lets do some version control yall

LICENSE

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+Copyright 2010 Bob Potter. All rights reserved.
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to
+deal in the Software without restriction, including without limitation the
+rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+sell copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+IN THE SOFTWARE.

README.md

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+node-gossip implements a gossip protocol w/failure detection, allowing you to create a fault-tolerant, self-managing cluster of node.js processes.  Each server in the cluster has it's own set of key-value pairs which are propogated to the others peers in the cluster.  The API allows you to make changes to the local state, listen for changes in state, listen for new peers and be notified when a peer appears to be dead or appears to have come back to life.
+
+The library is currently in 'hey it seems to work for me' state, there are probably some bugs lurking around. The API will probably change and suggestions on how to improve it are very welcome.
+
+Check out the the scripts in the simulations/ directory for some examples.
+
+### Usage
+
+    var Gossiper = require('gossiper').Gossiper;
+    // Create a seed peer.
+    var seed = new Gossiper(9000, []);
+    seed.start();
+
+    // Create 20 new peers and point them at the seed (usually this would happen in 20 separate processes)
+    // To prevent having a single point of failure you would probably have multiple seeds
+    for(var i = 9001; i <= 9020;i++) {
+      var g = new Gossiper(i, ['127.0.0.1:9000']);
+      g.start();
+      
+      g.on('update', function(peer, k, v) {
+        console.log("peer " + peer + " set " + k + " to " + v); // peer 127.0.0.1:9999 set somekey to somevalue
+      });
+    }
+
+    // Add another peer which updates it's state after 15 seconds
+    var updater = new Gossiper(9999, ['127.0.0.1:9000']);
+    updater.start();
+    setTimeout(function() {
+      updater.setLocalState('somekey', 'somevalue');
+    }, 15000);
+
+
+### API
+
+Gossiper methods:
+
+    allPeeers()
+    livePeers()
+    deadPeers()
+    peerValue(peer, key)
+    peerKeys(peer)
+    getLocalState(key)
+    setLocalSate(key, value)
+
+Gossiper events:
+
+    on('update', function(peer_name, key, value) {})
+    on('new_peer', function(peer_name) {})
+    on('peer_alive', function(peer_name) {})
+    on('peer_failed', function(peer_name) {})
+
+### Tests
+
+    expresso -I lib test/*
+
+### TODO
+
+* test edge cases
+* Cluster name -- dont allow peers to accidentally join the wrong cluster
+The scuttlebutt paper mentions a couple things we don't current do:
+  * congestion throttling
+  * make digests only be random subsets
+
+### Acknowledgements
+
+Both the gossip protocol and the failure detection algorithms are based off of academic papers and Cassandra's (http://www.cassandra.org/) implementation of those papers.  This library is highly indebted to both.
+
+* ["Efficient reconciliation and flow control for anti-entropy protocols"](http://www.cs.cornell.edu/home/rvr/papers/flowgossip.pdf)
+* ["The Phi accrual failure detector"](http://vsedach.googlepages.com/HDY04.pdf)

lib/accrual_failure_detector.js

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+var AccrualFailureDetector = exports.AccrualFailureDetector = function() {
+  this.last_time = undefined;
+  this.intervals = [];
+}
+
+AccrualFailureDetector.prototype.add = function(arrival_time) {
+  if(this.last_time == undefined) {
+    var i = 750;
+  } else {
+    var i = arrival_time - this.last_time;
+  }
+
+  this.last_time = arrival_time;
+  this.intervals.push(i);
+  if(this.intervals.length > 1000) {
+    this.intervals.shift();
+  }
+};
+
+AccrualFailureDetector.prototype.phi = function(current_time) {
+  var current_interval = current_time - this.last_time;
+  var exp = -1 * current_interval / this.interval_mean();
+
+  var p = Math.pow(Math.E, exp);
+  return -1 * (Math.log(p) / Math.log(10));
+};
+
+AccrualFailureDetector.prototype.interval_mean = function(current_time) {
+  sum = 0;
+  for(i in this.intervals) {
+    sum += this.intervals[i];
+  }
+  return sum / this.intervals.length;
+};

