func (h *handler) sendContinuousChangesByWebSocket(inChannels base.Set, options db.ChangesOptions) error {
	handler := func(conn *websocket.Conn) {
		h.logStatus(101, "Upgraded to WebSocket protocol")
		defer func() {
			conn.Close()
			base.LogTo("HTTP+", "#%03d:     --> WebSocket closed", h.serialNumber)
		}()

		// Read changes-feed options from an initial incoming WebSocket message in JSON format:
		if msg, err := readWebSocketMessage(conn); err != nil {
			return
		} else {
			var channelNames []string
			var err error
			if _, options, _, channelNames, err = h.readChangesOptionsFromJSON(msg); err != nil {
				return
			}
			if channelNames != nil {
				inChannels, _ = channels.SetFromArray(channelNames, channels.ExpandStar)
			}
		}

		options.Terminator = make(chan bool)
		defer close(options.Terminator)

		caughtUp := false
		h.generateContinuousChanges(inChannels, options, func(changes []*db.ChangeEntry) error {
			var data []byte
			if changes != nil {
				data, _ = json.Marshal(changes)
			} else if !caughtUp {
				caughtUp = true
				data, _ = json.Marshal([]*db.ChangeEntry{})
			} else {
				data = []byte{}
			}
			_, err := conn.Write(data)
			return err
		})
	}
	server := websocket.Server{
		Handshake: func(*websocket.Config, *http.Request) error { return nil },
		Handler:   handler,
	}
	server.ServeHTTP(h.response, h.rq)
	return nil
}

// Top-level handler for _changes feed requests. Accepts GET or POST requests.
func (h *handler) handleChanges() error {
	// http://wiki.apache.org/couchdb/HTTP_database_API#Changes
	// http://docs.couchdb.org/en/latest/api/database/changes.html
	restExpvars.Add("changesFeeds_total", 1)
	restExpvars.Add("changesFeeds_active", 1)
	defer restExpvars.Add("changesFeeds_active", -1)

	var feed string
	var options db.ChangesOptions
	var filter string
	var channelsArray []string
	var docIdsArray []string

	if h.rq.Method == "GET" {
		// GET request has parameters in URL:
		feed = h.getQuery("feed")
		var err error
		if options.Since, err = h.db.ParseSequenceID(h.getJSONStringQuery("since")); err != nil {
			return err
		}
		options.Limit = int(h.getIntQuery("limit", 0))
		options.Conflicts = (h.getQuery("style") == "all_docs")
		options.ActiveOnly = h.getBoolQuery("active_only")
		options.IncludeDocs = (h.getBoolQuery("include_docs"))
		filter = h.getQuery("filter")
		channelsParam := h.getQuery("channels")
		if channelsParam != "" {
			channelsArray = strings.Split(channelsParam, ",")
		}

		docidsParam := h.getQuery("doc_ids")
		if docidsParam != "" {
			var docidKeys []string
			err := json.Unmarshal([]byte(docidsParam), &docidKeys)
			if err != nil {
				err = base.HTTPErrorf(http.StatusBadRequest, "Bad doc id's")
			}
			if len(docidKeys) > 0 {
				docIdsArray = docidKeys
			}
		}

		options.HeartbeatMs = getRestrictedIntQuery(
			h.rq.URL.Query(),
			"heartbeat",
			kDefaultHeartbeatMS,
			kMinHeartbeatMS,
			h.server.config.MaxHeartbeat*1000,
			true,
		)
		options.TimeoutMs = getRestrictedIntQuery(
			h.rq.URL.Query(),
			"timeout",
			kDefaultTimeoutMS,
			0,
			kMaxTimeoutMS,
			true,
		)

	} else {
		// POST request has parameters in JSON body:
		body, err := h.readBody()
		if err != nil {
			return err
		}
		feed, options, filter, channelsArray, docIdsArray, _, err = h.readChangesOptionsFromJSON(body)
		if err != nil {
			return err
		}
	}

	// Get the channels as parameters to an imaginary "bychannel" filter.
	// The default is all channels the user can access.
	userChannels := channels.SetOf(channels.AllChannelWildcard)
	if filter != "" {
		if filter == "sync_gateway/bychannel" {
			if channelsArray == nil {
				return base.HTTPErrorf(http.StatusBadRequest, "Missing 'channels' filter parameter")
			}
			var err error
			userChannels, err = channels.SetFromArray(channelsArray, channels.ExpandStar)
			if err != nil {
				return err
			}
			if len(userChannels) == 0 {
				return base.HTTPErrorf(http.StatusBadRequest, "Empty channel list")
			}
		} else if filter == "_doc_ids" {
			if docIdsArray == nil {
				return base.HTTPErrorf(http.StatusBadRequest, "Missing 'doc_ids' filter parameter")
			}
			if len(docIdsArray) == 0 {
				return base.HTTPErrorf(http.StatusBadRequest, "Empty doc_ids list")
			}
		} else {
			return base.HTTPErrorf(http.StatusBadRequest, "Unknown filter; try sync_gateway/bychannel or _doc_ids")
		}
	}

//.........这里部分代码省略.........

