X-Forwarded-Host header is copied into the Host header

[pablobastidasv]

Given:

public class App {
    public static void main(String[] args) {
        get("/hello", (req, res) -> req.host());
    }
}

When:

curl --request GET \
  --url http://localhost:4567/hello \
  --header 'Host: localhost:4567' \
  --header 'x-forwarded-host: proxy.mydomain.com'

or

curl --request GET \
  --url http://localhost:4567/hello \
  --header 'x-forwarded-host: proxy.mydomain.com'

Then: I expect my response with localhost:4567 but I get proxy.mydomain.com.

Questions:

1. Is my assumption wrong?
2. How can I get the Host header value when my service is behind a proxy?

[perwendel]

This is territory where I'm not confident on how it should work. Will have to investigate.

[Lloyd-Pottiger]

I would like to try to fix this issue.

[Lloyd-Pottiger]

When I debug the process to reproduce the issue, I find that the Host of HttpServletRequest passed in /src/main/java/spark/embeddedserver/jetty/JettyHandler.doHandle() method is proxy.mydomain.com, which means it is not a bug in code. After searching for answear, I find this link may help you understand the problem.