Question

I am working on a Flatiron Union-based app, and it seems that the simple logger I am developing logs before the routes are run, so it does not accurately report what happened. I took the logger sample code from the Union examples. Here’s a stripped down code sample:

 var
   union = require('union')
   , server;

 server = union.createServer({
   before: [ function (req,res) {
     console.log('before');
     res.writeHead(404, {"Content-Type": "text/plain"});
     res.end("Hello World");
   } ],
   after: [
     function LoggerStream() {
         var stream   = new union.ResponseStream();
         stream.once("pipe", function (req) {
           console.log({res: this.res.statusCode, method: this.req.method});
         });
         return stream;
     }
   ]
 });

 server.listen(8800);
 console.log('union running on 8800');

Here’s what appears in my console:

 $ DEBUG=*  node ./union.js
 union running on 8800
 { res: 200, method: 'GET' }
 before

Note that the reported status is 200 when the http server actually returned a 404.

Why is this running out of order?

Answer 1

Here’s a recent reply to your question from our mailing list by indexzero:

Stuart,

This is actually expected behavior. A pipe chain is constructed by a
union.RoutingStream instance from:

union.ResponseStream() –> after0 –> after1 –> after2 –> … –>
aftern –> http.Response() (see
https://github.com/flatiron/union/blob/master/lib/routing-stream.js#L74-83)

So the pipe event on every Stream in the after chain is invoked
immediately, but everyone of those Streams has an opportunity to
modify the data sent to the response by implementing their own .pipe()
method.

So for example if your LoggingStream was

var stream = new union.ResponseStream(); stream.once(“data”,
function (req) { console.log({res: this.res.statusCode, method:
this.req.method}); }); return stream;

You would see the console.log statements fire in the order you expect.
It might be useful to read Max Ogden’s recent blog post on Streams in
node.js and how they work: http://maxogden.com/node-streams

Cheers, Charlie

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