catch rejected promises returned from router.param

add test for catching rejected promises

add error middleware test

move isPromise into util folder

update README with router.params promise info

switch to using npm package is-promise

README.md

@@ -115,6 +115,10 @@ Maps the specified path parameter `name` to a specialized param-capturing middle
 
 This function positions the middleware in the same stack as `.use`.
 
+If a `Promise` object is returned from the `param_middleware` function, the router
+will attach an `onRejected` callback using `.then`. If the promise is rejected,
+`next` will be called with the rejected value, or an error if the value is falsy.
+
 Parameter mapping is used to provide pre-conditions to routes
 which use normalized placeholders. For example a _:user_id_ parameter
 could automatically load a user's information from the database without

index.js

@@ -19,6 +19,7 @@ var mixin = require('utils-merge')
 var parseUrl = require('parseurl')
 var Route = require('./lib/route')
 var setPrototypeOf = require('setprototypeof')
+var isPromise = require('is-promise')
 
 /**
  * Module variables.
@@ -634,7 +635,12 @@ function processParams (params, layer, called, req, res, done) {
     if (!fn) return param()
 
     try {
-      fn(req, res, paramCallback, paramVal, key.name)
+      var ret = fn(req, res, paramCallback, paramVal, key.name)
+      if (isPromise(ret)) {
+        ret.then(null, function (error) {
+          paramCallback(error || new Error('Rejected promise'))
+        })
+      }
     } catch (e) {
       paramCallback(e)
     }

lib/layer.js

@@ -13,6 +13,7 @@
  */
 
 var pathRegexp = require('path-to-regexp')
+var isPromise = require('is-promise')
 
 /**
  * Module variables.
@@ -187,20 +188,6 @@ function decodeParam (val) {
   }
 }
 
-/**
- * Returns true if the val is a Promise.
- *
- * @param {*} val
- * @return {boolean}
- * @private
- */
-
-function isPromise (val) {
-  return val &&
-    typeof val === 'object' &&
-    typeof val.then === 'function'
-}
-
 /**
  * Loosens the given path for path-to-regexp matching.
  */

package.json

@@ -10,6 +10,7 @@
   "repository": "pillarjs/router",
   "dependencies": {
     "array-flatten": "3.0.0",
+    "is-promise": "^2.1.0",
     "methods": "~1.1.2",
     "parseurl": "~1.3.3",
     "path-to-regexp": "3.2.0",

test/param.js

@@ -254,6 +254,24 @@ describe('Router', function () {
         .expect(500, /Error: boom/, done)
     })
 
+    it('should catch rejected promises returned from fn', function (done) {
+      var router = new Router()
+      var server = createServer(router)
+
+      router.param('user', function parseUser (req, res, next, user) {
+        return Promise.reject(new Error('boom'))
+      })
+
+      router.get('/user/:user', function (req, res) {
+        res.setHeader('Content-Type', 'text/plain')
+        res.end('get user ' + req.params.id)
+      })
+
+      request(server)
+        .get('/user/bob')
+        .expect(500, /Error: boom/, done)
+    })
+
     describe('next("route")', function () {
       it('should cause route with param to be skipped', function (done) {
         var cb = after(3, done)

test/router.js

@@ -608,6 +608,24 @@ describe('Router', function () {
           .get('/')
           .expect(500, done)
       })
+      it('should invoke error function after router.param returns rejected promise', function (done) {
+        var router = new Router()
+        var server = createServer(router)
+
+        router.param('user', function (req, res, next, user) {
+          return Promise.reject(new Error('boom!'))
+        })
+
+        router.get('/:user', function handle (req, res, next) {
+          res.end()
+        })
+
+        router.use(sawError)
+
+        request(server)
+          .get('/username')
+          .expect(200, 'saw Error: boom!', done)
+      })
     })
 
     describe('next("route")', function () {