Closer file structure to desired

embed/challenge/js-pow-sha256/runtime/runtime.go

@@ -0,0 +1,103 @@
+package main
+
+import (
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/binary"
+	"git.gammaspectra.live/git/go-away/lib/challenge"
+	"git.gammaspectra.live/git/go-away/lib/challenge/inline"
+	"math/bits"
+	"strconv"
+)
+
+//go:generate tinygo build -target wasip1 -buildmode=c-shared -opt=2 -scheduler=none -gc=leaking -no-debug -o runtime.wasm runtime.go
+func main() {
+
+}
+
+func getChallenge(key []byte, params map[string]string) ([]byte, uint64) {
+	difficulty := uint64(20)
+	var err error
+	if diffStr, ok := params["difficulty"]; ok {
+		difficulty, err = strconv.ParseUint(diffStr, 10, 64)
+		if err != nil {
+			panic(err)
+		}
+	}
+	hasher := sha256.New()
+	hasher.Write(binary.LittleEndian.AppendUint64(nil, difficulty))
+	hasher.Write(key)
+	return hasher.Sum(nil), difficulty
+}
+
+//go:wasmexport MakeChallenge
+func MakeChallenge(in challenge.Allocation) (out challenge.Allocation) {
+	return challenge.MakeChallengeDecode(func(in challenge.MakeChallengeInput, out *challenge.MakeChallengeOutput) {
+		c, difficulty := getChallenge(in.Key, in.Parameters)
+
+		// create target
+		target := make([]byte, len(c))
+		nBits := difficulty
+		for i := 0; i < len(target); i++ {
+			var v uint8
+			for j := 0; j < 8; j++ {
+				v <<= 1
+				if nBits == 0 {
+					v |= 1
+				} else {
+					nBits--
+				}
+			}
+			target[i] = v
+		}
+
+		dst := make([]byte, inline.EncodedLen(len(c)))
+		dst = dst[:inline.Encode(dst, c)]
+
+		targetDst := make([]byte, inline.EncodedLen(len(target)))
+		targetDst = targetDst[:inline.Encode(targetDst, target)]
+
+		out.Data = []byte("{\"challenge\": \"" + string(dst) + "\", \"target\": \"" + string(targetDst) + "\", \"difficulty\": " + strconv.FormatUint(difficulty, 10) + "}")
+		out.Headers.Set("Content-Type", "application/json; charset=utf-8")
+	}, in)
+}
+
+//go:wasmexport VerifyChallenge
+func VerifyChallenge(in challenge.Allocation) (out challenge.VerifyChallengeOutput) {
+	return challenge.VerifyChallengeDecode(func(in challenge.VerifyChallengeInput) challenge.VerifyChallengeOutput {
+		c, difficulty := getChallenge(in.Key, in.Parameters)
+
+		result := make([]byte, inline.DecodedLen(len(in.Result)))
+		n, err := inline.Decode(result, in.Result)
+		if err != nil {
+			return challenge.VerifyChallengeOutputError
+		}
+		result = result[:n]
+
+		if len(result) < 8 {
+			return challenge.VerifyChallengeOutputError
+		}
+
+		// verify we used same challenge
+		if subtle.ConstantTimeCompare(result[:len(result)-8], c) != 1 {
+			return challenge.VerifyChallengeOutputFailed
+		}
+
+		hash := sha256.Sum256(result)
+
+		var leadingZeroesCount int
+		for i := 0; i < len(hash); i++ {
+			leadingZeroes := bits.LeadingZeros8(hash[i])
+			leadingZeroesCount += leadingZeroes
+			if leadingZeroes < 8 {
+				break
+			}
+		}
+
+		if leadingZeroesCount < int(difficulty) {
+			return challenge.VerifyChallengeOutputFailed
+		}
+
+		return challenge.VerifyChallengeOutputOK
+	}, in)
+}