Add json log format

Add an option to to format logs in json format. This can be useful for
programs running limactl that want to consume some content from the logs
in the program own logs.

    Example:

    % _output/bin/limactl -h
    ...
    Flags:
          --debug               debug mode
      -h, --help                help for limactl
          --log-format string   Set the logging format [text, json] (default "text")
          --log-level string    Set the logging level [trace, debug, info, warn, error]
      ...

    % _output/bin/limactl start --log-format json --plain --vm-type vz --tty=false
    {"level":"info","msg":"Terminal is not available, proceeding without opening an editor","time":"2024-09-02T05:12:28+03:00"}
    {"level":"info","msg":"Starting the instance \"default\" with VM driver \"vz\"","time":"2024-09-02T05:12:28+03:00"}
    ...

Discussed in #2576

Fixes #2583
Signed-off-by: Nir Soffer <[email protected]>

Author: nirs

cmd/limactl/main.go

@@ -60,6 +60,7 @@ func newApp() *cobra.Command {
 		DisableAutoGenTag: true,
 	}
 	rootCmd.PersistentFlags().String("log-level", "", "Set the logging level [trace, debug, info, warn, error]")
+	rootCmd.PersistentFlags().String("log-format", "text", "Set the logging format [text, json]")
 	rootCmd.PersistentFlags().Bool("debug", false, "debug mode")
 	// TODO: "survey" does not support using cygwin terminal on windows yet
 	rootCmd.PersistentFlags().Bool("tty", isatty.IsTerminal(os.Stdout.Fd()), "Enable TUI interactions such as opening an editor. Defaults to true when stdout is a terminal. Set to false for automation.")
@@ -72,6 +73,24 @@ func newApp() *cobra.Command {
 			}
 			logrus.SetLevel(lvl)
 		}
+
+		logFormat, _ := cmd.Flags().GetString("log-format")
+		switch logFormat {
+		case "json":
+			formatter := new(logrus.JSONFormatter)
+			logrus.StandardLogger().SetFormatter(formatter)
+		case "text":
+			// logrus use text format by default.
+			if runtime.GOOS == "windows" && isatty.IsCygwinTerminal(os.Stderr.Fd()) {
+				formatter := new(logrus.TextFormatter)
+				// the default setting does not recognize cygwin on windows
+				formatter.ForceColors = true
+				logrus.StandardLogger().SetFormatter(formatter)
+			}
+		default:
+			return fmt.Errorf("unsupported log-format: %q", logFormat)
+		}
+
 		debug, _ := cmd.Flags().GetBool("debug")
 		if debug {
 			logrus.SetLevel(logrus.DebugLevel)
@@ -83,12 +102,6 @@ func newApp() *cobra.Command {
 			return errors.New("limactl is running under rosetta, please reinstall lima with native arch")
 		}
 
-		if runtime.GOOS == "windows" && isatty.IsCygwinTerminal(os.Stderr.Fd()) {
-			formatter := new(logrus.TextFormatter)
-			// the default setting does not recognize cygwin on windows
-			formatter.ForceColors = true
-			logrus.StandardLogger().SetFormatter(formatter)
-		}
 		if os.Geteuid() == 0 && cmd.Name() != "generate-doc" {
 			return errors.New("must not run as the root user")
 		}