From f5ac9b072122908c45a1cdcbb9796aafe4763ee0 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Fri, 13 Dec 2019 15:06:17 +0200
Subject: [PATCH] lib/logger: add `-loggerFormat` for choosing log message
 formats

Supported formats: default, json

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/265
---
 lib/logger/logger.go | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/lib/logger/logger.go b/lib/logger/logger.go
index 80e7a97a7..f886427f0 100644
--- a/lib/logger/logger.go
+++ b/lib/logger/logger.go
@@ -16,7 +16,10 @@ import (
 	"github.com/VictoriaMetrics/metrics"
 )
 
-var loggerLevel = flag.String("loggerLevel", "INFO", "Minimum level of errors to log. Possible values: INFO, ERROR, FATAL, PANIC")
+var (
+	loggerLevel  = flag.String("loggerLevel", "INFO", "Minimum level of errors to log. Possible values: INFO, ERROR, FATAL, PANIC")
+	loggerFormat = flag.String("loggerFormat", "default", "Format for logs. Possible values: default, json")
+)
 
 // Init initializes the logger.
 //
@@ -25,6 +28,7 @@ var loggerLevel = flag.String("loggerLevel", "INFO", "Minimum level of errors to
 // There is no need in calling Init from tests.
 func Init() {
 	validateLoggerLevel()
+	validateLoggerFormat()
 	go errorsLoggedCleaner()
 	logAllFlags()
 }
@@ -38,6 +42,15 @@ func validateLoggerLevel() {
 	}
 }
 
+func validateLoggerFormat() {
+	switch *loggerFormat {
+	case "default", "json":
+	default:
+		// We cannot use logger.Pancif here, since the logger isn't initialized yet.
+		panic(fmt.Errorf("FATAL: unsupported `-loggerFormat` value: %q; supported values are: default, json", *loggerFormat))
+	}
+}
+
 var stdErrorLogger = log.New(&logWriter{}, "", 0)
 
 // StdErrorLogger returns standard error logger.
@@ -101,7 +114,7 @@ func (lw *logWriter) Write(p []byte) (int, error) {
 }
 
 func logMessage(level, msg string, skipframes int) {
-	timestamp := time.Now().UTC().Format("2006-01-02T15:04:05.000+0000")
+	timestamp := time.Now().UTC().Format("2006-01-02T15:04:05.000Z")
 	levelLowercase := strings.ToLower(level)
 	_, file, line, ok := runtime.Caller(skipframes)
 	if !ok {
@@ -115,7 +128,14 @@ func logMessage(level, msg string, skipframes int) {
 	for len(msg) > 0 && msg[len(msg)-1] == '\n' {
 		msg = msg[:len(msg)-1]
 	}
-	logMsg := fmt.Sprintf("%s\t%s\t%s:%d\t%s\n", timestamp, levelLowercase, file, line, msg)
+	var logMsg string
+	switch *loggerFormat {
+	case "json":
+		caller := fmt.Sprintf("%s:%d", file, line)
+		logMsg = fmt.Sprintf(`{"ts":%q,"level":%q,"caller":%q,"msg":%q}`+"\n", timestamp, levelLowercase, caller, msg)
+	default:
+		logMsg = fmt.Sprintf("%s\t%s\t%s:%d\t%s\n", timestamp, levelLowercase, file, line, msg)
+	}
 
 	// Serialize writes to log.
 	mu.Lock()