feat(logging): add a new flag for preprending a prefix to each field in the logs (close #659)

pkg/modules/logging/logging.go

@@ -32,8 +32,9 @@ const (
 
 // Logging is a module which implements the gotenberg.LoggerProvider interface.
 type Logging struct {
-	level  string
-	format string
+	level        string
+	format       string
+	fieldsPrefix string
 }
 
 // Descriptor returns a Logging's module descriptor.
@@ -42,8 +43,9 @@ func (Logging) Descriptor() gotenberg.ModuleDescriptor {
 		ID: "logging",
 		FlagSet: func() *flag.FlagSet {
 			fs := flag.NewFlagSet("logging", flag.ExitOnError)
-			fs.String("log-level", infoLoggingLevel, fmt.Sprintf("Set the log level - %s, %s, %s, or %s", errorLoggingLevel, warnLoggingLevel, infoLoggingLevel, debugLoggingLevel))
-			fs.String("log-format", autoLoggingFormat, fmt.Sprintf("Set log format - %s, %s, or %s", autoLoggingFormat, jsonLoggingFormat, textLoggingFormat))
+			fs.String("log-level", infoLoggingLevel, fmt.Sprintf("Choose the level of logging detail. Options include %s, %s, %s, or %s", errorLoggingLevel, warnLoggingLevel, infoLoggingLevel, debugLoggingLevel))
+			fs.String("log-format", autoLoggingFormat, fmt.Sprintf("Specify the format of logging. Options include %s, %s, or %s", autoLoggingFormat, jsonLoggingFormat, textLoggingFormat))
+			fs.String("log-fields-prefix", "", "Prepend a specified prefix to each field in the logs")
 
 			return fs
 		}(),
@@ -57,6 +59,7 @@ func (log *Logging) Provision(ctx *gotenberg.Context) error {
 
 	log.level = flags.MustString("log-level")
 	log.format = flags.MustString("log-format")
+	log.fieldsPrefix = flags.MustString("log-fields-prefix")
 
 	return nil
 }
@@ -101,29 +104,64 @@ func (log Logging) Logger(mod gotenberg.Module) (*zap.Logger, error) {
 			return nil, fmt.Errorf("get log encoder: %w", err)
 		}
 
-		core := zapcore.NewCore(encoder, os.Stderr, lvl)
-		logger = zap.New(core)
-
-		// nolint
-		defer logger.Sync()
+		logger = zap.New(customCore{
+			Core:         zapcore.NewCore(encoder, os.Stderr, lvl),
+			fieldsPrefix: log.fieldsPrefix,
+		})
 	}
 
 	return logger.Named(mod.Descriptor().ID), nil
 }
 
-func newLogLevel(level string) (zapcore.Level, error) {
-	switch level {
-	case errorLoggingLevel:
-		return zap.ErrorLevel, nil
-	case warnLoggingLevel:
-		return zap.WarnLevel, nil
-	case infoLoggingLevel:
-		return zap.InfoLevel, nil
-	case debugLoggingLevel:
-		return zap.DebugLevel, nil
-	default:
-		return -2, fmt.Errorf("%s is not a recognized log level", level)
+// See https://github.com/gotenberg/gotenberg/issues/659.
+type customCore struct {
+	zapcore.Core
+	fieldsPrefix string
+}
+
+func (c customCore) With(fields []zapcore.Field) zapcore.Core {
+	if c.fieldsPrefix != "" {
+		for i := range fields {
+			fields[i].Key = c.fieldsPrefix + "_" + fields[i].Key
+		}
 	}
+
+	return customCore{
+		Core:         c.Core.With(fields),
+		fieldsPrefix: c.fieldsPrefix,
+	}
+}
+
+func (c customCore) Check(ent zapcore.Entry, ce *zapcore.CheckedEntry) *zapcore.CheckedEntry {
+	// This is a copy from the zapcore.ioCore implementation. Indeed, by doing
+	// so, we are able to prefix the fields given to the logger methods like
+	// Debug, Info, Warn, Error, etc.
+	if c.Enabled(ent.Level) {
+		return ce.AddCore(ent, c)
+	}
+
+	return ce
+}
+
+func (c customCore) Write(entry zapcore.Entry, fields []zapcore.Field) error {
+	if c.fieldsPrefix != "" {
+		for i := range fields {
+			fields[i].Key = c.fieldsPrefix + "_" + fields[i].Key
+		}
+	}
+
+	return c.Core.Write(entry, fields)
+}
+
+func newLogLevel(level string) (zapcore.Level, error) {
+	lvl := zapcore.InvalidLevel
+
+	err := lvl.UnmarshalText([]byte(level))
+	if err != nil {
+		return lvl, fmt.Errorf("%q is not a recognized log level: %w", level, err)
+	}
+
+	return lvl, nil
 }
 
 func newLogEncoder(format string) (zapcore.Encoder, error) {
@@ -158,6 +196,7 @@ func newLogEncoder(format string) (zapcore.Encoder, error) {
 	}
 }
 
+// Singleton so that we instantiate our logger only once.
 var logger *zap.Logger = nil
 
 // Interface guards.
@@ -166,4 +205,5 @@ var (
 	_ gotenberg.Provisioner    = (*Logging)(nil)
 	_ gotenberg.Validator      = (*Logging)(nil)
 	_ gotenberg.LoggerProvider = (*Logging)(nil)
+	_ zapcore.Core             = (*customCore)(nil)
 )