Add unpack for evm revert errors (umbracle#151)

* Add unpack for evm revert errors

* Rebase

abi/revert.go

@@ -0,0 +1,23 @@
+package abi
+
+import (
+	"bytes"
+	"fmt"
+)
+
+var revertId = []byte{0x8, 0xC3, 0x79, 0xA0}
+
+func UnpackRevertError(b []byte) (string, error) {
+	if !bytes.HasPrefix(b, revertId) {
+		return "", fmt.Errorf("revert error prefix not found")
+	}
+
+	b = b[4:]
+	tt := MustNewType("tuple(string)")
+	vals, err := tt.Decode(b)
+	if err != nil {
+		return "", err
+	}
+	revVal := vals.(map[string]interface{})["0"].(string)
+	return revVal, nil
+}

abi/revert_test.go

@@ -0,0 +1,18 @@
+package abi
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUnpackRevertError(t *testing.T) {
+	data := "08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000d72657665727420726561736f6e00000000000000000000000000000000000000"
+
+	raw, err := decodeHex(data)
+	assert.NoError(t, err)
+
+	reason, err := UnpackRevertError(raw)
+	assert.NoError(t, err)
+	assert.Equal(t, "revert reason", reason)
+}