user memory allocation in read and write callbacks

[AchaInChina]

hello，I have some suggestions，can we add the last custom allocated memory address to the stream req to help determine whether to automatically reclaim the memory or let the user reclaim it in the read and write callbacks.

[AchaInChina]

Hello everyone, in some scenarios, such as IOT gateways, there are many connected devices, 10,000+, and it is a bit wasteful to allocate new memory each time it is received. In session design, each link can be allocated a ring buffer, so that the performance may be better.