Allow param middleware to access param name

lib/layer.js

@@ -177,7 +177,7 @@ Layer.prototype.param = function (param, fn) {
   const stack = this.stack;
   const params = this.paramNames;
   const middleware = function (ctx, next) {
-    return fn.call(this, ctx.params[param], ctx, next);
+    return fn.call(middleware, ctx.params[param], ctx, next);
   };
   middleware.param = param;
 

test/lib/layer.js

@@ -175,6 +175,33 @@ describe('Layer', function() {
         if (!id) return ctx.status = 404;
         return next();
       });
+      router.stack.push(route);
+      app.use(router.middleware());
+      request(http.createServer(app.callback()))
+        .get('/users/3')
+        .expect(200)
+        .end(function(err, res) {
+          if (err) return done(err);
+          res.should.have.property('body');
+          res.body.should.have.property('name', 'alex');
+          done();
+        });
+    });
+
+    it('composes middleware for generic param fn', function(done) {
+      const app = new Koa();
+      const router = new Router();
+      const route = new Layer('/users/:user', ['GET'], [function (ctx) {
+        ctx.body = ctx.user;
+      }]);
+      route.param('user', constructFromParam);
+
+      function constructFromParam (id, ctx, next) {
+        ctx[this.param] = { name: 'alex', fromParam: this.param}
+        if (!id) return ctx.status = 404
+        return next()
+      }
+
       router.stack.push(route);
       app.use(router.middleware());
       request(http.createServer(app.callback()))
@@ -184,6 +211,7 @@ describe('Layer', function() {
         if (err) return done(err);
         res.should.have.property('body');
         res.body.should.have.property('name', 'alex');
+        res.body.should.have.property('fromParam', 'user');
         done();
       });
     });
@@ -269,4 +297,4 @@ describe('Layer', function() {
       prefix.path.should.equal(false)
     });
   });
-});
+});