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###### websocket::stream::async_accept (2 of 3 overloads)

Start reading and responding to a WebSocket HTTP Upgrade request.

Synopsis

    template<
        class ConstBufferSequence,
        class AcceptHandler>
    DEDUCED
    async_accept(
        ConstBufferSequence const& buffers,
        AcceptHandler&& handler);

Description

This function is used to asynchronously read an HTTP WebSocket Upgrade request and send the HTTP response. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

- The request is received and the response finishes sending.
- An error occurs on the stream.

This operation is implemented in terms of one or more calls to the next layer's `async_read_some` and `async_write_some` functions, and is known as a composed operation. The program must ensure that the stream performs no other asynchronous operations until this operation completes.

If the stream receives a valid HTTP WebSocket Upgrade request, an HTTP response is sent back indicating a successful upgrade. When the completion handler is invoked, the stream is then ready to send and receive WebSocket protocol frames and messages. If the HTTP Upgrade request is invalid or cannot be satisfied, an HTTP response is sent indicating the reason and status code (typically 400, "Bad Request"). This counts as a failure, and the completion handler will be invoked with a suitable error code set.

The implementation uses fixed size internal storage to receive the request. If the request is too large, the error `websocket::buffer_overflow` will be indicated. Applications that wish to receive larger requests should first read the request using their own buffer and a suitable overload of `http::read` or `http::async_read`, then call `websocket::stream::accept` or `websocket::stream::async_accept` with the request.

Parameters

Name | Description
--- | ---
`buffers` | Caller provided data that has already been received on the stream. This may be used for implementations allowing multiple protocols on the same stream. The buffered data will first be applied to the handshake, and then to received WebSocket frames. The implementation will copy the caller provided data before the function returns.
`handler` | Invoked when the operation completes. The handler may be moved or copied as needed. The equivalent function signature of the handler must be:
     void handler(
        error_code const& ec    // Result of operation
    );
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 `boost::asio::io_context::post`.