Method append

libcaf_net/caf/net/lp/framing.test.cpp:35–39

class buffer {
public:
  void append(std::string str) {
    std::scoped_lock guard{mtx_};
    entries_.emplace_back(std::move(str));
    cv_.notify_all();
  }

  void set_error(error err) {
    std::scoped_lock guard{mtx_};