Echo server: Difference between revisions

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@@ Line 361: / Line 361: @@
 #define BUF_LEN 256
 #define PORT_STR "12321"
+/* ------------------------------------------------------------ */
+/* How to clean up after dead child processes                   */
+/* ------------------------------------------------------------ */
 void wait_for_zombie(int s)
 {
-   while(waitpid(-1, NULL, WNOHANG) > 0) ;
+    while(waitpid(-1, NULL, WNOHANG) > 0) ;
 }
+/* ------------------------------------------------------------ */
+/* Core of implementation of a child process                    */
+/* ------------------------------------------------------------ */
+void echo_lines(int csock)
+{
+    char buf[BUF_LEN];
+    int r;
+    while( (r = read(csock, buf, BUF_LEN)) > 0 ) {
+        (void)write(csock, buf, r);
+    }
+    exit(EXIT_SUCCESS);
+}
+/* ------------------------------------------------------------ */
+/* Core of implementation of the parent process                 */
+/* ------------------------------------------------------------ */
+void take_connections_forever(int ssock)
+{
+    for(;;) {
+        struct sockaddr addr;
+        socklen_t addr_size = sizeof(addr);
+        int csock;
+        /* Block until we take one connection to the server socket */
+        csock = accept(ssock, &addr, &addr_size);
+        /* If it was a successful connection, spawn a worker process to service it */
+        if ( csock == -1 ) {
+            perror("accept");
+        } else if ( fork() == 0 ) {
+            close(ssock);
+            echo_lines(csock);
+        } else {
+            close(csock);
+        }
+    }
+}
+/* ------------------------------------------------------------ */
+/* The server process's one-off setup code                      */
+/* ------------------------------------------------------------ */
 int main()
 {
     struct addrinfo hints, *res;
-    struct sockaddr addr;
     struct sigaction sa;
-    socklen_t addr_size;
     int sock;
+    /* Look up the address to bind to */
     memset(&hints, 0, sizeof(struct addrinfo));
     hints.ai_family = AF_UNSPEC;
     hints.ai_socktype = SOCK_STREAM;
     hints.ai_flags = AI_PASSIVE;
     if ( getaddrinfo(NULL, PORT_STR, &hints, &res) != 0 ) {
         perror("getaddrinfo");
@@ Line 385: / Line 432: @@
     }
+    /* Make a socket */
     if ( (sock = socket(res->ai_family, res->ai_socktype, res->ai_protocol)) == -1 ) {
         perror("socket");
@@ Line 390: / Line 438: @@
     }
+    /* Arrange to clean up child processes (the workers) */
     sa.sa_handler = wait_for_zombie;
     sigemptyset(&sa.sa_mask);
     sa.sa_flags = SA_RESTART;
-    if ( sigaction(SIGCHLD, &sa, NULL) == - 1 ) {
+    if ( sigaction(SIGCHLD, &sa, NULL) == -1 ) {
         perror("sigaction");
         exit(EXIT_FAILURE);
     }
+    /* Associate the socket with its address */
-    if ( bind(sock, res->ai_addr, res->ai_addrlen) == 0 ) {
+    if ( bind(sock, res->ai_addr, res->ai_addrlen) != 0 ) {
-        freeaddrinfo(res);
+        perror("bind");
-        if ( listen(sock, MAX_ENQUEUED) == 0 ) {
+        exit(EXIT_FAILURE);
+    }
-            /* Serve the listening socket infinitely often */
-            for(;;) {
-                addr_size = sizeof(addr);
-                int csock = accept(sock, &addr, &addr_size);
-                if ( csock == -1 ) {
-                    perror("accept");
-                } else {
-                    if ( fork() == 0 ) {
-                        close(sock);
+    freeaddrinfo(res);
-                        /* Echo loop */
-                        char buf[BUF_LEN];
-                        int r;
-                        while( (r = read(csock, buf, BUF_LEN)) > 0 ) {
-                            (void)write(csock, buf, r);
-                        }
-                        exit(EXIT_SUCCESS);
+    /* State that we've opened a server socket and are listening for connections */
-                    }
+    if ( listen(sock, MAX_ENQUEUED) != 0 ) {
-                    close(csock);
-                }
+        perror("listen");
-            }
-        } else {
-            perror("listen");
-            exit(EXIT_FAILURE);
-        }
-    } else {
-        perror("bind");
         exit(EXIT_FAILURE);
     }
+    /* Serve the listening socket until killed */
+    take_connections_forever(sock);
     return EXIT_SUCCESS;
 }</lang>