Add proxy differ

Signed-off-by: Derek McGowan <derek@mcg.dev>

diff/proxy/differ.go

@@ -0,0 +1,131 @@
+/*
+   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 proxy
+
+import (
+	"context"
+
+	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/pkg/epoch"
+	"github.com/containerd/containerd/protobuf"
+	ptypes "github.com/containerd/containerd/protobuf/types"
+	"github.com/opencontainers/go-digest"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+
+	"google.golang.org/protobuf/types/known/timestamppb"
+)
+
+// NewDiffApplier returns a new comparer and applier which communicates
+// over a GRPC connection.
+func NewDiffApplier(client diffapi.DiffClient) interface{} {
+	return &diffRemote{
+		client: client,
+	}
+}
+
+type diffRemote struct {
+	client diffapi.DiffClient
+}
+
+func (r *diffRemote) Apply(ctx context.Context, desc ocispec.Descriptor, mounts []mount.Mount, opts ...diff.ApplyOpt) (ocispec.Descriptor, error) {
+	var config diff.ApplyConfig
+	for _, opt := range opts {
+		if err := opt(ctx, desc, &config); err != nil {
+			return ocispec.Descriptor{}, err
+		}
+	}
+
+	payloads := make(map[string]*ptypes.Any)
+	for k, v := range config.ProcessorPayloads {
+		payloads[k] = protobuf.FromAny(v)
+	}
+
+	req := &diffapi.ApplyRequest{
+		Diff:     fromDescriptor(desc),
+		Mounts:   fromMounts(mounts),
+		Payloads: payloads,
+	}
+	resp, err := r.client.Apply(ctx, req)
+	if err != nil {
+		return ocispec.Descriptor{}, errdefs.FromGRPC(err)
+	}
+	return toDescriptor(resp.Applied), nil
+}
+
+func (r *diffRemote) Compare(ctx context.Context, a, b []mount.Mount, opts ...diff.Opt) (ocispec.Descriptor, error) {
+	var config diff.Config
+	for _, opt := range opts {
+		if err := opt(&config); err != nil {
+			return ocispec.Descriptor{}, err
+		}
+	}
+	if tm := epoch.FromContext(ctx); tm != nil && config.SourceDateEpoch == nil {
+		config.SourceDateEpoch = tm
+	}
+	var sourceDateEpoch *timestamppb.Timestamp
+	if config.SourceDateEpoch != nil {
+		sourceDateEpoch = timestamppb.New(*config.SourceDateEpoch)
+	}
+	req := &diffapi.DiffRequest{
+		Left:            fromMounts(a),
+		Right:           fromMounts(b),
+		MediaType:       config.MediaType,
+		Ref:             config.Reference,
+		Labels:          config.Labels,
+		SourceDateEpoch: sourceDateEpoch,
+	}
+	resp, err := r.client.Diff(ctx, req)
+	if err != nil {
+		return ocispec.Descriptor{}, errdefs.FromGRPC(err)
+	}
+	return toDescriptor(resp.Diff), nil
+}
+
+func toDescriptor(d *types.Descriptor) ocispec.Descriptor {
+	return ocispec.Descriptor{
+		MediaType:   d.MediaType,
+		Digest:      digest.Digest(d.Digest),
+		Size:        d.Size,
+		Annotations: d.Annotations,
+	}
+}
+
+func fromDescriptor(d ocispec.Descriptor) *types.Descriptor {
+	return &types.Descriptor{
+		MediaType:   d.MediaType,
+		Digest:      d.Digest.String(),
+		Size:        d.Size,
+		Annotations: d.Annotations,
+	}
+}
+
+func fromMounts(mounts []mount.Mount) []*types.Mount {
+	apiMounts := make([]*types.Mount, len(mounts))
+	for i, m := range mounts {
+		apiMounts[i] = &types.Mount{
+			Type:    m.Type,
+			Source:  m.Source,
+			Target:  m.Target,
+			Options: m.Options,
+		}
+	}
+	return apiMounts
+}