net: use linked lists.

lib/http/rpc.js

@@ -327,7 +327,7 @@ RPC.prototype.getinfo = co(function* getinfo(args) {
     balance: Amount.btc(balance.unconfirmed, true),
     blocks: this.chain.height,
     timeoffset: this.network.time.offset,
-    connections: this.pool.peers.all.length,
+    connections: this.pool.peers.size(),
     proxy: '',
     difficulty: this._getDifficulty(),
     testnet: this.network.type !== Network.main,
@@ -379,7 +379,7 @@ RPC.prototype.getnetworkinfo = co(function* getnetworkinfo(args) {
     protocolversion: constants.VERSION,
     localservices: this.pool.services,
     timeoffset: this.network.time.offset,
-    connections: this.pool.peers.all.length,
+    connections: this.pool.peers.size(),
     networks: [],
     relayfee: Amount.btc(this.network.getMinRelay(), true),
     localaddresses: [],
@@ -413,7 +413,7 @@ RPC.prototype.addnode = co(function* addnode(args) {
     case 'onetry':
       if (!this.pool.peers.get(addr)) {
         peer = this.pool.createPeer(addr);
-        this.pool.peers.addPending(peer);
+        this.pool.peers.addOutbound(peer);
       }
       break;
   }
@@ -450,47 +450,46 @@ RPC.prototype.getaddednodeinfo = co(function* getaddednodeinfo(args) {
     peer = this.pool.peers.get(addr);
     if (!peer)
       throw new RPCError('Node has not been added.');
-    peers = [peer];
+    return [this._toAddedNode(peer)];
-  } else {
-    peers = this.pool.peers.all;
   }
 
-  for (i = 0; i < peers.length; i++) {
+  for (peer = this.pool.peers.head(); peer; peer = peer.next)
-    peer = peers[i];
+    out.push(this._toAddedNode(peer));
-    out.push({
-      addednode: peer.hostname,
-      connected: peer.connected,
-      addresses: [
-        {
-          address: peer.hostname,
-          connected: peer.outbound
-            ? 'outbound'
-            : 'inbound'
-        }
-      ]
-    });
-  }
 
   return out;
 });
 
+RPC.prototype._toAddedNode = function _toAddedNode(peer) {
+  return {
+    addednode: peer.hostname,
+    connected: peer.connected,
+    addresses: [
+      {
+        address: peer.hostname,
+        connected: peer.outbound
+          ? 'outbound'
+          : 'inbound'
+      }
+    ]
+  };
+};
+
 RPC.prototype.getconnectioncount = co(function* getconnectioncount(args) {
   if (args.help || args.length !== 0)
     throw new RPCError('getconnectioncount');
 
-  return this.pool.peers.all.length;
+  return this.pool.peers.size();
 });
 
 RPC.prototype.getnettotals = co(function* getnettotals(args) {
   var sent = 0;
   var recv = 0;
-  var i, peer;
+  var peer;
 
   if (args.help || args.length > 0)
     throw new RPCError('getnettotals');
 
-  for (i = 0; i < this.pool.peers.all.length; i++) {
+  for (peer = this.pool.peers.head(); peer; peer = peer.next) {
-    peer = this.pool.peers.all[i];
     sent += peer.socket.bytesWritten;
     recv += peer.socket.bytesRead;
   }
@@ -504,13 +503,12 @@ RPC.prototype.getnettotals = co(function* getnettotals(args) {
 
 RPC.prototype.getpeerinfo = co(function* getpeerinfo(args) {
   var peers = [];
-  var i, peer;
+  var peer;
 
   if (args.help || args.length !== 0)
     throw new RPCError('getpeerinfo');
 
-  for (i = 0; i < this.pool.peers.all.length; i++) {
+  for (peer = this.pool.peers.head(); peer; peer = peer.next) {
-    peer = this.pool.peers.all[i];
     peers.push({
       id: peer.id,
       addr: peer.hostname,
@@ -538,13 +536,11 @@ RPC.prototype.getpeerinfo = co(function* getpeerinfo(args) {
 });
 
 RPC.prototype.ping = co(function* ping(args) {
-  var i;
-
   if (args.help || args.length !== 0)
     throw new RPCError('ping');
 
