MVC ProxyExchange returns ResponseEntity<> that causes a error for the client in some cases

Bug Report

I am using ProxyExchange to proxy a call through to the backend, and want to return the response unchanged upstream.
In some cases this works, in others it does not.

When it does not work, curl displays the following error: "curl: (56) Illegal or missing hexadecimal sequence in chunked-encoding"

I attached two projects: demo-projects.zip

• backend: contains one endpoint, with a required requestParameter and returns a simple object
• gateway: contains one endpoint with @RequestMapping(value = "/**), and it uses ProxyExchange to map all the incoming request onto the backend

Steps to reproduce the problem (backend runs on port 8787, gateway runs on port 7878):

1. Run the two projects
2. Call GET http://localhost:8787/resource?requestParam=1
   The response is 200: { "content": "hello" }
3. Call GET http://localhost:8787/resource
   The response is

400: {
"timestamp": "2018-11-22T14:50:11.949+0000",
"status": 400,
"error": "Bad Request",
"message": "Required Integer parameter 'requestParam' is not present",
"path": "/resource"
}

4. Call GET http://localhost:7878/resource?requestParam=1
   The response is 200: { "content": "hello" }
5. Call GET http://localhost:7878/resource
   This gives the error mentioned above:

curl: (56) Illegal or missing hexadecimal sequence in chunked-encoding

I do not see a reason why both cases should be handled differently by the gateway, and think this behaviour is a bug. I expect the gateway to just forward the ResponseEntity<?> objects.

I can fix the unexcpeted chunked-encoding error by constructing a new ResponseEntity by copying the body, status and headers from the ResponseEntity returned by the ProxyExchange, but when copying over the headers I remove the Transfer-Encoding

Start with the attached demo-projects.zip, running the backend on port 8787 and the gateway on port 7878. Reproduce the two GET requests with and without requestParam, then inspect the gateway endpoint using ProxyExchange and compare the returned headers. Done means the gateway forwards both responses unchanged without curl reporting a chunked-encoding error.