Updates for improved mDNS support and DNS-SD

bin/digd.js

@@ -31,6 +31,7 @@ cli.parse({
 , 'address': [ false, 'ip address(es) to listen on (defaults to 0.0.0.0,::0)', 'string' ]
 , 'port': [ 'p', 'port (defaults to 53 for dns and 5353 for mdns)', 'int' ]
 , 'nameserver': [ false, 'the nameserver(s) to use for recursive lookups (defaults to ' + defaultNameservers.join(',') + ')', 'string' ]
+, 'send': [ false, 'send query and response messages to the parent process', 'boolean', false ]
 //, 'serve': [ 's', 'path to json file with array of responses to issue for given queries', 'string' ]
 //, 'type': [ 't', 'type (defaults to ANY for dns and PTR for mdns)', 'string' ]
 //, 'query': [ 'q', 'a superfluous explicit option to set the query as a command line flag' ]
@@ -90,35 +91,61 @@ cli.main(function (args, cli) {
     if (!('timeout' in cli)) {
       cli.timeout = 3000;
     }
+    cli.norecurse = true;
   } else {
     if (!cli.port) {
       cli.port = cli.p = 53;
     }
   }
 
+  cli.send = cli.send && (typeof process.send === 'function');
+  function sendMsg(msg) {
+    if (cli.send)
+      process.send(msg);
+  }
+
   var engine;
   var path = require('path');
   var engineOpts = { filepath: path.resolve(cli.input) };
   var dnsd = {};
   dnsd.onMessage = function (nb, cb) {
-    var byteOffset = nb._dnsByteOffset || nb.byteOffset;
-    var queryAb = nb.buffer.slice(byteOffset, byteOffset + nb.byteLength);
     var query;
     var count;
+    var byteLength = 0;
+    if (typeof nb === 'object') {
+      byteLength = nb.byteLength;
+      var byteOffset = nb._dnsByteOffset || nb.byteOffset;
+      var queryAb = nb.buffer.slice(byteOffset, byteOffset + nb.byteLength);
 
-    try {
-      query = dnsjs.DNSPacket.parse(queryAb);
-    } catch(e) {
-      // TODO log bad queries (?)
-      console.error("Could not parse DNS query, ignoring.");
-      console.error(e);
       try {
-        hexdump = require('hexdump.js').hexdump;
+        query = dnsjs.DNSPacket.parse(queryAb);
-        console.error(hexdump(queryAb));
-        console.error('');
       } catch(e) {
-        // ignore
+        // TODO log bad queries (?)
+        console.error("Could not parse DNS query, ignoring.");
+        console.error(e);
+        try {
+          hexdump = require('hexdump.js').hexdump;
+          console.error(hexdump(queryAb));
+          console.error('');
+        } catch(e) {
+          // ignore
+        }
+        return;
       }
+    } else {
+      // Special mDNS only startup query to advertise DNS-SD records
+      query = {
+        header: { id: 0, qr: 0, opcode: 0, aa: 1, tc: 0, rd: 0, ra: 0, rcode: 0 }
+      , question: [{ name: nb, type: 12, typeName: 'PTR', class: 1, className: 'IN', unicastResponse: false }]
+      , answer: []
+      , authority: []
+      , additional: []
+      , dns_sd_startup: true
+      };
+    }
+
+    if (cli.mdns && query.header.qr) {
+      console.log('Ignoring mDNS answer loopback');
       return;
     }
 
