The “Host” header field in a request provides the host and port information from the target URI, enabling the origin server to distinguish among resources while servicing requests for multiple host names.
When I send a request to http://127.0.0.1:8080 I see
GET / HTTP/1.1
Accept-Encoding: gzip
Accept-Encoding: x-gzip
User-Agent: Jersey/2.45 (Netty 4.1.93.Final)
host: 127.0.0.1
If the port is non-standard then it should be present in the Host: header that is sent as part of the request.