req.Header.Set(xForwardedProto, "http")
		}
	}

	if xfPort := req.Header.Get(xForwardedPort); xfPort == "" {
		req.Header.Set(xForwardedPort, forwardedPort(req))
	}

	if xfHost := req.Header.Get(xForwardedHost); xfHost == "" && req.Host != "" {
		req.Header.Set(xForwardedHost, req.Host)
	}
}

func forwardedPort(req *http.Request) string {
	if req == nil {
		return ""
	}

	"net/http"
	"regexp"
	"strings"
)

var (
	// De-facto standard header keys.
	xForwardedFor    = http.CanonicalHeaderKey("X-Forwarded-For")
	xForwardedHost   = http.CanonicalHeaderKey("X-Forwarded-Host")
	xForwardedPort   = http.CanonicalHeaderKey("X-Forwarded-Port")
	xForwardedProto  = http.CanonicalHeaderKey("X-Forwarded-Proto")
	xForwardedScheme = http.CanonicalHeaderKey("X-Forwarded-Scheme")