package main
import (
"crypto/rand"
"crypto/sha256"
"encoding/hex"
"fmt"
"html/template"
"log"
"net/http"
"strconv"
"sync"
"time"
)
const (
port = 3000
difficulty = 20
)
var (
challengeStore = make(map[string]time.Time)
storeMutex sync.Mutex
)
func generateChallenge() string {
b := make([]byte, 12)
_, err := rand.Read(b)
if err != nil {
panic(err)
}
return hex.EncodeToString(b)
}
func checkDifficulty(hash []byte, bits int) bool {
i := 0
for bits > 0 {
b := hash[i]
if bits >= 8 {
if b != 0 {
return false
}
bits -= 8
} else {
mask := byte(0xFF << (8 - bits))
if b&mask != 0 {
return false
}
bits = 0
}
i++
}
return true
}
func indexHandler(w http.ResponseWriter, r *http.Request) {
challenge := generateChallenge()
storeMutex.Lock()
challengeStore[challenge] = time.Now()
storeMutex.Unlock()
tmpl.Execute(w, map[string]string{
"Challenge": challenge,
"Difficulty": strconv.Itoa(difficulty),
})
}
func postHandler(w http.ResponseWriter, r *http.Request) {
challenge := r.FormValue("challenge")
nonce := r.FormValue("nonce")
storeMutex.Lock()
_, ok := challengeStore[challenge]
if ok {
delete(challengeStore, challenge)
}
storeMutex.Unlock()
if !ok {
fmt.Fprint(w, "Invalid challenge.
Try again")
return
}
hash := sha256.Sum256([]byte(challenge + nonce))
if checkDifficulty(hash[:], difficulty) {
fmt.Fprint(w, "Success! Valid nonce.
Try again")
} else {
fmt.Fprint(w, "Invalid nonce.
Try again")
}
}
var tmpl = template.Must(template.New("page").Parse(`
NOJSCAP demo
NOJSCAP demo
https://git.libroot.org/libroot/NOJSCAP/
If you don't already have the NOJSCAP client:
$ git clone https://git.libroot.org/libroot/NOJSCAP/$ cd NOJSCAP/client/
$ python3 pow_client.py {{.Challenge}} {{.Difficulty}}
Go:
$ go run pow_client.go {{.Challenge}} {{.Difficulty}}
Node.js:
$ node pow_client.js {{.Challenge}} {{.Difficulty}}
Rust:
$ rustc pow_client.rs -o pow_client_rs$ pow_client_rs {{.Challenge}} {{.Difficulty}}
C:
$ gcc -O2 -o pow_client pow_client.c -lssl -lcrypto$ ./pow_client {{.Challenge}} {{.Difficulty}}
`))
func main() {
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
if r.Method == http.MethodPost {
postHandler(w, r)
} else {
indexHandler(w, r)
}
})
fmt.Printf("Running on http://localhost:%d\n", port)
log.Fatal(http.ListenAndServe(fmt.Sprintf(":%d", port), nil))
}