socket: Add new test for connect

This commit adds a simple bind/accept/connect test for an IPv4 TCP
connection to a local process via the loopback interface.

Reviewed-by: Arjun Shankar <arjun@redhat.com>

socket/Makefile

@@ -70,6 +70,7 @@ tests := \
   tst-accept4 \
   tst-cmsg_cloexec \
   tst-cmsghdr \
+  tst-connect \
   tst-sockopt \
   # tests
 

socket/tst-connect.c

@@ -0,0 +1,113 @@
+/* Test the connect function.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <arpa/inet.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <support/check.h>
+#include <support/xsocket.h>
+#include <support/xunistd.h>
+#include <sys/socket.h>
+#include <stdio.h>
+
+static struct sockaddr_in server_address;
+
+int
+open_socket_inet_tcp (void)
+{
+  int fd = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP);
+  if (fd < 0)
+    {
+      if (errno == EAFNOSUPPORT)
+        FAIL_UNSUPPORTED ("The host does not support IPv4");
+      else
+        FAIL_EXIT1 ("socket (AF_INET, SOCK_STREAM, IPPROTO_TCP): %m\n");
+    }
+  return fd;
+}
+
+static pid_t
+start_server (void)
+{
+  server_address.sin_family = AF_INET;
+  server_address.sin_port = 0;
+  server_address.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
+
+  int server_sock = open_socket_inet_tcp ();
+
+  xbind (server_sock, (struct sockaddr *) &server_address,
+         sizeof (server_address));
+
+  socklen_t sa_len = sizeof (server_address);
+  xgetsockname (server_sock, (struct sockaddr *) &server_address, &sa_len);
+  xlisten (server_sock, 5);
+
+  pid_t my_pid = xfork ();
+  if (my_pid > 0)
+    {
+      xclose (server_sock);
+      return my_pid;
+    }
+
+  struct sockaddr_in client_address;
+  socklen_t ca_len = sizeof (server_address);
+  int client_sock = xaccept (server_sock, (struct sockaddr *) &client_address,
+                             &ca_len);
+  printf ("socket accepted %d\n", client_sock);
+
+  _exit (0);
+}
+
+static int
+do_test (void)
+{
+  pid_t serv_pid;
+  struct sockaddr_in peer;
+  socklen_t peer_len;
+
+  serv_pid = start_server ();
+  int client_sock = open_socket_inet_tcp ();
+  xconnect (client_sock, (const struct sockaddr *) &server_address,
+            sizeof (server_address));
+
+  /* A second connect with same arguments should fail with EISCONN.  */
+  int result = connect (client_sock,
+                        (const struct sockaddr *) &server_address,
+                        sizeof (server_address));
+  if (result == 0 || errno != EISCONN)
+    FAIL_EXIT1 ("Second connect (%d), should fail with EISCONN: %m",
+                client_sock);
+
+  peer_len = sizeof (peer);
+  xgetpeername (client_sock, (struct sockaddr *) &peer, &peer_len);
+  TEST_COMPARE (peer_len, sizeof (peer));
+  TEST_COMPARE (peer.sin_port, server_address.sin_port);
+  TEST_COMPARE_BLOB (&peer.sin_addr, sizeof (peer.sin_addr),
+                     &server_address.sin_addr,
+                     sizeof (server_address.sin_addr));
+
+  int status;
+  xwaitpid (serv_pid, &status, 0);
+  TEST_COMPARE (status, 0);
+
+  return 0;
+}
+
+#include <support/test-driver.c>