Adding a cross-task eventing server.

testing/legion/lib/event_server.py

+# Copyright 2016 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.
+
+"""A server to allow events to be passed from one task to another.
+
+This server supports getting, setting, and deleting of arbitrary event names.
+This is a "pull" style of server, so its on the producer and consumer to
+proactively get, set, and delete the events.
+
+
+Operation | Url            | Action
+-------------------------------------------------------------------------------
+GET       | /events/<NAME> | Returns 200 for an event that is set.
+          |                | Returns 404 for an event that is not set
+-------------------------------------------------------------------------------
+PUT       | /events/<NAME> | Sets the event and returns 200.
+-------------------------------------------------------------------------------
+DELETE    | /events/<NAME> | Deletes the event and returns 200.
+-------------------------------------------------------------------------------
+
+Errors
+Error | Action | Reason
+-------------------------------------------------------------------------------
+403   | GET    | Category is not specified
+-------------------------------------------------------------------------------
+404   | GET    | Event doesn't exist or isn't set
+-------------------------------------------------------------------------------
+501   | All    | Incorrect URL format (must be events/<NAME>)
+-------------------------------------------------------------------------------
+"""
+
+import BaseHTTPServer
+import httplib
+import re
+import SimpleHTTPServer
+import SocketServer
+import threading
+
+from legion.lib import common_lib
+
+
+class ThreadedServer(SocketServer.ThreadingMixIn,
+                     BaseHTTPServer.HTTPServer):
+  """An extension of the HTTPServer class which handles requests in threads."""
+
+  def __init__(self, address=''):
+    self._port = common_lib.GetUnusedPort()
+    self._address = address
+    BaseHTTPServer.HTTPServer.__init__(self,
+                                       (self._address, self._port),
+                                       HttpRequestHandler)
+
+  @property
+  def port(self):
+    return self._port
+
+  @property
+  def address(self):
+    return self._address
+
+  def start(self):
+    """Starts the server in another thread.
+
+    The thread will stay active until shutdown() is called. There is no reason
+    to hold a reference to the thread object.
+    """
+    threading.Thread(target=self.serve_forever).start()
+
+
+class EventHandler(object):
+  """Handles event set/get/delete operations."""
+
+  _REGEX = re.compile('^/events/(?P<name>[a-zA-Z0-9]*)')
+  _events = {}
+  _event_lock = threading.Lock()
+
+  def _GetName(self, request):
+    """Gets the event name from the URL."""
+    match = self._REGEX.match(request.path)
+    if not match:
+      return None
+    return match.group('name')
+
+
+  def do_GET(self, request):
+    """Handles GET requests."""
+    name = self._GetName(request)
+    if not name:
+      return request.send_error(501, 'Event name required')
+    with self._event_lock:
+      if name not in self._events:
+        return request.send_error(404, 'Event: %s not found' % name)
+      else:
+        return request.send_response(200)
+
+  def do_PUT(self, request):
+    """Handles PUT requests."""
+    name = self._GetName(request)
+    if not name:
+      return request.send_error(501, 'Event name required')
+    with self._event_lock:
+      self._events[name] = 1
+      return request.send_response(200)
+
+  def do_DELETE(self, request):
+    """Handles DELETE requests."""
+    name = self._GetName(request)
+    if not name:
+      return request.send_error(501, 'Event name required')
+    with self._event_lock:
+      if name in self._events:
+        del self._events[name]
+        return request.send_response(200)
+      else:
+        return request.send_error(404, 'Event not found')
+
+
+class HttpRequestHandler(SimpleHTTPServer.SimpleHTTPRequestHandler):
+  """Request handler which dispatches requests to the correct subhandler.
+
+  To extend this functionality implement a class that handles do_GET, do_PUT,
+  and do_DELETE methods, then add the name/class to the _HANDLERS dict.
+  """
+
+  _REGEX = re.compile('/(?P<category>[a-zA-Z0-9]*)')
+
+  _HANDLERS = {
+      'events': EventHandler,
+      }
+
+  def log_message(self, *args, **kwargs):
+    """Silence those pesky server-side print statements."""
+    pass
+
+  def _GetCategoryName(self):
+    """Extracts and returns the category name."""
+    match = self._REGEX.match(self.path)
+    if not match:
+      return
+    return match.group('category')
+
+  def _GetHandler(self):
+    """Returns the category handler object if it exists."""
+    category = self._GetCategoryName()
+    if not category:
+      return self.send_error(403, 'Category must be supplied')
+    handler = self._HANDLERS.get(category)
+    if not handler:
+      return self.send_error(501, '/%s is not supported' % category)
+    return handler()
+
+  def do_GET(self):
+    """Handles GET requests."""
+    handler = self._GetHandler()
+    if handler:
+      handler.do_GET(self)
+
+  def do_PUT(self):
+    """Handles PUT requests."""
+    handler = self._GetHandler()
+    if handler:
+      handler.do_PUT(self)
+
+  def do_DELETE(self):
+    """Handles DELETE requests."""
+    handler = self._GetHandler()
+    if handler:
+      handler.do_DELETE(self)