bugfix: support application/octet-stream during pull

Even though application/octet-stream issue has been fixed in docker,
there exists lots of images which contains the invalid mediatype.

In order to pull those images, containerd client side modifies the
manifest content before insert/update image reference.

Signed-off-by: Wei Fu <fuweid89@gmail.com>

client.go

@@ -403,12 +403,22 @@ func (c *Client) fetch(ctx context.Context, rCtx *RemoteContext, ref string, lim
 	}
 
 	var (
-		schema1Converter *schema1.Converter
 		handler images.Handler
+
+		isConvertible bool
+		converterFunc func(context.Context, ocispec.Descriptor) (ocispec.Descriptor, error)
 	)
+
 	if desc.MediaType == images.MediaTypeDockerSchema1Manifest && rCtx.ConvertSchema1 {
-		schema1Converter = schema1.NewConverter(store, fetcher)
+		schema1Converter := schema1.NewConverter(store, fetcher)
+
 		handler = images.Handlers(append(rCtx.BaseHandlers, schema1Converter)...)
+
+		isConvertible = true
+
+		converterFunc = func(ctx context.Context, _ ocispec.Descriptor) (ocispec.Descriptor, error) {
+			return schema1Converter.Convert(ctx)
+		}
 	} else {
 		// Get all the children for a descriptor
 		childrenHandler := images.ChildrenHandler(store)
@@ -421,18 +431,34 @@ func (c *Client) fetch(ctx context.Context, rCtx *RemoteContext, ref string, lim
 			childrenHandler = images.LimitManifests(childrenHandler, rCtx.PlatformMatcher, limit)
 		}
 
+		// set isConvertible to true if there is application/octet-stream media type
+		convertibleHandler := images.HandlerFunc(
+			func(_ context.Context, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
+				if desc.MediaType == docker.LegacyConfigMediaType {
+					isConvertible = true
+				}
+
+				return []ocispec.Descriptor{}, nil
+			},
+		)
+
 		handler = images.Handlers(append(rCtx.BaseHandlers,
 			remotes.FetchHandler(store, fetcher),
+			convertibleHandler,
 			childrenHandler,
 		)...)
+
+		converterFunc = func(ctx context.Context, desc ocispec.Descriptor) (ocispec.Descriptor, error) {
+			return docker.ConvertManifest(ctx, store, desc)
+		}
 	}
 
 	if err := images.Dispatch(ctx, handler, desc); err != nil {
 		return images.Image{}, err
 	}
-	if schema1Converter != nil {
-		desc, err = schema1Converter.Convert(ctx)
-		if err != nil {
+
+	if isConvertible {
+		if desc, err = converterFunc(ctx, desc); err != nil {
 			return images.Image{}, err
 		}
 	}

remotes/docker/converter.go

@@ -0,0 +1,88 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package docker
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"github.com/containerd/containerd/content"
+	"github.com/containerd/containerd/images"
+	"github.com/containerd/containerd/log"
+	"github.com/containerd/containerd/remotes"
+	digest "github.com/opencontainers/go-digest"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
+)
+
+// LegacyConfigMediaType should be replaced by OCI image spec.
+//
+// More detail: docker/distribution#1622
+const LegacyConfigMediaType = "application/octet-stream"
+
+// ConvertManifest changes application/octet-stream to schema2 config media type if need.
+//
+// NOTE:
+// 1. original manifest will be deleted by next gc round.
+// 2. don't cover manifest list.
+func ConvertManifest(ctx context.Context, store content.Store, desc ocispec.Descriptor) (ocispec.Descriptor, error) {
+	if !(desc.MediaType == images.MediaTypeDockerSchema2Manifest ||
+		desc.MediaType == ocispec.MediaTypeImageManifest) {
+
+		log.G(ctx).Warnf("do nothing for media type: %s", desc.MediaType)
+		return desc, nil
+	}
+
+	// read manifest data
+	mb, err := content.ReadBlob(ctx, store, desc)
+	if err != nil {
+		return ocispec.Descriptor{}, errors.Wrap(err, "failed to read index data")
+	}
+
+	var manifest ocispec.Manifest
+	if err := json.Unmarshal(mb, &manifest); err != nil {
+		return ocispec.Descriptor{}, errors.Wrap(err, "failed to unmarshal data into manifest")
+	}
+
+	// check config media type
+	if manifest.Config.MediaType != LegacyConfigMediaType {
+		return desc, nil
+	}
+
+	manifest.Config.MediaType = images.MediaTypeDockerSchema2Config
+	data, err := json.MarshalIndent(manifest, "", "   ")
+	if err != nil {
+		return ocispec.Descriptor{}, errors.Wrap(err, "failed to marshal manifest")
+	}
+
+	// update manifest with gc labels
+	desc.Digest = digest.Canonical.FromBytes(data)
+	desc.Size = int64(len(data))
+
+	labels := map[string]string{}
+	for i, c := range append([]ocispec.Descriptor{manifest.Config}, manifest.Layers...) {
+		labels[fmt.Sprintf("containerd.io/gc.ref.content.%d", i)] = c.Digest.String()
+	}
+
+	ref := remotes.MakeRefKey(ctx, desc)
+	if err := content.WriteBlob(ctx, store, ref, bytes.NewReader(data), desc, content.WithLabels(labels)); err != nil {
+		return ocispec.Descriptor{}, errors.Wrap(err, "failed to update content")
+	}
+	return desc, nil
+}