onProxyReq not fired

Is this a bug report?

Yes.

Expected behavior

onProxyReq runs, allowing me to modify the request.

Actual behavior

onProxyReq is not run when a body is included in the request message, when C#'s HttpClient is used to issue the request.

The setup here is a little non-standard. I have a C# client that uses HttpClient. It makes a request which goes to a node server running http-proxy-middleware.

HttpClient is adding an Expect header for some reason – something it is entitled to do, but which browser don’t do. Usually, an Expect header indicates that we’re doing a 100-continue type hand signal. Microsoft’s implementation of HttpClient is presumably correct. Developers are not supposed to be explicitly modifying the Expect header.

When I issue a POST with no body, onProxyReq is fired. But when I issue a POST with a body, onProxyReq is never fired. I traced this to one of the latest commits in node-http-proxy – link. The problem is fixed if that change is undone.

I don’t see any reason why they changed this upstream.

It’s not clear to me what actions I can take to make http-proxy-middleware proxy my requests that have bodies. I can’t modify the implementation or usage of HttpClient, only the server.

I have sizable headers, but the request body itself can be as short as “{}” in order to trigger this bug.

Setup

• http-proxy-middleware: 1.0.6
• http-proxy-middleware configuration

app.use(`/mypath`, createProxyMiddleware({

  target: 'http://foobar.com',
  changeOrigin: true,
  headers: {
    'X-Custom-Header': 'foobar'
  },
  preserveHeaderKeyCase: true,
  logLevel: 'debug'
  onProxyReq(proxyReq, req, res) {
    console.log('onProxyReq was fired');
  }
}));

• server: express 4.17.1

client info

.NET 4.7.2’s HttpClient

target server info

Target agnostic – I’ve pointed it at an express server that just prints out information about requests that it receives.

Reproducible Demo

No demo at the moment.