backup: Return exit status code 3 when failing to read source data

The backup command used to return a zero exit code as long as a snapshot
could be created successfully, even if some of the source files could not
be read (in which case the snapshot would contain the rest of the files).

This made it hard for automation/scripts to detect failures/incomplete
backups by looking at the exit code. Restic now returns the following exit
codes for the backup command:

 - 0 when the command was successful
 - 1 when there was a fatal error (no snapshot created)
 - 3 when some source data could not be read (incomplete snapshot created)

cmd/restic/cmd_backup.go

@@ -39,10 +39,9 @@ given as the arguments.
 EXIT STATUS
 ===========
 
-Exit status is 0 if the command was successful, and non-zero if there was any error.
-
-Note that some issues such as unreadable or deleted files during backup
-currently doesn't result in a non-zero error exit status.
+Exit status is 0 if the command was successful.
+Exit status is 1 if there was a fatal error (no snapshot created).
+Exit status is 3 if some source data could not be read (incomplete snapshot created).
 `,
 	PreRun: func(cmd *cobra.Command, args []string) {
 		if backupOptions.Host == "" {
@@ -99,6 +98,9 @@ type BackupOptions struct {
 
 var backupOptions BackupOptions
 
+// Error sentinel for invalid source data
+var InvalidSourceData = errors.New("Failed to read all source data during backup.")
+
 func init() {
 	cmdRoot.AddCommand(cmdBackup)
 
@@ -557,7 +559,11 @@ func runBackup(opts BackupOptions, gopts GlobalOptions, term *termstatus.Termina
 	arch.SelectByName = selectByNameFilter
 	arch.Select = selectFilter
 	arch.WithAtime = opts.WithAtime
-	arch.Error = p.Error
+	success := true
+	arch.Error = func(item string, fi os.FileInfo, err error) error {
+		success = false
+		return p.Error(item, fi, err)
+	}
 	arch.CompleteItem = p.CompleteItem
 	arch.StartFile = p.StartFile
 	arch.CompleteBlob = p.CompleteBlob
@@ -594,6 +600,9 @@ func runBackup(opts BackupOptions, gopts GlobalOptions, term *termstatus.Termina
 	if !gopts.JSON {
 		p.P("snapshot %s saved\n", id.Str())
 	}
+	if !success {
+		return InvalidSourceData
+	}
 
 	// Return error if any
 	return err

cmd/restic/integration_test.go

@@ -13,6 +13,7 @@ import (
 	"os"
 	"path/filepath"
 	"regexp"
+	"runtime"
 	"strings"
 	"syscall"
 	"testing"
@@ -54,7 +55,7 @@ func testRunInit(t testing.TB, opts GlobalOptions) {
 	t.Logf("repository initialized at %v", opts.Repo)
 }
 
-func testRunBackup(t testing.TB, dir string, target []string, opts BackupOptions, gopts GlobalOptions) {
+func testRunBackupAssumeFailure(t testing.TB, dir string, target []string, opts BackupOptions, gopts GlobalOptions) error {
 	ctx, cancel := context.WithCancel(gopts.ctx)
 	defer cancel()
 
@@ -69,7 +70,7 @@ func testRunBackup(t testing.TB, dir string, target []string, opts BackupOptions
 		defer cleanup()
 	}
 
-	rtest.OK(t, runBackup(opts, gopts, term, target))
+	backupErr := runBackup(opts, gopts, term, target)
 
 	cancel()
 
@@ -77,6 +78,13 @@ func testRunBackup(t testing.TB, dir string, target []string, opts BackupOptions
 	if err != nil {
 		t.Fatal(err)
 	}
+
+	return backupErr
+}
+
+func testRunBackup(t testing.TB, dir string, target []string, opts BackupOptions, gopts GlobalOptions) {
+	err := testRunBackupAssumeFailure(t, dir, target, opts, gopts)
+	rtest.Assert(t, err == nil, "Error while backing up")
 }
 
 func testRunList(t testing.TB, tpe string, opts GlobalOptions) restic.IDs {
@@ -436,6 +444,36 @@ func TestBackupExclude(t *testing.T) {
 		"expected file %q not in first snapshot, but it's included", "passwords.txt")
 }
 
+func TestBackupErrors(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		return
+	}
+	env, cleanup := withTestEnvironment(t)
+	defer cleanup()
+
+	datafile := filepath.Join("testdata", "backup-data.tar.gz")
+
+	rtest.SetupTarTestFixture(t, env.testdata, datafile)
+
+	testRunInit(t, env.gopts)
+
+	// Assume failure
+	inaccessibleFile := filepath.Join(env.testdata, "0", "0", "9", "0")
+	os.Chmod(inaccessibleFile, 0000)
+	defer func() {
+		os.Chmod(inaccessibleFile, 0644)
+	}()
+	opts := BackupOptions{}
+	gopts := env.gopts
+	gopts.stderr = ioutil.Discard
+	err := testRunBackupAssumeFailure(t, filepath.Dir(env.testdata), []string{"testdata"}, opts, gopts)
+	rtest.Assert(t, err != nil, "Assumed failure, but no error occured.")
+	rtest.Assert(t, err == InvalidSourceData, "Wrong error returned")
+	snapshotIDs := testRunList(t, "snapshots", env.gopts)
+	rtest.Assert(t, len(snapshotIDs) == 1,
+		"expected one snapshot, got %v", snapshotIDs)
+}
+
 const (
 	incrementalFirstWrite  = 10 * 1042 * 1024
 	incrementalSecondWrite = 1 * 1042 * 1024

cmd/restic/main.go

@@ -103,9 +103,13 @@ func main() {
 	}
 
 	var exitCode int
-	if err != nil {
+	switch err {
+	case nil:
+		exitCode = 0
+	case InvalidSourceData:
+		exitCode = 3
+	default:
 		exitCode = 1
 	}
-
 	Exit(exitCode)
 }