asyncio: Add streams.start_server(), by Gustavo Carneiro.

Lib/asyncio/streams.py

 """Stream-related things."""
 
-__all__ = ['StreamReader', 'StreamReaderProtocol', 'open_connection']
+__all__ = ['StreamReader', 'StreamReaderProtocol',
+           'open_connection', 'start_server',
+           ]
 
 import collections
 
@@ -43,6 +45,42 @@ def open_connection(host=None, port=None, *,
     return reader, writer
 
 
+@tasks.coroutine
+def start_server(client_connected_cb, host=None, port=None, *,
+                 loop=None, limit=_DEFAULT_LIMIT, **kwds):
+    """Start a socket server, call back for each client connected.
+
+    The first parameter, `client_connected_cb`, takes two parameters:
+    client_reader, client_writer.  client_reader is a StreamReader
+    object, while client_writer is a StreamWriter object.  This
+    parameter can either be a plain callback function or a coroutine;
+    if it is a coroutine, it will be automatically converted into a
+    Task.
+
+    The rest of the arguments are all the usual arguments to
+    loop.create_server() except protocol_factory; most common are
+    positional host and port, with various optional keyword arguments
+    following.  The return value is the same as loop.create_server().
+
+    Additional optional keyword arguments are loop (to set the event loop
+    instance to use) and limit (to set the buffer limit passed to the
+    StreamReader).
+
+    The return value is the same as loop.create_server(), i.e. a
+    Server object which can be used to stop the service.
+    """
+    if loop is None:
+        loop = events.get_event_loop()
+
+    def factory():
+        reader = StreamReader(limit=limit, loop=loop)
+        protocol = StreamReaderProtocol(reader, client_connected_cb,
+                                        loop=loop)
+        return protocol
+
+    return (yield from loop.create_server(factory, host, port, **kwds))
+
+
 class StreamReaderProtocol(protocols.Protocol):
     """Trivial helper class to adapt between Protocol and StreamReader.
 
@@ -52,13 +90,24 @@ class StreamReaderProtocol(protocols.Protocol):
     call inappropriate methods of the protocol.)
     """
 
-    def __init__(self, stream_reader):
+    def __init__(self, stream_reader, client_connected_cb=None, loop=None):
         self._stream_reader = stream_reader
+        self._stream_writer = None
         self._drain_waiter = None
         self._paused = False
+        self._client_connected_cb = client_connected_cb
+        self._loop = loop  # May be None; we may never need it.
 
     def connection_made(self, transport):
         self._stream_reader.set_transport(transport)
+        if self._client_connected_cb is not None:
+            self._stream_writer = StreamWriter(transport, self,
+                                               self._stream_reader,
+                                               self._loop)
+            res = self._client_connected_cb(self._stream_reader,
+                                            self._stream_writer)
+            if tasks.iscoroutine(res):
+                tasks.Task(res, loop=self._loop)
 
     def connection_lost(self, exc):
         if exc is None:

Lib/test/test_asyncio/test_streams.py

@@ -359,6 +359,72 @@ class StreamReaderTests(unittest.TestCase):
         test_utils.run_briefly(self.loop)
         self.assertIs(stream._waiter, None)
 
+    def test_start_server(self):
+
+        class MyServer:
+
+            def __init__(self, loop):
+                self.server = None
+                self.loop = loop
+
+            @tasks.coroutine
+            def handle_client(self, client_reader, client_writer):
+                data = yield from client_reader.readline()
+                client_writer.write(data)
+
+            def start(self):
+                self.server = self.loop.run_until_complete(
+                    streams.start_server(self.handle_client,
+                                         '127.0.0.1', 12345,
+                                         loop=self.loop))
+
+            def handle_client_callback(self, client_reader, client_writer):
+                task = tasks.Task(client_reader.readline(), loop=self.loop)
+
+                def done(task):
+                    client_writer.write(task.result())
+
+                task.add_done_callback(done)
+
+            def start_callback(self):
+                self.server = self.loop.run_until_complete(
+                    streams.start_server(self.handle_client_callback,
+                                         '127.0.0.1', 12345,
+                                         loop=self.loop))
+
+            def stop(self):
+                if self.server is not None:
+                    self.server.close()
+                    self.loop.run_until_complete(self.server.wait_closed())
+                    self.server = None
+
+        @tasks.coroutine
+        def client():
+            reader, writer = yield from streams.open_connection(
+                '127.0.0.1', 12345, loop=self.loop)
+            # send a line
+            writer.write(b"hello world!\n")
+            # read it back
+            msgback = yield from reader.readline()
+            writer.close()
+            return msgback
+
+        # test the server variant with a coroutine as client handler
+        server = MyServer(self.loop)
+        server.start()
+        msg = self.loop.run_until_complete(tasks.Task(client(),
+                                                      loop=self.loop))
+        server.stop()
+        self.assertEqual(msg, b"hello world!\n")
+
+        # test the server variant with a callback as client handler
+        server = MyServer(self.loop)
+        server.start_callback()
+        msg = self.loop.run_until_complete(tasks.Task(client(),
+                                                      loop=self.loop))
+        server.stop()
+        self.assertEqual(msg, b"hello world!\n")
+
 
 if __name__ == '__main__':
     unittest.main()