// This is the core functionality of both the HTTP and WebSocket-based continuous change feed.
// It defers to a callback function 'send()' to actually send the changes to the client.
// It will call send(nil) to notify that it's caught up and waiting for new changes, or as
// a periodic heartbeat while waiting.
func (h *handler) generateContinuousChanges(inChannels base.Set, options db.ChangesOptions, send func([]*db.ChangeEntry) error) (error, bool) {
	// Set up heartbeat/timeout
	var timeoutInterval time.Duration
	var timer *time.Timer
	var heartbeat <-chan time.Time
	if options.HeartbeatMs > 0 {
		ticker := time.NewTicker(time.Duration(options.HeartbeatMs) * time.Millisecond)
		defer ticker.Stop()
		heartbeat = ticker.C
	} else if options.TimeoutMs > 0 {
		timeoutInterval = time.Duration(options.TimeoutMs) * time.Millisecond
		defer func() {
			if timer != nil {
				timer.Stop()
			}
		}()
	}

	options.Wait = true       // we want the feed channel to wait for changes
	options.Continuous = true // and to keep sending changes indefinitely
	var lastSeq db.SequenceID
	var feed <-chan *db.ChangeEntry
	var timeout <-chan time.Time
	var err error

	var closeNotify <-chan bool
	cn, ok := h.response.(http.CloseNotifier)
	if ok {
		closeNotify = cn.CloseNotify()
	} else {
		base.LogTo("Changes", "continuous changes cannot get Close Notifier from ResponseWriter")
	}

	forceClose := false

loop:
	for {
		if feed == nil {
			// Refresh the feed of all current changes:
			if lastSeq.IsNonZero() { // start after end of last feed
				options.Since = lastSeq
			}
			if h.db.IsClosed() {
				forceClose = true
				break loop
			}
			feed, err = h.db.MultiChangesFeed(inChannels, options)
			if err != nil || feed == nil {
				return err, forceClose
			}
		}

		if timeoutInterval > 0 && timer == nil {
			// Timeout resets after every change is sent
			timer = time.NewTimer(timeoutInterval)
			timeout = timer.C
		}

		// Wait for either a new change, a heartbeat, or a timeout:
		select {
		case entry, ok := <-feed:
			if !ok {
				feed = nil
			} else if entry == nil {
				err = send(nil)
			} else if entry.Err != nil {
				break loop // error returned by feed - end changes
			} else {
				entries := []*db.ChangeEntry{entry}
				waiting := false
				// Batch up as many entries as we can without waiting:
			collect:
				for len(entries) < 20 {
					select {
					case entry, ok = <-feed:
						if !ok {
							feed = nil
							break collect
						} else if entry == nil {
							waiting = true
							break collect
						} else if entry.Err != nil {
							break loop // error returned by feed - end changes
						}
						entries = append(entries, entry)
					default:
						break collect
					}
				}
				base.LogTo("Changes", "sending %d change(s)", len(entries))
				err = send(entries)

				if err == nil && waiting {
					err = send(nil)
				}

//.........这里部分代码省略.........

func (h *handler) updateChangesOptionsFromQuery(feed *string, options *db.ChangesOptions, filter *string, channelsArray []string, docIdsArray []string) (newChannelsArray []string, newDocIdsArray []string, err error) {

	if h.rq.URL.RawQuery == "" {
		return channelsArray, docIdsArray, nil
	}

	values := h.rq.URL.Query()

	if _, ok := values["feed"]; ok {
		*feed = h.getQuery("feed")
	}

	if _, ok := values["since"]; ok {
		if options.Since, err = h.db.ParseSequenceID(h.getJSONStringQuery("since")); err != nil {
			return nil, nil, err
		}
	}

	if _, ok := values["limit"]; ok {
		options.Limit = int(h.getIntQuery("limit", 0))
	}

	if _, ok := values["style"]; ok {
		options.Conflicts = (h.getQuery("style") == "all_docs")
	}

	if _, ok := values["active_only"]; ok {
		options.ActiveOnly = h.getBoolQuery("active_only")
	}

	if _, ok := values["include_docs"]; ok {
		options.IncludeDocs = (h.getBoolQuery("include_docs"))
	}

	if _, ok := values["filter"]; ok {
		*filter = h.getQuery("filter")
	}

	if _, ok := values["channels"]; ok {
		channelsParam := h.getQuery("channels")
		if channelsParam != "" {
			channelsArray = strings.Split(channelsParam, ",")
		}
	}

