Re: [asio-users] boost/asio/buffer.hpp silent runtime breaking change 1.79->1.80

[Allen <all...@gm...>]

Would your code work correctly on all versions of boost >= 1.66 (which
added buffer.size) if you did this:

size_t chunk_size=min(16, buf.size());
auto buf2= boost::asio::buffer(buf.data(),chunk_size);

Definitely frustrating to work around a breaking change, but better
solution is to get your code working on all versions, IMO.

(FYI, I am not affiliated with boost or asio projects.)

On Sat, Mar 25, 2023, 12:06 AM Marian Klein <mkl...@gm...> wrote:

> Hey guys.
>
> This is my first message on this forum.
> I believed the project follows the principle:
> If the code compiles over the change it has to have the same or
> equivalent meaning at the runtime under any use (or none) of the
> pre-existing preprocessor definitions.
> It is better to break something at compile time over the change rather
> than wasting time debugging applications. Wasting 3 days to cluelessly
> debug an application is no fun.
>
> https://www.boost.org/doc/libs/1_80_0/doc/html/boost_asio/history.html
>
> Asio 1.24.0 / Boost 1.80
> "Added buffer() overloads for contiguous containers, such as std::span".
>
> Example:
> BOOST_ASIO_NO_DEPRECATED is undefined, I use (Visual Studio 2019, x86
> build  C++17 standard enabled)
>
> void  broken(const boost::asio::const_buffer& data)
> {
>   auto buf=boost::asio::buffer(data);//works in 1.79 and in 1.80.1.81,
>   in all versions invokes/uses  correctly boost/asio/buffer.hpp:942
>  //buf is const_buffers_1 type
>
> size_t chunk_size=16;
>  auto buf2= boost::asio::buffer(buf,chunk_size);
>    //for me it works in version 1.79  (intended behaviour getting left
> part of buffer of chunk_size),
>    // the code compiles ,but it does not work the same in 1.80/1.81
>     //invokes boost/asio/buffer.hpp:954 in 1.79 correctly, but
> silently  invokes/calls  new code in boost/asio/buffer.hpp:1705 in
> 1.80/1.81
>     //with buf2 pointing to buff class , rather than its underlying data.
>
> //buf2 is const_buffers_1 type
> }
>
> You should have maintained original binding (as if const_buffer type)
> if the type is both  (sequence of const_buffer of size 1)
> const_buffers_1 and (base class) const_buffer.
>  And new changing behaviour must be requested explicitly with a new define
> BOOST_ASIO_BUFFERS_1_IS_BUFFER_SEQUENCE
> Can you rectify in 1.82 , please?
> Thank you.
> Best Regards
>
> boost/asio/buffer.hpp:954 :
>
> /// Create a new non-modifiable buffer from an existing buffer.
> /**
>  * @returns A const_buffer value equivalent to:
>  * @code const_buffer(
>  *     b.data(),
>  *     min(b.size(), max_size_in_bytes)); @endcode
>  */
> BOOST_ASIO_NODISCARD inline BOOST_ASIO_CONST_BUFFER buffer(
>     const const_buffer& b,
>     std::size_t max_size_in_bytes) BOOST_ASIO_NOEXCEPT
> {
>   return BOOST_ASIO_CONST_BUFFER(b.data(),
>       b.size() < max_size_in_bytes
>       ? b.size() : max_size_in_bytes
> #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
>       , b.get_debug_check()
> #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
>       );
> }
>
>
>
> boost/asio/buffer.hpp:1705:
>
> /// Create a new non-modifiable buffer from a contiguous container.
> /**
>  * @returns A const_buffer value equivalent to:
>  * @code const_buffer(
>  *     data.size() ? &data[0] : 0,
>  *     min(
>  *       data.size() * sizeof(typename T::value_type),
>  *       max_size_in_bytes)); @endcode
>  */
> template <typename T>
> BOOST_ASIO_NODISCARD inline BOOST_ASIO_CONST_BUFFER buffer(
>     const T& data, std::size_t max_size_in_bytes,
>     typename constraint<
>       is_contiguous_iterator<typename T::const_iterator>::value,
>       defaulted_constraint
>     >::type = defaulted_constraint()) BOOST_ASIO_NOEXCEPT
> {
>   return BOOST_ASIO_CONST_BUFFER(
>       data.size() ? detail::to_address(data.begin()) : 0,
>       data.size() * sizeof(typename T::value_type) < max_size_in_bytes
>       ? data.size() * sizeof(typename T::value_type) : max_size_in_bytes);
> }
>
>
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