@@ -154,19 +181,20 @@ cli.main(function (args, cli) {
       printer(q);
     }
     if (query.answer.length) {
-      console.error('[ERROR] Query contains an answer section:');
+      if (!cli.mdns)
+        console.log('[ERROR] Query contains an answer section:');
       console.log(';; ANSWER SECTION:');
       query.answer.forEach(print);
     }
     if (query.authority.length) {
       console.log('');
-      console.error('[ERROR] Query contains an authority section:');
+      console.log('[ERROR] Query contains an authority section:');
       console.log(';; AUTHORITY SECTION:');
       query.authority.forEach(print);
     }
     if (query.additional.length) {
       console.log('');
-      console.error('[ERROR] Query contains an additional section:');
+      console.log('[ERROR] Query contains an additional section:');
       console.log(';; ADDITIONAL SECTION:');
       query.additional.forEach(print);
     }
@@ -179,6 +207,7 @@ cli.main(function (args, cli) {
       common.writeQuery(cli, query, queryAb);
       //common.writeResponse(opts, query, nb, packet);
     }
+    sendMsg({query: query});
 
     function sendEmptyResponse(query, rcode) {
       // rcode
@@ -189,7 +218,7 @@ cli.main(function (args, cli) {
       var newAb;
       var emptyResp = {
         header: {
-          id: query.header.id // require('crypto').randomBytes(2).readUInt16BE(0)
+          id: query.header.id || require('crypto').randomBytes(2).readUInt16BE(0)
         , qr: 1
         , opcode: 0
         , aa: 0     // TODO it may be authoritative
@@ -213,22 +242,44 @@ cli.main(function (args, cli) {
         });
       });
 
-      try {
+      if (!cli.mdns) { // no empty response for mDNS
-        newAb = dnsjs.DNSPacket.write(emptyResp);
+        try {
-      } catch(e) {
+          newAb = dnsjs.DNSPacket.write(emptyResp);
-        console.error("Could not write empty DNS response");
+        } catch(e) {
-        console.error(e);
+          console.error("Could not write empty DNS response");
-        console.error(emptyResp);
+          console.error(e);
-        cb(e, null, '[DEV] response sent (empty)');
+          console.error(emptyResp);
-        return;
+          cb(e, null, '[DEV] response sent (empty)');
-      }
+          return;
+        }
 
-      cb(null, newAb, '[DEV] response sent (empty)');
+        cb(null, newAb, '[DEV] response sent (empty)');
+      }
     }
 
     function sendResponse(newPacket) {
+      if (cli.mdns && !query.question[0].unicastResponse) {
+        newPacket.question = [];
+      }
+
       var newAb;
 
+      if (cli.mdns) {
+        let answers = [];
+        newPacket.answer.forEach(a => {
+          // Don't send response if it is already in known answers in query
+          if (query.answer.find(q => { return q.data === a.data; })) {
+            console.log('Not sending local response for', a.data, '- already known');
+          } else {
+            answers.push(a);
+          }
+        });
+        if (!answers.length)
+          return;
+
+        newPacket.answer = answers;
+      }
+
       try {
         newAb = dnsjs.DNSPacket.write(newPacket);
       } catch(e) {
@@ -239,7 +290,26 @@ cli.main(function (args, cli) {
         return;
       }
 
-      cb(null, newAb, '[DEV] response sent (local query)');
+      if (cli.mdns) {
+        // mDNS requires id in response header to be 0. Force it here as DNSPacket.write doesn't know about mDNS
+        newAb.writeUInt16LE(0, 0);
+        newPacket.header.id = 0;
+      }
+
+      if (cli.mdns && !query.question[0].unicastResponse) {
+        // mDNS requires a random delay between 20 and 120ms to avoid collisions
+        setTimeout(() => {
+          cb(null, newAb, '[DEV] response sent (local query)', query.question[0].unicastResponse||false)
+          sendMsg({local: newPacket});
+          if (query.dns_sd_startup && query.question[0].name === '_services._dns-sd._udp.local')
+            newPacket.answer.forEach(a => dnsd.onMessage(a.data, cb)); // advertise the records referenced by the startup _services query
+          }, 20 + (100.0 * Math.random()) >> 0
+        );
+
+      } else {
+        cb(null, newAb, '[DEV] response sent (local query)', query.question[0].unicastResponse||false);
+        sendMsg({local: newPacket});
+      }
     }
 
