http500.js

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

var port = 3000;

http.createServer(dispatchRequest).listen(port);
sys.puts('Server running on port ' + port);


// This is the web framework, which wants to send
// a '500 Internal Server Error' to the client
// if the application using the framework
// throws an exception.

function dispatchRequest(req, res)
{
        process.exceptionCatcher = function (e) {
                sys.error(e.stack);
                if (!res.sentHeaders) {
                        // 500 Internal Server Error
                        res.sendHeader(500, { 'Content-Type': 'text/plain'});
                }
                res.sendBody('Internal Server Error: '
                        + e.message + '\n\n' + e.stack + '\n');
                res.finish();
        };

        // No point calling handleRequest() in a try {} block,
        // because it is async and will simply return after
        // setting up some I/O callbacks.

        handleRequest(req, res);
}


// This is the application using the web framework.

function handleRequest(req, res)
{
        // Simple simulation of a request handler that normally
        // works fine after doing some I/O (simulated by setTimeout)
        // but under certain buggy conditions can throw exceptions.

        setTimeout(function () {
                if (req.url === '/throw-before-headers') {
                        throw new Error('throw-before-headers');
                }

                res.sendHeader(200, { 'Content-Type': 'text/plain'});
                res.sentHeaders = true;
                res.sendBody('Some page content.\n');

                if (req.url === '/throw-after-headers') {
                        throw new Error('throw-after-headers');
                }

                res.sendBody('You requested ' + req.url + '\n');
                res.finish();
        }, 100);

        // handleRequest returns before the callback throws any exeptions.
}