Improve sync TestKit backend performance

The sync version of the TestKit backend was over 4 times as slow as its async
counterpart. The reason is that the TCPServer shipped with Python hands out an
unbuffered writer by default.

I don't quite understand why this wasn't a problem earlier. The sync backend
code did not change, neither did the TCPServer implementation in the standard
library. It shall remain a mystery *insert mystical sound effect*.

Author: robsdedude

testkitbackend/_async/backend.py

@@ -201,11 +201,11 @@ async def send_response(self, name, data):
         self._wr.write(log_output.encode("utf-8"))
         response = {"name": name, "data": data}
         response = dumps(response)
-        log.info(">>> " + name + dumps(data))
         self._wr.write(b"#response begin\n")
-        self._wr.write(bytes(response+"\n", "utf-8"))
+        self._wr.write(bytes(response + "\n", "utf-8"))
         self._wr.write(b"#response end\n")
         if isinstance(self._wr, asyncio.StreamWriter):
             await self._wr.drain()
         else:
             self._wr.flush()
+        log.info(">>> " + name + dumps(data))

testkitbackend/_sync/backend.py

@@ -201,11 +201,11 @@ def send_response(self, name, data):
         self._wr.write(log_output.encode("utf-8"))
         response = {"name": name, "data": data}
         response = dumps(response)
-        log.info(">>> " + name + dumps(data))
         self._wr.write(b"#response begin\n")
-        self._wr.write(bytes(response+"\n", "utf-8"))
+        self._wr.write(bytes(response + "\n", "utf-8"))
         self._wr.write(b"#response end\n")
         if isinstance(self._wr, asyncio.StreamWriter):
             self._wr.drain()
         else:
             self._wr.flush()
+        log.info(">>> " + name + dumps(data))

testkitbackend/server.py

@@ -31,6 +31,9 @@ class Server(TCPServer):
 
     def __init__(self, address):
         class Handler(StreamRequestHandler):
+            # undocumented config but unbearably slow without
+            wbufsize = 2 ** 16  # 64 KiB
+
             def handle(self):
                 backend = Backend(self.rfile, self.wfile)
                 try: