what is blocking and non-blocking web server, what difference between both?
Using a blocking socket, execution will wait (ie. "block") until the full socket operation has taken place. So, you can process any results/responses in your code immediately after. These are also called synchronous sockets.
A non-blocking socket operation will allow execution to resume immediately and you can handle the server's response with a callback or event. These are called asynchronous sockets.