	if _, ok := values["doc_ids"]; ok {
		docidsParam := h.getQuery("doc_ids")
		if docidsParam != "" {
			var querydocidKeys []string
			err := json.Unmarshal([]byte(docidsParam), &querydocidKeys)
			if err == nil {
				if len(querydocidKeys) > 0 {
					docIdsArray = querydocidKeys
				}
			} else {
				//This is not a JSON array so treat as a simple
				//comma separated list of doc id's
				docIdsArray = strings.Split(docidsParam, ",")
			}
		}
	}

	if _, ok := values["heartbeat"]; ok {
		options.HeartbeatMs = getRestrictedIntQuery(
			h.rq.URL.Query(),
			"heartbeat",
			kDefaultHeartbeatMS,
			kMinHeartbeatMS,
			h.server.config.MaxHeartbeat*1000,
			true,
		)
	}

	if _, ok := values["timeout"]; ok {
		options.TimeoutMs = getRestrictedIntQuery(
			h.rq.URL.Query(),
			"timeout",
			kDefaultTimeoutMS,
			0,
			kMaxTimeoutMS,
			true,
		)
	}
	return channelsArray, docIdsArray, nil
}

func (h *handler) sendContinuousChangesByWebSocket(inChannels base.Set, options db.ChangesOptions) (error, bool) {

	forceClose := false
	handler := func(conn *websocket.Conn) {
		h.logStatus(101, "Upgraded to WebSocket protocol")
		defer func() {
			conn.Close()
			base.LogTo("HTTP+", "#%03d:     --> WebSocket closed", h.serialNumber)
		}()

		// Read changes-feed options from an initial incoming WebSocket message in JSON format:
		var wsoptions db.ChangesOptions
		var compress bool
		if msg, err := readWebSocketMessage(conn); err != nil {
			return
		} else {
			var channelNames []string
			var err error
			if _, wsoptions, _, channelNames, _, compress, err = h.readChangesOptionsFromJSON(msg); err != nil {
				return
			}
			if channelNames != nil {
				inChannels, _ = ch.SetFromArray(channelNames, ch.ExpandStar)
			}
		}

		//Copy options.Terminator to new WebSocket options
		//options.Terminator will be closed automatically when
		//changes feed completes
		wsoptions.Terminator = options.Terminator

		// Set up GZip compression
		var writer *bytes.Buffer
		var zipWriter *gzip.Writer
		if compress {
			writer = bytes.NewBuffer(nil)
			zipWriter = GetGZipWriter(writer)
		}

		caughtUp := false
		_, forceClose = h.generateContinuousChanges(inChannels, wsoptions, func(changes []*db.ChangeEntry) error {
			var data []byte
			if changes != nil {
				data, _ = json.Marshal(changes)
			} else if !caughtUp {
				caughtUp = true
				data, _ = json.Marshal([]*db.ChangeEntry{})
			} else {
				data = []byte{}
			}
			if compress && len(data) > 8 {
				// Compress JSON, using same GZip context, and send as binary msg:
				zipWriter.Write(data)
				zipWriter.Flush()
				data = writer.Bytes()
				writer.Reset()
				conn.PayloadType = websocket.BinaryFrame
			} else {
				conn.PayloadType = websocket.TextFrame
			}
			_, err := conn.Write(data)
			return err
		})

		if zipWriter != nil {
			ReturnGZipWriter(zipWriter)
		}
	}
	server := websocket.Server{
		Handshake: func(*websocket.Config, *http.Request) error { return nil },
		Handler:   handler,
	}
	server.ServeHTTP(h.response, h.rq)
	return nil, forceClose
}

// Top-level handler for _changes feed requests. Accepts GET or POST requests.
func (h *handler) handleChanges() error {
	// http://wiki.apache.org/couchdb/HTTP_database_API#Changes
	// http://docs.couchdb.org/en/latest/api/database/changes.html
	restExpvars.Add("changesFeeds_total", 1)
	restExpvars.Add("changesFeeds_active", 1)
	defer restExpvars.Add("changesFeeds_active", -1)

	var feed string
	var options db.ChangesOptions
	var filter string
	var channelsArray []string
	if h.rq.Method == "GET" {
		// GET request has parameters in URL:
		feed = h.getQuery("feed")
		var err error
		if options.Since, err = db.ParseSequenceID(h.getQuery("since")); err != nil {
			return err
		}
		options.Limit = int(h.getIntQuery("limit", 0))
		options.Conflicts = (h.getQuery("style") == "all_docs")
		options.IncludeDocs = (h.getBoolQuery("include_docs"))
		filter = h.getQuery("filter")
		channelsParam := h.getQuery("channels")
		if channelsParam != "" {
			channelsArray = strings.Split(channelsParam, ",")
		}

		options.HeartbeatMs = getRestrictedIntQuery(h.rq.URL.Query(), "heartbeat", 0, kMinHeartbeatMS, 0)
		options.TimeoutMs = getRestrictedIntQuery(h.rq.URL.Query(), "timeout", kDefaultTimeoutMS, 0, kMaxTimeoutMS)

