Add errorFn option to breaker to filter errors

lib/circuit-breaker.js

@@ -18,6 +18,7 @@ var CircuitBreaker = module.exports = function (func, options) {
   this.timeout = this.options.timeout || 10000; // default 10 second timeout (ms)
   this.resetTimeout = this.options.resetTimeout || 60000; // default 1 minute reset timeout (ms)
   this.maxFailures = this.options.maxFailures || 5; // default max number of failures to open circuit
+  this.errorFn = this.options.errorFn || function () { return true; }; // optional function to break based on custom conditions for error object
 
   // Initially circuit is always closed
   this.forceClosed();
@@ -90,7 +91,9 @@ CircuitBreaker.prototype._callbackHandler = function(deferred, timeoutID, startT
     self.emit('latency', (new Date() - startTime) );
 
     if(err) {
-      self.handleFailure(err);
+      if(self.errorFn(err)) {
+        self.handleFailure(err);
+      }
       deferred.reject(err);
     } else {
       self.handleSuccess();

package.json

@@ -1,6 +1,6 @@
 {
   "name": "circuitbreaker",
-  "version": "0.2.1",
+  "version": "0.3.0",
   "description": "circuit breaker is used to provide stability and prevent cascading failures in distributed systems",
   "main": "index.js",
   "scripts": {

test/circuitbreaker-test.js

@@ -371,4 +371,53 @@ describe('Circuit Breaker', function(){
     });
 
   });
+
+  describe('errorFn', function () {
+    it('should break based on error function parameter', function (done) {
+      var breakerFn = function(id, callback) {
+        if (id < 0) {
+          return callback(id);
+        } else {
+          return callback(null, 'data for id ' + id);
+        }
+      };
+
+      var breaker = new CircuitBreaker(breakerFn, {timeout: 10, maxFailures: 3, resetTimeout: 30, errorFn: function (error) { if (error === -2) { return false; } return true }});
+      var noop = function () {};
+
+      breaker.invoke(-1).fail(noop);
+      breaker.invoke(-2).fail(noop);
+      breaker.invoke(-1).fail(noop);
+      breaker.isClosed().should.be.true;
+
+      breaker.invoke(-1).fail(noop);
+      breaker.isOpen().should.be.true;
+
+      done();
+    });
+
+    it('should break the circuit normally without an error function', function (done) {
+      var breakerFn = function(id, callback) {
+        if (id < 0) {
+          return callback(id);
+        } else {
+          return callback(null, 'data for id ' + id);
+        }
+      };
+
+      var breaker = new CircuitBreaker(breakerFn, {timeout: 10, maxFailures: 3, resetTimeout: 30});
+      var noop = function () {};
+
+      breaker.invoke(-1).fail(noop);
+      breaker.invoke(-2).fail(noop);
+      breaker.invoke(-1).fail(noop);
+      breaker.isClosed().should.be.false;
+
+      breaker.invoke(-1).fail(noop);
+      breaker.isOpen().should.be.true;
+
+      done();
+    });
+
+  });
 });