Peek at the incoming data on the stream. Returns the number of bytes read. Throws an exception on failure.

template<
    typename MutableBufferSequence>
std::size_t peek(
    const MutableBufferSequence & buffers);
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Peek at the incoming data on the stream. Returns the number of bytes read, or 0 if an error occurred.

template<
    typename MutableBufferSequence>
std::size_t peek(
    const MutableBufferSequence & buffers,
    asio::error_code & ec);
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