Function echo_once

example/cpp17/coroutines_ts/refactored_echo_server.cpp:26–31

namespace this_coro = boost::asio::this_coro;

awaitable<void> echo_once(tcp::socket& socket)
{
  char data[128];
  std::size_t n = co_await socket.async_read_some(boost::asio::buffer(data), use_awaitable);
  co_await async_write(socket, boost::asio::buffer(data, n), use_awaitable);
}

awaitable<void> echo(tcp::socket socket)
{