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// ServeHTTP serves a series of encoded events via HTTP with Transfer-Encoding: chunked
// or over a websocket connection.
func (s *WatchServer) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	...

	for {
		select {
		case <-done:
			return
		case <-timeoutCh:
			return
		case event, ok := <-ch:
			...

			obj := s.Fixup(event.Object)
			if err := s.EmbeddedEncoder.Encode(obj, buf); err != nil {
				// unexpected error
				utilruntime.HandleError(fmt.Errorf("unable to encode watch object %T: %v", obj, err))
				return
			}

			...
		}
	}
}

// TODO: the functionality in this method and in WatchServer.Serve is not cleanly decoupled.
func serveWatch(watcher watch.Interface, scope *RequestScope, mediaTypeOptions negotiation.MediaTypeOptions, req *http.Request, w http.ResponseWriter, timeout time.Duration) {
	...
  
	server := &WatchServer{
		...

		Fixup: func(obj runtime.Object) runtime.Object {
			result, err := transformObject(ctx, obj, options, mediaTypeOptions, scope, req)
			if err != nil {
				utilruntime.HandleError(fmt.Errorf("failed to transform object %v: %v", reflect.TypeOf(obj), err))
				return obj
			}
			// When we are transformed to a table, use the table options as the state for whether we
			// should print headers - on watch, we only want to print table headers on the first object
			// and omit them on subsequent events.
			if tableOptions, ok := options.(*metav1.TableOptions); ok {
				tableOptions.NoHeaders = true
			}
			return result
		},

		TimeoutFactory: &realTimeoutFactory{timeout},
	}

	server.ServeHTTP(w, req)
}

// transformObject takes the object as returned by storage and ensures it is in
// the client's desired form, as well as ensuring any API level fields like self-link
// are properly set.
func transformObject(ctx context.Context, obj runtime.Object, opts interface{}, mediaType negotiation.MediaTypeOptions, scope *RequestScope, req *http.Request) (runtime.Object, error) {
	if co, ok := obj.(runtime.CacheableObject); ok {
		if mediaType.Convert != nil {
			// Non-nil mediaType.Convert means that some conversion of the object
			// has to happen. Currently conversion may potentially modify the
			// object or assume something about it (e.g. asTable operates on
			// reflection, which won't work for any wrapper).
			// To ensure it will work correctly, let's operate on base objects
			// and not cache it for now.
			//
			// TODO: Long-term, transformObject should be changed so that it
			// implements runtime.Encoder interface.
			return doTransformObject(ctx, co.GetObject(), opts, mediaType, scope, req)
		}
	}
	return doTransformObject(ctx, obj, opts, mediaType, scope, req)
}

func doTransformObject(ctx context.Context, obj runtime.Object, opts interface{}, mediaType negotiation.MediaTypeOptions, scope *RequestScope, req *http.Request) (runtime.Object, error) {
	...
  
	if err := setObjectSelfLink(ctx, obj, req, scope.Namer); err != nil {
		return nil, err
	}

	...
}

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// GetObject implements runtime.CacheableObject interface.
// It returns deep-copy of the wrapped object to return ownership of it
// to the called according to the contract of the interface.
func (o *cachingObject) GetObject() runtime.Object {
	o.lock.RLock()
	defer o.lock.RUnlock()
	return o.object.DeepCopyObject().(metaRuntimeInterface)
}

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// newCachingObject performs a deep copy of the given object and wraps it
// into a cachingObject.
// An error is returned if it's not possible to cast the object to
// metav1.Object type.
func newCachingObject(object runtime.Object) (*cachingObject, error) {
	if obj, ok := object.(metaRuntimeInterface); ok {
		result := &cachingObject{object: obj.DeepCopyObject().(metaRuntimeInterface)}
		result.serializations.Store(make(serializationsCache))
		return result, nil
	}
	return nil, fmt.Errorf("can't cast object to metav1.Object: %#v", object)
}

