Add reserve() methods to dynamic buffers

[mst7555]

It seems that async_read_some triggers the handler for every 0.5k chunk of data - is there a way to control size of it ?

[vinniefalco]

Are you talking about http::async_read_some? That can be indirectly controlled by the choice of dynamic buffer. Which one are you using?

[mst7555]

Yes it is http::async_read_some and I currently use boost::beast::flat_buffer.

[vinniefalco]

We have confirmed the problem you are experiencing. What you need is to call flat_buffer::reserve to ensure a certain minimum capacity before calling async_read_some (or async_read). Unfortunately, that function does not exist yet. But you can use this function as a work-around:

/** Guarantee a minimum capacity.

    Any buffers obtained using @ref data or @prepare will be invalidated.

    @param n The desired minimum capacity. The actual capacity upon return may
        be greater than this value.
*/
template<class Allocator>
void reserve(boost::beast::basic_flat_buffer<Allocator>& b, std::size_t n)
{
    if(n < b.capacity())
        return;
    if(b.size() > 0 && b.size() >= b.capacity())
        return;
    if(n >= b.max_size())
        return;
    b.prepare(n - b.size());
    BOOST_ASSERT(b.capacity() >= n);
}

I'll add this as a member function but it won't ship until Boost 1.70

[mst7555]

Great! Thanks for a very quick response! I've tried your code and modified it to make it work.
First problem was bad parameter type of the buffer - there should be:
void reserve(boost::beast::basic_flat_buffer<Allocator>& b, std::size_t n)
Another thing was that initially both b.size() and b.capacity() for flat_buffer returns 0 what fulfils 2nd if condition preventing reserve() from doing anything. I've changed it to:
if (b.size() > 0 && b.size() >= b.capacity())
And everything started to work as expected!
Cheers!

[vinniefalco]

I've edited my response to incorporate your changes, thanks!