Add support for listening on UNIX domain socket

src/server.h

@@ -8,6 +8,7 @@
 #include <stdlib.h>
 #include <stdbool.h>
 #include <signal.h>
+#include <unistd.h>
 #include <errno.h>
 #include <string.h>
 #include <fcntl.h>
@@ -78,6 +79,7 @@ struct tty_server {
     bool readonly;                            // whether not allow clients to write to the TTY
     bool check_origin;                        // whether allow websocket connection from different origin
     bool once;                                // whether accept only one client and exit on disconnection
+    char *socket_path;                        // UNIX domain socket path
     pthread_mutex_t lock;
 };