Update from https://crrev.com/315085

testing/legion/discovery_server.py

Index: testing/legion/discovery_server.py
diff --git a/testing/legion/discovery_server.py b/testing/legion/discovery_server.py
new file mode 100644
index 0000000000000000000000000000000000000000..94786ce684bf2575fdbbdf7c95f9ba945f27682d
--- /dev/null
+++ b/testing/legion/discovery_server.py
@@ -0,0 +1,55 @@
+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""The discovery server used to register clients.
+
+The discovery server is started by the host controller and allows the clients
+to register themselves when they start. Authentication of the client controllers
+is based on an OTP passed to the client controller binary on startup.
+"""
+
+import logging
+import threading
+import xmlrpclib
+import SimpleXMLRPCServer
+
+#pylint: disable=relative-import
+import common_lib
+
+
+class DiscoveryServer(object):
+  """Discovery server run on the host."""
+
+  def __init__(self):
+    self._expected_clients = {}
+    self._rpc_server = None
+    self._thread = None
+
+  def _RegisterClientRPC(self, otp, ip):
+    """The RPC used by a client to register with the discovery server."""
+    assert otp in self._expected_clients
+    cb = self._expected_clients.pop(otp)
+    cb(ip)
+
+  def RegisterClientCallback(self, otp, callback):
+    """Registers a callback associated with an OTP."""
+    assert callable(callback)
+    self._expected_clients[otp] = callback
+
+  def Start(self):
+    """Starts the discovery server."""
+    logging.debug('Starting discovery server')
+    self._rpc_server = SimpleXMLRPCServer.SimpleXMLRPCServer(
+        (common_lib.SERVER_ADDRESS, common_lib.SERVER_PORT),
+        allow_none=True, logRequests=False)
+    self._rpc_server.register_function(
+        self._RegisterClientRPC, 'RegisterClient')
+    self._thread = threading.Thread(target=self._rpc_server.serve_forever)
+    self._thread.start()
+
+  def Shutdown(self):
+    """Shuts the discovery server down."""
+    if self._thread and self._thread.is_alive():
+      logging.debug('Shutting down discovery server')
+      self._rpc_server.shutdown()