fix: support for decode/encode of Constr with tag 102 (#110)

Fixes #109

Signed-off-by: Aurora Gaffney <[email protected]>

Author: agaffney

data/data_test.go

@@ -98,6 +98,15 @@ var testDefs = []struct {
 		),
 		CborHex: "d8799fa1d8799f00190196ffd8799f1b17f2495b03141751ffff",
 	},
+	{
+		Data: NewConstr(
+			999,
+			NewInteger(big.NewInt(6)),
+			NewInteger(big.NewInt(7)),
+		),
+		// 102([999, [_ 6, 7]])
+		CborHex: "d866821903e79f0607ff",
+	},
 }
 
 func TestPlutusDataEncode(t *testing.T) {

data/decode.go

@@ -1,7 +1,6 @@
 package data
 
 import (
-	"errors"
 	"fmt"
 	"math/big"
 
@@ -197,8 +196,15 @@ func decodeRawTag(tag cbor.RawTag) (PlutusData, error) {
 		ret, retErr = decodeBignum(tag.Content, true)
 
 	case 102:
-		return nil, errors.New("tagged data (tag 102) not implemented")
-
+		var tmpData struct {
+			_           struct{} `cbor:",toarray"`
+			Alternative uint64
+			FieldsRaw   cbor.RawMessage
+		}
+		if err := cbor.Unmarshal(tag.Content, &tmpData); err != nil {
+			return nil, err
+		}
+		ret, retErr = decodeConstr(tmpData.Alternative, tmpData.FieldsRaw)
 	default:
 		return nil, fmt.Errorf("unknown CBOR tag for PlutusData: %d", tag.Number)
 	}

data/encode.go

@@ -1,7 +1,6 @@
 package data
 
 import (
-	"errors"
 	"fmt"
 	"math/big"
 	"slices"
@@ -78,8 +77,9 @@ func encodeConstr(c *Constr) (any, error) {
 	case c.Tag >= 7 && c.Tag <= 127:
 		// Tags 7-127 map to CBOR tags 1280-1400
 		cborTag = 1280 + uint64(c.Tag-7)
-	case c.Tag == 102:
-		return nil, errors.New("tagged data (tag 102) not implemented")
+	case c.Tag >= 128:
+		cborTag = 102
+		fields = []any{c.Tag, fields}
 	default:
 		return nil, fmt.Errorf("unsupported Constr tag: %d", c.Tag)
 	}