Add a new :opt:listen_on option in kitty.conf

Also allow using environment variables in this option
Fixes #2569

docs/changelog.rst

@@ -37,6 +37,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - Marks: Fix marks not handling wide characters and tab characters correctly
   (:iss:`2534`)
 
+- Add a new :opt:`listen_on` option in kitty.conf to set :option:`kitty --listen-on`
+  globally. Also allow using environment variables in this option (:iss:`2569`).
+
 - Allow sending mouse events in kittens (:pull:`2538`)
 
 - icat kitten: Fix display of 16-bit depth images (:iss:`2542`)

kitty/cli.py

@@ -624,12 +624,15 @@ Tell kitty to listen on the specified address for control
 messages. For example, :option:`{appname} --listen-on`=unix:/tmp/mykitty or
 :option:`{appname} --listen-on`=tcp:localhost:12345. On Linux systems, you can
 also use abstract UNIX sockets, not associated with a file, like this:
-:option:`{appname} --listen-on`=unix:@mykitty.  To control kitty, you can send
+:option:`{appname} --listen-on`=unix:@mykitty. Environment variables
+in the setting are expanded and relative paths are resolved with
+respect to the temporary directory. To control kitty, you can send
 it commands with :italic:`kitty @` using the :option:`kitty @ --to` option to
 specify this address. This option will be ignored, unless you set
 :opt:`allow_remote_control` to yes in :file:`kitty.conf`. Note that if you run
 :italic:`kitty @` within a kitty window, there is no need to specify the :italic:`--to`
-option as it is read automatically from the environment.
+option as it is read automatically from the environment. For UNIX sockets, this
+can also be specified in :file:`kitty.conf`.
 
 
 --start-as

kitty/config.py

@@ -576,7 +576,7 @@ def handle_deprecated_macos_show_window_title_in_menubar_alias(key: str, val: st
     ans['macos_show_window_title_in'] = macos_show_window_title_in
 
 
-def expandvars(val: str, env: Dict[str, str]) -> str:
+def expandvars(val: str, env: Dict[str, str] = {}) -> str:
 
     def sub(m: Match) -> str:
         key = m.group(1)

kitty/config_data.py

@@ -1012,6 +1012,20 @@ you want to prevent programs running on a remote computer over ssh from
 controlling kitty.
 '''))
 
+
+o('listen_on', 'none', long_text=_('''
+Tell kitty to listen to the specified unix/tcp 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 flag. This
+option accepts only UNIX sockets, such as unix:${TEMP}/mykitty or (on Linux)
+unix:@mykitty. Environment variables are expanded. If {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. This option is ignored unless
+you also set :opt:`allow_remote_control` to enable remote control. See the
+help for :option:`kitty --listen-on` for more details.
+'''))
+
+
 o(
     '+env', '',
     add_to_default=False,

kitty/main.py

@@ -15,7 +15,7 @@ from .child import set_default_env
 from .cli import create_opts, parse_args
 from .cli_stub import CLIOptions
 from .conf.utils import BadLine
-from .config import cached_values_for, initial_window_size_func
+from .config import cached_values_for, initial_window_size_func, expandvars
 from .constants import (
     appname, beam_cursor_data_file, config_dir, glfw_path, is_macos,
     is_wayland, kitty_exe, logo_data_file, running_in_kitty
@@ -230,6 +230,22 @@ def get_editor_from_env(shell_env: Mapping[str, str]) -> Optional[str]:
                 return editor
 
 
+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:
+        listen_on += '-{kitty_pid}'
+    listen_on = listen_on.replace('{kitty_pid}', str(os.getpid()))
+    if listen_on.startswith('unix:'):
+        path = listen_on[len('unix:'):]
+        if not path.startswith('@'):
+            if path.startswith('~'):
+                listen_on = f'unix:{os.path.expanduser(path)}'
+            elif not os.path.isabs(path):
+                import tempfile
+                listen_on = f'unix:{os.path.join(tempfile.gettempdir(), path)}'
+    return listen_on
+
+
 def setup_environment(opts: OptionsStub, cli_opts: CLIOptions) -> None:
     extra_env = opts.env.copy()
     if opts.editor == '.':
@@ -241,7 +257,12 @@ def setup_environment(opts: OptionsStub, cli_opts: CLIOptions) -> None:
             os.environ['EDITOR'] = editor
     else:
         os.environ['EDITOR'] = opts.editor
-    if cli_opts.listen_on:
+    from_config_file = False
+    if not cli_opts.listen_on and opts.listen_on.startswith('unix:'):
+        cli_opts.listen_on = opts.listen_on
+        from_config_file = True
+    if cli_opts.listen_on and opts.allow_remote_control != 'n':
+        cli_opts.listen_on = expand_listen_on(cli_opts.listen_on, from_config_file)
         os.environ['KITTY_LISTEN_ON'] = cli_opts.listen_on
     set_default_env(extra_env)