Serves as a proxy using node-http-proxy

Hi there,

I am new to koa/node.js so please forgive my ignorance if this looks like a basic question to you.

I am looking into writing a proxy server to one of my HTTP server. I would like to use a library like https://github.com/nodejitsu/node-http-proxy and koa/koa-router to do this.

I basically followed the documentation available in node-http-proxy/koa/koa-router to write some code snippet like this:

  var koa = require('koa');
  var router = require('koa-router');
  var app = koa();
  app.use(router(app));
  ...
  app.get('/proxy/*', function *(next) {
      proxy.web(this.req, this.res, { target: 'http://www.google.com' });
  });

But I got some error like

_http_outgoing.js:331
    throw new Error('Can\'t set headers after they are sent.');
          ^
Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:331:11)
    at .../node_modules/http-proxy/lib/http-proxy/passes/web-outgoing.js:58:11

I went through koa wiki pages/examples but I am not really sure what goes wrong here. I did find several similar koa issues logged, including https://github.com/koajs/koa/issues/95, https://github.com/koajs/koa/pull/139, and https://github.com/koajs/koa/issues/142, but I didn’t have any idea how I can address my problem here after reviewing all these. Could you please help to shed some light on this? Thanks so much.

[jonathanong]

you don’t need to shoehorn into koa. koa makes some opinions, and unfortunately i haven’t found a way to make it compatible with the regular req, res, next signature.

just use it outside of express:

var app = koa()
var callback = app.callback()

http.createServer(function (req, res) {
  var path = url.parse(req.url).pathname
  if (/^\/proxy\/.*/.test(path)) return proxy.web(req, res, {proxy: '' })
  callback(req, res)
})

@visionmedia do you want to add a this.response = false flag so people can skip koa’s default response handling? it would avoid support issues, but i think 99% of the time they are doing it wrong if they need to do that.

[jonathanong]

yeah you can mount koa as a connect/express app, which is pretty much what my example above is. you just can’t pass a callback to app.callback() though since it won’t work like a connect/express app if we supported that (unless we executed the callback only on errors, but that’s weird).