fix: Check if docker daemon can be reached

The client can be created just fine without an active docker daemon. It
needs to be actively checked before usage for tailfin to not hang.

Author: hogklint

cmd/tailfincmd/cmd.go

@@ -113,7 +113,6 @@ func (o *options) Complete(args []string) error {
 	}
 
 	var err error
-	// TODO More error handling here. err == nil even if no daemon is found
 	o.dockerClient, err = dockerclient.NewClientWithOpts(dockerclient.FromEnv, dockerclient.WithAPIVersionNegotiation())
 	if err != nil {
 		panic(err)
@@ -143,6 +142,11 @@ func (o *options) Run(cmd *cobra.Command) error {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
+	_, err = o.dockerClient.Ping(ctx)
+	if err != nil {
+		return err
+	}
+
 	return stern.RunDocker(ctx, o.dockerClient, config)
 }