Add service plugin and support in process integration.

Signed-off-by: Lantao Liu <lantaol@google.com>

services/diff/local.go

@@ -0,0 +1,178 @@
+/*
+   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 diff
+
+import (
+	diffapi "github.com/containerd/containerd/api/services/diff/v1"
+	"github.com/containerd/containerd/api/types"
+	"github.com/containerd/containerd/diff"
+	"github.com/containerd/containerd/errdefs"
+	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/plugin"
+	"github.com/containerd/containerd/services"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
+	"golang.org/x/net/context"
+	"google.golang.org/grpc"
+)
+
+type config struct {
+	// Order is the order of preference in which to try diff algorithms, the
+	// first differ which is supported is used.
+	// Note when multiple differs may be supported, this order will be
+	// respected for which is choosen. Each differ should return the same
+	// correct output, allowing any ordering to be used to prefer
+	// more optimimal implementations.
+	Order []string `toml:"default"`
+}
+
+type differ interface {
+	diff.Comparer
+	diff.Applier
+}
+
+func init() {
+	plugin.Register(&plugin.Registration{
+		Type: plugin.ServicePlugin,
+		ID:   services.DiffService,
+		Requires: []plugin.Type{
+			plugin.DiffPlugin,
+		},
+		Config: defaultDifferConfig,
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			differs, err := ic.GetByType(plugin.DiffPlugin)
+			if err != nil {
+				return nil, err
+			}
+
+			orderedNames := ic.Config.(*config).Order
+			ordered := make([]differ, len(orderedNames))
+			for i, n := range orderedNames {
+				differp, ok := differs[n]
+				if !ok {
+					return nil, errors.Errorf("needed differ not loaded: %s", n)
+				}
+				d, err := differp.Instance()
+				if err != nil {
+					return nil, errors.Wrapf(err, "could not load required differ due plugin init error: %s", n)
+				}
+
+				ordered[i], ok = d.(differ)
+				if !ok {
+					return nil, errors.Errorf("differ does not implement Comparer and Applier interface: %s", n)
+				}
+			}
+
+			return &local{
+				differs: ordered,
+			}, nil
+		},
+	})
+}
+
+type local struct {
+	differs []differ
+}
+
+var _ diffapi.DiffClient = &local{}
+
+func (l *local) Apply(ctx context.Context, er *diffapi.ApplyRequest, _ ...grpc.CallOption) (*diffapi.ApplyResponse, error) {
+	var (
+		ocidesc ocispec.Descriptor
+		err     error
+		desc    = toDescriptor(er.Diff)
+		mounts  = toMounts(er.Mounts)
+	)
+
+	for _, differ := range l.differs {
+		ocidesc, err = differ.Apply(ctx, desc, mounts)
+		if !errdefs.IsNotImplemented(err) {
+			break
+		}
+	}
+
+	if err != nil {
+		return nil, errdefs.ToGRPC(err)
+	}
+
+	return &diffapi.ApplyResponse{
+		Applied: fromDescriptor(ocidesc),
+	}, nil
+
+}
+
+func (l *local) Diff(ctx context.Context, dr *diffapi.DiffRequest, _ ...grpc.CallOption) (*diffapi.DiffResponse, error) {
+	var (
+		ocidesc ocispec.Descriptor
+		err     error
+		aMounts = toMounts(dr.Left)
+		bMounts = toMounts(dr.Right)
+	)
+
+	var opts []diff.Opt
+	if dr.MediaType != "" {
+		opts = append(opts, diff.WithMediaType(dr.MediaType))
+	}
+	if dr.Ref != "" {
+		opts = append(opts, diff.WithReference(dr.Ref))
+	}
+	if dr.Labels != nil {
+		opts = append(opts, diff.WithLabels(dr.Labels))
+	}
+
+	for _, d := range l.differs {
+		ocidesc, err = d.Compare(ctx, aMounts, bMounts, opts...)
+		if !errdefs.IsNotImplemented(err) {
+			break
+		}
+	}
+	if err != nil {
+		return nil, errdefs.ToGRPC(err)
+	}
+
+	return &diffapi.DiffResponse{
+		Diff: fromDescriptor(ocidesc),
+	}, nil
+}
+
+func toMounts(apim []*types.Mount) []mount.Mount {
+	mounts := make([]mount.Mount, len(apim))
+	for i, m := range apim {
+		mounts[i] = mount.Mount{
+			Type:    m.Type,
+			Source:  m.Source,
+			Options: m.Options,
+		}
+	}
+	return mounts
+}
+
+func toDescriptor(d *types.Descriptor) ocispec.Descriptor {
+	return ocispec.Descriptor{
+		MediaType: d.MediaType,
+		Digest:    d.Digest,
+		Size:      d.Size_,
+	}
+}
+
+func fromDescriptor(d ocispec.Descriptor) *types.Descriptor {
+	return &types.Descriptor{
+		MediaType: d.MediaType,
+		Digest:    d.Digest,
+		Size_:     d.Size,
+	}
+}