pkg/epoch: extract parsing SOURCE_DATE_EPOCH to a function

This introduces a ParseSourceDateEpoch function, which can be used
to parse "SOURCE_DATE_EPOCH" values for situations where those
values are not passed through an env-var (or the env-var has been
read through other means).

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/epoch/epoch.go

@@ -37,12 +37,11 @@ func SourceDateEpoch() (*time.Time, error) {
 	if !ok || v == "" {
 		return nil, nil // not an error
 	}
-	i64, err := strconv.ParseInt(v, 10, 64)
+	t, err := ParseSourceDateEpoch(v)
 	if err != nil {
-		return nil, fmt.Errorf("invalid %s value %q: %w", SourceDateEpochEnv, v, err)
+		return nil, fmt.Errorf("invalid %s value: %w", SourceDateEpochEnv, err)
 	}
-	unix := time.Unix(i64, 0).UTC()
+	return t, nil
-	return &unix, nil
 }
 
 // SourceDateEpochOrNow returns the SOURCE_DATE_EPOCH time if available,
@@ -58,6 +57,20 @@ func SourceDateEpochOrNow() time.Time {
 	return time.Now().UTC()
 }
 
+// ParseSourceDateEpoch parses the given source date epoch, as *time.Time.
+// It returns an error if sourceDateEpoch is empty or not well-formatted.
+func ParseSourceDateEpoch(sourceDateEpoch string) (*time.Time, error) {
+	if sourceDateEpoch == "" {
+		return nil, fmt.Errorf("value is empty")
+	}
+	i64, err := strconv.ParseInt(sourceDateEpoch, 10, 64)
+	if err != nil {
+		return nil, fmt.Errorf("invalid value: %w", err)
+	}
+	unix := time.Unix(i64, 0).UTC()
+	return &unix, nil
+}
+
 // SetSourceDateEpoch sets the SOURCE_DATE_EPOCH env var.
 func SetSourceDateEpoch(tm time.Time) {
 	_ = os.Setenv(SourceDateEpochEnv, strconv.Itoa(int(tm.Unix())))

pkg/epoch/epoch_test.go

@@ -19,6 +19,7 @@ package epoch
 import (
 	"os"
 	"runtime"
+	"strconv"
 	"testing"
 	"time"
 
@@ -56,19 +57,25 @@ func TestSourceDateEpoch(t *testing.T) {
 	})
 
 	t.Run("WithEmptySourceDateEpoch", func(t *testing.T) {
-		t.Setenv(SourceDateEpochEnv, "")
+		const emptyValue = ""
+		t.Setenv(SourceDateEpochEnv, emptyValue)
 
 		vp, err := SourceDateEpoch()
 		require.NoError(t, err)
 		require.Nil(t, vp)
 
+		vp, err = ParseSourceDateEpoch(emptyValue)
+		require.Error(t, err, "value is empty")
+		require.Nil(t, vp)
+
 		now := time.Now().UTC()
 		v := SourceDateEpochOrNow()
 		require.True(t, rightAfter(now, v), "now: %s, v: %s", now, v)
 	})
 
 	t.Run("WithSourceDateEpoch", func(t *testing.T) {
-		sourceDateEpoch, err := time.Parse(time.RFC3339, "2022-01-23T12:34:56Z")
+		const rfc3339Str = "2022-01-23T12:34:56Z"
+		sourceDateEpoch, err := time.Parse(time.RFC3339, rfc3339Str)
 		require.NoError(t, err)
 
 		SetSourceDateEpoch(sourceDateEpoch)
@@ -76,6 +83,10 @@ func TestSourceDateEpoch(t *testing.T) {
 
 		vp, err := SourceDateEpoch()
 		require.NoError(t, err)
+		require.True(t, vp.Equal(sourceDateEpoch.UTC()))
+
+		vp, err = ParseSourceDateEpoch(strconv.Itoa(int(sourceDateEpoch.Unix())))
+		require.NoError(t, err)
 		require.True(t, vp.Equal(sourceDateEpoch))
 
 		v := SourceDateEpochOrNow()
@@ -83,12 +94,17 @@ func TestSourceDateEpoch(t *testing.T) {
 	})
 
 	t.Run("WithInvalidSourceDateEpoch", func(t *testing.T) {
-		t.Setenv(SourceDateEpochEnv, "foo")
+		const invalidValue = "foo"
+		t.Setenv(SourceDateEpochEnv, invalidValue)
 
 		vp, err := SourceDateEpoch()
 		require.ErrorContains(t, err, "invalid SOURCE_DATE_EPOCH value")
 		require.Nil(t, vp)
 
+		vp, err = ParseSourceDateEpoch(invalidValue)
+		require.ErrorContains(t, err, "invalid value:")
+		require.Nil(t, vp)
+
 		now := time.Now().UTC()
 		v := SourceDateEpochOrNow()
 		require.True(t, rightAfter(now, v), "now: %s, v: %s", now, v)