minetest.register_abm( {
    nodenames = { 'hopper:hopper' },
    interval = 1.0,
    chance = 1,
    action = function ( pos, node )
        local fromnode, tonode,
        local frompos = { x = pos.x, y = pos.y, z = pos.z }
        local topos = { x = pos.x, y = pos.y, z = pos.z }
        local facedir = node.param2
        if facedir == 0 then
            frompos.y = frompos.y + 1
            topos.y = topos.y - 1
        elseif facedir == 1 then
            frompos.y = frompos.y + 1
            topos.y = topos.y - 1
        elseif facedir == 2 then
            frompos.y = frompos.y + 1
            topos.y = topos.y - 1
        elseif facedir == 3 then
            frompos.y = frompos.y + 1
            topos.y = topos.y - 1
        end

        fromnode = minetest.get_node( frompos ).name
        tonode = minetest.get_node( topos ).name

        if hopper_transactions[fromnode] and hopper_transactions[tonode] then
            local wl = hopper_transactions[tonode].wishlist
            if wl == nil and hopper_transactions[tonode].get_wishlist ~= nil then
                wl = hopper_transactions[tonode].get_wishlist( topos )
            end
            hopper_transactions[tonode].add(
                topos,
                hopper_transactions[fromnode].get( frompos, wl ),
                function ( thing )
                    hopper_transactions[fromnode].add( frompos, thing )
                end
            )
        end
    end
} )