Fix #8 - emit clientError events

README.md

@@ -23,7 +23,7 @@ Configuration
 -------------
 Redlock can use [node redis](https://github.com/mranney/node_redis), [ioredis](https://github.com/luin/ioredis) or any other compatible redis library to keep its client connections.
 
-A redlock object is instantiated with an array of at least one redis client and an optional`options` object. Properties of the Redlock object should NOT be changed after it is firstused, as doing so could have unintended consequences for live locks.
+A redlock object is instantiated with an array of at least one redis client and an optional `options` object. Properties of the Redlock object should NOT be changed after it is firstused, as doing so could have unintended consequences for live locks.
 
 ```js
 var client1 = require('redis').createClient(6379, 'redis1.example.com');
@@ -39,18 +39,36 @@ var redlock = new Redlock(
 		// the expected clock drift; for more details
 		// see http://redis.io/topics/distlock
 		driftFactor: 0.01,
-		
+
 		// the max number of times Redlock will attempt
 		// to lock a resource before erroring
 		retryCount:  3,
-		
+
 		// the time in ms between attempts
 		retryDelay:  200
 	}
 );
 ```
 
 
+Error Handling
+--------------
+
+Because redlock is designed for high availability, it does not care if a minority of redis instances/clusters fail at an operation. If you want to write logs or take another action when a redis client fails, you can listen for the `clientError` event:
+
+```js
+
+// ...
+
+redlock.on('clientError', function(err) {
+	console.error('A redis error has occurred:', err);
+});
+
+// ...
+
+```
+
+
 Usage (promise style)
 ---------------------
 
@@ -170,7 +188,7 @@ redlock.lock(resource, ttl, function(err, lock) {
 	if(err) {
 		// ...
 	}
-	
+
 	// we have the lock
 	else {
 
@@ -195,7 +213,7 @@ redlock.lock('locks:account:322456', 1000, function(err, lock) {
 	if(err) {
 		// ...
 	}
-	
+
 	// we have the lock
 	else {
 

redlock.js

@@ -1,7 +1,8 @@
 'use strict';
 
-var util    = require('util');
-var Promise = require('bluebird');
+var util         = require('util');
+var Promise      = require('bluebird');
+var EventEmitter = require('events');
 
 // constants
 var unlockScript = 'if redis.call("get", KEYS[1]) == ARGV[1] then return redis.call("del", KEYS[1]) else return 0 end';
@@ -71,13 +72,17 @@ function Redlock(clients, options) {
 	this.driftFactor = typeof options.driftFactor === 'number' ? options.driftFactor : defaults.driftFactor;
 	this.retryCount  = typeof options.retryCount  === 'number' ? options.retryCount  : defaults.retryCount;
 	this.retryDelay  = typeof options.retryDelay  === 'number' ? options.retryDelay  : defaults.retryDelay;
-	
+
 	// set the redis servers from additional arguments
 	this.servers = clients;
 	if(this.servers.length === 0)
 		throw new Error('Redlock must be instantiated with at least one redis server.');
 }
 
+// Inherit all the EventEmitter methods, like `on`, and `off`
+util.inherits(Redlock, EventEmitter);
+
+
 // Attach a reference to LockError per issue #7, which allows the application to use instanceof
 // to destinguish between error types.
 Redlock.LockError = LockError;
@@ -148,6 +153,7 @@ Redlock.prototype.unlock = function unlock(lock, callback) {
 		});
 
 		function loop(err, response) {
+			if(err) self.emit('clientError', err);
 			if(waiting-- > 1) return;
 			return resolve();
 		}
@@ -215,7 +221,7 @@ Redlock.prototype.extend = function extend(lock, ttl, callback) {
 Redlock.prototype._lock = function _lock(resource, value, ttl, callback) {
 	var self = this;
 	return new Promise(function(resolve, reject) {
-		var request; 
+		var request;
 
 		// the number of times we have attempted this lock
 		var attempts = 0;
@@ -252,6 +258,7 @@ Redlock.prototype._lock = function _lock(resource, value, ttl, callback) {
 			var waiting = self.servers.length;
 
 			function loop(err, response) {
+				if(err) self.emit('clientError', err);
 				if(response) votes++;
 				if(waiting-- > 1) return;