-  for (i = 0; i < this.pool.peers.all.length; i++)
+  for (peer = this.pool.peers.head(); peer; peer = peer.next)
-    this.pool.peers.all[i].sendPing();
+    peer.sendPing();
 
   return null;
 });
@@ -1538,7 +1534,7 @@ RPC.prototype.getblocktemplate = co(function* getblocktemplate(args) {
   }
 
   if (!this.network.selfConnect) {
-    if (this.pool.peers.all.length === 0)
+    if (this.pool.peers.size() === 0)
       throw new RPCError('Bitcoin is not connected!');
 
     if (!this.chain.isFull())

lib/http/server.js

@@ -631,7 +631,6 @@ HTTPServer.prototype._init = function _init() {
   this.get('/', function(req, res, send, next) {
     var totalTX = this.mempool ? this.mempool.totalTX : 0;
     var size = this.mempool ? this.mempool.getSize() : 0;
-    var loader = this.pool.peers.load ? 1 : 0;
 
     send(200, {
       version: constants.USER_VERSION,
@@ -644,9 +643,9 @@ HTTPServer.prototype._init = function _init() {
       },
       pool: {
         services: this.pool.services.toString(2),
-        outbound: this.pool.peers.outbound.length + loader,
+        outbound: this.pool.peers.outbound,
-        pending: this.pool.peers.pending.length,
+        pending: this.pool.peers.pending,
-        inbound: this.pool.peers.inbound.length
+        inbound: this.pool.peers.inbound
       },
       mempool: {
         tx: totalTX,

lib/net/peer.js

@@ -26,6 +26,7 @@ var BIP152 = require('./bip152');
 var Block = require('../primitives/block');
 var TX = require('../primitives/tx');
 var errors = require('../btc/errors');
+var List = require('../utils/list');
 var packetTypes = packets.types;
 var VerifyResult = errors.VerifyResult;
 
@@ -93,6 +94,7 @@ function Peer(pool, addr, socket) {
   this.version = null;
   this.destroyed = false;
   this.ack = false;
+  this.pending = true;
   this.connected = false;
   this.ts = 0;
   this.preferHeaders = false;
@@ -119,6 +121,9 @@ function Peer(pool, addr, socket) {
   this.drainSize = 0;
   this.drainQueue = [];
 
+  this.next = null;
+  this.prev = null;
+
   this.challenge = null;
   this.lastPong = -1;
   this.lastPing = -1;
@@ -134,8 +139,8 @@ function Peer(pool, addr, socket) {
   this.requestTimeout = 10000;
   this.requestMap = {};
 
-  this.queueBlock = [];
+  this.queueBlock = new List();
-  this.queueTX = [];
+  this.queueTX = new List();
 
   this.uid = 0;
   this.id = Peer.uid++;
@@ -154,6 +159,7 @@ function Peer(pool, addr, socket) {
   } else {
     this.socket = socket;
     this.connected = true;
+    this.pending = false;
   }
 
   if (this.options.bip151) {
@@ -491,7 +497,7 @@ Peer.prototype._finalize = co(function* _finalize() {
   yield this.updateWatch();
 
   // Announce our currently broadcasted items.
-  yield this.announce(this.pool.invItems);
+  yield this.announce(this.pool.invItems.toArray());
 
   // Set a fee rate filter.
   if (this.pool.feeRate !== -1)
@@ -1883,7 +1889,7 @@ Peer.prototype._handleAddr = function _handleAddr(packet) {
     'Received %d addrs (hosts=%d, peers=%d) (%s).',
     addrs.length,
     this.pool.hosts.items.length,
-    this.pool.peers.all.length,
+    this.pool.peers.size(),
     this.hostname);
 
   this.fire('addr', addrs);

lib/net/pool.js

@@ -29,6 +29,7 @@ var tcp = require('./tcp');
 var request = require('../http/request');
 var VerifyError = errors.VerifyError;
 var VerifyResult = errors.VerifyResult;
+var List = require('../utils/list');
 
 /**
  * A pool of peers for handling all network activity.
@@ -145,7 +146,7 @@ function Pool(options) {
 
   // Currently broadcasted objects.
   this.invMap = {};
-  this.invItems = [];
+  this.invItems = new List();
   this.invTimeout = 60000;
 
   this.scheduled = false;
@@ -327,14 +328,14 @@ Pool.prototype._open = co(function* _open() {
  */
 
