)]
 5 - ping response (pong)
-[uint8_t id (5)][uint64_t ping_id]
+[uint8_t id (5)][uint64_t ping_id (0 is invalid)]
 8 - onion packet (same format as initial onion packet (See: Prevent 
 tracking.txt) but packet id is 8 instead of 128)
 9 - onion packet response (same format as onion packet with id 142 but id is 9 

toxcore/TCP_server.c

@@ -26,6 +26,8 @@
 #include <sys/ioctl.h>
 #endif
 
+#include "util.h"
+
 /* return 1 if valid
  * return 0 if not valid
  */
@@ -168,6 +170,8 @@ static int add_accepted(TCP_Server *TCP_server, TCP_Secure_Connection *con)
     TCP_server->accepted_connection_array[index].status = TCP_STATUS_CONFIRMED;
     ++TCP_server->num_accepted_connections;
     TCP_server->accepted_connection_array[index].identifier = ++TCP_server->counter;
+    TCP_server->accepted_connection_array[index].last_pinged = unix_time();
+    TCP_server->accepted_connection_array[index].ping_id = 0;
     return index;
 }
 
@@ -640,14 +644,29 @@ static int handle_TCP_packet(TCP_Server *TCP_server, uint32_t con_id, uint8_t *d
             if (length != 1 + sizeof(uint64_t))
                 return -1;
 
-            break;
+            uint8_t response[1 + sizeof(uint64_t)];
+            response[0] = TCP_PACKET_PONG;
+            memcpy(response + 1, data + 1, sizeof(uint64_t));
+            write_packet_TCP_secure_connection(con, response, sizeof(response));
+            return 0;
         }
 
         case TCP_PACKET_PONG: {
             if (length != 1 + sizeof(uint64_t))
                 return -1;
 
-            break;
+            uint64_t ping_id;
+            memcpy(&ping_id, data + 1, sizeof(uint64_t));
+
+            if (ping_id) {
+                if (ping_id == con->ping_id) {
+                    con->ping_id = 0;
+                }
+
+                return 0;
+            } else {
+                return -1;
+            }
         }
 
         case TCP_PACKET_ONION_REQUEST: {
@@ -898,6 +917,29 @@ static void do_TCP_confirmed(TCP_Server *TCP_server)
         if (conn->status != TCP_STATUS_CONFIRMED)
             continue;
 
+        if (is_timeout(conn->last_pinged, TCP_PING_FREQUENCY)) {
+            uint8_t ping[1 + sizeof(uint64_t)];
+            ping[0] = TCP_PACKET_PING;
+            uint64_t ping_id = random_64b();
+
+            if (!ping_id)
+                ++ping_id;
+
+            memcpy(ping + 1, &ping_id, sizeof(uint64_t));
+            int ret = write_packet_TCP_secure_connection(conn, ping, sizeof(ping));
+
+            if (ret == 1) {
+                conn->last_pinged = unix_time();
+                conn->ping_id = ping_id;
+            }
+        }
+
+        if (conn->ping_id && is_timeout(conn->last_pinged, TCP_PING_TIMEOUT)) {
+            kill_TCP_connection(conn);
+            del_accepted(TCP_server, i);
+            continue;
+        }
+
         send_pending_data(conn);
         uint8_t packet[MAX_PACKET_SIZE];
         int len;
@@ -920,6 +962,8 @@ static void do_TCP_confirmed(TCP_Server *TCP_server)
 
 void do_TCP_server(TCP_Server *TCP_server)
 {
+    unix_time_update();
+
     do_TCP_accept_new(TCP_server);
     do_TCP_incomming(TCP_server);
     do_TCP_unconfirmed(TCP_server);

toxcore/TCP_server.h

@@ -49,6 +49,10 @@
 
 #define TCP_ONION_FAMILY (AF_INET6 + 1)
 
+/* frequency to ping connected nodes and timeout in seconds */
+#define TCP_PING_FREQUENCY 30
+#define TCP_PING_TIMEOUT 20
+
 enum {
     TCP_STATUS_NO_STATUS,
     TCP_STATUS_CONNECTED,
@@ -75,6 +79,9 @@ typedef struct TCP_Secure_Connection {
     uint16_t last_packet_sent;
 
     uint64_t identifier;
+
+    uint64_t last_pinged;
+    uint64_t ping_id;
 } TCP_Secure_Connection;