files returned from unixfsnode should be traversable back to their substrate

Author: willscott

file/file.go

@@ -5,6 +5,8 @@ import (
 	"io"
 
 	"github.com/ipld/go-ipld-prime"
+	"github.com/ipld/go-ipld-prime/adl"
+	"github.com/ipld/go-ipld-prime/datamodel"
 )
 
 // NewUnixFSFile attempts to construct an ipld node from the base protobuf node representing the
@@ -54,7 +56,7 @@ func NewUnixFSFileWithPreload(ctx context.Context, substrate ipld.Node, lsys *ip
 
 // A LargeBytesNode is an ipld.Node that can be streamed over. It is guaranteed to have a Bytes type.
 type LargeBytesNode interface {
-	ipld.Node
+	adl.ADL
 	AsLargeBytes() (io.ReadSeeker, error)
 }
 
@@ -66,6 +68,10 @@ func (f *singleNodeFile) AsLargeBytes() (io.ReadSeeker, error) {
 	return &singleNodeReader{f, 0}, nil
 }
 
+func (f *singleNodeFile) Substrate() datamodel.Node {
+	return f.Node
+}
+
 type singleNodeReader struct {
 	ipld.Node
 	offset int

file/shard.go

@@ -9,6 +9,7 @@ import (
 	"github.com/ipfs/go-unixfsnode/data"
 	dagpb "github.com/ipld/go-codec-dagpb"
 	"github.com/ipld/go-ipld-prime"
+	"github.com/ipld/go-ipld-prime/adl"
 	cidlink "github.com/ipld/go-ipld-prime/linking/cid"
 	"github.com/ipld/go-ipld-prime/node/basicnode"
 	"github.com/multiformats/go-multicodec"
@@ -24,7 +25,7 @@ type shardNodeFile struct {
 	unpackLk sync.Once
 }
 
-var _ ipld.Node = (*shardNodeFile)(nil)
+var _ adl.ADL = (*shardNodeFile)(nil)
 
 type shardNodeReader struct {
 	*shardNodeFile
@@ -233,6 +234,10 @@ func (s *shardNodeFile) AsLargeBytes() (io.ReadSeeker, error) {
 	return &shardNodeReader{s, nil, 0, 0}, nil
 }
 
+func (s *shardNodeFile) Substrate() ipld.Node {
+	return s.substrate
+}
+
 func protoFor(link ipld.Link) ipld.NodePrototype {
 	if lc, ok := link.(cidlink.Link); ok {
 		if lc.Cid.Prefix().Codec == uint64(multicodec.DagPb) {