     function recurse() {
@@ -259,7 +329,7 @@ cli.main(function (args, cli) {
 
       var newResponse = {
         header: {
-          id: query.header.id // require('crypto').randomBytes(2).readUInt16BE(0)
+          id: query.header.id || require('crypto').randomBytes(2).readUInt16BE(0)
         , qr: 0
         , opcode: 0
         , aa: 0 // query.header.aa ? 1 : 0 // NA? not sure what this would do
@@ -297,6 +367,7 @@ cli.main(function (args, cli) {
             }
 
             cb(null, newAb, '[DEV] response sent');
+            sendMsg({recurse: newResponse});
           }
         }
 
@@ -306,6 +377,7 @@ cli.main(function (args, cli) {
           }
         , onMessage: function (packet) {
             // yay! recursion was available after all!
+            newResponse.header.qr = 1;
             newResponse.header.ra = 1;
             newResponse.header.rcode = NOERROR;
 
@@ -392,7 +464,16 @@ cli.main(function (args, cli) {
       respondWithResults(e);
       return;
     }
-    require('../lib/digd.js').query(engine, query, respondWithResults);
+    if (cli.mdns) {
+      // mdns allows multiple questions - should coalesce results...
+      query.question.forEach(q => {
+        let singleQ = query;
+        singleQ.question = [q];
+        require('../lib/digd.js').query(engine, singleQ, respondWithResults);
+      })
+    } else {
+      require('../lib/digd.js').query(engine, query, respondWithResults);
+    }
   };
 
   cli.defaultNameservers = defaultNameservers;
@@ -407,6 +488,8 @@ cli.main(function (args, cli) {
         console.log('index, defaultNameservers', index, cli.defaultNameservers);
       }
     }
+
+    sendMsg({ready: 'digd.js v' + pkg.version});
   });
   if (cli.tcp /* TODO v1.3 !cli.notcp */) {
     require('../lib/tcpd.js').create(cli, dnsd);

lib/digd.js

@@ -7,6 +7,7 @@ module.exports.ask = function (query, cb) {
 */
 
 var NOERROR = 0;
+var SERVFAIL = 2;
 var NXDOMAIN = 3;
 var REFUSED = 5;
 
@@ -242,7 +243,7 @@ module.exports.query = function (engine, query, cb) {
 
   var results = {
     header: {
-      id: query.header.id   // same as request
+      id: query.header.id || require('crypto').randomBytes(2).readUInt16BE(0) // same as request if not mDNS
     , qr: 1
     , opcode: 0             // pretty much always 0 QUERY
     , aa: 1                 // TODO right now we assume that if we have the record, we're authoritative
@@ -289,10 +290,10 @@ module.exports.query = function (engine, query, cb) {
       console.log('[SOA] looking for', qnames, 'and proudly serving', err, myDomains);
       if (err) { cb(err); return; }
 
-      // this should result in a REFUSED status
+      // this should result in a SERVFAIL status
       if (!myDomains.length) {
-        // REFUSED will have no records, so we could still recursion, if enabled
+        // SERVFAIL will have no records, so we could still recursion, if enabled
-        results.header.rcode = REFUSED;
+        results.header.rcode = SERVFAIL;
         cb(null, results);
         return;
       }
@@ -392,9 +393,14 @@ module.exports.query = function (engine, query, cb) {
 
         hasA = hasA || ('A' === r.type || 'A' === r.typeName || 'AAAA' === r.type || 'AAAA' === r.typeName);
 
