[log] tracing logger

log/tracing_logger.go

@@ -0,0 +1,76 @@
+package log
+
+import (
+	"fmt"
+
+	"github.com/pkg/errors"
+)
+
+// NewTracingLogger enables tracing by wrapping all errors (if they
+// implement stackTracer interface) in tracedError.
+//
+// All errors returned by https://github.com/pkg/errors implement stackTracer
+// interface.
+//
+// For debugging purposes only as it doubles the amount of allocations.
+func NewTracingLogger(next Logger) Logger {
+	return &tracingLogger{
+		next: next,
+	}
+}
+
+type stackTracer interface {
+	error
+	StackTrace() errors.StackTrace
+}
+
+type tracingLogger struct {
+	next Logger
+}
+
+func (l *tracingLogger) Info(msg string, keyvals ...interface{}) error {
+	return l.next.Info(msg, formatErrors(keyvals)...)
+}
+
+func (l *tracingLogger) Debug(msg string, keyvals ...interface{}) error {
+	return l.next.Debug(msg, formatErrors(keyvals)...)
+}
+
+func (l *tracingLogger) Error(msg string, keyvals ...interface{}) error {
+	return l.next.Error(msg, formatErrors(keyvals)...)
+}
+
+func (l *tracingLogger) With(keyvals ...interface{}) Logger {
+	return &tracingLogger{next: l.next.With(formatErrors(keyvals)...)}
+}
+
+func formatErrors(keyvals []interface{}) []interface{} {
+	newKeyvals := make([]interface{}, len(keyvals))
+	copy(newKeyvals, keyvals)
+	for i := 0; i < len(newKeyvals)-1; i += 2 {
+		if err, ok := newKeyvals[i+1].(stackTracer); ok {
+			newKeyvals[i+1] = tracedError{err}
+		}
+	}
+	return newKeyvals
+}
+
+// tracedError wraps a stackTracer and just makes the Error() result
+// always return a full stack trace.
+type tracedError struct {
+	wrapped stackTracer
+}
+
+var _ stackTracer = tracedError{}
+
+func (t tracedError) StackTrace() errors.StackTrace {
+	return t.wrapped.StackTrace()
+}
+
+func (t tracedError) Cause() error {
+	return t.wrapped
+}
+
+func (t tracedError) Error() string {
+	return fmt.Sprintf("%+v", t.wrapped)
+}