feat(log): add log-std-level-case to control standard output level casing

cmd/gotenberg.go

@@ -49,6 +49,7 @@ func Run() {
 	fs.String("log-fields-prefix", "", "Prepend a specified prefix to each log field key")
 	fs.String("log-std-format", gotenberg.AutoLoggingFormat, "Set the log format for standard output")
 	fs.Bool("log-std-enable-gcp-fields", false, "Use GCP-compatible field names in log output")
+	fs.String("log-std-level-case", gotenberg.LowerLevelCase, "Set the case of the level field in the standard output, either lower or upper")
 
 	// Deprecated logging flags.
 	fs.String("log-format", gotenberg.AutoLoggingFormat, "Set the log format")
@@ -123,6 +124,7 @@ func Run() {
 		LogFieldsPrefix:       parsedFlags.MustString("log-fields-prefix"),
 		LogStdFormat:          parsedFlags.MustDeprecatedString("log-format", "log-std-format"),
 		LogStdEnableGcpFields: parsedFlags.MustDeprecatedBool("log-enable-gcp-fields", "log-std-enable-gcp-fields"),
+		LogStdLevelCase:       parsedFlags.MustString("log-std-level-case"),
 	}
 	// LogLevel uses its own flag, not the format flag.
 	telemetryCfg.LogLevel = parsedFlags.MustString("log-level")

pkg/gotenberg/internal/log/stdhandler.go

@@ -50,7 +50,12 @@ func (h traceContextHandler) WithGroup(name string) slog.Handler {
 }
 
 // NewStdHandler returns a [slog.Handler] instance for the standard output.
-func NewStdHandler(level slog.Level, format string, fieldsPrefix string, enableGcpFields bool) (slog.Handler, error) {
+// upperLevelCase is the value of the level-case setting that keeps the level
+// field uppercase in the standard output. It mirrors gotenberg.UpperLevelCase,
+// duplicated here because the internal log package cannot import gotenberg.
+const upperLevelCase = "upper"
+
+func NewStdHandler(level slog.Level, format string, fieldsPrefix string, enableGcpFields bool, levelCase string) (slog.Handler, error) {
 	// #nosec: G115
 	isTerminal := term.IsTerminal(int(os.Stdout.Fd()))
 
@@ -82,7 +87,11 @@ func NewStdHandler(level slog.Level, format string, fieldsPrefix string, enableG
 				a.Key = "severity"
 				a.Value = slog.StringValue(gcpSeverity(l))
 			default:
-				a.Value = slog.StringValue(strings.ToLower(l.String()))
+				if levelCase == upperLevelCase {
+					a.Value = slog.StringValue(l.String())
+				} else {
+					a.Value = slog.StringValue(strings.ToLower(l.String()))
+				}
 			}
 		}
 

pkg/gotenberg/internal/log/stdhandler_test.go

@@ -0,0 +1,53 @@
+package log
+
+import (
+	"encoding/json"
+	"io"
+	"log/slog"
+	"os"
+	"testing"
+)
+
+func TestNewStdHandler_LevelCase(t *testing.T) {
+	for _, tc := range []struct {
+		name      string
+		levelCase string
+		want      string
+	}{
+		{"lower is the default behavior", "lower", "info"},
+		{"upper keeps slog casing", "upper", "INFO"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			original := os.Stderr
+			reader, writer, err := os.Pipe()
+			if err != nil {
+				t.Fatalf("create pipe: %v", err)
+			}
+			os.Stderr = writer
+			defer func() { os.Stderr = original }()
+
+			handler, err := NewStdHandler(slog.LevelInfo, "json", "", false, tc.levelCase)
+			if err != nil {
+				t.Fatalf("create handler: %v", err)
+			}
+
+			slog.New(handler).Info("hello")
+
+			if err := writer.Close(); err != nil {
+				t.Fatalf("close writer: %v", err)
+			}
+			out, err := io.ReadAll(reader)
+			if err != nil {
+				t.Fatalf("read output: %v", err)
+			}
+
+			var record map[string]any
+			if err := json.Unmarshal(out, &record); err != nil {
+				t.Fatalf("parse log line %q: %v", out, err)
+			}
+			if record["level"] != tc.want {
+				t.Errorf("level = %v, want %v", record["level"], tc.want)
+			}
+		})
+	}
+}

pkg/gotenberg/telemetry.go

@@ -30,6 +30,11 @@ const (
 	DebugLoggingLevel = "debug"
 )
 
+const (
+	LowerLevelCase = "lower"
+	UpperLevelCase = "upper"
+)
+
 // TelemetryConfig gathers the configuration data for Gotenberg's telemetry.
 type TelemetryConfig struct {
 	ServiceName    string
@@ -39,6 +44,7 @@ type TelemetryConfig struct {
 	LogFieldsPrefix       string
 	LogStdFormat          string
 	LogStdEnableGcpFields bool
+	LogStdLevelCase       string
 }
 
 func (cfg TelemetryConfig) slogLevel() slog.Level {
@@ -86,6 +92,16 @@ func (cfg TelemetryConfig) Validate() error {
 		)
 	}
 
+	switch cfg.LogStdLevelCase {
+	case LowerLevelCase, UpperLevelCase:
+		break
+	default:
+		err = errors.Join(
+			err,
+			fmt.Errorf("standard log level case must be either %s or %s", LowerLevelCase, UpperLevelCase),
+		)
+	}
+
 	return err
 }
 
@@ -93,7 +109,7 @@ func (cfg TelemetryConfig) Validate() error {
 func StartTelemetry(cfg TelemetryConfig) (shutdown func(context.Context) error, err error) {
 	var handlers []slog.Handler
 
-	stdHandler, err := log.NewStdHandler(cfg.slogLevel(), cfg.LogStdFormat, cfg.LogFieldsPrefix, cfg.LogStdEnableGcpFields)
+	stdHandler, err := log.NewStdHandler(cfg.slogLevel(), cfg.LogStdFormat, cfg.LogFieldsPrefix, cfg.LogStdEnableGcpFields, cfg.LogStdLevelCase)
 	if err != nil {
 		return nil, fmt.Errorf("get standard logger handler: %w", err)
 	}