myip/main.go

package main

import (
	"encoding/json"
	"errors"
	"log"
	"net/http"
	"net/netip"
)

// @title My IP
// @version 0.1
// @description Get the requseters Real IP, based on HTTP Requests
func main() {
    handler := http.NewServeMux()
    handler.HandleFunc("/", handleRoot)

    log.Fatal(http.ListenAndServe(":8080", handler))
}

type ResponseType string

const (
    TEXT ResponseType = "TEXT"
    JSON ResponseType = "JSON"
    DEFAULT ResponseType = TEXT
) 

func (r *ResponseType) IsValid() bool {

    // This is pretty ugly
    // TODO: Comapre with ignore-case
    if *r == TEXT {
        return true
    }

    if *r == JSON {
        return true
    }

    return false
}

func handleRoot(w http.ResponseWriter, r *http.Request) {

    if r.Method != "GET" {
        w.WriteHeader(http.StatusBadRequest)
        return
    }
    var Type ResponseType
    Type = ResponseType(r.URL.Query().Get("t"))
    
    if !Type.IsValid() {
        // Using defualt    
        Type = DEFAULT
    }

    log.Printf("Type: %v\n", Type)
    ip, err := determineRealIP(r)
    if err != nil {
        log.Println(err.Error())
        w.WriteHeader(http.StatusInternalServerError)
        return
    }

    err = writeFormattedIP(w, Type, ip)
    if err != nil {
        log.Println(err.Error())
        w.WriteHeader(http.StatusInternalServerError)
        return
    }
}

func determineRealIP(r *http.Request) (string, error) {
    ip := r.RemoteAddr

    xRealIP := r.Header.Get("X-Real-IP")
    if xRealIP != "" {
        ip = xRealIP
    }

    ipPort, err := netip.ParseAddrPort(ip)
    if err != nil {
        return "", err
    }


    if !ipPort.IsValid() {
        return "", errors.New("Zero IP")
    }

    ip = ipPort.Addr().String()

    return ip, nil
}

func writeFormattedIP(w http.ResponseWriter, Type ResponseType, ip string)  error {
    if Type == TEXT {
        _, err := w.Write([]byte(ip))
        if err != nil {
            return err
        }
        return nil
    }

    if Type == JSON {
        // TODO: Use MarshalIndent
        jsonResponse, err := json.Marshal(map[string]string{"ip": ip})
        if err != nil {
            return err
        }
        _, err = w.Write(jsonResponse)
        if err != nil {
            return err
        }
    }

    return nil
}