Use local sockets for client-spawned servers

This looks much less suspicious to the Windows firewall.

client/clinet.cpp

@@ -115,33 +115,23 @@ static void error_on_socket()
 }
 
 /**
-   Try to connect to a server:
-    - try to create a TCP socket to the given URL (default to
-      localhost:DEFAULT_SOCK_PORT).
-    - if successful:
-           - start monitoring the socket for packets from the server
-           - send a "login request" packet to the server
-       and - return 0
-    - if unable to create the connection, close the socket, put an error
-      message in ERRBUF and return the Unix error code (ie., errno, which
-      will be non-zero).
+ * Try to connect to a server:
+ *  - try to create a TCP socket to the given URL
+ *  - if successful:
+ *         - start monitoring the socket for packets from the server
+ *         - send a "login request" packet to the server
+ *     and - return 0
+ *  - if unable to create the connection, close the socket, put an error
+ *    message in ERRBUF and return the Unix error code (ie., errno, which
+ *    will be non-zero).
  */
 static int try_to_connect(const QUrl &url, char *errbuf, int errbufsize)
 {
-  // Apply defaults
-  auto url_copy = url;
-  if (url_copy.host().isEmpty()) {
-    url_copy.setHost(QStringLiteral("localhost"));
-  }
-  if (url_copy.port() <= 0) {
-    url_copy.setPort(DEFAULT_SOCK_PORT);
-  }
-
   connections_set_close_callback(client_conn_close_callback);
 
   // connection in progress? wait.
   if (client.conn.used) {
-    if (url_copy != connect_to) {
+    if (url != connect_to) {
       (void) fc_strlcpy(
           errbuf, _("Canceled previous connection, trying new connection."),
           errbufsize);
@@ -151,7 +141,7 @@ static int try_to_connect(const QUrl &url, char *errbuf, int errbufsize)
                     qobject_cast<QLocalSocket *>(client.conn.sock)) {
         local->abort();
       }
-      connect_to = url_copy;
+      connect_to = url;
     } else {
       (void) fc_strlcpy(errbuf, _("Connection in progress."), errbufsize);
       return -1;

client/connectdlg_common.cpp

@@ -19,6 +19,7 @@
 #include <QStandardPaths>
 #include <QTcpServer>
 #include <QUrl>
+#include <QUuid>
 
 #include <cstdio>
 #include <cstring>
@@ -238,15 +239,17 @@ bool client_start_server(const QString &user_name)
     return false;
   }
 
+  // Unique name for this game
+  auto uuid = QUuid::createUuid().toString(QUuid::WithoutBraces);
+
   ruleset = QString::fromUtf8(tileset_what_ruleset(tileset));
 
   // Set up the command-line parameters.
   port_buf = QString::number(internal_server_port);
   savesdir = QStringLiteral("%1/saves").arg(storage);
   scensdir = QStringLiteral("%1/scenarios").arg(storage);
 
-  arguments << QStringLiteral("-p") << port_buf << QStringLiteral("--bind")
-            << QStringLiteral("localhost") << QStringLiteral("-q")
+  arguments << QStringLiteral("--local") << uuid << QStringLiteral("-q")
             << QStringLiteral("1") << QStringLiteral("-e")
             << QStringLiteral("--saves") << savesdir
             << QStringLiteral("--scenarios") << scensdir
@@ -297,10 +300,9 @@ bool client_start_server(const QString &user_name)
 
   // Local server URL
   auto url = QUrl();
-  url.setScheme(QStringLiteral("fc21"));
+  url.setScheme(QStringLiteral("fc21+local"));
   url.setUserName(user_name);
-  url.setHost(QStringLiteral("localhost"));
-  url.setPort(internal_server_port);
+  url.setPath(uuid);
 
   // a reasonable number of tries
   while (connect_to_server(