Fix DLT-Multinode: Gateway does not recognize reset of passive node #551

src/daemon/dlt_daemon_event_handler.c

@@ -228,18 +228,28 @@ int dlt_daemon_handle_event(DltEventHandler *pEvent,
         if (pEvent->pfd[i].revents & DLT_EV_MASK_REJECTED) {
             /* An error occurred, we need to clean-up the concerned event
              */
-            if (type == DLT_CONNECTION_CLIENT_MSG_TCP)
+            if (type == DLT_CONNECTION_CLIENT_MSG_TCP) {
                 /* To transition to BUFFER state if this is final TCP client connection,
                  * call dedicated function. this function also calls
                  * dlt_event_handler_unregister_connection() inside the function.
                  */
                 dlt_daemon_close_socket(fd, daemon, daemon_local, 0);
-            else
-                dlt_event_handler_unregister_connection(pEvent,
-                                                        daemon_local,
-                                                        fd);
-
-            continue;
+                continue;
+            }
+            else if (type == DLT_CONNECTION_GATEWAY) {
+                /* Let the callback function
+                 * dlt_gateway_process_passive_node_messages handle the
+                 * disconnect which was triggered by TCP keepalive after a
+                 * network disconnect. If we directly called
+                 * dlt_event_handler_unregister_connection() here the dlt_gateway would
+                 * not notice that the connection was closed.
+                 */
+                dlt_vlog(LOG_DEBUG, "Connection to dlt gateway broken.\n");
+            }
+            else {
+                dlt_event_handler_unregister_connection(pEvent, daemon_local, fd);
+                continue;
+            }
         }
 
         /* Get the function to be used to handle the event */

src/gateway/dlt_gateway.c

@@ -985,8 +985,9 @@ int dlt_gateway_establish_connections(DltGateway *gateway,
                 }
             }
             else {
-                dlt_log(LOG_DEBUG,
-                        "Passive Node is not up. Connection failed.\n");
+                dlt_vlog(LOG_WARNING,
+                         "Passive Node %s is not up. Connection failed.\n",
+                         con->ecuid);
 
                 con->timeout_cnt++;
 

src/lib/dlt_client.c

@@ -73,6 +73,7 @@
 #else
 #   include <sys/socket.h> /* for socket(), connect(), send(), and recv() */
 #   include <arpa/inet.h> /* for sockaddr_in and inet_addr() */
+#   include <netinet/tcp.h>  /* for TCP keepalive: TCP_KEEPIDLE, TCP_KEEPCNT, TCP_KEEPINTVL */
 #   include <netdb.h>
 #   include <sys/stat.h>
 #   include <sys/un.h>
@@ -172,6 +173,14 @@ DltReturnValue dlt_client_init(DltClient *client, int verbose)
 DltReturnValue dlt_client_connect(DltClient *client, int verbose)
 {
     const int yes = 1;
+    // Keepalive: Opt flag to enable TCP keepalive
+    const int enablekeepalive = 1;
+    // Keepalive: Seconds of idle before sending keepalive probes
+    const int keepidle = 10;
+    // Keepalive: Number of probes to send before considering the connection dead
+    const int keepcount = 2;
+    // Keepalive: Interval between the probes
+    const int keepintvl = 3;
     char portnumbuffer[33] = {0};
     struct addrinfo hints, *servinfo, *p;
     struct sockaddr_un addr;
@@ -212,6 +221,45 @@ DltReturnValue dlt_client_connect(DltClient *client, int verbose)
                 continue;
             }
 
+            /* Enable TCP keepalive to detect broken connections due to network disconnects.
+             * Without this in cases where no TCP FIN or RST package is received from the server,
+             * the dlt_client will never notice that it was disconnected from the server and so
+             * it will not reconnect when the server is available again.
+             */
+            if (setsockopt(client->sock, SOL_SOCKET, SO_KEEPALIVE,
+                           &enablekeepalive, sizeof(enablekeepalive)) < 0) {
+                dlt_vlog(LOG_WARNING,
+                        "%s: Failed to set SO_KEEPALIVE on socket: %s\n",
+                        __func__, strerror(errno));
+                close(client->sock);
+                continue;
+            }
+
+            if (setsockopt(client->sock, IPPROTO_TCP, TCP_KEEPIDLE,
+                            &keepidle, sizeof(keepidle)) < 0) {
+                dlt_vlog(LOG_WARNING,
+                         "%s: Failed to set TCP_KEEPIDLE on socket: %s\n",
+                         __func__, strerror(errno));
+                close(client->sock);
+                continue;
+            }
+            if (setsockopt(client->sock, IPPROTO_TCP, TCP_KEEPCNT,
+                            &keepcount, sizeof(keepcount)) < 0) {
+                dlt_vlog(LOG_WARNING,
+                         "%s: Failed to set TCP_KEEPCNT on socket: %s\n",
+                         __func__, strerror(errno));
+                close(client->sock);
+                continue;
+            }
+            if (setsockopt(client->sock, IPPROTO_TCP, TCP_KEEPINTVL,
+                            &keepintvl, sizeof(keepintvl)) < 0) {
+                dlt_vlog(LOG_WARNING,
+                         "%s: Failed to set TCP_KEEPINTVL on socket: %s\n",
+                         __func__, strerror(errno));
+                close(client->sock);
+                continue;
+            }
+
             /* Set socket to Non-blocking mode */
             if(fcntl(client->sock, F_SETFL, fcntl(client->sock,F_GETFL,0) | O_NONBLOCK) < 0)
             {
@@ -273,8 +321,10 @@ DltReturnValue dlt_client_connect(DltClient *client, int verbose)
 
         if (p == NULL) {
             dlt_vlog(LOG_ERR,
-                     "%s: ERROR: failed to connect! %s\n",
+                     "%s: ERROR: failed to connect to %s:%s! %s\n",
                      __func__,
+                     client->servIP,
+                     portnumbuffer,
                      strerror(connect_errno));
             return DLT_RETURN_ERROR;
         }