Strange behavior in node.js

Question

I'm reading a tutorial in http://www.nodebeginner.org and I have a strange behavior in data output. I know, there's a similar question on Stackoverflow but there's no answer. So I have this code of web-server:

//server.js
var http = require('http')
var url = require('url')

function start(route, handle) {
    function onRequest(request, response) {
        var postData = ""
        var pathname = url.parse(request.url).pathname
        console.log("Request for " + pathname + " recieved.")

        request.setEncoding('utf8')
        request.addListener("data", function(postDataChunk) {
            postData += postDataChunk
            console.log("Recieved POST data chunk '" + postDataChunk +"'.")
        })

        request.addListener("end", function() {
            route(handle, pathname, response, postData)
        })
        var content = route(handle, pathname, response)
    }

    http.createServer(onRequest).listen(80, '192.168.1.34')
    console.log("Server has started")
}

exports.start = start

Code of router.js which calls requestHandler.upload - my buggy function

//router.js
function route(handle, pathname, response, postData) {
    console.log("About to route a request for " + pathname)
    if (typeof handle[pathname] === 'function') {
        handle[pathname](response, postData) //calls requestHandler.upload 
    } else {
        console.log("No request handler found for " + pathname)
        response.writeHead(404, {'Content-Type' : 'text/plain'})
        response.write("404 Not found")
        response.end()
    }
}

And the code of requestHandler.upload

//requestHandler.js
function upload(response, postData) {
    console.log("Request handler 'upload' was called with POST data: " + postData); //works fine
    response.writeHead(200, {"Content-Type": "text/plain"});
    response.write("You've sent: " + postData); //works ugly
    response.end();
}

Let's assume that in POST data there is a string text=123. The first line of this function outputs real data like "Request handler 'upload' was called with POST data: text=123". Although, this line response.write("You've sent: " + postData); outputs in browser next message: You've sent: undefined. What am I doing wrong?

Stuart Wakefield Stuart Wakefield · Accepted Answer · 2012-09-07T22:34:41

In your code in server.js the line:

var content = route(handle, pathname, response)

Is being run first before the call in the "end" event listener, executing the function but omitting the postData argument. It runs...

response.write("You've sent: " + postData);
response.end();

Therefore, the response sent back to the browser is:

You've sent: undefined

The "end" event is being triggered afterwards and the event listener calls...

route(handle, pathname, response, postData)

Which correctly passes the postData and this gets correctly output to the console. The call to response.write(...) is not posted back to the browser the second time because the response at this point has ended.

I hope that explains the problem.

EDIT The answer is to remove the call

var content = route(handle, pathname, response)

The "end" event will then be called when the client has finished posting data and you are correctly running the route function at that point.

Strange behavior in node.js

1 Answers