 Pool.prototype._close = co(function* close() {
-  var i, items, hashes, hash;
+  var i, next, item, hashes, hash;
 
   this.stopSync();
 
-  items = this.invItems.slice();
+  for (item = this.invItems.head; item; item = next) {
-
+    next = item.next;
-  for (i = 0; i < items.length; i++)
+    item.finish();
-    items[i].finish();
+  }
 
   hashes = Object.keys(this.requestMap);
 
@@ -467,7 +468,7 @@ Pool.prototype._handleLeech = function _handleLeech(socket) {
 
   addr = NetworkAddress.fromSocket(socket, this.network);
 
-  if (this.peers.inbound.length >= this.maxInbound) {
+  if (this.peers.inbound >= this.maxInbound) {
     this.logger.debug('Ignoring leech: too many inbound (%s).', addr.hostname);
     socket.destroy();
     return;
@@ -613,7 +614,9 @@ Pool.prototype.addLoader = function addLoader() {
 
   this.logger.info('Added loader peer (%s).', peer.hostname);
 
-  this.peers.addLoader(peer);
+  assert(!this.peers.load);
+  this.peers.load = peer;
+  this.peers.add(peer);
   this.fillPeers();
 
   util.nextTick(function() {
@@ -675,13 +678,13 @@ Pool.prototype.startSync = function startSync() {
  */
 
 Pool.prototype.sync = function sync() {
-  var i;
+  var peer;
 
-  if (this.peers.load)
+  for (peer = this.peers.head(); peer; peer = peer.next) {
-    this.peers.load.trySync();
+    if (!peer.outbound || peer.pending)
-
+      continue;
-  for (i = 0; i < this.peers.outbound.length; i++)
+    peer.trySync();
-    this.peers.outbound[i].trySync();
+  }
 };
 
 /**
@@ -690,15 +693,11 @@ Pool.prototype.sync = function sync() {
  */
 
 Pool.prototype.forceSync = function forceSync() {
-  var i, peer;
+  var peer;
 
-  if (this.peers.load) {
+  for (peer = this.peers.head(); peer; peer = peer.next) {
-    this.peers.load.syncSent = false;
+    if (!peer.outbound || peer.pending)
-    this.peers.load.trySync();
+      continue;
-  }
-
-  for (i = 0; i < this.peers.outbound.length; i++) {
-    peer = this.peers.outbound[i];
     peer.syncSent = false;
     peer.trySync();
   }
@@ -709,7 +708,7 @@ Pool.prototype.forceSync = function forceSync() {
  */
 
 Pool.prototype.stopSync = function stopSync() {
-  var i;
+  var peer;
 
   if (!this.syncing)
     return;
@@ -722,11 +721,11 @@ Pool.prototype.stopSync = function stopSync() {
   this.stopInterval();
   this.stopTimeout();
 
-  if (this.peers.load)
+  for (peer = this.peers.head(); peer; peer = peer.next) {
-    this.peers.load.syncSent = false;
+    if (!peer.outbound || peer.pending)
-
+      continue;
-  for (i = 0; i < this.peers.outbound.length; i++)
+    peer.syncSent = false;
-    this.peers.outbound[i].syncSent = false;
+  }
 };
 
 /**
@@ -991,9 +990,9 @@ Pool.prototype._handleBlock = co(function* _handleBlock(block, peer) {
       this.chain.total,
       this.chain.orphan.count,
       this.activeBlocks,
-      peer.queueBlock.length,
+      peer.queueBlock.size,
       block.bits,
-      this.peers.all.length,
+      this.peers.size(),
       this.chain.locker.pending.length,
       this.chain.locker.jobs.length);
   }
@@ -1011,13 +1010,13 @@ Pool.prototype._handleBlock = co(function* _handleBlock(block, peer) {
  */
 
 Pool.prototype.sendMempool = function sendMempool() {
-  var i;
+  var peer;
 
-  if (this.peers.load)
+  for (peer = this.peers.head(); peer; peer = peer.next) {
-    this.peers.load.sendMempool();
+    if (!peer.outbound || peer.pending)
-
+      continue;
-  for (i = 0; i < this.peers.outbound.length; i++)
+    peer.sendMempool();
-    this.peers.outbound[i].sendMempool();
+  }
 };
 
 /**
@@ -1026,16 +1025,10 @@ Pool.prototype.sendMempool = function sendMempool() {
  */
 
