Added `CommandStream` class.

This abstraction is used to write and read commands over a UNIX socket.

platypush/commands/__init__.py

@@ -0,0 +1,5 @@
+from ._base import Command
+from ._commands import RestartCommand, StopCommand
+from ._stream import CommandStream
+
+__all__ = ["Command", "CommandStream", "RestartCommand", "StopCommand"]

platypush/commands/_stream.py

@@ -0,0 +1,138 @@
+from multiprocessing import Queue
+import os
+from queue import Empty
+import socket
+import tempfile
+from typing import Optional
+from typing_extensions import override
+
+from platypush.process import ControllableProcess
+
+from ._base import Command
+from ._reader import CommandReader
+from ._writer import CommandWriter
+
+
+class CommandStream(ControllableProcess):
+    """
+    The command stream is an abstraction built around a UNIX socket that allows
+    the application to communicate commands to its controller.
+
+    :param path: Path to the UNIX socket
+    """
+
+    _max_queue_size = 100
+    """Maximum number of commands that can be queued in the stream."""
+
+    _default_sock_path = tempfile.gettempdir() + '/platypush-cmd-stream.sock'
+    """Default path to the UNIX socket."""
+
+    _close_timeout = 5.0
+    """Close the client socket after this amount of seconds."""
+
+    def __init__(self, path: Optional[str] = None):
+        super().__init__(name='platypush-cmd-stream')
+        self.path = os.path.abspath(os.path.expanduser(path or self._default_sock_path))
+        self._sock: Optional[socket.socket] = None
+        self._cmd_queue: Queue["Command"] = Queue()
+
+    def reset(self):
+        if self._sock is not None:
+            try:
+                self._sock.close()
+            except socket.error:
+                pass
+
+            self._sock = None
+
+        try:
+            os.unlink(self.path)
+        except FileNotFoundError:
+            pass
+
+        self._cmd_queue.close()
+        self._cmd_queue = Queue()
+
+    @override
+    def close(self) -> None:
+        self.reset()
+        return super().close()
+
+    def __enter__(self) -> "CommandStream":
+        self.reset()
+        sock = self._sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+        sock.bind(self.path)
+        os.chmod(self.path, 0o600)
+        sock.listen(1)
+        return self
+
+    def __exit__(self, *_, **__):
+        self.terminate()
+        self.join()
+        self.close()
+
+    def _serve(self, sock: socket.socket):
+        """
+        Serves the command stream.
+
+        :param sock: Client socket to serve
+        """
+        reader = CommandReader()
+        cmd = reader.read(sock)
+        if cmd:
+            self._cmd_queue.put_nowait(cmd)
+
+    def read(self, timeout: Optional[float] = None) -> Optional[Command]:
+        """
+        Reads commands from the command stream.
+
+        :param timeout: Maximum time to wait for a command.
+        :return: The command that was received, if any.
+        """
+        try:
+            return self._cmd_queue.get(timeout=timeout)
+        except Empty:
+            return None
+
+    def write(self, cmd: Command) -> None:
+        """
+        Writes a command to the command stream.
+
+        :param cmd: Command to write
+        :raise AssertionError: If the command cannot be written
+        """
+        sock = self._sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+        try:
+            sock.connect(self.path)
+            self.logger.debug('Sending command: %s', cmd)
+            CommandWriter().write(cmd, sock)
+        except OSError as e:
+            raise AssertionError(f'Unable to connect to socket {self.path}: {e}') from e
+        finally:
+            sock.close()
+
+    @staticmethod
+    def _close_client(sock: socket.socket):
+        try:
+            sock.close()
+        except OSError:
+            pass
+
+    @override
+    def main(self):
+        while self._sock and not self.should_stop:
+            sock = self._sock
+
+            try:
+                conn, _ = sock.accept()
+            except ConnectionResetError:
+                continue
+            except KeyboardInterrupt:
+                break
+
+            try:
+                self._serve(conn)
+            except Exception as e:
+                self.logger.warning('Unexpected socket error: %s', e, exc_info=True)
+            finally:
+                self._close_client(conn)