Correctly handle not found errors in partial routes

Take care of obvious case. A router with a route to '/foo/bar' but not
for '/foo', should give a not found error.

lib/error.js

@@ -0,0 +1,14 @@
+var util = require('util')
+
+function NotFound(message, options) {
+  Error.call(this)
+  options = options || {}
+  this.message = message || ''
+  this.location = options.location || ''
+}
+
+util.inherits(NotFound, Error)
+
+module.exports = {
+  NotFound: NotFound
+}

lib/route-node.js

@@ -1,4 +1,5 @@
 'use strict'
+var NotFoundError = require('./error').NotFound
 var utils = require('./utils')
 
 var assign = utils.assign
@@ -10,8 +11,8 @@ var noop = utils.noop
 function RouteNode (options) {
   options = options || {}
   this._children = Object.create(null)
-  this._regExs = Object.create(null)
   this._funcs = Object.create(null)
+  this._regExs = Object.create(null)
 }
 
 assign(RouteNode.prototype, {
@@ -71,7 +72,7 @@ assign(RouteNode.prototype, {
       return results.node.get(parts, args.concat(results.args), done)
     }
 
-    return done(new Error('not found'))
+    return done(new NotFoundError('not found', {location: parts}))
   },
 
   _getRegexChild: function _getRegexChild(part) {

lib/router.js

@@ -1,10 +1,12 @@
 'use strict'
 var url = require('url')
+var NotFoundError = require('./error').NotFound
 var RouteNode = require('./route-node')
 var utils = require('./utils')
 
 var assign = utils.assign
 var isArray = utils.isArray
+var isFunction = utils.isFunction
 var isString = utils.isString
 var noop = utils.noop
 
@@ -25,7 +27,11 @@ assign(Router.prototype, {
       if (err) {
         return done(err)
       } else {
-        return done(null, func.apply(context, args))
+        if (isFunction(func)) {
+          return done(null, func.apply(context, args))
+        } else {
+          return done(new NotFoundError('not found', {location: path}))
+        }
       }
     })
   },
@@ -53,7 +59,7 @@ assign(Router.prototype, {
 })
 
 Router.isNotFound = function isNotFound(err) {
-  return err instanceof Error && /not found/.exec(err.message) !== null
+  return err instanceof NotFoundError
 }
 
 module.exports = Router

test/router.js

@@ -1,5 +1,6 @@
 var expect = require('expect')
 var Router = require('../lib/router')
+var NotFoundError = require('../lib/error').NotFound
 
 describe('Router', function () {
   it('→ exists', function () {
@@ -26,6 +27,15 @@ describe('Router', function () {
     })
   })
 
+  it('→ partial route is a not found error', function (done) {
+    var router = new Router()
+    router.add(['/user', /^(\d+)$/], function (number) { return number })
+    router.route('/user/', function (err) {
+      expect(err).toBeA(NotFoundError)
+      done()
+    })
+  })
+
   it('→ get error in callback for missing handler', function (done) {
     var router = new Router()
     router.route('/some/fake/path', function (err, handlerResult) {