internal/debug: add switch to format logs with json (#22207)

adds a flag --log.json which if enabled makes the client format logs with JSON.

internal/debug/flags.go

@@ -41,6 +41,10 @@ var (
 		Usage: "Logging verbosity: 0=silent, 1=error, 2=warn, 3=info, 4=debug, 5=detail",
 		Value: 3,
 	}
+	logjsonFlag = cli.BoolFlag{
+		Name:  "log.json",
+		Usage: "Format logs with JSON",
+	}
 	vmoduleFlag = cli.StringFlag{
 		Name:  "vmodule",
 		Usage: "Per-module verbosity: comma-separated list of <pattern>=<level> (e.g. eth/*=5,p2p=4)",
@@ -114,7 +118,7 @@ var (
 
 // Flags holds all command-line flags required for debugging.
 var Flags = []cli.Flag{
-	verbosityFlag, vmoduleFlag, backtraceAtFlag, debugFlag,
+	verbosityFlag, logjsonFlag, vmoduleFlag, backtraceAtFlag, debugFlag,
 	pprofFlag, pprofAddrFlag, pprofPortFlag, memprofilerateFlag,
 	blockprofilerateFlag, cpuprofileFlag, traceFlag,
 }
@@ -124,24 +128,29 @@ var DeprecatedFlags = []cli.Flag{
 	legacyBlockprofilerateFlag, legacyCpuprofileFlag,
 }
 
-var (
-	ostream log.Handler
-	glogger *log.GlogHandler
-)
+var glogger *log.GlogHandler
 
 func init() {
-	usecolor := (isatty.IsTerminal(os.Stderr.Fd()) || isatty.IsCygwinTerminal(os.Stderr.Fd())) && os.Getenv("TERM") != "dumb"
+	glogger = log.NewGlogHandler(log.StreamHandler(os.Stderr, log.TerminalFormat(false)))
+	glogger.Verbosity(log.LvlInfo)
+	log.Root().SetHandler(glogger)
+}
+
+// Setup initializes profiling and logging based on the CLI flags.
+// It should be called as early as possible in the program.
+func Setup(ctx *cli.Context) error {
+	var ostream log.Handler
 	output := io.Writer(os.Stderr)
+	if ctx.GlobalBool(logjsonFlag.Name) {
+		ostream = log.StreamHandler(output, log.JSONFormat())
+	} else {
+		usecolor := (isatty.IsTerminal(os.Stderr.Fd()) || isatty.IsCygwinTerminal(os.Stderr.Fd())) && os.Getenv("TERM") != "dumb"
 		if usecolor {
 			output = colorable.NewColorableStderr()
 		}
 		ostream = log.StreamHandler(output, log.TerminalFormat(usecolor))
-	glogger = log.NewGlogHandler(ostream)
 	}
-
-// Setup initializes profiling and logging based on the CLI flags.
-// It should be called as early as possible in the program.
-func Setup(ctx *cli.Context) error {
+	glogger.SetHandler(ostream)
 	// logging
 	log.PrintOrigins(ctx.GlobalBool(debugFlag.Name))
 	glogger.Verbosity(log.Lvl(ctx.GlobalInt(verbosityFlag.Name)))