Swarm mode check fails on non-standard Info responses (#376)

* Swarm mode check fails on non-standard Info responses

* Add unit test

* Remove balena tests, add note to docs

cmd/backup/stop_restart.go

@@ -81,6 +81,16 @@ func awaitContainerCountForService(cli *client.Client, serviceID string, count i
 	}
 }
 
+func isSwarm(c interface {
+	Info(context.Context) (types.Info, error)
+}) (bool, error) {
+	info, err := c.Info(context.Background())
+	if err != nil {
+		return false, errwrap.Wrap(err, "error getting docker info")
+	}
+	return info.Swarm.LocalNodeState != "" && info.Swarm.LocalNodeState != swarm.LocalNodeStateInactive, nil
+}
+
 // stopContainersAndServices stops all Docker containers that are marked as to being
 // stopped during the backup and returns a function that can be called to
 // restart everything that has been stopped.
@@ -89,11 +99,10 @@ func (s *script) stopContainersAndServices() (func() error, error) {
 		return noop, nil
 	}
 
-	dockerInfo, err := s.cli.Info(context.Background())
+	isDockerSwarm, err := isSwarm(s.cli)
 	if err != nil {
-		return noop, errwrap.Wrap(err, "error getting docker info")
+		return noop, errwrap.Wrap(err, "error determining swarm state")
 	}
-	isDockerSwarm := dockerInfo.Swarm.LocalNodeState != "inactive"
 
 	labelValue := s.c.BackupStopDuringBackupLabel
 	if s.c.BackupStopContainerLabel != "" {

cmd/backup/stop_restart_test.go

@@ -0,0 +1,85 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/api/types/swarm"
+)
+
+type mockInfoClient struct {
+	result types.Info
+	err    error
+}
+
+func (m *mockInfoClient) Info(context.Context) (types.Info, error) {
+	return m.result, m.err
+}
+
+func TestIsSwarm(t *testing.T) {
+	tests := []struct {
+		name        string
+		client      *mockInfoClient
+		expected    bool
+		expectError bool
+	}{
+		{
+			"swarm",
+			&mockInfoClient{
+				result: types.Info{
+					Swarm: swarm.Info{
+						LocalNodeState: swarm.LocalNodeStateActive,
+					},
+				},
+			},
+			true,
+			false,
+		},
+		{
+			"compose",
+			&mockInfoClient{
+				result: types.Info{
+					Swarm: swarm.Info{
+						LocalNodeState: swarm.LocalNodeStateInactive,
+					},
+				},
+			},
+			false,
+			false,
+		},
+		{
+			"balena",
+			&mockInfoClient{
+				result: types.Info{
+					Swarm: swarm.Info{
+						LocalNodeState: "",
+					},
+				},
+			},
+			false,
+			false,
+		},
+		{
+			"error",
+			&mockInfoClient{
+				err: errors.New("the dinosaurs escaped"),
+			},
+			false,
+			true,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			result, err := isSwarm(test.client)
+			if (err != nil) != test.expectError {
+				t.Errorf("Unexpected error value %v", err)
+			}
+			if test.expected != result {
+				t.Errorf("Expected %v, got %v", test.expected, result)
+			}
+		})
+	}
+}

docs/index.md

@@ -100,6 +100,11 @@ docker pull ghcr.io/offen/docker-volume-backup:v2
 
 Documentation references Docker Hub, but all examples will work using ghcr.io just as well.
 
+### Supported Engines
+
+This tool is developed and tested against the Docker CE engine exclusively.
+While it may work against different implementations (e.g. Balena Engine), there are no guarantees about support for non-Docker engines.
+
 ## Differences to `jareware/docker-volume-backup`
 
 This image is heavily inspired by `jareware/docker-volume-backup`. We decided to publish this image as a simpler and more lightweight alternative because of the following requirements: