const baggageHeader … type Baggage … var _ … // Inject sets baggage key-values from ctx into the carrier. func (b Baggage) Inject(ctx context.Context, carrier TextMapCarrier) { … } // Extract returns a copy of parent with the baggage from the carrier added. func (b Baggage) Extract(parent context.Context, carrier TextMapCarrier) context.Context { … } // Fields returns the keys who's values are set with Inject. func (b Baggage) Fields() []string { … }