sws: try to remove socket and retry bind

If sws is killed it might leave a stale socket file on the filesystem
which would cause an EADDRINUSE error. After this patch, it is checked
whether the socket is really stale and if so, the socket file gets
removed and another bind is executed.

Signed-off-by: Peter Wu <peter@lekensteyn.nl>

tests/server/sws.c

@@ -2143,6 +2143,48 @@ int main(int argc, char *argv[])
     me.sau.sun_family = AF_UNIX;
     strncpy(me.sau.sun_path, unix_socket, sizeof(me.sau.sun_path));
     rc = bind(sock, &me.sa, sizeof(me.sau));
+    if(0 != rc && errno == EADDRINUSE) {
+      struct stat statbuf;
+      /* socket already exists. Perhaps it is stale? */
+      int unixfd = socket(AF_UNIX, SOCK_STREAM, 0);
+      if(CURL_SOCKET_BAD == unixfd) {
+        error = SOCKERRNO;
+        logmsg("Error binding socket, failed to create socket at %s: (%d) %s",
+               unix_socket, error, strerror(error));
+        goto sws_cleanup;
+      }
+      /* check whether the server is alive */
+      rc = connect(unixfd, &me.sa, sizeof(me.sau));
+      error = errno;
+      close(unixfd);
+      if(ECONNREFUSED != error) {
+        logmsg("Error binding socket, failed to connect to %s: (%d) %s",
+               unix_socket, error, strerror(error));
+        goto sws_cleanup;
+      }
+      /* socket server is not alive, now check if it was actually a socket.
+       * Systems which have UNIX sockets will also have lstat */
+      rc = lstat(unix_socket, &statbuf);
+      if (0 != rc) {
+        logmsg("Error binding socket, failed to stat %s: (%d) %s",
+               unix_socket, errno, strerror(errno));
+        goto sws_cleanup;
+      }
+      if((statbuf.st_mode & S_IFSOCK) != S_IFSOCK) {
+        logmsg("Error binding socket, failed to stat %s: (%d) %s",
+               unix_socket, error, strerror(error));
+        goto sws_cleanup;
+      }
+      /* dead socket, cleanup and retry bind */
+      rc = unlink(unix_socket);
+      if(0 != rc) {
+        logmsg("Error binding socket, failed to unlink %s: (%d) %s",
+               unix_socket, errno, strerror(errno));
+        goto sws_cleanup;
+      }
+      /* stale socket is gone, retry bind */
+      rc = bind(sock, &me.sa, sizeof(me.sau));
+    }
     break;
 #endif /* USE_UNIX_SOCKETS */
   }