feat(container): read-write versioned dag-cbor

pkg/container/reader.go

@@ -98,13 +98,32 @@ func FromCbor(r io.Reader) (Reader, error) {
 	if err != nil {
 		return nil, err
 	}
-	if n.Kind() != datamodel.Kind_List {
-		return nil, fmt.Errorf("not a list")
+	if n.Kind() != datamodel.Kind_Map {
+		return nil, fmt.Errorf("invalid container format: expected map")
 	}
 
-	ctn := make(Reader, n.Length())
+	vNode, err := n.LookupByString("version")
+	if err != nil {
+		return nil, fmt.Errorf("invalid container format: missing version")
+	}
+	version, err := vNode.AsString()
+	if err != nil {
+		return nil, fmt.Errorf("invalid container format: version must be string")
+	}
+	if version != defaultContainerVersion {
+		return nil, fmt.Errorf("unsupported container version: %s", version)
+	}
 
-	it := n.ListIterator()
+	tokensNode, err := n.LookupByString("tokens")
+	if err != nil {
+		return nil, fmt.Errorf("invalid container format: missing tokens")
+	}
+	if tokensNode.Kind() != datamodel.Kind_List {
+		return nil, fmt.Errorf("invalid container format: tokens must be a list")
+	}
+
+	ctn := make(Reader, tokensNode.Length())
+	it := tokensNode.ListIterator()
 	for !it.Done() {
 		_, val, err := it.Next()
 		if err != nil {
@@ -119,6 +138,7 @@ func FromCbor(r io.Reader) (Reader, error) {
 			return nil, err
 		}
 	}
+
 	return ctn, nil
 }
 

pkg/container/writer.go

@@ -14,6 +14,8 @@ import (
 
 // TODO: should we have a multibase to wrap the cbor? but there is no reader/write in go-multibase :-(
 
+const defaultContainerVersion = "ctn-v1"
+
 // Writer is a token container writer. It provides a convenient way to aggregate and serialize tokens together.
 type Writer map[cid.Cid][]byte
 
@@ -44,10 +46,14 @@ func (ctn Writer) ToCarBase64(w io.Writer) error {
 }
 
 func (ctn Writer) ToCbor(w io.Writer) error {
-	node, err := qp.BuildList(basicnode.Prototype.Any, int64(len(ctn)), func(la datamodel.ListAssembler) {
-		for _, bytes := range ctn {
-			qp.ListEntry(la, qp.Bytes(bytes))
-		}
+	// Create a map with version and tokens
+	node, err := qp.BuildMap(basicnode.Prototype.Any, 2, func(ma datamodel.MapAssembler) {
+		qp.MapEntry(ma, "version", qp.String(defaultContainerVersion))
+		qp.MapEntry(ma, "tokens", qp.List(int64(len(ctn)), func(la datamodel.ListAssembler) {
+			for _, bytes := range ctn {
+				qp.ListEntry(la, qp.Bytes(bytes))
+			}
+		}))
 	})
 	if err != nil {
 		return err