mist-connections/mist-connections.go

package main

//go:generate go-bindata -o assets/assets_gen.go -pkg assets public/...

import (
	"container/list"
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"net"
	"net/http"
	"os"
	"os/user"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/gabriel-vasile/mimetype"
	"varia.zone/mist-connections/assets"
)

func init() {
	// silence underlying http logger which complains about the awful hacks we
	// use to override the request/response handler. this keeps the command-line
	// free from endless spurious logger warnings
	log.SetOutput(ioutil.Discard)
}

const help = `mist connections

A missed connection is a type of personal advertisement which arises after two
people meet but are too shy or otherwise unable to exchange contact details.

Options:
	-n    misty identifier (default: your system username)
	-p    path to serve (default: current working directory)
	-h    output help
`

const indexPagePortFlag = 1312
const homePagePortFlag = 5555

var helpFlag bool
var mistyID string
var sharePath string

func main() {
	systemUser, err := user.Current()
	if err != nil {
		log.Fatal(err)
	}

	handleCliFlags(systemUser.Name)

	sharePathAbs, err := filepath.Abs(sharePath)
	if err != nil {
		log.Fatal(err)
	}

	if helpFlag {
		fmt.Printf(help)
		os.Exit(0)
	}

	conf := &config{
		MistyID:       mistyID,
		IndexPagePort: indexPagePortFlag,
		HomePagePort:  homePagePortFlag,
		SharePath:     sharePathAbs,
	}

	serve(conf)
}

func handleCliFlags(defaultUsername string) {
	flag.StringVar(&mistyID, "n", defaultUsername, "misty identifier")
	flag.StringVar(&sharePath, "p", ".", "path to serve")
	flag.BoolVar(&helpFlag, "h", false, "output help")
	flag.Parse()
}

type config struct {
	MistyID       string `json:"mistyID"`
	IndexPagePort int    `json:"webPort"`
	HomePagePort  int    `json:"filePort"`
	SharePath     string `json:"sharePath"`
}

type announcer struct {
	conf *config
}

type nodeInfo struct {
	MistyID       string `json:"mistyID"`
	Addr          string `json:"addr"`
	IndexPagePort int    `json:"webPort"`
	LastMulticast int64  `json:"lastMulticast"`
}

var (
	nodeMutex sync.Mutex
)

func newAnnouncePacket(n *nodeInfo) (string, error) {
	jsonMessage, err := json.Marshal(n)
	if err != nil {
		return "", err
	}

	message := fmt.Sprintf("%s%s%s", header, nodeAnnounceCommand, jsonMessage)

	return message, nil
}

func announceNode(nodeInfo *nodeInfo) {
	address, err := net.ResolveUDPAddr("udp", multicastAddress)
	if err != nil {
		return
	}

	conn, err := net.DialUDP("udp", nil, address)
	if err != nil {
		return
	}

	for {
		message, err := newAnnouncePacket(nodeInfo)
		if err != nil {
			log.Fatal(err)
		}

		conn.Write([]byte(message))
		time.Sleep(announceIntervalSec * time.Second)
	}
}

const (
	multicastAddress    = "239.6.6.6:1337"
	multicastBufferSize = 4096
	nodeAnnounceCommand = "\x01"
	header              = "\x60\x0D\xF0\x0D"
	minPackageSize      = 6
	expireTimeoutSec    = 15
	announceIntervalSec = 10
)

func announcedNodeHandler(ninfo *nodeInfo, nodeList *list.List) {
	nodeMutex.Lock()
	updateNodeList(ninfo, nodeList)
	nodeMutex.Unlock()
}

func updateNodeList(ninfo *nodeInfo, nodeList *list.List) {
	nodeExists := false
	for el := nodeList.Front(); el != nil; el = el.Next() {
		tmp := el.Value.(*nodeInfo)

		if tmp.MistyID == ninfo.MistyID {
			tmp.LastMulticast = time.Now().Unix()
			nodeExists = true
			break
		}
	}

	for el := nodeList.Front(); el != nil; el = el.Next() {
		tmp := el.Value.(*nodeInfo)
		if isNodeExpired(tmp, expireTimeoutSec) {
			nodeList.Remove(el)
		}
	}

	if !nodeExists {
		ninfo.LastMulticast = time.Now().Unix()
		nodeList.PushBack(ninfo)
	}
}

func isNodeExpired(nodeInfo *nodeInfo, timeout int) bool {
	diff := time.Now().Unix() - nodeInfo.LastMulticast
	return diff > int64(timeout)
}