lib/gossiper.js

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+var PeerState = require('peer_state').PeerState,
+    Scuttle = require('scuttle').Scuttle,
+    EventEmitter = require('events').EventEmitter,
+    PeerState = require('peer_state').PeerState,
+    net          = require('net'), 
+    sys          = require('sys'),
+    child_process = require('child_process'),
+    dns         = require('dns'),
+    msgpack     = require('msgpack'); 
+
+var Gossiper = exports.Gossiper = function(port, seeds, ip_to_bind) {
+  EventEmitter.call(this);
+  this.peers    = {};
+  this.ip_to_bind     = ip_to_bind;
+  this.port     = port;
+  this.my_state = new PeerState();
+  this.scuttle  = new Scuttle(this.peers, this.my_state);
+
+  for(var i in seeds) {
+    var s = seeds[i];
+    this.peers[s] = new PeerState(s);
+  }
+}
+
+sys.inherits(Gossiper, EventEmitter);
+
+Gossiper.prototype.start = function(msg) {
+  var self = this;
+
+  // Create Server
+  this.server = net.createServer(function (net_stream) {
+    var mp_stream = new msgpack.Stream(net_stream);
+    mp_stream.on('msg', function(msg) { self.handleMessage(net_stream, mp_stream, msg) });
+  });
+
+  // Bind to ip/port
+  if(this.ip_to_bind) {
+    this.peer_name    = [this.address, this.port.toString()].join(':');
+    this.peers[this.peer_name] = this.my_state;
+    this.server.listen(this.port, this.ip_to_bind);
+  } else {
+    child_process.exec('hostname', function(error, stdout, stderr) {
+      var l = stdout.length;
+      var hostname = stdout.slice(0, l - 1);
+      dns.lookup(hostname, 4, function(err,address, family) {
+        self.peer_name    = [address, self.port.toString()].join(':');
+        self.peers[self.peer_name] = self.my_state;
+        self.server.listen(self.port, address);
+      });
+    });
+  }
+
+  this.heartBeatTimer = setInterval(function() { self.my_state.beatHeart() }, 1000 );
+  this.gossipTimer = setInterval(function() { self.gossip() }, 1000);
+}
+
+Gossiper.prototype.stop = function() {
+  this.server.close();
+  clearInterval(this.heartBeatTimer);
+  clearInterval(this.gossipTimer);
+}
+
+
+// The method of choosing whice peer(s) to gossip to is borrowed from Cassandra.
+// They seemed to have worked out all of the edge cases
+// http://wiki.apache.org/cassandra/ArchitectureGossip
+Gossiper.prototype.gossip = function() {
+  // Find a live peer to gossip to
+  if(this.livePeers() > 0) {
+    var live_peer = this.chooseRandom(this.livePeers());
+    this.gossipToPeer(live_peer);
+  }
+
+  // Possilby gossip to a dead peer
+  var prob = this.deadPeers().length / (this.livePeers().length + 1)
+  if(Math.random() < prob) {
+    var dead_peer = this.chooseRandom(this.deadPeers());
+    this.gossipToPeer(dead_peer);
+  }
+
+  // Gossip to seed under certain conditions
+  if(live_peer && !this.seeds[live_peer] && this.livePeers().length < this.seeds.length) {
+    if(Math.random() < (this.seeds / this.allPeers.size())) {
+      this.gossipToPeer(chooseRandom(this.peers));
+    }
+  }
+
+  // Check health of peers
+  for(var i in this.peers) {
+    var peer = this.peers[i];
+    if(peer != this.my_state) {
+      peer.isSuspect();
+    }
+  }
+}
+
+Gossiper.prototype.chooseRandom = function(peers) {
+  // Choose random peer to gossip to
+  var i = Math.floor(Math.random()*1000000) % peers.length;