 Pool.prototype.sendAlert = function sendAlert(alert) {
-  var i;
+  var peer;
 
-  if (this.peers.load)
+  for (peer = this.peers.head(); peer; peer = peer.next)
-    this.peers.load.sendAlert(alert);
+    peer.sendAlert(alert);
-
-  for (i = 0; i < this.peers.outbound.length; i++)
-    this.peers.outbound[i].sendAlert(alert);
-
-  for (i = 0; i < this.peers.inbound.length; i++)
-    this.peers.inbound[i].sendAlert(alert);
 };
 
 /**
@@ -1077,7 +1070,7 @@ Pool.prototype.createPeer = function createPeer(addr, socket) {
     self.stopInterval();
     self.stopTimeout();
 
-    if (self.peers.size() === 0) {
+    if (self.peers.outbound === 0) {
       self.logger.warning('%s %s %s',
         'Could not connect to any peers.',
         'Do you have a network connection?',
@@ -1415,7 +1408,7 @@ Pool.prototype.addLeech = function addLeech(addr, socket) {
 
   this.logger.info('Added leech peer (%s).', peer.hostname);
 
-  this.peers.addLeech(peer);
+  this.peers.add(peer);
 
   util.nextTick(function() {
     self.emit('leech', peer);
@@ -1435,7 +1428,7 @@ Pool.prototype.addPeer = function addPeer() {
   if (!this.loaded)
     return;
 
-  if (this.peers.isFull())
+  if (this.peers.outbound >= this.maxOutbound)
     return;
 
   // Hang back if we don't have a loader peer yet.
@@ -1449,7 +1442,7 @@ Pool.prototype.addPeer = function addPeer() {
 
   peer = this.createPeer(addr);
 
-  this.peers.addPending(peer);
+  this.peers.add(peer);
 
   util.nextTick(function() {
     self.emit('peer', peer);
@@ -1465,7 +1458,7 @@ Pool.prototype.fillPeers = function fillPeers() {
   var i;
 
   this.logger.debug('Refilling peers (%d/%d).',
-    this.peers.all.length - this.peers.inbound.length,
+    this.peers.outbound,
     this.maxOutbound);
 
   for (i = 0; i < this.maxOutbound - 1; i++)
@@ -1541,19 +1534,18 @@ Pool.prototype.unwatch = function unwatch() {
 
 Pool.prototype.updateWatch = function updateWatch() {
   var self = this;
-  var i;
+  var peer;
 
   if (this.pendingWatch != null)
     return;
 
   this.pendingWatch = setTimeout(function() {
     self.pendingWatch = null;
-
+    for (peer = self.peers.head(); peer; peer = peer.next) {
-    if (self.peers.load)
+      if (!peer.outbound || peer.pending)
-      self.peers.load.updateWatch();
+        continue;
-
+      peer.updateWatch();
-    for (i = 0; i < self.peers.outbound.length; i++)
+    }
-      self.peers.outbound[i].updateWatch();
   }, 50);
 };
 
@@ -1634,16 +1626,15 @@ Pool.prototype.getTX = function getTX(peer, hash) {
 
   item = new LoadRequest(this, peer, this.txType, hash);
 
-  if (peer.queueTX.length === 0) {
+  if (peer.queueTX.size === 0) {
     util.nextTick(function() {
       self.logger.debug(
         'Requesting %d/%d txs from peer with getdata (%s).',
-        peer.queueTX.length,
+        peer.queueTX.size,
         self.activeTX,
         peer.hostname);
 
-      peer.getData(peer.queueTX);
+      peer.getData(peer.queueTX.slice());
-      peer.queueTX.length = 0;
     });
   }
 
@@ -1709,29 +1700,29 @@ Pool.prototype.scheduleRequests = co(function* scheduleRequests(peer) {
  */
 
 Pool.prototype.sendRequests = function sendRequests(peer) {
-  var i, size, items;
+  var i, size, items, item;
 
-  if (peer.queueBlock.length === 0)
+  if (peer.queueBlock.size === 0)
     return;
 
   if (this.options.spv) {
-    if (this.activeBlocks >= 500)
+    if (this.activeBlocks >= 2000)
       return;
 
