Add watch mechanism to apiserver

Implemented via HTTP and websocket. A test is present but this isn't
yet wired into anything.

Eventual purpose of this is to allow a scheduler to watch for new pods.
Or allow replication controller to watch for new items it controlls.
Generally, it'll be good to turn everything possible into a push instead
of a poll.

pkg/watch/watch.go

@@ -0,0 +1,96 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package watch
+
+import (
+	"sync"
+)
+
+// Interface can be implemented by anything that knows how to watch and report changes.
+type Interface interface {
+	// Stops watching. Will close the channel returned by ResultChan(). Releases
+	// any resources used by the watch.
+	Stop()
+
+	// Returns a chan which will receive all the events. If an error occurs
+	// or Stop() is called, this channel will be closed, in which case the
+	// watch should be completely cleaned up.
+	ResultChan() <-chan *Event
+}
+
+// EventType defines the possible types of events.
+type EventType string
+
+const (
+	Added    EventType = "ADDED"
+	Modified EventType = "MODIFIED"
+	Deleted  EventType = "DELETED"
+)
+
+// Event represents a single event to a watched resource.
+type Event struct {
+	Type EventType
+
+	// If Type == Deleted, then this is the state of the object
+	// immediately before deletion.
+	Object interface{}
+}
+
+// FakeWatcher lets you test anything that consumes a watch.Interface; threadsafe.
+type FakeWatcher struct {
+	result  chan *Event
+	Stopped bool
+	sync.Mutex
+}
+
+func NewFake() *FakeWatcher {
+	return &FakeWatcher{
+		result: make(chan *Event),
+	}
+}
+
+// Stop implements Interface.Stop().
+func (f *FakeWatcher) Stop() {
+	f.Lock()
+	defer f.Unlock()
+	close(f.result)
+	f.Stopped = true
+}
+
+func (f *FakeWatcher) ResultChan() <-chan *Event {
+	return f.result
+}
+
+// Add sends an add event.
+func (f *FakeWatcher) Add(obj interface{}) {
+	f.result <- &Event{Added, obj}
+}
+
+// Modify sends a modify event.
+func (f *FakeWatcher) Modify(obj interface{}) {
+	f.result <- &Event{Modified, obj}
+}
+
+// Delete sends a delete event.
+func (f *FakeWatcher) Delete(lastValue interface{}) {
+	f.result <- &Event{Deleted, lastValue}
+}
+
+// Action sends an event of the requested type, for table-based testing.
+func (f *FakeWatcher) Action(action EventType, obj interface{}) {
+	f.result <- &Event{action, obj}
+}