feat: initial commit

internal/anubis/pow.go

@@ -0,0 +1,63 @@
+// Package anubis implements a native Go client for getting past the Anubis
+// (TecharoHQ) proof-of-work anti-scraper proxy without a headless browser.
+//
+// The challenge is embedded in the interstitial HTML as a JSON document inside
+// a <script id="anubis_challenge"> element. The client must find an integer
+// nonce such that SHA-256(randomData + nonce) has `difficulty` leading hex-zero
+// digits, then submit it to the pass-challenge endpoint to obtain a signed-JWT
+// auth cookie.
+package anubis
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"strconv"
+)
+
+// sha256Hex returns the hex-encoded SHA-256 of s. This is the answer to a
+// "preact" Anubis challenge: result = SHA256(randomData).
+func sha256Hex(s string) string {
+	sum := sha256.Sum256([]byte(s))
+	return hex.EncodeToString(sum[:])
+}
+
+// Solve performs the Anubis proof-of-work: it searches for the smallest nonce
+// (starting at 0) such that SHA-256(randomData + nonce) has `difficulty`
+// leading hex-zero digits. It returns the hex-encoded hash and the nonce.
+//
+// The zero check mirrors the Anubis worker: the first floor(difficulty/2)
+// bytes must be zero and, when difficulty is odd, the high nibble of the next
+// byte must also be zero.
+func Solve(randomData string, difficulty int) (hash string, nonce uint64) {
+	prefix := []byte(randomData)
+	zeroBytes := difficulty / 2
+	oddNibble := difficulty%2 != 0
+
+	// Reusable buffer: challenge prefix + decimal nonce, refilled each round.
+	buf := make([]byte, 0, len(prefix)+20)
+
+	for n := uint64(0); ; n++ {
+		buf = append(buf[:0], prefix...)
+		buf = strconv.AppendUint(buf, n, 10)
+		sum := sha256.Sum256(buf)
+
+		if leadingZeros(sum[:], zeroBytes, oddNibble) {
+			return hex.EncodeToString(sum[:]), n
+		}
+	}
+}
+
+// leadingZeros reports whether sum has the required number of leading hex-zero
+// digits: zeroBytes fully-zero bytes, plus (when oddNibble) a zero high nibble
+// in the following byte.
+func leadingZeros(sum []byte, zeroBytes int, oddNibble bool) bool {
+	for i := range zeroBytes {
+		if sum[i] != 0 {
+			return false
+		}
+	}
+	if oddNibble {
+		return sum[zeroBytes]>>4 == 0
+	}
+	return true
+}