Update fetch handling

Fix issue where manifest content must always be fetched
even if it is already fully downloaded or shared locally.
Simplify children label setting and platform filtering.
Prevent getting a fetcher when content shared locally.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

remotes/handlers.go

@@ -2,7 +2,6 @@ package remotes
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
 	"io"
 	"math/rand"
@@ -102,83 +101,27 @@ func fetch(ctx context.Context, ingester content.Ingester, fetcher Fetcher, desc
 		break
 	}
 
+	ws, err := cw.Status()
+	if err != nil {
+		return err
+	}
+
+	if ws.Offset == desc.Size {
+		// If writer is already complete, commit and return
+		err := cw.Commit(ctx, desc.Size, desc.Digest)
+		if err != nil && !errdefs.IsAlreadyExists(err) {
+			return errors.Wrapf(err, "failed commit on ref %q", ws.Ref)
+		}
+		return nil
+	}
+
 	rc, err := fetcher.Fetch(ctx, desc)
 	if err != nil {
 		return err
 	}
 	defer rc.Close()
 
-	r, opts := commitOpts(desc, rc)
-	return content.Copy(ctx, cw, r, desc.Size, desc.Digest, opts...)
-}
-
-// commitOpts gets the appropriate content options to alter
-// the content info on commit based on media type.
-func commitOpts(desc ocispec.Descriptor, r io.Reader) (io.Reader, []content.Opt) {
-	var childrenF func(r io.Reader) ([]ocispec.Descriptor, error)
-
-	// TODO(AkihiroSuda): use images/oci.GetChildrenDescriptors?
-	switch desc.MediaType {
-	case images.MediaTypeDockerSchema2Manifest, ocispec.MediaTypeImageManifest:
-		childrenF = func(r io.Reader) ([]ocispec.Descriptor, error) {
-			var (
-				manifest ocispec.Manifest
-				decoder  = json.NewDecoder(r)
-			)
-			if err := decoder.Decode(&manifest); err != nil {
-				return nil, err
-			}
-
-			return append([]ocispec.Descriptor{manifest.Config}, manifest.Layers...), nil
-		}
-	case images.MediaTypeDockerSchema2ManifestList, ocispec.MediaTypeImageIndex:
-		childrenF = func(r io.Reader) ([]ocispec.Descriptor, error) {
-			var (
-				index   ocispec.Index
-				decoder = json.NewDecoder(r)
-			)
-			if err := decoder.Decode(&index); err != nil {
-				return nil, err
-			}
-
-			return index.Manifests, nil
-		}
-	default:
-		return r, nil
-	}
-
-	pr, pw := io.Pipe()
-
-	var children []ocispec.Descriptor
-	errC := make(chan error)
-
-	go func() {
-		defer close(errC)
-		ch, err := childrenF(pr)
-		if err != nil {
-			errC <- err
-		}
-		children = ch
-	}()
-
-	opt := func(info *content.Info) error {
-		err := <-errC
-		if err != nil {
-			return errors.Wrap(err, "unable to get commit labels")
-		}
-
-		if len(children) > 0 {
-			if info.Labels == nil {
-				info.Labels = map[string]string{}
-			}
-			for i, ch := range children {
-				info.Labels[fmt.Sprintf("containerd.io/gc.ref.content.%d", i)] = ch.Digest.String()
-			}
-		}
-		return nil
-	}
-
-	return io.TeeReader(r, pw), []content.Opt{opt}
+	return content.Copy(ctx, cw, rc, desc.Size, desc.Digest)
 }
 
 // PushHandler returns a handler that will push all content from the provider
@@ -243,7 +186,7 @@ func PushContent(ctx context.Context, pusher Pusher, desc ocispec.Descriptor, pr
 	pushHandler := PushHandler(pusher, provider)
 
 	handlers := append(baseHandlers,
-		images.ChildrenHandler(provider, platforms.Default()),
+		images.FilterPlatform(platforms.Default(), images.ChildrenHandler(provider)),
 		filterHandler,
 		pushHandler,
 	)