-        return passCnames || ((r.type && r.type === query.question[0].type)
+        const isDNS_SD_Record = ('SRV' === r.type) || ('TXT' === r.type);
-          || (r.type && r.type === query.question[0].typeName)
+
-          || (r.typeName && r.typeName === query.question[0].typeName)
+        return passCnames || (
+          (r.type && r.type === query.question[0].type) ||
+          (r.type && r.type === query.question[0].typeName) ||
+          (r.typeName && r.typeName === query.question[0].typeName) ||
+          (('A' === r.type) && (('PTR' === query.question[0].typeName) || ('SRV' === query.question[0].typeName))) ||
+          isDNS_SD_Record
         );
       });
 
@@ -407,6 +413,15 @@ module.exports.query = function (engine, query, cb) {
       }
     }
 
+    // DNS-SD requires selected matching records to be put into additional records - rfc6763 12.1, 12.2
+    myRecords = myRecords.filter(function (r) {
+      if (query.question[0].name !== r.name) {
+        results.additional.push(dbToResourceRecord(r));
+        return false;
+      } else
+        return true;
+    });
+
     if (myRecords.length) {
       myRecords.forEach(function (r) {
         results.answer.push(dbToResourceRecord(r));

lib/store.json.js

@@ -369,7 +369,8 @@ module.exports.create = function (opts) {
       });
     }
   , get: function (query, cb) {
-      var myRecords = db.records.slice(0).filter(function (r) {
+      const localRecords = db.records.slice(0);
+      var myRecords = localRecords.filter(function (r) {
 
         if ('string' !== typeof r.name) {
           return false;
@@ -383,6 +384,26 @@ module.exports.create = function (opts) {
           }
         }
       });
+
+      // DNS-SD requires selected matching records to be put into additional records - rfc6763 12.1, 12.2
+      myRecords.slice(0).forEach(r => {
+        if ('PTR' === r.type) {
+          localRecords.forEach(l => {
+            if ((l.name === r.data) && (('SRV' === l.type) || ('TXT' === l.type)))
+              myRecords.push(l);
+          });
+        }
+      });
+
+      myRecords.slice(0).forEach(r => {
+        if ('SRV' === r.type) {
+          localRecords.forEach(l => {
+            if ((l.name === r.target) && (('A' === l.type) || ('AAAA' === l.type)))
+              myRecords.push(l);
+          });
+        }
+      });
+
       process.nextTick(function () {
         cb(null, myRecords);
       });

lib/udpd.js

@@ -32,11 +32,12 @@ module.exports.create = function (cli, dnsd) {
       //console.log('[DEBUG] got a UDP message', nb.length);
       //console.log(nb.toString('hex'));
 
-      dnsd.onMessage(nb, function (err, newAb, dbgmsg) {
+      dnsd.onMessage(nb, function (err, newAb, dbgmsg, unicastResponse) {
         // TODO send legit error message
-        if (err) { server.send(Buffer.from([0x00]), rinfo.port, rinfo.address); return; }
+        const address = cli.mdns && !unicastResponse ? '224.0.0.251' : rinfo.address;
-        server.send(newAb, rinfo.port, rinfo.address, function () {
+        if (err) { server.send(Buffer.from([0x00]), rinfo.port, address); return; }
-          console.log('[dnsd.onMessage] ' + dbgmsg, rinfo.port, rinfo.address);
+        server.send(newAb, rinfo.port, address, function () {
+          console.log('[dnsd.onMessage] ' + dbgmsg, rinfo.port, address);
         });
       });
     };
@@ -46,13 +47,17 @@ module.exports.create = function (cli, dnsd) {
       var server = this;
 
       if (cli.mdns || '224.0.0.251' === cli.nameserver) {
-        server.setBroadcast(true);
         server.addMembership(cli.nameserver);
       }
 
       console.log('');
       console.log('Bound and Listening:');
       console.log(server.address().address + '#' + server.address().port + ' (' + server.type + ')');
+
+      if (cli.mdns) {
+        // special startup case to advertise local dns-sd records
+        handlers.onMessage('_services._dns-sd._udp.local', { address: '224.0.0.251', port: 5353 });
+      }
     };
 
     server.on('error', handlers.onError);