Add support for decimal128 to bsonproto (#44)

bsonproto/bsonproto.go

@@ -11,7 +11,7 @@ import (
 //
 // CString is not included as it is not a real BSON type.
 type ScalarType interface {
-	float64 | string | Binary | ObjectID | bool | time.Time | NullType | Regex | int32 | Timestamp | int64
+	float64 | string | Binary | ObjectID | bool | time.Time | NullType | Regex | int32 | Timestamp | int64 | Decimal128
 }
 
 // Size returns a size of the encoding of value v in bytes.
@@ -46,6 +46,8 @@ func SizeAny(v any) int {
 		return SizeTimestamp
 	case int64:
 		return SizeInt64
+	case Decimal128:
+		return SizeDecimal128
 	default:
 		panic(fmt.Sprintf("unsupported type %T", v))
 	}
@@ -89,6 +91,8 @@ func EncodeAny(b []byte, v any) {
 		EncodeTimestamp(b, v)
 	case int64:
 		EncodeInt64(b, v)
+	case Decimal128:
+		EncodeDecimal128(b, v)
 	default:
 		panic(fmt.Sprintf("unsupported type %T", v))
 	}
@@ -133,6 +137,8 @@ func DecodeAny(b []byte, v any) error {
 		*v, err = DecodeTimestamp(b)
 	case *int64:
 		*v, err = DecodeInt64(b)
+	case *Decimal128:
+		*v, err = DecodeDecimal128(b)
 	default:
 		panic(fmt.Sprintf("unsupported type %T", v))
 	}

bsonproto/bsonproto_test.go

@@ -71,6 +71,9 @@ func TestScalars(t *testing.T) {
 	}, {
 		v: int64(1234567890123456789),
 		b: []byte{0x15, 0x81, 0xe9, 0x7d, 0xf4, 0x10, 0x22, 0x11},
+	}, {
+		v: Decimal128{H: 2024, L: 404},
+		b: []byte{0x94, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xe8, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
 	}} {
 		t.Run(fmt.Sprintf("%[1]d_%[2]T(%[2]v)", i, tc.v), func(t *testing.T) {
 			s := SizeAny(tc.v)
@@ -269,6 +272,10 @@ func TestScalarsDecodeErrors(t *testing.T) {
 		b:   []byte{0x42},
 		v:   int64(0),
 		err: ErrDecodeShortInput,
+	}, {
+		b:   []byte{0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42},
+		v:   Decimal128{},
+		err: ErrDecodeShortInput,
 	}} {
 		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
 			v := reflect.New(reflect.TypeOf(tc.v)).Interface() // v := new(T)

bsonproto/decimal128.go

@@ -0,0 +1,40 @@
+package bsonproto
+
+import (
+	"encoding/binary"
+	"fmt"
+)
+
+// Decimal128 represents BSON scalar type decimal128.
+type Decimal128 struct {
+	L uint64
+	H uint64
+}
+
+// SizeDecimal128 is a size of the encoding of [Decimal128] in bytes.
+const SizeDecimal128 = 16
+
+// EncodeDecimal128 encodes [Decimal128] value v into b.
+//
+// b must be at least 16 ([SizeDecimal128]) bytes long; otherwise, EncodeDecimal128 will panic.
+// Only b[0:16] bytes are modified.
+func EncodeDecimal128(b []byte, v Decimal128) {
+	binary.LittleEndian.PutUint64(b, uint64(v.L))
+	binary.LittleEndian.PutUint64(b[8:], uint64(v.H))
+}
+
+// DecodeDecimal128 decodes [Decimal128] value from b.
+//
+// If there is not enough bytes, DecodeDecimal128 will return a wrapped [ErrDecodeShortInput].
+func DecodeDecimal128(b []byte) (Decimal128, error) {
+	var res Decimal128
+
+	if len(b) < SizeDecimal128 {
+		return res, fmt.Errorf("DecodeDecimal128: expected at least %d bytes, got %d: %w", SizeDecimal128, len(b), ErrDecodeShortInput)
+	}
+
+	res.L = binary.LittleEndian.Uint64(b[:8])
+	res.H = binary.LittleEndian.Uint64(b[8:])
+
+	return res, nil
+}