func parseAnnouncePacket(size int, addr *net.UDPAddr, packet []byte) (*nodeInfo, error) {
	if size <= minPackageSize {
		return nil, fmt.Errorf("Invalid packet size")
	}

	if strings.Compare(string(packet[0:len(header)]), header) != 0 {
		return nil, fmt.Errorf("Invalid packet header")
	}

	if string(packet[len(header):len(header)+1]) != nodeAnnounceCommand[0:] {
		return nil, fmt.Errorf("Command different than nodeAnnounceCommand")
	}

	payload := string(packet[len(header)+1:])
	payload = strings.Trim(payload, "\x00")

	nodeInfo := &nodeInfo{}

	err := json.Unmarshal([]byte(payload), nodeInfo)
	nodeInfo.Addr = addr.IP.String()
	nodeInfo.MistyID = fmt.Sprintf("%s", nodeInfo.MistyID)
	if err != nil {
		return nil, err
	}

	return nodeInfo, nil
}

func listenForNodes(nodeList *list.List) {
	address, err := net.ResolveUDPAddr("udp", multicastAddress)
	if err != nil {
		return
	}

	conn, err := net.ListenMulticastUDP("udp", nil, address)
	if err != nil {
		return
	}

	conn.SetReadBuffer(multicastBufferSize)

	for {
		packet := make([]byte, multicastBufferSize)
		size, udpAddr, err := conn.ReadFromUDP(packet)
		if err != nil {
			log.Fatal(err)
		}

		nodeInfo, err := parseAnnouncePacket(size, udpAddr, packet)
		if err != nil {
			log.Fatal(err)
		}

		go announcedNodeHandler(nodeInfo, nodeList)
	}
}

func (a *announcer) Start(nodeList *list.List) {
	nodeInfo := &nodeInfo{
		MistyID:       a.conf.MistyID,
		Addr:          "",
		IndexPagePort: a.conf.IndexPagePort,
		LastMulticast: 0,
	}

	go announceNode(nodeInfo)
	go listenForNodes(nodeList)
}

func startAnnouncer(conf *config, nodeList *list.List) {
	announcer := &announcer{conf: conf}
	announcer.Start(nodeList)
}

func serve(conf *config) {
	nodeList := list.New()

	go startAnnouncer(conf, nodeList)
	go fileServe(conf)
	go dashboardServe(conf, nodeList)

	fmt.Printf("getting misty @ http://localhost:%v :: %s\n", conf.HomePagePort, conf.SharePath)

	select {} // hack to hang here forever until ctrl-c
}

var topHTML = `
<html>
<head>
<style>
	a { color: magenta; }
</style>
</head>
<body>`

var bottomHTML = `
<hr></hr>
<a href="../">Back</a>
<a href="http://localhost:5555">Home</a>
</body>
</html>`

func fileServe(conf *config) {
	fs := http.FileServer(http.Dir(conf.SharePath))

	var handler http.HandlerFunc
	handler = func(w http.ResponseWriter, r *http.Request) {
		r.Header.Del("If-Modified-Since") // squash cache

		fpath := filepath.Join(conf.SharePath, r.RequestURI)
		mtype, _ := mimetype.DetectFile(fpath)
		renderHTML := mtype.String() == "application/octet-stream"

		if renderHTML {
			w.Write([]byte(topHTML))
		}

		fs.ServeHTTP(w, r)

		if renderHTML {
			w.Write([]byte(bottomHTML))
		}
	}

	address := fmt.Sprintf("0.0.0.0:%v", conf.IndexPagePort)
	http.ListenAndServe(address, handler)
}

func nodesHandler(nodeList *list.List) func(http.ResponseWriter, *http.Request) {
	return func(w http.ResponseWriter, r *http.Request) {
		nodes := make([]*nodeInfo, 0)
		for el := nodeList.Front(); el != nil; el = el.Next() {
			tmp := el.Value.(*nodeInfo)
			nodes = append(nodes, tmp)
		}

		data, err := json.Marshal(nodes)
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			return
		}

		w.Header().Add("Content-Type", "application/json")
		w.Write(data)
	}
}

func dashboardServe(conf *config, nodeList *list.List) {
	mux := http.NewServeMux()
	mux.Handle("/", http.FileServer(assets.AssetFS()))
	mux.HandleFunc("/api/nodes", nodesHandler(nodeList))

	address := fmt.Sprintf("%s:%v", "0.0.0.0", conf.HomePagePort)
	err := http.ListenAndServe(address, mux)
	if err != nil {
		log.Fatal(err)
	}
}