Add REST implementation for Validator's ProposeBeaconBlock (#11731)

* WIP

* WIP

* WIP

* Add tests

* WIP

* Add more tests

* Address DeepSource errors

* Remove unused param

* Add more tests

* Address PR comments

* Address PR comments

* Fix formatting

* Remove unused parameter

* Fix TestLittleEndianBytesToBigInt

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

encoding/bytesutil/bytes.go

@@ -4,6 +4,7 @@ package bytesutil
 import (
 	"encoding/binary"
 	"fmt"
+	"math/big"
 	"math/bits"
 	"regexp"
 
@@ -438,3 +439,9 @@ func IsRoot(root []byte) bool {
 func IsValidRoot(root []byte) bool {
 	return IsRoot(root) && !ZeroRoot(root)
 }
+
+// LittleEndianBytesToBigInt takes bytes of a number stored as little-endian and returns a big integer
+func LittleEndianBytesToBigInt(bytes []byte) *big.Int {
+	// Integers are stored as little-endian, but big.Int expects big-endian. So we need to reverse the byte order before decoding.
+	return new(big.Int).SetBytes(ReverseByteOrder(bytes))
+}

encoding/bytesutil/bytes_test.go

@@ -2,7 +2,9 @@ package bytesutil_test
 
 import (
 	"bytes"
+	"encoding/binary"
 	"fmt"
+	"math/big"
 	"reflect"
 	"testing"
 
@@ -634,3 +636,11 @@ func TestToBytes48Array(t *testing.T) {
 		assert.DeepEqual(t, tt.b, b)
 	}
 }
+
+func TestLittleEndianBytesToBigInt(t *testing.T) {
+	bytes := make([]byte, 8)
+	binary.LittleEndian.PutUint64(bytes, 1234567890)
+	converted := bytesutil.LittleEndianBytesToBigInt(bytes)
+	expected := new(big.Int).SetInt64(1234567890)
+	assert.DeepEqual(t, expected, converted)
+}