archive: add WithSourceDateEpoch() for whiteouts

This makes diff archives to be reproducible.

The value is expected to be passed from CLI applications via the $SOUCE_DATE_EPOCH env var.

See https://reproducible-builds.org/docs/source-date-epoch/
for the $SOURCE_DATE_EPOCH specification.

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

pkg/epoch/epoch_test.go

@@ -0,0 +1,78 @@
+/*
+   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 (
+	"os"
+	"runtime"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func rightAfter(t1, t2 time.Time) bool {
+	if runtime.GOOS == "windows" {
+		// Low timer resolution on Windows
+		return (t2.After(t1) && t2.Before(t1.Add(100*time.Millisecond))) || t2.Equal(t1)
+	}
+	return t2.After(t1) && t2.Before(t1.Add(10*time.Millisecond))
+}
+
+func TestSourceDateEpoch(t *testing.T) {
+	if s, ok := os.LookupEnv(SourceDateEpochEnv); ok {
+		t.Logf("%s is already set to %q, unsetting", SourceDateEpochEnv, s)
+		t.Setenv(SourceDateEpochEnv, "")
+	}
+
+	t.Run("WithoutSourceDateEpoch", func(t *testing.T) {
+		vp, err := SourceDateEpoch()
+		require.NoError(t, err)
+		require.Nil(t, vp)
+
+		now := time.Now()
+		v := SourceDateEpochOrNow()
+		require.True(t, rightAfter(now, v))
+	})
+
+	t.Run("WithSourceDateEpoch", func(t *testing.T) {
+		sourceDateEpoch, err := time.Parse(time.RFC3339, "2022-01-23T12:34:56Z")
+		require.NoError(t, err)
+
+		SetSourceDateEpoch(sourceDateEpoch)
+		t.Cleanup(UnsetSourceDateEpoch)
+
+		vp, err := SourceDateEpoch()
+		require.NoError(t, err)
+		require.True(t, vp.Equal(sourceDateEpoch))
+
+		v := SourceDateEpochOrNow()
+		require.True(t, v.Equal(sourceDateEpoch))
+	})
+
+	t.Run("WithInvalidSourceDateEpoch", func(t *testing.T) {
+		t.Setenv(SourceDateEpochEnv, "foo")
+
+		vp, err := SourceDateEpoch()
+		require.ErrorContains(t, err, "invalid SOURCE_DATE_EPOCH value")
+		require.Nil(t, vp)
+
+		now := time.Now()
+		v := SourceDateEpochOrNow()
+		require.True(t, rightAfter(now, v))
+	})
+}