-    items = peer.queueBlock.slice();
+    size = peer.queueBlock.size;
-    peer.queueBlock.length = 0;
   } else {
     size = this.network.getBatchSize(this.chain.height);
 
     if (this.activeBlocks >= size)
       return;
-
-    items = peer.queueBlock.slice(0, size);
-    peer.queueBlock = peer.queueBlock.slice(size);
   }
 
-  for (i = 0; i < items.length; i++)
+  items = peer.queueBlock.slice(size);
-    items[i] = items[i].start();
+
+  for (i = 0; i < items.length; i++) {
+    item = items[i];
+    item.start();
+  }
 
   this.logger.debug(
     'Requesting %d/%d blocks from peer with getdata (%s).',
@@ -1799,13 +1790,13 @@ Pool.prototype.broadcast = function broadcast(msg) {
  */
 
 Pool.prototype.announce = function announce(msg) {
-  var i;
+  var peer;
 
-  if (this.peers.load)
+  for (peer = this.peers.head(); peer; peer = peer.next) {
-    this.peers.load.tryAnnounce(msg);
+    if (!peer.outbound || peer.pending)
-
+      continue;
-  for (i = 0; i < this.peers.outbound.length; i++)
+    peer.tryAnnounce(msg);
-    this.peers.outbound[i].tryAnnounce(msg);
+  }
 };
 
 /**
@@ -1814,15 +1805,15 @@ Pool.prototype.announce = function announce(msg) {
  */
 
 Pool.prototype.setFeeRate = function setFeeRate(rate) {
-  var i;
+  var peer;
 
   this.feeRate = rate;
 
-  if (this.peers.load)
+  for (peer = this.peers.head(); peer; peer = peer.next) {
-    this.peers.load.sendFeeRate(rate);
+    if (!peer.outbound || peer.pending)
-
+      continue;
-  for (i = 0; i < this.peers.outbound.length; i++)
+    peer.sendFeeRate(rate);
-    this.peers.outbound[i].sendFeeRate(rate);
+  }
 };
 
 /**
@@ -1978,52 +1969,48 @@ Pool.prototype.getIP2 = co(function* getIP2() {
 
 function PeerList(pool) {
   this.pool = pool;
-  // Peers that are loading blocks themselves
-  this.outbound = [];
-  // Peers that are still connecting
-  this.pending = [];
-  // Peers that connected to us
-  this.inbound = [];
-  // Peers that are loading block ids
-  this.load = null;
-  // All peers
-  this.all = [];
-  // Map of hostnames
   this.map = {};
+  this.list = new List();
+  this.load = null;
+  this.inbound = 0;
+  this.outbound = 0;
+  this.pending = 0;
 }
 
-PeerList.prototype.addLoader = function addLoader(peer) {
+PeerList.prototype.head = function head() {
-  this.load = peer;
+  return this.list.head;
-  this.all.push(peer);
-  assert(!this.map[peer.hostname]);
-  this.map[peer.hostname] = peer;
 };
 
-PeerList.prototype.addPending = function addPending(peer) {
+PeerList.prototype.tail = function tail() {
-  this.pending.push(peer);
+  return this.list.tail;
-  this.all.push(peer);
-  assert(!this.map[peer.hostname]);
-  this.map[peer.hostname] = peer;
 };
 
-PeerList.prototype.addLeech = function addLeech(peer) {
+PeerList.prototype.size = function size() {
-  this.inbound.push(peer);
+  return this.list.size;
-  this.all.push(peer);
-  assert(!this.map[peer.hostname]);
-  this.map[peer.hostname] = peer;
 };
 
 PeerList.prototype.promote = function promote(peer) {
-  if (util.binaryRemove(this.pending, peer, compare))
+  assert(peer.outbound);
-    util.binaryInsert(this.outbound, peer, compare);
+  assert(peer.pending);
+  peer.pending = false;
+  this.pending--;
+};
+
+PeerList.prototype.add = function add(peer) {
+  assert(this.list.push(peer));
+  assert(!this.map[peer.hostname]);
+  this.map[peer.hostname] = peer;
+  if (peer.outbound) {
+    this.outbound++;
+    if (peer.pending)
+      this.pending++;
+  } else {
+    this.inbound++;
+  }
 };
 
