epoch: propagate SOURCE_DATE_EPOCH via ctx

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

archive/tar.go

@@ -30,6 +30,7 @@ import (
 	"time"
 
 	"github.com/containerd/containerd/log"
+	"github.com/containerd/containerd/pkg/epoch"
 	"github.com/containerd/containerd/pkg/userns"
 	"github.com/containerd/continuity/fs"
 )
@@ -80,6 +81,10 @@ func WriteDiff(ctx context.Context, w io.Writer, a, b string, opts ...WriteDiffO
 			return fmt.Errorf("failed to apply option: %w", err)
 		}
 	}
+	if tm := epoch.FromContext(ctx); tm != nil && options.SourceDateEpoch == nil {
+		options.SourceDateEpoch = tm
+	}
+
 	if options.writeDiffFunc == nil {
 		options.writeDiffFunc = writeDiffNaive
 	}

cmd/ctr/commands/client.go

@@ -20,7 +20,9 @@ import (
 	gocontext "context"
 
 	"github.com/containerd/containerd"
+	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/namespaces"
+	"github.com/containerd/containerd/pkg/epoch"
 	"github.com/urfave/cli"
 )
 
@@ -42,6 +44,12 @@ func AppContext(context *cli.Context) (gocontext.Context, gocontext.CancelFunc)
 	} else {
 		ctx, cancel = gocontext.WithCancel(ctx)
 	}
+	if tm, err := epoch.SourceDateEpoch(); err != nil {
+		log.L.WithError(err).Warn("Failed to read SOURCE_DATE_EPOCH")
+	} else if tm != nil {
+		log.L.Debugf("Using SOURCE_DATE_EPOCH: %v", tm)
+		ctx = epoch.WithSourceDateEpoch(ctx, tm)
+	}
 	return ctx, cancel
 }
 

cmd/ctr/commands/snapshots/snapshots.go

@@ -31,7 +31,6 @@ import (
 	"github.com/containerd/containerd/diff"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/mount"
-	"github.com/containerd/containerd/pkg/epoch"
 	"github.com/containerd/containerd/pkg/progress"
 	"github.com/containerd/containerd/rootfs"
 	"github.com/containerd/containerd/snapshots"
@@ -142,14 +141,7 @@ var diffCommand = cli.Command{
 			diff.WithReference(context.String("ref")),
 			diff.WithLabels(labels),
 		}
-
+		// SOURCE_DATE_EPOCH is propagated via the ctx, so no need to specify diff.WithSourceDateEpoch here
-		ep, err := epoch.SourceDateEpoch()
-		if err != nil {
-			return err
-		}
-		if ep != nil {
-			opts = append(opts, diff.WithSourceDateEpoch(ep))
-		}
 
 		if idB == "" {
 			desc, err = rootfs.CreateDiff(ctx, idA, snapshotter, client.DiffService(), opts...)

diff.go

@@ -24,6 +24,7 @@ import (
 	"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"
@@ -81,6 +82,9 @@ func (r *diffRemote) Compare(ctx context.Context, a, b []mount.Mount, opts ...di
 			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)

diff/walking/differ.go

@@ -32,6 +32,7 @@ import (
 	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/pkg/epoch"
 	digest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 )
@@ -64,6 +65,9 @@ func (s *walkingDiff) Compare(ctx context.Context, lower, upper []mount.Mount, o
 			return emptyDesc, err
 		}
 	}
+	if tm := epoch.FromContext(ctx); tm != nil && config.SourceDateEpoch == nil {
+		config.SourceDateEpoch = tm
+	}
 
 	var writeDiffOpts []archive.WriteDiffOpt
 	if config.SourceDateEpoch != nil {

diff/windows/windows.go

@@ -36,6 +36,7 @@ import (
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/metadata"
 	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/pkg/epoch"
 	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
 	"github.com/opencontainers/go-digest"
@@ -177,6 +178,9 @@ func (s windowsDiff) Compare(ctx context.Context, lower, upper []mount.Mount, op
 			return emptyDesc, err
 		}
 	}
+	if tm := epoch.FromContext(ctx); tm != nil && config.SourceDateEpoch == nil {
+		config.SourceDateEpoch = tm
+	}
 
 	layers, err := mountPairToLayerStack(lower, upper)
 	if err != nil {

pkg/epoch/context.go

@@ -0,0 +1,41 @@
+/*
+   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 epoch
+
+import (
+	"context"
+	"time"
+)
+
+type (
+	epochKey struct{}
+)
+
+// WithSourceDateEpoch associates the context with the epoch.
+func WithSourceDateEpoch(ctx context.Context, tm *time.Time) context.Context {
+	return context.WithValue(ctx, epochKey{}, tm)
+}
+
+// FromContext returns the epoch associated with the context.
+// FromContext does not fall back to read the SOURCE_DATE_EPOCH env var.
+func FromContext(ctx context.Context) *time.Time {
+	v := ctx.Value(epochKey{})
+	if v == nil {
+		return nil
+	}
+	return v.(*time.Time)
+}