WebSocket message receiver client for Slack

slackrtm.go

package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"net/http"
	"net/url"
	"os"
	"os/signal"
	"syscall"

	"golang.org/x/net/websocket"
)

const (
	Version     = "0.1.0"
	URLRTMStart = "https://slack.com/api/rtm.start"

	originURL = "http://localhost/"
)

var (
	token = flag.String("t", "", "token")
	help  = flag.Bool("h", false, "Show help message")
	args  = flag.Args
)

func main() {
	var sts int
	defer func() { os.Exit(sts) }()

	flag.Parse()

	if *help {
		printHelp()
		return
	}

	// slack websocket URL by API token for your bot
	websocketURL, err := getWebSocketURL(*token)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Failed to getWebSocketURL: %+v\n", err)
		sts = 1
		return
	}

	// connect websocket
	ws, err := websocket.Dial(websocketURL, "", originURL)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Failed to websocket.Dial: %+v\n", err)
		sts = 1
		return
	}
	defer ws.Close()

	// start redeiver of Slack Real Time Message
	chWsRecv := make(chan string)
	defer close(chWsRecv)
	go receiver(ws, chWsRecv)

	chSig := make(chan os.Signal)
	defer close(chSig)
	signal.Notify(chSig, os.Interrupt, syscall.SIGTERM)

	// wait received message
	for {
		select {
		case <-chSig:
			fmt.Fprintln(os.Stderr, "CTRL-C; exiting by SIGTERM")
			sts = 1
			return
		case msg, ok := <-chWsRecv:
			if !ok {
				fmt.Fprintf(os.Stderr, "Message receive returned false: %v", msg)
				sts = 1
				return
			}
			// TODO write process using receive message
			fmt.Printf("[RECEIVE] msg: %s\n", msg)
		}
	}
}

func getWebSocketURL(token string) (string, error) {
	values := url.Values{}
	values.Add("token", token)

	resp, err := http.PostForm(URLRTMStart, values)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	b, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return "", err
	}

	var v interface{}
	err = json.Unmarshal(b, &v)
	if err != nil {
		return "", err
	}

	m, ok := v.(map[string]interface{})
	if !ok {
		return "", fmt.Errorf("API response is not map type\n")
	}

	u, ok := m["url"]
	if !ok {
		return "", fmt.Errorf("API response does not have websocket url param\n")
	}

	return u.(string), nil
}

func receiver(ws *websocket.Conn, chWsRecv chan string) {
	for {
		var recvMsg string
		websocket.Message.Receive(ws, &recvMsg)
		chWsRecv <- recvMsg
	}
}

func printHelp() {
	h := `
Usage:
  slackrtm [OTHER OPTIONS]

Application Options:
  -t                 Your API token

Help Options:
  -h, --help         Show this help message
`
	os.Stderr.Write([]byte(h))
}