Start an asynchronous operation to read a certain amount of data at the specified offset.

template<
    typename AsyncRandomAccessReadDevice,
    typename MutableBufferSequence,
    typename ReadHandler>
void async_read_at(
    AsyncRandomAccessReadDevice & d,
    boost::uint64_t offset,
    const MutableBufferSequence & buffers,
    ReadHandler handler);

template<
    typename AsyncRandomAccessReadDevice,
    typename MutableBufferSequence,
    typename CompletionCondition,
    typename ReadHandler>
void async_read_at(
    AsyncRandomAccessReadDevice & d,
    boost::uint64_t offset,
    const MutableBufferSequence & buffers,
    CompletionCondition completion_condition,
    ReadHandler handler);

template<
    typename AsyncRandomAccessReadDevice,
    typename Allocator,
    typename ReadHandler>
void async_read_at(
    AsyncRandomAccessReadDevice & d,
    boost::uint64_t offset,
    basic_streambuf< Allocator > & b,
    ReadHandler handler);

template<
    typename AsyncRandomAccessReadDevice,
    typename Allocator,
    typename CompletionCondition,
    typename ReadHandler>
void async_read_at(
    AsyncRandomAccessReadDevice & d,
    boost::uint64_t offset,
    basic_streambuf< Allocator > & b,
    CompletionCondition completion_condition,
    ReadHandler handler);