adlin/validator/login.go

package main

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

type loginChecker struct{
	students []Student
}

type loginUpload struct {
	Username string
	Password string
}

func (l loginChecker) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if addr := r.Header.Get("X-Forwarded-For"); addr != "" {
		r.RemoteAddr = addr
	}
	log.Printf("%s \"%s %s\" [%s]\n", r.RemoteAddr, r.Method, r.URL.Path, r.UserAgent())

	w.Header().Set("Content-Type", "text/plain")

	// Check request type and size
	if r.Method != "POST" {
		http.Error(w,
			"Invalid request",
			http.StatusBadRequest)
		return
	} else if r.ContentLength < 0 || r.ContentLength > 1023 {
		http.Error(w,
			"Request entity too large",
			http.StatusRequestEntityTooLarge)
		return
	}

	dec := json.NewDecoder(r.Body)
	var lu loginUpload
	if err := dec.Decode(&lu); err != nil {
		http.Error(w,
			err.Error(),
			http.StatusBadRequest)
		return
	}

	// Perform login check
	canContinue := false
	for _, std := range l.students {
		if std.Login == lu.Username {
			canContinue = true
		}
	}

	if !canContinue {
		log.Println("Login not found:", lu.Username, "at", r.RemoteAddr)
		http.Error(w, "Login not found in whitelist.", http.StatusUnauthorized)
		return
	}

	if err := l.lateLoginAction(lu.Username, r.RemoteAddr); err != nil {
		log.Println("Error on late login action:", err)
		http.Error(w, "Internal server error. Please retry in a few minutes", http.StatusInternalServerError)
		return
	}

	log.Println("Successful login of", lu.Username, "at", r.RemoteAddr)
	http.Error(w, "Success", http.StatusOK)
}

func (l loginChecker) lateLoginAction(username, remoteAddr string) error {
	// Find corresponding MAC
	var fname string
	spl := strings.SplitN(remoteAddr, ":", 2)
	if ip := net.ParseIP(spl[0]); ip == nil {
		return errors.New("Unable to parse given IPv4: " + spl[0])
	} else if arptable, err := ARPAnalyze(); err != nil {
		return err
	} else if arpent := ARPContainsIP(arptable, ip); arpent == nil {
		return errors.New("Unable to find MAC in ARP table")
	} else {
		fname = fmt.Sprintf("%02x-%02x-%02x-%02x-%02x-%02x-%02x", arpent.HWType, arpent.HWAddress[0], arpent.HWAddress[1], arpent.HWAddress[2], arpent.HWAddress[3], arpent.HWAddress[4], arpent.HWAddress[5])
	}

	if tpl, err := ioutil.ReadFile(path.Join(tftpDir, "pxelinux.cfg", "tpl")); err != nil {
		log.Println("Unable to open tpl: ", err)
	} else if file, err := os.OpenFile(path.Join(tftpDir, "pxelinux.cfg", fname), os.O_CREATE|os.O_WRONLY|os.O_TRUNC, os.FileMode(0644)); err != nil {
		log.Println("Unable to open destination file: ", err)
	} else {
		defer file.Close()

		if configTmpl, err := template.New("pxelinux.cfg").Parse(string(tpl)); err != nil {
			log.Println("Cannot create template: ", err)
		} else if err := configTmpl.Execute(file, map[string]string{"username": username, "remoteAddr": remoteAddr, "fname": fname}); err != nil {
			log.Println("An error occurs during template execution: ", err)
		}
	}

	return nil
}