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// newCachingObject performs a deep copy of the given object and wraps it
// into a cachingObject.
// An error is returned if it's not possible to cast the object to
// metav1.Object type.
func newCachingObject(object runtime.Object) (*cachingObject, error) {
	if obj, ok := object.(metaRuntimeInterface); ok {
		result := &cachingObject{
			object:     obj,
			deepCopied: false,
		}
		result.serializations.Store(make(serializationsCache))
		return result, nil
	}
	return nil, fmt.Errorf("can't cast object to metav1.Object: %#v", object)
}

func (o *cachingObject) SetSelfLink(selfLink string) {
	o.conditionalSet(
		func() bool { return o.object.GetSelfLink() == selfLink },
		func() { o.object.SetSelfLink(selfLink) },
	)
}

func (o *cachingObject) conditionalSet(isNoop func() bool, set func()) {
	if fastPath := func() bool {
		o.lock.RLock()
		defer o.lock.RUnlock()
		return isNoop()
	}(); fastPath {
		return
	}
	o.lock.Lock()
	defer o.lock.Unlock()
	if isNoop() {
		return
	}
	if !o.deepCopied {
		o.object = o.object.DeepCopyObject().(metaRuntimeInterface)
		o.deepCopied = true
	}
	o.invalidateCacheLocked()
	set()
}

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func setCachingObjects(event *watchCacheEvent, versioner storage.Versioner) {
	switch event.Type {
	case watch.Added, watch.Modified:
		if object, err := newCachingObject(event.Object); err == nil {
			event.Object = object
		} else {
			klog.Errorf("couldn't create cachingObject from: %#v", event.Object)
		}
		// Don't wrap PrevObject for update event (for create events it is nil).
		// We only encode those to deliver DELETE watch events, so if
		// event.Object is not nil it can be used only for watchers for which
		// selector was satisfied for its previous version and is no longer
		// satisfied for the current version.
		// This is rare enough that it doesn't justify making deep-copy of the
		// object (done by newCachingObject) every time.
	case watch.Deleted:
		// Don't wrap Object for delete events - these are not to deliver any
		// events. Only wrap PrevObject.
		if object, err := newCachingObject(event.PrevObject); err == nil {
			// Update resource version of the object.
			// event.PrevObject is used to deliver DELETE watch events and
			// for them, we set resourceVersion to <current> instead of
			// the resourceVersion of the last modification of the object.
			updateResourceVersion(object, versioner, event.ResourceVersion)
			event.PrevObject = object
		} else {
			klog.Errorf("couldn't create cachingObject from: %#v", event.Object)
		}
	}
}

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func (c *cacheWatcher) convertToWatchEvent(event *watchCacheEvent) *watch.Event {
	if event.Type == watch.Bookmark {
		return &watch.Event{Type: watch.Bookmark, Object: event.Object.DeepCopyObject()}
	}

	curObjPasses := event.Type != watch.Deleted && c.filter(event.Key, event.ObjLabels, event.ObjFields)
	oldObjPasses := false
	if event.PrevObject != nil {
		oldObjPasses = c.filter(event.Key, event.PrevObjLabels, event.PrevObjFields)
	}
	if !curObjPasses && !oldObjPasses {
		// Watcher is not interested in that object.
		return nil
	}

	switch {
	case curObjPasses && !oldObjPasses:
		return &watch.Event{Type: watch.Added, Object: getMutableObject(event.Object)}
	case curObjPasses && oldObjPasses:
		return &watch.Event{Type: watch.Modified, Object: getMutableObject(event.Object)}
	case !curObjPasses && oldObjPasses:
		// return a delete event with the previous object content, but with the event's resource version
		oldObj := getMutableObject(event.PrevObject)
		// We know that if oldObj is cachingObject (which can only be set via
		// setCachingObjects), its resourceVersion is already set correctly and
		// we don't need to update it. However, since cachingObject efficiently
		// handles noop updates, we avoid this microoptimization here.
		updateResourceVersion(oldObj, c.versioner, event.ResourceVersion)
		return &watch.Event{Type: watch.Deleted, Object: oldObj}
	}

	return nil
}