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

[lrettig]

Hello,

I'm running into the same issue that happened in #908 which was supposed to have been solved already, but it's occurring for me now on the latest v1.16.2. Trying to do a setHeader on the passed in proxyReq for a POST requests fails with:

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

It's happening for both node 4.3.2 and 6.1.0.

To reproduce:

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

Thank you.

[leth]

I've found a workaround:

proxyReq.headers = proxyReq.headers || {}
proxyReq.headers['x-my-header'] = 'value'

[XVincentX]

Most of the times the problem is because you're subscribed to the events more than once. proxy.once('proxyReq,…) usually solves the problem guys.

[fingerpich]

I would like to change headers and path on proxyReq like the following code

proxyReq.path="/abcd/abc" 

It works well with GET requests but it doesn't with POST requests

in post requests _headerSent is true

[skleeschulte]

In my case the problem was an Expect: 100-continue header sent by the client. See #1219