Running 'setHeader' during 'proxyReq' event fails for POST requests

[cdl]

Right now, it looks like trying to do a setHeader on the passed in proxyReq for POST requests fails. (see below:)

proxy.on('proxyReq', function(proxyReq, req, res, options) {
  proxyReq.setHeader('origin', 'https://example.com');
});

The following error is thrown when the above tries to execute:

Error: Can't set headers after they are sent.

This seems to work totally fine for GET requests, just not POST requests. Managed to hack around it at first by wrapping the .setHeader call in check to make sure proxyReq._header was null, but it looks like that totally fails when Firefox tries to perform a POST request (the header doesn't get set).

The same thing appears to happen when trying to do res.setHeader, as suggested by #819.

[jcrugzz]

@cdl what node version does this happen in? Could you write a reproducible test case? I want to establish if this is a deterministic issue and if not what conditions FULLY create it. Thanks!

[cdl]

@jcrugzz Happens in node 4.2.1. Will see about stubbing out a reproducible test case for it for sure.

[jcrugzz]

@cdl can you upgrade to node@4.2.2 there was an http bug in 4.2.1 that was resolved in the patch version. See if upgrading resolves this one as well. Let me know either way! Thanks

[cdl]

@jcrugzz Just tested in node@4.2.2, issue still persists. Will write up a gist demonstrating the issue shortly.

[jcrugzz]

@cdl sounds good, and if you can encapsulate it into a test that you can PR to this project that would get us closer to a solution :). Thanks for the update!

[stickystyle]

I had the same issue after upgrading to 1.12.0, downgrading back to 1.11.3 resolved it for me.

[jcrugzz]

@stickystyle could you post a sample of the code that you use for http-proxy? This doesn't seem like a bug in http-proxy since its part of the http semantic so this is very curious as nothing changed around this code.

[stickystyle]

@jcrugzz I've just made a scrubbed gist of the app.js and package.json that I'm using. It's a simple proxy that serves to layer JWT and caching on top of a RESTful API.
I too did a compare of the tag to master and didn't see anything that stood out, so it makes me think that one of the http-proxy dependencies that got updated is triggering it. I'm on node@4.2.2 as well.

https://gist.github.com/stickystyle/a35fa8bc7461018aad83

[stickystyle]

For me, this issue has gone away in the most recent v1.13.2