Start an asynchronous operation to read a certain amount of data from a stream.

template<
    typename AsyncReadStream,
    typename MutableBufferSequence,
    typename ReadHandler>
void async_read(
    AsyncReadStream & s,
    const MutableBufferSequence & buffers,
    ReadHandler handler);

template<
    typename AsyncReadStream,
    typename MutableBufferSequence,
    typename CompletionCondition,
    typename ReadHandler>
void async_read(
    AsyncReadStream & s,
    const MutableBufferSequence & buffers,
    CompletionCondition completion_condition,
    ReadHandler handler);

template<
    typename AsyncReadStream,
    typename Allocator,
    typename ReadHandler>
void async_read(
    AsyncReadStream & s,
    basic_streambuf< Allocator > & b,
    ReadHandler handler);

template<
    typename AsyncReadStream,
    typename Allocator,
    typename CompletionCondition,
    typename ReadHandler>
void async_read(
    AsyncReadStream & s,
    basic_streambuf< Allocator > & b,
    CompletionCondition completion_condition,
    ReadHandler handler);