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

Read part of a message asynchronously.

    class DynamicBuffer,
    class ReadHandler>
    DynamicBuffer& buffer,
    std::size_t limit,
    ReadHandler&& handler);

This function is used to asynchronously read part of a message from the stream. The function call always returns immediately. The asynchronous operation will continue until one of the following is true:

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 reads until this operation completes.

Received message data, if any, is appended to the input area of 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. The function websocket::stream::is_message_done may be called to determine if the message received by the last read operation is complete.

While this operation is active, the implementation will read incoming control frames and handle them automatically as follows:

Because of the need to handle control frames, asynchronous read operations can cause writes to take place. These writes are managed transparently; callers can still have one active asynchronous read and asynchronous write operation pending simultaneously (a user initiated call to websocket::stream::async_close counts as a write).





A dynamic buffer to hold the message data after any masking or decompression has been applied. This object must remain valid until the handler is called.


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.


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
    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 boost::asio::io_context::post.