 PeerList.prototype.remove = function remove(peer) {
-  util.binaryRemove(this.pending, peer, compare);
+  assert(this.list.remove(peer));
-  util.binaryRemove(this.outbound, peer, compare);
-  util.binaryRemove(this.inbound, peer, compare);
-  util.binaryRemove(this.all, peer, compare);
-
   assert(this.map[peer.hostname]);
   delete this.map[peer.hostname];
 
@@ -2031,66 +2018,38 @@ PeerList.prototype.remove = function remove(peer) {
     this.pool.logger.info('Removed loader peer (%s).', peer.hostname);
     this.load = null;
   }
-};
 
-PeerList.prototype.demoteLoader = function demoteLoader() {
+  if (peer.outbound) {
-  var peer = this.load;
+    this.outbound--;
-  assert(peer);
+    if (peer.pending)
-  this.load = null;
+      this.pending--;
-  if (peer.ack)
+  } else {
-    util.binaryInsert(this.outbound, peer, compare);
+    this.inbound--;
-  else
+  }
-    util.binaryInsert(this.pending, peer, compare);
 };
 
 PeerList.prototype.repurpose = function repurpose(peer) {
-  var r1, r2;
-
   assert(peer.outbound);
-
-  if (this.load)
-    this.demoteLoader();
-
-  r1 = util.binaryRemove(this.pending, peer, compare);
-  r2 = util.binaryRemove(this.outbound, peer, compare);
-
-  assert(r1 || r2);
-
   this.load = peer;
 };
 
-PeerList.prototype.isFull = function isFull() {
-  return this.size() >= this.pool.maxOutbound - 1;
-};
-
-PeerList.prototype.size = function size() {
-  return this.outbound.length + this.pending.length;
-};
-
 PeerList.prototype.get = function get(addr) {
   return this.map[addr.hostname];
 };
 
 PeerList.prototype.destroy = function destroy() {
-  var i, peers;
+  var peer, next;
 
-  if (this.load)
+  this.map = {};
-    this.load.destroy();
+  this.load = null;
+  this.inbound = 0;
+  this.outbound = 0;
+  this.pending = 0;
 
-  peers = this.outbound.slice();
+  for (peer = this.list.head; peer; peer = next) {
-
+    next = peer.next;
-  for (i = 0; i < peers.length; i++)
+    peer.destroy();
-    peers[i].destroy();
+  }
-
-  peers = this.pending.slice();
-
-  for (i = 0; i < peers.length; i++)
-    peers[i].destroy();
-
-  peers = this.inbound.slice();
-
-  for (i = 0; i < peers.length; i++)
-    peers[i].destroy();
 };
 
 /**
@@ -2341,10 +2300,12 @@ function LoadRequest(pool, peer, type, hash) {
   this.type = type;
   this.hash = hash;
   this.active = false;
-  this.id = this.pool.uid++;
   this.timeout = null;
   this.onTimeout = this._onTimeout.bind(this);
 
+  this.next = null;
+  this.prev = null;
+
   assert(!this.pool.requestMap[this.hash]);
   this.pool.requestMap[this.hash] = this;
 }
@@ -2408,9 +2369,9 @@ LoadRequest.prototype.finish = function finish() {
   }
 
   if (this.type === this.pool.txType)
-    util.binaryRemove(this.peer.queueTX, this, compare);
+    this.peer.queueTX.remove(this);
   else
-    util.binaryRemove(this.peer.queueBlock, this, compare);
+    this.peer.queueBlock.remove(this);
 
   if (this.timeout != null) {
     clearTimeout(this.timeout);
@@ -2502,7 +2463,7 @@ BroadcastItem.prototype.start = function start() {
   assert(!this.pool.invMap[this.hash], 'Already started.');
 
   this.pool.invMap[this.hash] = this;
-  util.binaryInsert(this.pool.invItems, this, compare);
+  assert(this.pool.invItems.push(this));
 
   this.refresh();
 
