normalize behavior of req.param('length) - (see #3738)

lib/hooks/http/initialize.js

@@ -165,6 +165,35 @@ module.exports = function(sails) {
          // This is also handled separately for virtual requests in `lib/router/`:
          // (see https://github.com/balderdashy/sails/pull/3599#issuecomment-195665040)
         req._sails = sails;
+
+        // Wrap `req.param()` in a shim that normalizes the behavior of `req.param('length')`.
+        // (see https://github.com/balderdashy/sails/issues/3738#issue-156095626)
+        var origReqParam = req.param; 
+        req.param = function getValForParam (name){
+          if (name === 'length') {
+            // If `req.params.length` is a string, instead of a number, then we know this request
+            // must have matched a route address like `/foo/bar/:length/baz`, so in that case, we'll
+            // allow `req.param('length')` to return the runtime value of `length` as a string.
+            if (_.isString(req.params.length)) {
+              return req.params.length; 
+            }
+            else if (!_.isArray(req.body) && _.isObject(req.body) && !_.isUndefined(req.body.length) && !_.isNull(req.body.length)) {
+              // > In future versions of Sails, this shim will likely be modified to allow the `null` literal to be received
+              // > as a value for a body parameter and accessed in `req.param()`.
+              // > (This is because `null` and `undefined` are distinct and lossless when serializing and deserializing to
+              // > and from JSON-- so it's really specifically for standard JSON response bodies.)
+              // >
+              // > However, this is a departure from the behavior of Express, and a breaking change- so it will
+              // > not happen until the release of Sails v1 (or possibly in a pre v1.0 minor version.)
+              return req.body.length;
+            }
+            else if (_.isObject(req.query) && !_.isUndefined(req.query.length) && !_.isNull(req.query.length)) {
+              return req.query.length;
+            }
+            else { return undefined; }
+          }
+          return origReqParam.apply(req, Array.prototype.slice.call(arguments));
+        };
 
         return next();
       });