add support for peer discovery to PeerManager and example of usage to examples/

PeerManager.js

@@ -213,4 +213,61 @@ PeerManager.prototype.getActiveConnections = function () {
   return this.connections.slice(0);
 };
 
+PeerManager.prototype.discoverPeers = function(callback) {
+  var self     = this;
+  var async    = imports.async || require('async');
+  var dns      = imports.dns || require('dns');
+  var networks = imports.networks || require('./networks')[this.config.network];
+  var seeds    = networks.dnsSeeds;
+
+  // keep track of tried seeds and results
+  self.seeds = {
+    resolved: [],
+    failed: [],
+    results: {}
+  };
+
+  var dnsExecutor = seeds.map(function(seed) {
+    return function(done) {
+      // have we already resolved this seed?
+      if (~self.seeds.resolved.indexOf(seed)) {
+        // if so, just pass back cached peer list
+        return done(null, self.seeds.results[seed]);
+      }
+      // has this seed failed to resolve?
+      if (~self.seeds.resolved.indexOf(seed)) {
+        // if so, pass back empty results
+        return done(null, []);
+      }
+      // otherwise resolve the dns seed to get some peers
+      dns.resolve(seed, function(err, peers) {
+        if (err) {
+          self.seeds.failed.push(seed);
+          return done(null, []);
+        }
+        self.seeds.resolved.push(seed);
+        self.seeds.results[seed] = peers;
+        return done(null, peers);
+      });
+    };
+  });
+
+  // try resolving all seeds
+  async.parallel(dnsExecutor, function(err, results) {
+    var peers = [];
+
+    // consolidate all resolved peers into one list
+    results.forEach(function(peerlist) {
+      peers = peers.concat(peerlist);
+    });
+
+    // transform that list into a list of Peer instances
+    peers = peers.map(function(ip) {
+      return new Peer(ip, networks.defaultClientPort);
+    });
+
+    callback(null, peers);
+  });
+};
+
 module.exports = require('soop')(PeerManager);

examples/PeerDiscovery.js

@@ -0,0 +1,15 @@
+var PeerManager = require('../PeerManager');
+var peerman     = new PeerManager();
+
+peerman.discoverPeers(function(err, peers) {
+  // we get an array of peer instances
+  console.log(peers);
+  // the peer manager caches the tried seeds and any results
+  console.log(peerman.seeds);
+  // we can use this array of peers to add to the manager
+  peers.forEach(function(p) {
+    peerman.addPeer(p);
+  });
+  // then we can start the manager
+  peerman.start();
+});

networks.js

@@ -19,7 +19,16 @@ exports.livenet = {
     prev_hash: buffertools.fill(new Buffer(32), 0),
     timestamp: 1231006505,
     bits: 486604799,
-  }
+  },
+  dnsSeeds: [
+    'seed.bitcoin.sipa.be',
+    'dnsseed.bluematt.me',
+    'dnsseed.bitcoin.dashjr.org',
+    'seed.bitcoinstats.com',
+    'seed.bitnodes.io',
+    'bitseed.xf2.org'
+  ],
+  defaultClientPort: 8333
 };
 
 exports.testnet = {
@@ -39,5 +48,10 @@ exports.testnet = {
     prev_hash: buffertools.fill(new Buffer(32), 0),
     timestamp: 1296688602,
     bits: 486604799,
-  }
+  },
+  dnsSeeds: [
+    'testnet-seed.bitcoin.petertodd.org',
+    'testnet-seed.bluematt.me'
+  ],
+  defaultClientPort: 18333
 };