CASSGO-2 Marshal big int returns variable length slice.

The marshalBigInt return 8 bytes slice in all cases except for big.Int,
which returns a variable length slice, but should be 8 bytes slice as well.

patch by Mykyta Oleksiienko; reviewed by João Reis for CASSGO-2

CHANGELOG.md

@@ -14,6 +14,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- CASSGO-2
+
 ## [1.7.0] - 2024-09-23
 
 This release is the first after the donation of gocql to the Apache Software Foundation (ASF)

marshal.go

@@ -77,7 +77,7 @@ type Unmarshaler interface {
 //	tinyint, smallint, int      | integer types      |
 //	tinyint, smallint, int      | string             | formatted as base 10 number
 //	bigint, counter             | integer types      |
-//	bigint, counter             | big.Int            |
+//	bigint, counter             | big.Int            | according to cassandra bigint specification the big.Int value limited to int64 size(an eight-byte two's complement integer.)
 //	bigint, counter             | string             | formatted as base 10 number
 //	float                       | float32            |
 //	double                      | float64            |
@@ -671,7 +671,10 @@ func marshalBigInt(info TypeInfo, value interface{}) ([]byte, error) {
 	case uint8:
 		return encBigInt(int64(v)), nil
 	case big.Int:
-		return encBigInt2C(&v), nil
+		if !v.IsInt64() {
+			return nil, marshalErrorf("marshal bigint: value %v out of range", &v)
+		}
+		return encBigInt(v.Int64()), nil
 	case string:
 		i, err := strconv.ParseInt(value.(string), 10, 64)
 		if err != nil {
@@ -773,6 +776,8 @@ func marshalVarint(info TypeInfo, value interface{}) ([]byte, error) {
 			retBytes = make([]byte, 8)
 			binary.BigEndian.PutUint64(retBytes, v)
 		}
+	case big.Int:
+		retBytes = encBigInt2C(&v)
 	default:
 		retBytes, err = marshalBigInt(info, value)
 	}

marshal_test.go

@@ -247,6 +247,20 @@ var marshalTests = []struct {
 		nil,
 		nil,
 	},
+	{
+		NativeType{proto: 2, typ: TypeBigInt},
+		[]byte("\xf7\x0c\x6b\x14\x84\x49\x3b\x36\x4a\x36\x1e\x03\x34\x05"),
+		"-78635384813432117863538481343211",
+		MarshalError("can not marshal string to bigint: strconv.ParseInt: parsing \"-78635384813432117863538481343211\": value out of range"),
+		nil,
+	},
+	{
+		NativeType{proto: 2, typ: TypeBigInt},
+		[]byte("\x20\x45\xce\x3b\x05\xef\x2d\xde\x51\xb9\x28\x76\x6d\x6e"),
+		"922337203685477692259749625974294",
+		MarshalError("can not marshal string to bigint: strconv.ParseInt: parsing \"922337203685477692259749625974294\": value out of range"),
+		nil,
+	},
 	{
 		NativeType{proto: 2, typ: TypeBoolean},
 		[]byte("\x00"),