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###### websocket::stream::async_read_some (1 of 2 overloads)

Read some message data asynchronously.

<h7> Synopsis </h7>

    template<
        class DynamicBuffer,
        class ReadHandler>
    async_read_some(
        DynamicBuffer& buffer,
        std::size_t limit,
        ReadHandler&& handler);

<h7> Description </h7>

This function is used to asynchronously read some message data. This call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

- Some message data is received.
- A close frame is received. In this case the error indicated by the function will be `websocket::closed`.
- An error occurs.

The algorithm, known as a composed asynchronous operation, is implemented in terms of calls to the next layer's `async_read_some` and `async_write_some` functions. The program must ensure that no other calls to `websocket::stream::read`, `websocket::stream::read_some`, `websocket::stream::async_read`, or `websocket::stream::async_read_some` are performed until this operation completes. Received message data is appended to the buffer. The functions `websocket::stream::got_binary` and `websocket::stream::got_text` may be used to query the stream and determine the type of the last received message. Until the operation completes, the implementation will read incoming control frames and handle them automatically as follows:

- The `websocket::stream::control_callback` will be invoked for each control frame.
- For each received ping frame, a pong frame will be automatically sent.
- If a close frame is received, the WebSocket close procedure is performed. In this case, when the function returns, the error `websocket::closed` will be indicated.

Pong frames and close frames sent by the implementation while the read operation is outstanding do not prevent the application from also writing message data, sending pings, sending pongs, or sending close frames.

<h7> Parameters </h7>

Name | Description
--- | ---
`buffer` | A dynamic buffer to append message data to.
`limit` | An upper limit on the number of bytes this function will append into the buffer. If this value is zero, then a reasonable size will be chosen automatically.

`handler`

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& ec,       // Result of operation
        std::size_t bytes_written   // Number of bytes appended to buffer
    );

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 `net::post`.