toWebsocket.go

package library

import (
	"encoding/json"
	"errors"
	"github.com/gorilla/websocket"
	"github.com/nytlabs/streamtools/st/blocks" // blocks
	"github.com/nytlabs/streamtools/st/util"   // utils
	"log"
	"net/http"
	"time"
)

// specify those channels we're going to use to communicate with streamtools
type toWebsocket struct {
	blocks.Block
	queryrule chan chan interface{}
	inrule    chan interface{}
	in        chan interface{}
	out       chan interface{}
	quit      chan interface{}
}

// we need to build a simple factory so that streamtools can make new blocks of this kind
func NewToWebsocket() blocks.BlockInterface {
	return &toWebsocket{}
}

// Setup is called once before running the block. We build up the channels and specify what kind of block this is.
func (b *toWebsocket) Setup() {
	b.Kind = "toWebsocket"
	b.in = b.InRoute("in")
	b.inrule = b.InRoute("rule")
	b.queryrule = b.QueryRoute("rule")
	b.quit = b.Quit()
}

var h = hub{
	broadcast:   make(chan []byte),
	register:    make(chan *connection),
	unregister:  make(chan *connection),
	connections: make(map[*connection]bool),
}

// Run is the block's main loop. Here we listen on the different channels we set up.
func (b *toWebsocket) Run() {

	var addr string
	var err error

	go h.run()

	for {
		select {
		case ruleI := <-b.inrule:
			// set a parameter of the block
			rule, ok := ruleI.(map[string]interface{})
			if !ok {
				b.Error(errors.New("couldn't assert rule to map"))
			}
			addr, err = util.ParseString(rule, "port")
			if err != nil {
				b.Error(err)
			}
			http.HandleFunc("/ws", serveWs)
			go http.ListenAndServe(":"+addr, nil)
			if err != nil {
				b.Error(err)
			}
		case <-b.quit:
			// quit the block
			return
		case msg := <-b.in:
			if addr == "" {
				continue
			}
			out, err := json.Marshal(msg)
			if err != nil {
				b.Error(err)
			}
			h.broadcast <- out

		case c := <-b.queryrule:
			// deal with a query request
			c <- map[string]interface{}{
				"port": addr,
			}
		}
	}
	log.Println("done")
}

type hub struct {
	// Registered connections.
	connections map[*connection]bool

	// Inbound messages from the connections.
	broadcast chan []byte

	// Register requests from the connections.
	register chan *connection

	// Unregister requests from connections.
	unregister chan *connection
}

func (h *hub) run() {
	for {
		select {
		case c := <-h.register:
			h.connections[c] = true
		case c := <-h.unregister:
			delete(h.connections, c)
			close(c.send)
		case m := <-h.broadcast:
			for c := range h.connections {
				select {
				case c.send <- m:
				default:
					close(c.send)
					delete(h.connections, c)
				}
			}
		}
	}
}

const (
	// Time allowed to write a message to the peer.
	writeWait = 10 * time.Second

	// Time allowed to read the next pong message from the peer.
	pongWait = 60 * time.Second

	// Send pings to peer with this period. Must be less than pongWait.
	pingPeriod = (pongWait * 9) / 10

	// Maximum message size allowed from peer.
	maxMessageSize = 512
)

// connection is an middleman between the websocket connection and the hub.
type connection struct {
	// The websocket connection.
	ws *websocket.Conn

	// Buffered channel of outbound messages.
	send chan []byte
}

// readPump pumps messages from the websocket connection to the hub.
func (c *connection) readPump() {
	defer func() {
		h.unregister <- c
		c.ws.Close()
	}()
	c.ws.SetReadLimit(maxMessageSize)
	c.ws.SetReadDeadline(time.Now().Add(pongWait))
	c.ws.SetPongHandler(func(string) error { c.ws.SetReadDeadline(time.Now().Add(pongWait)); return nil })
	for {
		_, message, err := c.ws.ReadMessage()
		if err != nil {
			break
		}
		h.broadcast <- message
	}
}

// write writes a message with the given message type and payload.
func (c *connection) write(mt int, payload []byte) error {
	c.ws.SetWriteDeadline(time.Now().Add(writeWait))
	return c.ws.WriteMessage(mt, payload)
}

// writePump pumps messages from the hub to the websocket connection.
func (c *connection) writePump() {
	ticker := time.NewTicker(pingPeriod)
	defer func() {
		ticker.Stop()
		c.ws.Close()
	}()
	for {
		select {
		case message, ok := <-c.send:
			if !ok {
				c.write(websocket.CloseMessage, []byte{})
				return
			}
			if err := c.write(websocket.TextMessage, message); err != nil {
				return
			}
		case <-ticker.C:
			if err := c.write(websocket.PingMessage, []byte{}); err != nil {
				return
			}
		}
	}
}

// serverWs handles webocket requests from the peer.
func serveWs(w http.ResponseWriter, r *http.Request) {
	if r.Method != "GET" {
		http.Error(w, "Method not allowed", 405)
		return
	}
	/*
		if r.Header.Get("Origin") != "http://"+r.Host {
			log.Println("403")
			http.Error(w, "Origin not allowed", 403)
			return
		}
	*/
	ws, err := websocket.Upgrade(w, r, nil, 1024, 1024)
	if _, ok := err.(websocket.HandshakeError); ok {
		http.Error(w, "Not a websocket handshake", 400)
		return
	} else if err != nil {
		log.Println(err)
		return
	}
	c := &connection{send: make(chan []byte, 256), ws: ws}
	h.register <- c
	go c.writePump()
	c.readPump()
}