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#### async_write

Write all output from a BuffersGenerator asynchronously to a stream.

##### Synopsis

Defined in header `<boost/beast/core/buffers_generator.hpp>`

    template<
        class AsyncWriteStream,
        class BuffersGenerator,
        class CompletionToken = net::default_completion_token_t<executor_type<AsyncWriteStream>>>
    DEDUCED
    async_write(
        AsyncWriteStream& stream,
        BuffersGenerator generator,
        CompletionToken&& token = net::default_completion_token_t< executor_type< AsyncWriteStream > >{});

##### Description

This function is used to write all of the buffers generated by a caller-provided `BuffersGenerator` to a stream. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

- A call to the generator's `is_done` returns `false`.
- An error occurs.

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 writes until this operation completes.

##### Parameters

Name | Description
--- | ---
`stream` | The stream to which the data is to be written. The type must support the SyncWriteStream concept.
`generator` | The generator to use.
`token` | The completion handler to invoke when the operation completes. The implementation takes ownership of the handler by performing a decay-copy. The equivalent function signature of the handler must be:
    void handler(
        error_code const & error,        // result of operation
        std::size_t bytes_transferred   // the number of bytes written to the stream
    );
If the handler has an associated immediate executor, an immediate completion will be dispatched to it. Otherwise, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using `net::post`.

##### See Also

BuffersGenerator