behavior of http.createServer

[bfang-yseop]

I am running through stream-adventure: http server when I first stumbled upon this oddity.

when I wrote my code like so:

var through = require('through');
var http = require('http');

var ts = through(function (buf){
    this.queue(buf.toString().toUpperCase());
})

var server = http.createServer(function (req, res) {


    if (req.method === 'POST'){
        req.pipe(ts).pipe(res);
    } else {
        res.end("Will I dream? \n")
    }
});

server.listen(process.argv[2])

I got extra results that I could not explain. However, when I moved var ts = ... into createServer's callback function the program ran as expected.

Can anyone explain what happened? Why would declaring ts outside of createServer produce different results?

[timoxley]

• createServer's callback is fired for every new request.
• the through stream is a queue.
• declaring the through stream outside the createServer means all connections are sharing the same queue
• a connection's response reads data from the shared queue (ts.pipe(res))
• highly likely it will read data which was put in there by a different connection's request. (req.pipe(ts))

i.e. through has an internal buffer. The response is mangled because concurrent requests are reading from the same buffer.

[bfang-yseop]

I see, that makes sense. Thanks for the reply.

[timoxley]

👍

[relaxedtomato]

@timoxley thanks for clarifying this concept 👍