Advanced Shows and Lists: Throwing Redirects

Throw a 404 error

To throw a 404 from inside a _show or _list func .. the easiest way is:

•     throw (['error', 'not_found', 'Some message like Page not found'])

That will be caught by the top level loop thing and turned into a nice response.

Return a redirect

There's no top level catcher thing for redirects, so you can't *throw a redirect*, you have to 'return' it.

To do a redirect, there's a library function that will do it for you:

•     var redirect = require("vendor/couchapp/lib/redirect");
      return redirect.permanent('http://some.new/place');

You can use the path lib to help get some neat urls, have a look at vendor/couchapp/lib/path.js source ..

What this actually does is the equivalent of:

•     return { code : 301, headers : { "Location" : 'http://some.new/place' } };

The 'code' is the http response code, the http response would be something like:

•     HTTP/1.1 301 Moved Permanently
      Vary: Accept
      Server: CouchDB/1.0.1 (Erlang OTP/R13B)
      Location: http://foot:5984/products/dvrs/standalone-h.264-16-channel-dvr
      Etag: "CYFPH3WEUO9R5B8S26QWV3NK4"
      Date: Sat, 11 Sep 2010 04:51:37 GMT
      Content-Type: application/json
      Content-Length: 0

Case study, Making a Redirect Throwable

If you're deep in a lib/mystuff.js func, I use this sort of style for a certain checker function.

In this example I have different product lines in my rewrites, of the form:

•     [
          {
              "from":   "/products/dvrs",
              "to":     "_list/dvrs",
              "method": "GET" 
          },
          {
              "from":   "/products/dvrs/new",
              "to":     "_show/dvr-new",
              "method": "GET" 
          },
          {
              "from":   "/products/dvrs/new",
              "to":     "_show/dvr-save",
              "method": "POST" 
          },
          {
              "from":   "/products/dvrs/*",
              "to":     "_show/dvr/*",
              "method": "GET" 
          },
          // Then a bunch of similar things for other product lines (like /products/cameras/ etc ..)
      ]

The trouble is if someone uses the wrong url for the type of product, I want to put them right, this will help keep the search engine optimization good too. So if someone goes:

•     http://mysite.kom/products/cameras/id_of_a_dvr

It will call the _show/camera method with the id of a document that has {type: 'dvr'}. Which is bad because I use a different template but also bad because SEO will freak out if it ends up in google.

To fix it I did the following:

In my _show or _list func I put:

•     var rewrite = require("lib/rewritehelper").init(req);
      // If we're trying to use this view to see something other than a dvr, make sure we're looking at the right type
        try {rewrite.checkType(doc, 'camera');} catch (e) {return e;}

I know people will yell at me for puting too much on one line. But I'm using this in all my _show and _list funcs, I want it to be nice and short.

In my *lib/rewritehelper.js* file I check the type and all that and if it's wrong I throw an exception, which the _show func catches and returns as is. Here's the full code for my lib function so far:

•     /* Helps you get the rewrites right.
  
      Complements the rewrites.json .. really both should be updated at the same time. Saves having to update every place you
      put a path to something.
  
      */
  
      exports.init = function(req) {
  
          rewrite = {};
  
          rewrite.url4doc = function (_id, prodType) {
              /* Returns a url to a product, takes doc._id and doc._type */
              // See if it's a product
              switch (prodType) {
                  case "forum-topic":
                  case "forum-post":
                      return "http://" + req.headers.Host + "/forums/" + prodType + "s/" + _id;
                  case "support":
                      return "http://" + req.headers.Host + "/support/" + prodType + "s/" + _id;
                  case "dvr": 
                  case "camera": 
                      return "http://" + req.headers.Host + "/products/" + prodType + "s/" + _id;
                  default:
                      return {code: 404, body: 'Page not found!'}
              };
          };
          rewrite.checkType = function (doc, desiredType) {
              /* Checks a document type and throws an exception that should be returned straight to the client if caught.
                 If no exception is raised, the check has passed */
              if ((doc) && (doc.type != desiredType)) {
                  var newURL = rewrite.url4doc(doc._id, doc.type);
                  if (newURL.body == undefined) {
                      // If it's a url string, throw a redirect error
                      throw { code : 301, headers : { "Location" : newURL } };
                  } else {
                      // If it's a {code: 404} block, throw it straight
                      throw newURL;
                  }
              } else {
                  return null;
              }
          }
  
          return rewrite;
      };

So the cool thing here is the 'throw' statements, if we're totally in the wrong place, I want to get out ASAP.