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

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)
+			}
+		})
+	}
+}