async_write (6 of 6 overloads)

Start an asynchronous operation to write a certain amount of data to a stream.

template<
    typename AsyncWriteStream,
    typename Allocator,
    typename CompletionCondition,
    typename WriteHandler>
DEDUCED async_write(
    AsyncWriteStream & s,
    basic_streambuf< Allocator > & b,
    CompletionCondition completion_condition,
    WriteHandler && handler);

This function is used to asynchronously write a certain number of bytes of data to a stream. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

All of the data in the supplied basic_streambuf has been written.
The completion_condition function object returns 0.

This operation is implemented in terms of zero or more calls to the stream's async_write_some function, and is known as a composed operation. The program must ensure that the stream performs no other write operations (such as async_write, the stream's async_write_some function, or any other composed operations that perform writes) until this operation completes.

Parameters

s

The stream to which the data is to be written. The type must support the AsyncWriteStream concept.

b

A basic_streambuf object from which data will be written. Ownership of the streambuf is retained by the caller, which must guarantee that it remains valid until the handler is called.

completion_condition

The function object to be called to determine whether the write operation is complete. The signature of the function object must be:

std::size_t completion_condition(
  // Result of latest async_write_some operation.
  const asio::error_code& error,

  // Number of bytes transferred so far.
  std::size_t bytes_transferred
);

A return value of 0 indicates that the write operation is complete. A non-zero return value indicates the maximum number of bytes to be written on the next call to the stream's async_write_some function.

handler

The handler to be called when the write operation completes. Copies will be made of the handler as required. The function signature of the handler must be:

void handler(
  const asio::error_code& error, // Result of operation.

  std::size_t bytes_transferred           // Number of bytes written from the
                                          // buffers. If an error occurred,
                                          // this will be less than the sum
                                          // of the buffer sizes.
);

Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using asio::io_context::post().