@Override
    public final ChannelFuture doWriteTrailers(int id, int streamId, HttpHeaders headers) {
        if (!isWritable(id)) {
            return newClosedSessionFuture();
        }

        return write(id, convertTrailers(headers), true);
    }
The map which maps a request ID to its related pending response.
core/src/main/java/com/linecorp/armeria/internal/common/Http1ObjectEncoder.java