add util function for converting txid:nout to claimID

util/blockchain.go

@@ -0,0 +1,47 @@
+package util
+
+import (
+	"crypto/sha256"
+	"encoding/binary"
+	"encoding/hex"
+
+	"golang.org/x/crypto/ripemd160"
+)
+
+// rev reverses a byte slice. useful for switching endian-ness
+func rev(b []byte) []byte {
+	r := make([]byte, len(b))
+	for left, right := 0, len(b)-1; left < right; left, right = left+1, right-1 {
+		r[left], r[right] = b[right], b[left]
+	}
+	return r
+}
+
+func ClaimIDFromOutpoint(txid string, nout int) (string, error) {
+	// convert transaction id to byte array
+	txidBytes, err := hex.DecodeString(txid)
+	if err != nil {
+		return "", err
+	}
+
+	// reverse (make big-endian)
+	txidBytes = rev(txidBytes)
+
+	// append nout
+	noutBytes := make([]byte, 4) // num bytes in uint32
+	binary.BigEndian.PutUint32(noutBytes, uint32(nout))
+	txidBytes = append(txidBytes, noutBytes...)
+
+	// sha256 it
+	s := sha256.New()
+	s.Write(txidBytes)
+
+	// ripemd it
+	r := ripemd160.New()
+	r.Write(s.Sum(nil))
+
+	// reverse (make little-endian)
+	res := rev(r.Sum(nil))
+
+	return hex.EncodeToString(res), nil
+}