daemon: change rpcsock default to "unix" where available

The daemon by default listens for RPC over a socket.
Before this change, this socket was a TCP/IP network socket (over localhost),
but now we change it to be a unix domain socket by default (if available).

This socket is used not only when sending commands over JSON-RPC,
but also when using the CLI, and to a tiny extent even used when running the GUI.
The type of socket used (and hence this change) is invisible to CLI and GUI users.
JSON-RPC users might want to use either the --rpcsock CLI flag
or set the "rpcsock" config key (to "tcp") to switch back to using a TCP/IP socket.

In practice it seems unix domain sockets are available on
all mainstream OSes/platforms, except for Windows.

closes https://github.com/spesmilo/electrum/issues/7553

electrum/daemon.py

@@ -33,6 +33,7 @@ from typing import Dict, Optional, Tuple, Iterable, Callable, Union, Sequence, M
 from base64 import b64decode, b64encode
 from collections import defaultdict
 import json
+import socket
 
 import aiohttp
 from aiohttp import web, client_exceptions
@@ -64,7 +65,12 @@ class DaemonNotRunning(Exception):
 def get_rpcsock_defaultpath(config: SimpleConfig):
     return os.path.join(config.path, 'daemon_rpc_socket')
 
-def get_rpcsock_default_type(osname):
+def get_rpcsock_default_type():
+    # Use unix domain sockets when available,
+    # with the extra paranoia that in case windows "implements" them,
+    # we want to test it before making it the default there.
+    if hasattr(socket, 'AF_UNIX') and sys.platform != 'win32':
+        return 'unix'
     return 'tcp'
 
 def get_lockfile(config: SimpleConfig):
@@ -245,7 +251,7 @@ class CommandsServer(AuthenticatedServer):
         self.fd = fd
         self.config = daemon.config
         sockettype = self.config.get('rpcsock', 'auto')
-        self.socktype = sockettype if sockettype != 'auto' else get_rpcsock_default_type(os.name)
+        self.socktype = sockettype if sockettype != 'auto' else get_rpcsock_default_type()
         self.sockpath = self.config.get('rpcsockpath', get_rpcsock_defaultpath(self.config))
         self.host = self.config.get('rpchost', '127.0.0.1')
         self.port = self.config.get('rpcport', 0)