@@ -2550,7 +2511,7 @@ BroadcastItem.prototype.finish = function finish(err) {
   this.timeout = null;
 
   delete this.pool.invMap[this.hash];
-  util.binaryRemove(this.pool.invItems, this, compare);
+  assert(this.pool.invItems.remove(this));
 
   for (i = 0; i < this.callback.length; i++)
     this.callback[i](err);

lib/utils/list.js

@@ -0,0 +1,237 @@
+'use strict';
+
+var assert = require('assert');
+
+/**
+ * A linked list.
+ * @exports List
+ * @constructor
+ */
+
+function List() {
+  if (!(this instanceof List))
+    return new List();
+
+  this.head = null;
+  this.tail = null;
+  this.size = 0;
+}
+
+/**
+ * Reset the cache. Clear all items.
+ */
+
+List.prototype.reset = function reset() {
+  var item, next;
+
+  for (item = this.head; item; item = next) {
+    next = item.next;
+    item.prev = null;
+    item.next = null;
+  }
+
+  assert(!item);
+
+  this.head = null;
+  this.tail = null;
+  this.size = 0;
+};
+
+/**
+ * Remove the first item in the list.
+ */
+
+List.prototype.shift = function shift() {
+  var item = this.head;
+
+  if (!item)
+    return;
+
+  this.remove(item);
+
+  return item;
+};
+
+/**
+ * Prepend an item to the linked list (sets new head).
+ * @private
+ * @param {ListItem}
+ */
+
+List.prototype.unshift = function unshift(item) {
+  return this.insert(null, item);
+};
+
+/**
+ * Append an item to the linked list (sets new tail).
+ * @private
+ * @param {ListItem}
+ */
+
+List.prototype.push = function push(item) {
+  return this.insert(this.tail, item);
+};
+
+/**
+ * Remove the last item in the list.
+ */
+
+List.prototype.pop = function pop() {
+  var item = this.tail;
+
+  if (!item)
+    return;
+
+  this.remove(item);
+
+  return item;
+};
+
+/**
+ * Insert item into the linked list.
+ * @private
+ * @param {ListItem|null} ref
+ * @param {ListItem} item
+ */
+
+List.prototype.insert = function insert(ref, item) {
+  if (item.prev || item.next || item === this.head)
+    return false;
+
+  assert(!item.prev);
+  assert(!item.next);
+
+  if (ref == null) {
+    if (!this.head) {
+      this.head = item;
+      this.tail = item;
+    } else {
+      this.head.prev = item;
+      item.next = this.head;
+      this.head = item;
+    }
+    this.size++;
+    return true;
+  }
+
+  item.next = ref.next;
+  item.prev = ref;
+  ref.next = item;
+
+  if (ref === this.tail)
+    this.tail = item;
+
+  this.size++;
+
+  return true;
+};
+
+/**
+ * Remove item from the linked list.
+ * @private
+ * @param {ListItem}
+ */
+
+List.prototype.remove = function remove(item) {
+  if (!item.prev && !item.next && item !== this.head)
+    return false;
+
+  if (item.prev)
+    item.prev.next = item.next;
+
+  if (item.next)
+    item.next.prev = item.prev;
+
+  if (item === this.head)
+    this.head = item.next;
+
+  if (item === this.tail)
+    this.tail = item.prev || this.head;
+
+  if (!this.head)
+    assert(!this.tail);
+
+  if (!this.tail)
+    assert(!this.head);
+
+  item.prev = null;
+  item.next = null;
+
+  this.size--;
+
+  return true;
+};
+
+/**
+ * Slice the list to an array of items.
+ * @param {Number} total
+ * @returns {Object[]}
+ */
+
+List.prototype.slice = function slice(total) {
+  var items = [];
+  var item, next;
+
+  if (total == null)
+    total = Infinity;
+
+  for (item = this.head; item; item = next) {
+    next = item.next;
+    item.prev = null;
+    item.next = null;
+
+    this.size--;
+
+    items.push(item);
+
+    if (items.length === total)
+      break;
+  }
+
+  if (next) {
+    this.head = next;
+    next.prev = null;
+  } else {
+    this.head = null;
+    this.tail = null;
+  }
+
+  return items;
+};
+
+/**
+ * Convert the list to an array of items.
+ * @returns {Object[]}
+ */
+
+List.prototype.toArray = function toArray() {
+  var items = [];
+  var item;
+
+  for (item = this.head; item; item = item.next)
+    items.push(item);
+
+  return items;
+};
+
+/**
+ * Represents an LRU item.
+ * @constructor
+ * @private
+ * @param {String} key
+ * @param {Object} value
+ */
+
+function ListItem(value) {
+  this.next = null;
+  this.prev = null;
+}
+
+/*
+ * Expose
+ */
+
+exports = List;
+exports.Item = ListItem;
+
+module.exports = exports;