Manipulate or cancel proxyRes

[cmawhorter]

It'd be nice to have the ability to manipulate or abort a proxyRes. This is a solution for #737.

Not the prettiest but is 100% backwards compat and has almost non-existent perf penalty. Test included.

[cmawhorter]

Guess I should include an example:

proxy.on('proxyRes', function(proxyRes, req, res) {
  // conditionally proxy to a different target 
  if (proxyRes.statusCode === 404) {
    proxyRes.abort(); // leave http-proxy handling
    proxy.web(req, res, { target: 'http://a-different.example.com' });
  }
  // respond directly
  else if (proxyRes.statusCode === 301) {
    proxyRes.abort();
    var someStream = ...;
    someStream.pipe(res);
    res.end();
  }
});

[prust]

+1 we needed this in order to transparently follow 307 redirects in the proxy for the client

[prust]

@indexzero, @jcrugzz: I can rebase this on the latest master if you guys are open to merging it.

[euprogramador]

Guys,

I think exactly like that, but I would like to have control over the continuation of the flow as between sending the response from the server to the client I want to run some asynchronous code.

[acanimal]

@euprogramador I don't know if it is exactly what you need, but some time ago I was working on ClydeIO project (now stopped due I have no free time to spent on it) which allows to configure a set of middlewares before/after sending request to http-proxy. See image: https://github.com/clydeio/clydeio/wiki/Data-Workflow

[thetrevdev]

This is super useful. Sad to see it wasn't merged

[sibnerian]

👍 Among other things, this is extremely useful for catching a proxy error page and sending a prettier version. Would love to see this merged!

For posterity: I was able to hack around it by overriding the ServerResponse methods after sending the response.

onProxyRes(proxyRes, req, res) {
  if (proxyRes.statusCode >= 400) {
    renderErrorResponse(req, res);
    // Overwrite the methods in https://nodejs.org/api/http.html#http_class_http_serverresponse
    ['addTrailers', 'end', 'setHeader', 'write', 'writeContinue', 'writeHead'].forEach((k) => {
      res[k] = noop;
    });
  }
}

This is a hack, so caveat emptor. It won't work if renderErrorResponse is asynchronous. I'll be getting rid of this when (if?) this PR is merged.

[cmawhorter]

anyone still in need of a nodejs proxy should look at anyproxy. it has a ton of its own problems, but is at least actively maintained by alibaba. it's perfect for dev, which is all i ever used node proxy for anyway.