[#150] Add dropped logs metric

Signed-off-by: Pavel Pogodaev <p.pogodaev@yadro.com>

cmd/http-gw/settings.go

@@ -182,6 +182,11 @@ var ignore = map[string]struct{}{
 	cmdVersion: {},
 }
 
+type Logger struct {
+	logger *zap.Logger
+	lvl    zap.AtomicLevel
+}
+
 func settings() *viper.Viper {
 	v := viper.New()
 	v.AutomaticEnv()
@@ -418,7 +423,11 @@ func mergeConfig(v *viper.Viper, fileName string) error {
 	return v.MergeConfig(cfgFile)
 }
 
-func pickLogger(v *viper.Viper) (*zap.Logger, zap.AtomicLevel) {
+type LoggerAppSettings interface {
+	DroppedLogsInc()
+}
+
+func pickLogger(v *viper.Viper, settings LoggerAppSettings) *Logger {
 	lvl, err := getLogLevel(v)
 	if err != nil {
 		panic(err)
@@ -428,9 +437,9 @@ func pickLogger(v *viper.Viper) (*zap.Logger, zap.AtomicLevel) {
 
 	switch dest {
 	case destinationStdout:
-		return newStdoutLogger(v, lvl)
+		return newStdoutLogger(v, lvl, settings)
 	case destinationJournald:
-		return newJournaldLogger(v, lvl)
+		return newJournaldLogger(v, lvl, settings)
 	default:
 		panic(fmt.Sprintf("wrong destination for logger: %s", dest))
 	}
@@ -447,18 +456,20 @@ func pickLogger(v *viper.Viper) (*zap.Logger, zap.AtomicLevel) {
 // Logger records a stack trace for all messages at or above fatal level.
 //
 // See also zapcore.Level, zap.NewProductionConfig, zap.AddStacktrace.
-func newStdoutLogger(v *viper.Viper, lvl zapcore.Level) (*zap.Logger, zap.AtomicLevel) {
+func newStdoutLogger(v *viper.Viper, lvl zapcore.Level, settings LoggerAppSettings) *Logger {
 	stdout := zapcore.AddSync(os.Stderr)
 	level := zap.NewAtomicLevelAt(lvl)
 
 	consoleOutCore := zapcore.NewCore(newLogEncoder(), stdout, level)
-	consoleOutCore = samplingEnabling(v, consoleOutCore)
+	consoleOutCore = applyZapCoreMiddlewares(consoleOutCore, v, settings)
 
-	l := zap.New(consoleOutCore, zap.AddStacktrace(zap.NewAtomicLevelAt(zap.FatalLevel)))
-	return l, level
+	return &Logger{
+		logger: zap.New(consoleOutCore, zap.AddStacktrace(zap.NewAtomicLevelAt(zap.FatalLevel))),
+		lvl:    level,
+	}
 }
 
-func newJournaldLogger(v *viper.Viper, lvl zapcore.Level) (*zap.Logger, zap.AtomicLevel) {
+func newJournaldLogger(v *viper.Viper, lvl zapcore.Level, settings LoggerAppSettings) *Logger {
 	level := zap.NewAtomicLevelAt(lvl)
 
 	encoder := zapjournald.NewPartialEncoder(newLogEncoder(), zapjournald.SyslogFields)
@@ -470,11 +481,12 @@ func newJournaldLogger(v *viper.Viper, lvl zapcore.Level) (*zap.Logger, zap.Atom
 		zapjournald.SyslogPid(),
 	})
 
-	coreWithContext = samplingEnabling(v, coreWithContext)
+	coreWithContext = applyZapCoreMiddlewares(coreWithContext, v, settings)
 
-	l := zap.New(coreWithContext, zap.AddStacktrace(zap.NewAtomicLevelAt(zap.FatalLevel)))
-
-	return l, level
+	return &Logger{
+		logger: zap.New(coreWithContext, zap.AddStacktrace(zap.NewAtomicLevelAt(zap.FatalLevel))),
+		lvl:    level,
+	}
 }
 
 func newLogEncoder() zapcore.Encoder {
@@ -484,19 +496,17 @@ func newLogEncoder() zapcore.Encoder {
 	return zapcore.NewConsoleEncoder(c)
 }
 
-func samplingEnabling(v *viper.Viper, core zapcore.Core) zapcore.Core {
-	// Zap samples by logging the first cgfLoggerSamplingInitial entries with a given level
-	// and message within the specified time interval.
-	// In the above config, only the first cgfLoggerSamplingInitial log entries with the same level and message
-	// are recorded in cfgLoggerSamplingInterval interval. Every other log entry will be dropped within the interval since
-	// cfgLoggerSamplingThereafter is specified here.
+func applyZapCoreMiddlewares(core zapcore.Core, v *viper.Viper, settings LoggerAppSettings) zapcore.Core {
 	if v.GetBool(cfgLoggerSamplingEnabled) {
-		core = zapcore.NewSamplerWithOptions(
-			core,
+		core = zapcore.NewSamplerWithOptions(core,
 			v.GetDuration(cfgLoggerSamplingInterval),
 			v.GetInt(cfgLoggerSamplingInitial),
 			v.GetInt(cfgLoggerSamplingThereafter),
-		)
+			zapcore.SamplerHook(func(_ zapcore.Entry, dec zapcore.SamplingDecision) {
+				if dec&zapcore.LogDropped > 0 {
+					settings.DroppedLogsInc()
+				}
+			}))
 	}
 
 	return core