bpo-32662: Implement Server.start_serving() and Server.serve_forever() (#5312)

* bpo-32662: Implement Server.start_serving() and Server.serve_forever()

New methods:

* Server.start_serving(),
* Server.serve_forever(), and
* Server.is_serving().

Add 'start_serving' keyword parameter to loop.create_server() and
loop.create_unix_server().

Lib/asyncio/base_events.py

@@ -157,38 +157,32 @@ def _run_until_complete_cb(fut):
 
 class Server(events.AbstractServer):
 
-    def __init__(self, loop, sockets):
+    def __init__(self, loop, sockets, protocol_factory, ssl_context, backlog,
+                 ssl_handshake_timeout):
         self._loop = loop
-        self.sockets = sockets
+        self._sockets = sockets
         self._active_count = 0
         self._waiters = []
+        self._protocol_factory = protocol_factory
+        self._backlog = backlog
+        self._ssl_context = ssl_context
+        self._ssl_handshake_timeout = ssl_handshake_timeout
+        self._serving = False
+        self._serving_forever_fut = None
 
     def __repr__(self):
         return f'<{self.__class__.__name__} sockets={self.sockets!r}>'
 
     def _attach(self):
-        assert self.sockets is not None
+        assert self._sockets is not None
         self._active_count += 1
 
     def _detach(self):
         assert self._active_count > 0
         self._active_count -= 1
-        if self._active_count == 0 and self.sockets is None:
+        if self._active_count == 0 and self._sockets is None:
             self._wakeup()
 
-    def close(self):
-        sockets = self.sockets
-        if sockets is None:
-            return
-        self.sockets = None
-        for sock in sockets:
-            self._loop._stop_serving(sock)
-        if self._active_count == 0:
-            self._wakeup()
-
-    def get_loop(self):
-        return self._loop
-
     def _wakeup(self):
         waiters = self._waiters
         self._waiters = None
@@ -196,8 +190,73 @@ class Server(events.AbstractServer):
             if not waiter.done():
                 waiter.set_result(waiter)
 
+    def _start_serving(self):
+        if self._serving:
+            return
+        self._serving = True
+        for sock in self._sockets:
+            sock.listen(self._backlog)
+            self._loop._start_serving(
+                self._protocol_factory, sock, self._ssl_context,
+                self, self._backlog, self._ssl_handshake_timeout)
+
+    def get_loop(self):
+        return self._loop
+
+    def is_serving(self):
+        return self._serving
+
+    @property
+    def sockets(self):
+        if self._sockets is None:
+            return []
+        return list(self._sockets)
+
+    def close(self):
+        sockets = self._sockets
+        if sockets is None:
+            return
+        self._sockets = None
+
+        for sock in sockets:
+            self._loop._stop_serving(sock)
+
+        self._serving = False
+
+        if (self._serving_forever_fut is not None and
+                not self._serving_forever_fut.done()):
+            self._serving_forever_fut.cancel()
+            self._serving_forever_fut = None
+
+        if self._active_count == 0:
+            self._wakeup()
+
+    async def start_serving(self):
+        self._start_serving()
+
+    async def serve_forever(self):
+        if self._serving_forever_fut is not None:
+            raise RuntimeError(
+                f'server {self!r} is already being awaited on serve_forever()')
+        if self._sockets is None:
+            raise RuntimeError(f'server {self!r} is closed')
+
+        self._start_serving()
+        self._serving_forever_fut = self._loop.create_future()
+
+        try:
+            await self._serving_forever_fut
+        except futures.CancelledError:
+            try:
+                self.close()
+                await self.wait_closed()
+            finally:
+                raise
+        finally:
+            self._serving_forever_fut = None
+
     async def wait_closed(self):
-        if self.sockets is None or self._waiters is None:
+        if self._sockets is None or self._waiters is None:
             return
         waiter = self._loop.create_future()
         self._waiters.append(waiter)
@@ -1059,7 +1118,8 @@ class BaseEventLoop(events.AbstractEventLoop):
             ssl=None,
             reuse_address=None,
             reuse_port=None,
-            ssl_handshake_timeout=None):
+            ssl_handshake_timeout=None,
+            start_serving=True):
         """Create a TCP server.
 
         The host parameter can be a string, in that case the TCP server is
@@ -1149,12 +1209,14 @@ class BaseEventLoop(events.AbstractEventLoop):
                 raise ValueError(f'A Stream Socket was expected, got {sock!r}')
             sockets = [sock]
 
-        server = Server(self, sockets)
         for sock in sockets:
-            sock.listen(backlog)
             sock.setblocking(False)
-            self._start_serving(protocol_factory, sock, ssl, server, backlog,
-                                ssl_handshake_timeout)
+
+        server = Server(self, sockets, protocol_factory,
+                        ssl, backlog, ssl_handshake_timeout)
+        if start_serving:
+            server._start_serving()
+
         if self._debug:
             logger.info("%r is serving", server)
         return server