support.endpoint: allow waiting for incoming connection.

Some protocols start with the server sending some data as soon as the
client connects. If such data is not sent, the client will not proceed
with its first message.

When send is called before a client is connected, it is immediately
discarded. To wait for data sent by the client, a server implementation
can call recv_wait. This commit makes recv_wait return after a client
connects, too.

software/glasgow/support/endpoint.py

@@ -88,6 +88,7 @@ def connection_made(self, transport):
             self._log(logging.INFO, "closing old connection")
             self._transport.close()
             self._new_transport = transport
+        self.data_received(b"")
 
     def connection_lost(self, exc):
         peername = self._transport.get_extra_info("peername")

software/tests/support/test_endpoint.py

@@ -117,3 +117,21 @@ async def do_test_tcp(self):
     def test_tcp(self):
         asyncio.get_event_loop().run_until_complete(
             self.do_test_tcp())
+
+    async def do_test_server_banner(self):
+        sock = ("tcp", "localhost", 2345)
+        endp = await ServerEndpoint("test_server_banner", logging.getLogger(__name__), sock)
+
+        async def endpoint_task():
+            await endp.recv_wait()
+            await endp.send(b"Hello")
+        asyncio.create_task(endpoint_task())
+
+        conn_rd, _ = await asyncio.open_connection(*sock[1:])
+        r = await conn_rd.read(5)
+        self.assertEqual(r, b"Hello")
+
+    def test_server_banner(self):
+        logging.basicConfig(level=logging.TRACE)
+        asyncio.get_event_loop().run_until_complete(
+            self.do_test_server_banner())