That kind of pull is not one of the situations SAMP is designed to address.  It would be possible in principle to define an MType that worked like a pull - but if that's the functionality you want, you might as well save yourself some effort and just use HTTP.  This example necessarily looks a bit complicated/contrived because to show something working you have to set up both ends. But in the places you'd use SAMP for real, a given bit of code would normally just concern itself with either sending or receiving a given message type, not orchestrating both.