boost::span rvalue is not supported by asio::buffers

[ujos]

I have a function that returns a buffer as a span to read the data from socket:

boost::span<std::byte> getRecvBuffer();

When I call tcp::socket::async_receive(asio::buffer(getRecvBuffer())),

socket_.async_receive(asio::buffer(getRecvBuffer()), [](auto&&...) {});

... I get an error:

error: no matching function for call to ‘boost::asio::mutable_buffer::mutable_buffer(const boost::asio::const_buffers_1&)’

The weird thing is that following code compiles:

auto b1 = asio::buffer(getRecvBuffer());

Following code compiles too:

auto buf = client.socketRecvBuffer_.recvBuffer();
socket_.async_receive(asio::buffer(buf), [](auto&&...) {});

It seems in order to create a mutable_buffer, I need a lvalue for the buffer, which makes sense in case of std::vector, but it does not make sense for boost::span.

[sbhutch]

I believe I have come across a related issue (Boost 1.83) where the following code does not work:

std::array buffers {
    boost::asio::buffer(packet1.getPayload()),
    boost::asio::buffer(packet2.getPayload()),
};

boost::asio::read(socket, buffers);

Where the Packet::getPayload signature is:

class Packet {
public:
    boost::span<unsigned char> getPayload();
};

Type deduction on the std::array is:

std::array<boost::asio::const_buffers_1, 2UL> buffers

The boost::asio::read function fails due to the const_buffers_1 deduction. However, if I provide the spans as an lvalue:

auto buffer1 = packet1.getPayload();
auto buffer2 = packet2.getPayload();

std::array buffers {
    boost::asio::buffer(buffer1),
    boost::asio::buffer(buffer2),
};

boost::asio::read(socket, buffers);

Type deduction on the std::array becomes:

std::array<boost::asio::mutable_buffers_1, 2UL> buffers

and all works well.