fix dns not found server crash error

Author: Wei Li

proxylab-handout/csapp.c

@@ -981,7 +981,15 @@ int open_clientfd(char *hostname, char *port) {
     hints.ai_socktype = SOCK_STREAM;  /* Open a connection */
     hints.ai_flags = AI_NUMERICSERV;  /* ... using a numeric port arg. */
     hints.ai_flags |= AI_ADDRCONFIG;  /* Recommended for connections */
-    Getaddrinfo(hostname, port, &hints, &listp);
+    
+    /* fixed by weili.
+     * To avoid crashing the server, we don't report an error directly
+     */
+    if (getaddrinfo(hostname, port, &hints, &listp) != 0) {
+        fprintf(stderr, "Could not resolve host: %s\n", hostname);
+        return -1;
+    }
+    // Getaddrinfo(hostname, port, &hints, &listp);
 
     /* Walk the list for one that we can successfully connect to */
     for (p = listp; p; p = p->ai_next) {

proxylab-handout/proxy.c

@@ -102,6 +102,7 @@ void forward_response(const char *key, int infd, int outfd)
     bytes_free(&response);
 }
 
+
 /* forward  -- forward the request to remote server and the response from
  * remote server
  */
@@ -211,6 +212,8 @@ void forward(int fromfd)
 #endif
     int clientfd = open_clientfd_ww(host, port);
     if (clientfd < 0) {
+        // TODO: is it ok to directly return?
+        // Maybe better error handling expected.
         return ;
     }
     if (rio_writen_ww(clientfd, request_buf, strlen(request_buf)) < 0) {
@@ -223,6 +226,7 @@ void forward(int fromfd)
     close_ww(clientfd);
 }
 
+
 /* thread  -- the things to do for each thread */
 void *thread(void *vargp)
 {