added validateResponse middleware

README.md

@@ -87,7 +87,8 @@ want to use them.
 The batteries middleware creates the following JSGI chain where `nextApp` is the JSGI appliance passed as the first parameter
 to `batteries`:
 
-    error - directory - parted - methodOverride - session - flash - bodyAdapter - stringReturnAdapter - nextApp
+    error -> validateResponse -> directory -> parted -> methodOverride 
+          -> session -> flash -> bodyAdapter -> stringReturnAdapter -> nextApp
 
 The binary middleware is configured to check the path of the request and if it corresponds to a potential directory in the 'public' directory,
 the request is routed to the `directory` middleware to serve a static file.

lib/middleware.js

@@ -151,7 +151,8 @@ exports.parted = exports.Parted = function(nextApp, opts) {
 /**
  * Translates rejected promises to a JSGI error response.
  *
- * @param errorResponse {Function}  A function that returns a JSGI response when passed an error.
+ * @param errorResponse {Function}  Optional. A function that returns a JSGI response when passed an error.
+ * @returns {Function} JSGI response.
  */
 exports.error = exports.Error = function(app, errorResponse) {
     errorResponse = errorResponse ||
@@ -180,6 +181,45 @@ exports.error = exports.Error = function(app, errorResponse) {
     };
 };
 
+/**
+ * Validates that the response from nextApp is a valid JSGI response.
+ * Rejects the promise if the response is invalid.
+ *
+ * @param {Function} nextApp  The next application in the JSGI chain.
+ * @returns {Function} JSGI response.
+ */
+exports.validateResponse = exports.ValidateResponse = function(nextApp) {
+  return function(req) {
+    return when(nextApp(req), function(resp) {
+      if (!resp) {
+        throw 'Response must be an object.'
+      }
+
+      if (!resp.body) {
+        throw 'Response must have a body property.'
+      }
+
+      if (!resp.body.forEach) {
+        throw 'Response body must have a forEach method.';
+      }
+
+      if (typeof resp.body.forEach !== 'function') {
+        throw 'Response body has a forEach method but the forEach method is not a function.'
+      }
+
+      if (!resp.status) {
+        throw 'Response must have a status property.';
+      }
+
+      if (typeof resp.status.constructor !== '[Function: Number]') {
+        throw 'Response has a status property but the status property must be a number.'
+      }
+
+      return resp;
+    });
+  };
+};
+
 var HTTP_METHODS = exports.HTTP_METHODS = {
     "GET": true,
     "HEAD": true,
@@ -569,7 +609,9 @@ exports.binary = function(conditional, appTrue, appFalse) {
  * All the goodies in one convenient middleware.
  *
  * Includes the following JSGI Chain:
- * error - directory - parted - methodOverride - session - flash - bodyAdapter - stringReturnAdapter - nextApp
+ *
+ * error -> validateResponse -> directory -> parted -> methodOverride 
+ *       -> session -> flash -> bodyAdapter -> stringReturnAdapter -> nextApp
  *
  * @param {Object} config   Optional configuration, if arity is two first parameter is config.
  * @param {Function} nextApp  The next application (Middleware, Bogart Router, etc...) in the JSGI chain.