+  return peers[i];
+}
+
+Gossiper.prototype.gossipToPeer = function(peer) {
+  var a = peer.split(":");
+  var gosipee = new net.createConnection(a[1], a[0]);
+  var self = this;
+  gosipee.on('connect', function(net_stream) {
+    var mp_stream = new msgpack.Stream(gosipee);
+    mp_stream.on('msg', function(msg) { self.handleMessage(gosipee, mp_stream, msg) });
+    mp_stream.send(self.requestMessage());
+  });
+  gosipee.on('error', function(exception) {
+//    console.log(self.peer_name + " received " + sys.inspect(exception));
+  });
+}
+
+Gossiper.REQUEST          = 0;
+Gossiper.FIRST_RESPONSE   = 1;
+Gossiper.SECOND_RESPONSE  = 2;
+
+Gossiper.prototype.handleMessage = function(net_stream, mp_stream, msg) {
+  switch(msg.type) {
+    case Gossiper.REQUEST:
+      mp_stream.send(this.firstResponseMessage(msg.digest));
+      break;
+    case Gossiper.FIRST_RESPONSE:
+      this.scuttle.updateKnownState(msg.updates);
+      mp_stream.send(this.secondResponseMessage(msg.request_digest));
+      net_stream.end();
+      break;
+    case Gossiper.SECOND_RESPONSE:
+      this.scuttle.updateKnownState(msg.updates);
+      net_stream.end();
+      break;
+    default:
+      // shit went bad
+      break;
+  }
+}
+
+// MESSSAGES
+
+
+Gossiper.prototype.handleNewPeers = function(new_peers) {
+  var self = this;
+  for(var i in new_peers) {
+    var peer_name = new_peers[i];
+    this.peers[peer_name] = new PeerState(peer_name);
+    this.emit('new_peer', peer_name);
+
+    var peer = this.peers[peer_name];
+    this.listenToPeer(peer);
+  }
+}
+
+Gossiper.prototype.listenToPeer = function(peer) {
+  var self = this;
+  peer.on('update', function(k,v) {
+    self.emit('update', peer.name, k, v);
+  });
+  peer.on('peer_alive', function() {
+    self.emit('peer_alive', peer.name);
+  });
+  peer.on('peer_failed', function() {
+    self.emit('peer_failed', peer.name);
+  });
+}
+
+Gossiper.prototype.requestMessage = function() {
+  var m = {
+    'type'    : Gossiper.REQUEST,
+    'digest'  : this.scuttle.digest(),
+  };
+  return m;
+};
+
+Gossiper.prototype.firstResponseMessage = function(peer_digest) {
+  var sc = this.scuttle.scuttle(peer_digest)
+  this.handleNewPeers(sc.new_peers);
+  var m = {
+    'type'            : Gossiper.FIRST_RESPONSE,
+    'request_digest'  : sc.requests,
+    'updates'         : sc.deltas
+  };
+  return m;
+};
+
+Gossiper.prototype.secondResponseMessage = function(requests) {
+  var m = {
+    'type'    : Gossiper.SECOND_RESPONSE,
+    'updates' : this.scuttle.fetchDeltas(requests)
+  };
+  return m;
+};
+
+Gossiper.prototype.setLocalState = function(k, v) {
+  this.my_state.updateLocal(k,v);
+}
+
+Gossiper.prototype.getLocalState = function(k) {
+  return this.my_state.getValue(k);
+}
+
+Gossiper.prototype.peerKeys = function(peer) {
+  return this.peers[peer].getKeys();
+}
+
+Gossiper.prototype.peerValue = function(peer, k) {
+  return this.peers[peer].getValue(k);
+}
+
+Gossiper.prototype.allPeers = function() {
+  var keys = [];
+  for(var k in this.peers) { keys.push(k) };
+  return keys;
+}
+
+Gossiper.prototype.livePeers = function() {
+  var keys = [];
+  for(var k in this.peers) { if(k.alive) { keys.push(k)} };
+  return keys;
+}
+
+Gossiper.prototype.deadPeers = function() {
+  var keys = [];
+  for(var k in this.peers) { if(!k.alive) { keys.push(k) } };
+  return keys;
+}