fix(cidlink): check for byte buffer

linking/cid/cidLink.go

@@ -30,20 +30,30 @@ func (lnk Link) Load(ctx context.Context, lnkCtx ipld.LinkContext, na ipld.NodeA
 	if !exists {
 		return fmt.Errorf("no decoder registered for multicodec %d", lnk.Prefix().Codec)
 	}
-	var hasher bytes.Buffer // multihash only exports bulk use, which is... really inefficient and should be fixed.
-	decodeErr := mcDecoder(na, io.TeeReader(r, &hasher))
-	// Error checking order here is tricky.
-	//  If decoding errored out, we should still run the reader to the end, to check the hash.
-	//  (We still don't implement this by running the hash to the end first, because that would increase the high-water memory requirement.)
-	//   ((Which we experience right now anyway because multihash's interface is silly, but we're acting as if that's fixed or will be soon.))
-	//  If the hash is rejected, we should return that error (and even if there was a decodeErr, it becomes irrelevant).
-	if decodeErr != nil {
-		_, err := io.Copy(&hasher, r)
-		if err != nil {
-			return err
+	var hasherBytes []byte
+	var decodeErr error
+	byteBuf, ok := r.(*bytes.Buffer)
+	if ok {
+		hasherBytes = byteBuf.Bytes()
+		decodeErr = mcDecoder(na, r)
+	} else {
+		var hasher bytes.Buffer // multihash only exports bulk use, which is... really inefficient and should be fixed.
+		decodeErr = mcDecoder(na, io.TeeReader(r, &hasher))
+		// Error checking order here is tricky.
+		//  If decoding errored out, we should still run the reader to the end, to check the hash.
+		//  (We still don't implement this by running the hash to the end first, because that would increase the high-water memory requirement.)
+		//   ((Which we experience right now anyway because multihash's interface is silly, but we're acting as if that's fixed or will be soon.))
+		//  If the hash is rejected, we should return that error (and even if there was a decodeErr, it becomes irrelevant).
+		if decodeErr != nil {
+			_, err := io.Copy(&hasher, r)
+			if err != nil {
+				return err
+			}
 		}
+		hasherBytes = hasher.Bytes()
 	}
-	cid, err := lnk.Prefix().Sum(hasher.Bytes())
+
+	cid, err := lnk.Prefix().Sum(hasherBytes)
 	if err != nil {
 		return err
 	}