feat(otel): add OpenTelemetry support

pkg/gotenberg/internal/log/handler.go

@@ -0,0 +1,171 @@
+package log
+
+import (
+	"context"
+	"errors"
+	"log/slog"
+)
+
+type gotenbergHandler struct {
+	slog.Handler
+	fieldsPrefix string
+	loggerName   string
+}
+
+func NewGotenbergHandler(next slog.Handler, prefix string) slog.Handler {
+	return &gotenbergHandler{Handler: next, fieldsPrefix: prefix}
+}
+
+func (h *gotenbergHandler) Handle(ctx context.Context, r slog.Record) error {
+	var newAttrs []slog.Attr
+
+	if h.loggerName != "" {
+		newAttrs = append(newAttrs, slog.String("logger", h.loggerName))
+	}
+
+	var needsNewRecord bool
+	if len(newAttrs) > 0 {
+		needsNewRecord = true
+	}
+
+	if h.fieldsPrefix != "" {
+		r.Attrs(func(a slog.Attr) bool {
+			if a.Key == "logger" || a.Key == "correlation_id" || a.Key == "trace_id" || a.Key == "span_id" {
+				newAttrs = append(newAttrs, a)
+				needsNewRecord = true
+				return true
+			}
+			a.Key = h.fieldsPrefix + "_" + a.Key
+			newAttrs = append(newAttrs, a)
+			needsNewRecord = true
+			return true
+		})
+	} else if needsNewRecord {
+		r.Attrs(func(a slog.Attr) bool {
+			newAttrs = append(newAttrs, a)
+			return true
+		})
+	}
+
+	if needsNewRecord {
+		newR := slog.NewRecord(r.Time, r.Level, r.Message, r.PC)
+		newR.AddAttrs(newAttrs...)
+		r = newR
+	}
+
+	return h.Handler.Handle(ctx, r)
+}
+
+func (h *gotenbergHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
+	var prefixed []slog.Attr
+	newLoggerName := h.loggerName
+
+	for _, a := range attrs {
+		if a.Key == "logger" {
+			if newLoggerName == "" {
+				newLoggerName = a.Value.String()
+			} else {
+				newLoggerName = newLoggerName + "." + a.Value.String()
+			}
+			continue
+		}
+
+		if h.fieldsPrefix != "" {
+			if a.Key == "correlation_id" || a.Key == "trace_id" || a.Key == "span_id" {
+				// Don't prefix these keys
+			} else {
+				a.Key = h.fieldsPrefix + "_" + a.Key
+			}
+		}
+		prefixed = append(prefixed, a)
+	}
+
+	newHandler := h.Handler
+	if len(prefixed) > 0 {
+		newHandler = h.Handler.WithAttrs(prefixed)
+	}
+
+	return &gotenbergHandler{
+		Handler:      newHandler,
+		fieldsPrefix: h.fieldsPrefix,
+		loggerName:   newLoggerName,
+	}
+}
+
+func (h *gotenbergHandler) WithGroup(name string) slog.Handler {
+	return &gotenbergHandler{
+		Handler:      h.Handler.WithGroup(name),
+		fieldsPrefix: h.fieldsPrefix,
+		loggerName:   h.loggerName,
+	}
+}
+
+type multiHandler struct {
+	handlers []slog.Handler
+}
+
+func FanOut(handlers ...slog.Handler) slog.Handler {
+	return &multiHandler{handlers: handlers}
+}
+
+func (m *multiHandler) Enabled(ctx context.Context, level slog.Level) bool {
+	for _, h := range m.handlers {
+		if h.Enabled(ctx, level) {
+			return true
+		}
+	}
+	return false
+}
+
+func (m *multiHandler) Handle(ctx context.Context, r slog.Record) error {
+	var errs []error
+	for _, h := range m.handlers {
+		if h.Enabled(ctx, r.Level) {
+			if err := h.Handle(ctx, r.Clone()); err != nil {
+				errs = append(errs, err)
+			}
+		}
+	}
+	return errors.Join(errs...)
+}
+
+func (m *multiHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
+	cloned := make([]slog.Handler, len(m.handlers))
+	for i, h := range m.handlers {
+		cloned[i] = h.WithAttrs(attrs)
+	}
+	return &multiHandler{handlers: cloned}
+}
+
+func (m *multiHandler) WithGroup(name string) slog.Handler {
+	cloned := make([]slog.Handler, len(m.handlers))
+	for i, h := range m.handlers {
+		cloned[i] = h.WithGroup(name)
+	}
+	return &multiHandler{handlers: cloned}
+}
+
+type levelHandler struct {
+	slog.Handler
+	level slog.Level
+}
+
+func LevelFilter(next slog.Handler, level slog.Level) slog.Handler {
+	return &levelHandler{Handler: next, level: level}
+}
+
+func (h *levelHandler) Enabled(ctx context.Context, level slog.Level) bool {
+	return level >= h.level && h.Handler.Enabled(ctx, level)
+}
+
+func (h *levelHandler) Handle(ctx context.Context, r slog.Record) error {
+	return h.Handler.Handle(ctx, r)
+}
+
+func (h *levelHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
+	return &levelHandler{Handler: h.Handler.WithAttrs(attrs), level: h.level}
+}
+
+func (h *levelHandler) WithGroup(name string) slog.Handler {
+	return &levelHandler{Handler: h.Handler.WithGroup(name), level: h.level}
+}