	} else {
		// POST request has parameters in JSON body:
		body, err := h.readBody()
		if err != nil {
			return err
		}
		feed, options, filter, channelsArray, err = readChangesOptionsFromJSON(body)
		if err != nil {
			return err
		}
	}

	// Get the channels as parameters to an imaginary "bychannel" filter.
	// The default is all channels the user can access.
	userChannels := channels.SetOf(channels.AllChannelWildcard)
	if filter != "" {
		if filter != "sync_gateway/bychannel" {
			return base.HTTPErrorf(http.StatusBadRequest, "Unknown filter; try sync_gateway/bychannel")
		}
		if channelsArray == nil {
			return base.HTTPErrorf(http.StatusBadRequest, "Missing 'channels' filter parameter")
		}
		var err error
		userChannels, err = channels.SetFromArray(channelsArray, channels.ExpandStar)
		if err != nil {
			return err
		}
		if len(userChannels) == 0 {
			return base.HTTPErrorf(http.StatusBadRequest, "Empty channel list")
		}
	}

	h.db.ChangesClientStats.Increment()
	defer h.db.ChangesClientStats.Decrement()

	options.Terminator = make(chan bool)
	defer close(options.Terminator)

	switch feed {
	case "normal", "":
		return h.sendSimpleChanges(userChannels, options)
	case "longpoll":
		options.Wait = true
		return h.sendSimpleChanges(userChannels, options)
	case "continuous":
		return h.sendContinuousChangesByHTTP(userChannels, options)
	case "websocket":
		return h.sendContinuousChangesByWebSocket(userChannels, options)
	default:
		return base.HTTPErrorf(http.StatusBadRequest, "Unknown feed type")
	}
}

// This is the core functionality of both the HTTP and WebSocket-based continuous change feed.
// It defers to a callback function 'send()' to actually send the changes to the client.
// It will call send(nil) to notify that it's caught up and waiting for new changes, or as
// a periodic heartbeat while waiting.
func (h *handler) generateContinuousChanges(inChannels base.Set, options db.ChangesOptions, send func([]*db.ChangeEntry) error) error {
	// Set up heartbeat/timeout
	var timeoutInterval time.Duration
	var timer *time.Timer
	var heartbeat <-chan time.Time
	if options.HeartbeatMs > 0 {
		ticker := time.NewTicker(time.Duration(options.HeartbeatMs) * time.Millisecond)
		defer ticker.Stop()
		heartbeat = ticker.C
	} else if options.TimeoutMs > 0 {
		timeoutInterval = time.Duration(options.TimeoutMs) * time.Millisecond
		defer func() {
			if timer != nil {
				timer.Stop()
			}
		}()
	}

	options.Wait = true       // we want the feed channel to wait for changes
	options.Continuous = true // and to keep sending changes indefinitely
	var lastSeq db.SequenceID
	var feed <-chan *db.ChangeEntry
	var timeout <-chan time.Time
	var err error

loop:
	for {
		if feed == nil {
			// Refresh the feed of all current changes:
			if lastSeq.Seq > 0 { // start after end of last feed
				options.Since = lastSeq
			}
			if h.db.IsClosed() {
				break loop
			}
			feed, err = h.db.MultiChangesFeed(inChannels, options)
			if err != nil || feed == nil {
				return err
			}
		}

		if timeoutInterval > 0 && timer == nil {
			// Timeout resets after every change is sent
			timer = time.NewTimer(timeoutInterval)
			timeout = timer.C
		}

		// Wait for either a new change, a heartbeat, or a timeout:
		select {
		case entry, ok := <-feed:
			if !ok {
				feed = nil
			} else if entry == nil {
				err = send(nil)
			} else {
				entries := []*db.ChangeEntry{entry}
				waiting := false
				// Batch up as many entries as we can without waiting:
			collect:
				for len(entries) < 20 {
					select {
					case entry, ok = <-feed:
						if !ok {
							feed = nil
							break collect
						} else if entry == nil {
							waiting = true
							break collect
						}
						entries = append(entries, entry)
					default:
						break collect
					}
				}
				base.LogTo("Changes", "sending %d change(s)", len(entries))
				err = send(entries)

				if err == nil && waiting {
					err = send(nil)
				}

				lastSeq = entries[len(entries)-1].Seq
				if options.Limit > 0 {
					if len(entries) >= options.Limit {
						break loop
					}
					options.Limit -= len(entries)
				}
			}
			// Reset the timeout after sending an entry:
			if timer != nil {
				timer.Stop()
				timer = nil
			}
		case <-heartbeat:
			err = send(nil)
//.........这里部分代码省略.........