'use strict'
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var util = require('util')
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var EventEmitter = require('events').EventEmitter
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var serviceName = require('multicast-dns-service-types')
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var dnsEqual = require('dns-equal')
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var dnsTxt = require('dns-txt')
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var TLD = '.local'
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var WILDCARD = '_services._dns-sd._udp' + TLD
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module.exports = Browser
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util.inherits(Browser, EventEmitter)
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/**
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* Start a browser
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*
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* The browser listens for services by querying for PTR records of a given
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* type, protocol and domain, e.g. _http._tcp.local.
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*
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* If no type is given, a wild card search is performed.
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*
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* An internal list of online services is kept which starts out empty. When
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* ever a new service is discovered, it's added to the list and an "up" event
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* is emitted with that service. When it's discovered that the service is no
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* longer available, it is removed from the list and a "down" event is emitted
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* with that service.
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*/
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function Browser (mdns, opts, onup) {
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if (typeof opts === 'function') return new Browser(mdns, null, opts)
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EventEmitter.call(this)
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this._mdns = mdns
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this._onresponse = null
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this._serviceMap = {}
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this._txt = dnsTxt(opts.txt)
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if (!opts || !opts.type) {
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this._name = WILDCARD
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this._wildcard = true
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} else {
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this._name = serviceName.stringify(opts.type, opts.protocol || 'tcp') + TLD
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if (opts.name) this._name = opts.name + '.' + this._name
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this._wildcard = false
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}
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this.services = []
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if (onup) this.on('up', onup)
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this.start()
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}
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Browser.prototype.start = function () {
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if (this._onresponse) return
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var self = this
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// List of names for the browser to listen for. In a normal search this will
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// be the primary name stored on the browser. In case of a wildcard search
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// the names will be determined at runtime as responses come in.
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var nameMap = {}
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if (!this._wildcard) nameMap[this._name] = true
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this._onresponse = function (packet, rinfo) {
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if (self._wildcard) {
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packet.answers.forEach(function (answer) {
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if (answer.type !== 'PTR' || answer.name !== self._name || answer.name in nameMap) return
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nameMap[answer.data] = true
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self._mdns.query(answer.data, 'PTR')
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})
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}
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Object.keys(nameMap).forEach(function (name) {
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// unregister all services shutting down
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goodbyes(name, packet).forEach(self._removeService.bind(self))
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// register all new services
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var matches = buildServicesFor(name, packet, self._txt, rinfo)
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if (matches.length === 0) return
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matches.forEach(function (service) {
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if (self._serviceMap[service.fqdn]) return // ignore already registered services
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self._addService(service)
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})
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})
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}
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this._mdns.on('response', this._onresponse)
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this.update()
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}
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Browser.prototype.stop = function () {
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if (!this._onresponse) return
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this._mdns.removeListener('response', this._onresponse)
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this._onresponse = null
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}
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Browser.prototype.update = function () {
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this._mdns.query(this._name, 'PTR')
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}
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Browser.prototype._addService = function (service) {
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this.services.push(service)
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this._serviceMap[service.fqdn] = true
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this.emit('up', service)
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}
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Browser.prototype._removeService = function (fqdn) {
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var service, index
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this.services.some(function (s, i) {
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if (dnsEqual(s.fqdn, fqdn)) {
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service = s
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index = i
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return true
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}
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})
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if (!service) return
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this.services.splice(index, 1)
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delete this._serviceMap[fqdn]
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this.emit('down', service)
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}
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// PTR records with a TTL of 0 is considered a "goodbye" announcement. I.e. a
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// DNS response broadcasted when a service shuts down in order to let the
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// network know that the service is no longer going to be available.
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//
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// For more info see:
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// https://tools.ietf.org/html/rfc6762#section-8.4
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//
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// This function returns an array of all resource records considered a goodbye
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// record
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function goodbyes (name, packet) {
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return packet.answers.concat(packet.additionals)
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.filter(function (rr) {
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return rr.type === 'PTR' && rr.ttl === 0 && dnsEqual(rr.name, name)
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})
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.map(function (rr) {
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return rr.data
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})
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}
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function buildServicesFor (name, packet, txt, referer) {
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var records = packet.answers.concat(packet.additionals).filter(function (rr) {
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return rr.ttl > 0 // ignore goodbye messages
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})
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return records
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.filter(function (rr) {
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return rr.type === 'PTR' && dnsEqual(rr.name, name)
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})
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.map(function (ptr) {
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var service = {
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addresses: []
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}
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records
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.filter(function (rr) {
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return (rr.type === 'SRV' || rr.type === 'TXT') && dnsEqual(rr.name, ptr.data)
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})
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.forEach(function (rr) {
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if (rr.type === 'SRV') {
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var parts = rr.name.split('.')
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var name = parts[0]
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var types = serviceName.parse(parts.slice(1, -1).join('.'))
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service.name = name
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service.fqdn = rr.name
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service.host = rr.data.target
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service.referer = referer
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service.port = rr.data.port
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service.type = types.name
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service.protocol = types.protocol
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service.subtypes = types.subtypes
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} else if (rr.type === 'TXT') {
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service.rawTxt = rr.data
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service.txt = txt.decode(rr.data)
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}
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})
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if (!service.name) return
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records
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.filter(function (rr) {
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return (rr.type === 'A' || rr.type === 'AAAA') && dnsEqual(rr.name, service.host)
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})
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.forEach(function (rr) {
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service.addresses.push(rr.data)
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})
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return service
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})
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.filter(function (rr) {
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return !!rr
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})
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}
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