From fb469ce424a487765c9490743af0e4c3f8de434a Mon Sep 17 00:00:00 2001
From: Marcin Gorzynski <marcin@gorzynski.me>
Date: Fri, 16 Feb 2024 12:21:30 +0100
Subject: [PATCH] add IsEIP191Message & MessageToEIP191

---
 signature.go      | 15 +++++++++++++++
 signature_test.go | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/signature.go b/signature.go
index b283a9d4..2d42ce20 100644
--- a/signature.go
+++ b/signature.go
@@ -1,6 +1,7 @@
 package sequence
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"math/big"
@@ -218,6 +219,20 @@ func IsValidUndeployedSignature(walletAddress common.Address, digest common.Hash
 	return V2IsValidUndeployedSignature(walletAddress, digest, seqSig, walletContext, chainID, provider)
 }
 
+func IsEIP191Message(msg []byte) bool {
+	return len(msg) > 0 && msg[0] == 0x19
+}
+
+func MessageToEIP191(msg []byte) []byte {
+	if !IsEIP191Message(msg) {
+		return bytes.Join([][]byte{
+			[]byte("\x19Ethereum Signed Message:\n"),
+			[]byte(fmt.Sprintf("%v", len(msg))),
+			msg}, nil)
+	}
+	return msg
+}
+
 func MessageDigest(message []byte) common.Hash {
 	return common.BytesToHash(ethcoder.Keccak256(message))
 }
diff --git a/signature_test.go b/signature_test.go
index 24530b2f..49450ded 100644
--- a/signature_test.go
+++ b/signature_test.go
@@ -1,5 +1,12 @@
 package sequence_test
 
+import (
+	"testing"
+
+	"github.com/0xsequence/go-sequence"
+	"github.com/stretchr/testify/assert"
+)
+
 /*
 const message = "hi!"
 
@@ -547,3 +554,42 @@ func areSignaturesIsomorphic(a *signature, b *signature) bool {
 	return true
 }
 */
+
+func TestIsEIP191Message(t *testing.T) {
+	t.Run("EIP191", func(t *testing.T) {
+		// EIP191 message
+		msg := []byte("\x19Ethereum Signed Message:\n5hello")
+		ok := sequence.IsEIP191Message(msg)
+		if !ok {
+			t.Error("expected EIP191 message")
+		}
+	})
+
+	t.Run("non-EIP191", func(t *testing.T) {
+		// non-EIP191 message
+		msg := []byte("hello")
+		ok := sequence.IsEIP191Message(msg)
+		if ok {
+			t.Error("expected non-EIP191 message")
+		}
+	})
+}
+
+func TestMessageToEIP191(t *testing.T) {
+	t.Run("EIP191_none", func(t *testing.T) {
+		// EIP191 message
+		msg := []byte("hello")
+		expectedEIP191 := []byte("\x19Ethereum Signed Message:\n5hello")
+
+		eip191 := sequence.MessageToEIP191(msg)
+		assert.Equal(t, eip191, expectedEIP191)
+	})
+
+	t.Run("EIP191_already", func(t *testing.T) {
+		// EIP191 message
+		msg := []byte("\x19Ethereum Signed Message:\n5hello")
+		eip191 := sequence.MessageToEIP191(msg)
+
+		assert.Equal(t, msg, eip191)
+	})
+}