simulator: shutdown connection

TCP is fun. If the server initiates the closing of the TCP connection
the socket needs to stay alive for some time according to the protocol
so that out-of-order and delayed packets have a chance to arrive. When
the simulator gets shut down those packets doesn't matter. Luckily there
is a way around, by setting SO_LINGER on the socket the connection is
closed with a "RESET" instead and the socket is immediately released in
the OS.

This commit also switches from signal(2) to sigaction(2) so that we can
avoid setting SA_RESTART so that signals interrupt blocking syscalls
like read.

It also introduces support for "SIGHUP" that can be used to simply
disconnect the client.

Author: NickeZ

test/simulator/README.md

@@ -0,0 +1,6 @@
+# Simulator
+
+## Signals
+
+The simulator can be forcefully shutdown with SIGTERM. It can also be told to
+disconnect from the client using SIGHUP.

test/simulator/simulator.c

@@ -42,7 +42,8 @@ static const char* _simulator_version = "1.0.0";
 int data_len;
 int commfd;
 
-static volatile sig_atomic_t sigint_called = false;
+static volatile sig_atomic_t quitting = false;
+static volatile sig_atomic_t hangup = false;
 static int sockfd;
 
 static int get_usb_message_socket(uint8_t* input)
@@ -71,17 +72,28 @@ static void simulate_firmware_execution(const uint8_t* input)
     usb_processing_process(usb_processing_hww());
 }
 
-static void _int_handler(int signum)
+static void _quit_handler(int signum)
 {
     (void)signum;
-    sigint_called = true;
-    close(sockfd);
+    quitting = true;
+}
+
+static void _hup_handler(int signum)
+{
+    (void)signum;
+    hangup = true;
 }
 
 int main(int argc, char* argv[])
 {
-    signal(SIGINT, _int_handler);
-    // Default port number
+    struct sigaction psa;
+    memset(&psa, 0, sizeof(struct sigaction));
+    psa.sa_handler = _quit_handler;
+    sigaction(SIGINT, &psa, NULL);
+    sigaction(SIGTERM, &psa, NULL);
+    psa.sa_handler = _hup_handler;
+    sigaction(SIGHUP, &psa, NULL);
+    //  Default port number
     int portno = 15423;
 
     struct option long_options[] = {
@@ -162,11 +174,12 @@ int main(int argc, char* argv[])
     while (1) {
         if ((commfd = accept(sockfd, (struct sockaddr*)&serv_addr, (socklen_t*)&serv_addr_len)) <
             0) {
-            if (sigint_called) {
-                printf("\nGot Ctrl-C, exiting\n");
+            if (quitting) {
+                printf("\nGot signal, exiting\n");
+                break;
             }
             perror("accept");
-            return 1;
+            break;
         }
         printf("Socket connection setup success\n");
 
@@ -175,7 +188,33 @@ int main(int argc, char* argv[])
         int temp_len;
         while (1) {
             // Simulator polls for USB messages from client and then processes them
-            if (!get_usb_message_socket(input)) break;
+            if (get_usb_message_socket(input) < 1) {
+                if (quitting) {
+                    printf("\nGot term/int signal, exiting\n");
+                    // Using LINGER we force a TCP RST instead of graceful shutdown. Without this
+                    // trick the port keeps being bound for 10s of seconds after the application has
+                    // died, hindering future executions.
+                    struct linger sol = {.l_onoff = 1, .l_linger = 0};
+                    int res = setsockopt(commfd, SOL_SOCKET, SO_LINGER, &sol, sizeof(sol));
+                    if (res) {
+                        perror("setsockopt");
+                    }
+                    shutdown(commfd, SHUT_RDWR);
+                    uint8_t buf[1024];
+                    while (read(commfd, buf, sizeof(buf)) > 0);
+                    close(commfd);
+                    goto after_main_loop;
+                }
+                if (hangup) {
+                    hangup = false;
+                    printf("\nGot hangup signal, disconnecting\n");
+                    shutdown(commfd, SHUT_RDWR);
+                    uint8_t buf[1024];
+                    while (read(commfd, buf, sizeof(buf)) > 0);
+                    close(commfd);
+                }
+                break;
+            }
             simulate_firmware_execution(input);
 
             // If the USB message to be sent from firmware is bigger than one packet,
@@ -196,5 +235,7 @@ int main(int argc, char* argv[])
         printf("Socket connection closed\n");
         printf("Waiting for new clients, CTRL+C to shut down the simulator\n");
     }
+after_main_loop:
+    close(sockfd);
     return 0;
 }