Remote control: Allow using a random TCP socket as the remote control socket and also allow using TCP sockets in kitty.conf

docs/changelog.rst

@@ -47,6 +47,8 @@ Detailed list of changes
 
 - kitten @ ls: Allow limiting output to matched windows/tabs (:iss:`6520`)
 
+- Remote control: Allow using a random TCP socket as the remote control socket and also allow using TCP sockets in :opt:`listen_on`
+
 - X11: Print an error to :file:`STDERR` instead of refusing to start when the user sets a custom window icon larger than 128x128 (:iss:`6507`)
 
 0.29.2 [2023-07-27]

kitty/boss.py

@@ -169,14 +169,18 @@ class OSWindowDict(TypedDict):
     wm_name: str
 
 
-def listen_on(spec: str) -> int:
+def listen_on(spec: str) -> Tuple[int, str]:
     import socket
     family, address, socket_path = parse_address_spec(spec)
     s = socket.socket(family)
     atexit.register(remove_socket_file, s, socket_path)
     s.bind(address)
     s.listen()
-    return s.fileno()
+    if isinstance(address, tuple):
+        h, resolved_port = s.getsockname()
+        sfamily, host, port = spec.split(':', 2)
+        spec = f'{sfamily}:{host}:{resolved_port}'
+    return s.fileno(), spec
 
 
 def data_for_at(w: Optional[Window], arg: str, add_wrap_markers: bool = False) -> Optional[str]:
@@ -357,8 +361,7 @@ def __init__(
             self.allow_remote_control = 'n'
         self.listening_on = ''
         if args.listen_on and self.allow_remote_control in ('y', 'socket', 'socket-only', 'password'):
-            listen_fd = listen_on(args.listen_on)
-            self.listening_on = args.listen_on
+            listen_fd, self.listening_on = listen_on(args.listen_on)
         self.child_monitor = ChildMonitor(
             self.on_child_death,
             DumpCommands(args) if args.dump_commands or args.dump_bytes else None,

kitty/cli.py

@@ -948,8 +948,8 @@ def options_spec() -> str:
 :italic:`{appname} @` within a kitty window, there is no need to specify the
 :option:`{appname} @ --to` option as it will automatically read from the
 environment. Note that this will be ignored unless :opt:`allow_remote_control`
-is set to either: :code:`yes`, :code:`socket` or :code:`socket-only`.  For UNIX
-sockets, this can also be specified in :file:`{conf_name}.conf`.
+is set to either: :code:`yes`, :code:`socket` or :code:`socket-only`. This can
+also be specified in :file:`kitty.conf`.
 
 
 --start-as

kitty/main.py

@@ -359,7 +359,7 @@ def macos_cmdline(argv_args: List[str]) -> List[str]:
 
 def expand_listen_on(listen_on: str, from_config_file: bool) -> str:
     listen_on = expandvars(listen_on)
-    if '{kitty_pid}' not in listen_on and from_config_file:
+    if '{kitty_pid}' not in listen_on and from_config_file and listen_on.startswith('unix:'):
         listen_on += '-{kitty_pid}'
     listen_on = listen_on.replace('{kitty_pid}', str(os.getpid()))
     if listen_on.startswith('unix:'):
@@ -370,6 +370,9 @@ def expand_listen_on(listen_on: str, from_config_file: bool) -> str:
             elif not os.path.isabs(path):
                 import tempfile
                 listen_on = f'unix:{os.path.join(tempfile.gettempdir(), path)}'
+    elif listen_on.startswith('tcp:') or listen_on.startswith('tcp6:'):
+        if from_config_file:  # use a random port
+            listen_on = ':'.join(listen_on.split(':', 2)[:2]) + ':0'
     return listen_on
 
 
@@ -432,7 +435,7 @@ def setup_manpath(env: Dict[str, str]) -> None:
 
 def setup_environment(opts: Options, cli_opts: CLIOptions) -> None:
     from_config_file = False
-    if not cli_opts.listen_on and opts.listen_on.startswith('unix:'):
+    if not cli_opts.listen_on:
         cli_opts.listen_on = opts.listen_on
         from_config_file = True
     if cli_opts.listen_on:

kitty/options/definition.py

@@ -2882,18 +2882,18 @@
 
 opt('listen_on', 'none',
     long_text='''
-Listen to the specified UNIX socket for remote control connections. Note that
-this will apply to all kitty instances. It can be overridden by the
-:option:`kitty --listen-on` command line option, which also supports listening
-on a TCP socket. This option accepts only UNIX sockets, such as
+Listen to the specified socket for remote control connections. Note that this
+will apply to all kitty instances. It can be overridden by the :option:`kitty
+--listen-on` command line option. For UNIX sockets, such as
 :code:`unix:${TEMP}/mykitty` or :code:`unix:@mykitty` (on Linux). Environment
 variables are expanded and relative paths are resolved with respect to the
 temporary directory. If :code:`{kitty_pid}` is present, then it is replaced by
 the PID of the kitty process, otherwise the PID of the kitty process is
-appended to the value, with a hyphen. See the help for :option:`kitty
---listen-on` for more details. Note that this will be ignored unless
-:opt:`allow_remote_control` is set to either: :code:`yes`, :code:`socket` or
-:code:`socket-only`.
+appended to the value, with a hyphen. For TCP sockets such as
+:code:`tcp:localhost:0` a random port is always used even if a non-zero port
+number is specified.  See the help for :option:`kitty --listen-on` for more
+details. Note that this will be ignored unless :opt:`allow_remote_control` is
+set to either: :code:`yes`, :code:`socket` or :code:`socket-only`.
 Changing this option by reloading the config is not supported.
 '''
     )