fix: traverser should skip over identity CIDs

ipldutil/traverser.go

@@ -1,6 +1,7 @@
 package ipldutil
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"io"
@@ -12,7 +13,9 @@ import (
 	"github.com/ipld/go-ipld-prime/node/basicnode"
 	"github.com/ipld/go-ipld-prime/traversal"
 	"github.com/ipld/go-ipld-prime/traversal/selector"
+	"github.com/multiformats/go-multihash"
 
+	"github.com/ipfs/go-cid"
 	"github.com/ipfs/go-graphsync/panics"
 )
 
@@ -165,7 +168,23 @@ func (t *traverser) NBlocksTraversed() int {
 	return t.blocksCount
 }
 
+func asIdentity(c cid.Cid) (digest []byte, ok bool, err error) {
+	dmh, err := multihash.Decode(c.Hash())
+	if err != nil {
+		return nil, false, err
+	}
+	ok = dmh.Code == multihash.IDENTITY
+	digest = dmh.Digest
+	return digest, ok, nil
+}
+
 func (t *traverser) loader(lnkCtx ipld.LinkContext, lnk ipld.Link) (io.Reader, error) {
+	if digest, ok, err := asIdentity(lnk.(cidlink.Link).Cid); ok {
+		return io.NopCloser(bytes.NewReader(digest)), nil
+	} else if err != nil {
+		return nil, err
+	}
+
 	// A StorageReadOpener call came in; update the state and release the lock.
 	// We can't simply unlock the mutex inside the <-t.responses case,
 	// as then we'd deadlock with the other side trying to send.