what-is-my-ip/server.go

package main

import (
	"io"
	"net"
	"net/http"
)

// Server that handles http responses
type Server struct {
	headerNames []string
	logger      LoggerHandler
}

func (s *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	for _, headerName := range s.headerNames {
		possibleIP := req.Header.Get(headerName)
		if possibleIP == "" {
			continue
		}

		ip, err := NewIP(possibleIP)
		if err != nil {
			continue
		}

		s.sendResponse(w, ip)
		return
	}

	addr, _, err := net.SplitHostPort(req.RemoteAddr)
	if err != nil {
		s.handleError(w, http.StatusBadRequest, err, "Could not get IP address from request")
		return
	}

	ip, err := NewIP(addr)
	if err != nil {
		s.handleError(w, http.StatusBadRequest, err, "Could not parse IP address"+addr)
		return
	}

	s.sendResponse(w, ip)
}

func (s *Server) sendResponse(resp http.ResponseWriter, ip *IP) {
	io.WriteString(resp, ip.String()+"\n")
	s.logger.Printf("Request from %s %s\n", ip.version, ip)
}

func (s *Server) handleError(resp http.ResponseWriter, status int, err error, message string) {
	resp.WriteHeader(status)
	io.WriteString(resp, message)
	s.logger.Printf("Error handling request: %s (%s)", message, err)
}