try to find callback in arguments

lib/mm.js

@@ -37,7 +37,18 @@ exports.error = function (mod, method, error, timeout) {
   }
   timeout = timeout || 0;
   muk(mod, method, function () {
-    var callback = arguments[arguments.length - 1];
+    var index = arguments.length - 1;
+    var callback = arguments[index];
+    while (typeof callback !== 'function') {
+      index--;
+      if (index < 0) {
+        break;
+      }
+      callback = arguments[index];
+    }
+    if (!callback) {
+      throw new TypeError('Can\'t find callback function');
+    }
     setTimeout(function () {
       callback(error);
     }, timeout);

test/foo.js

@@ -0,0 +1,26 @@
+/*!
+ * mm - test/foo.js
+ * Copyright(c) 2012 fengmk2 <fengmk2@gmail.com>
+ * MIT Licensed
+ */
+
+"use strict";
+
+/**
+ * Module dependencies.
+ */
+
+exports.get = function (query, callback, headers, cache) {
+  process.nextTick(callback.bind(null, null, {
+    query: query,
+    headers: headers,
+    cache: cache,
+  }));
+};
+
+exports.check = function (callback, a1, a2) {
+  process.nextTick(callback.bind(null, null, {
+    a1: a1,
+    a2: a2,
+  }));
+};

test/mm.test.js

@@ -100,6 +100,42 @@ describe('mm.test.js', function () {
       });
     });
 
+    it('should work for callback is not the last params case', function (done) {
+      var foo = require('./foo');
+      done = pedding(3, done);
+
+      mm.error(foo, 'get', 'mock foo.get error');
+      foo.get('q1', function (err, data) {
+        should.exist(err);
+        err.message.should.equal('mock foo.get error');
+        should.not.exist(data);
+        done();
+      });
+
+      foo.get('q2', function (err, data) {
+        should.exist(err);
+        err.message.should.equal('mock foo.get error');
+        should.not.exist(data);
+        done();
+      }, { h1: 'h1' }, false);
+
+      mm.error(foo, 'check', 'mock foo.check error');
+      foo.check(function (err, data) {
+        should.exist(err);
+        err.message.should.equal('mock foo.check error');
+        should.not.exist(data);
+        done();
+      }, { h1: 'h1' }, false);
+    });
+
+    it('should throw error', function () {
+      var foo = require('./foo');
+      mm.error(foo, 'check', 'mock foo.check error');
+      (function () {
+        foo.check();
+      }).should.throw('Can\'t find callback function');
+    });
+
   });
 
   describe('http(s).request()', function () {