--Simple test that shows how awful the net library is, and what makes it so impractical as a 'usermessage' alernative in source.
--The problems in the 'net' library stem from the fact that it sends it's queue out a frame earlier than usermessages, so they're received, and handled first.
--Because source engine relies on usermessages for entity creation, and everything else there's no guarentee.
--That these objects that should exist when the message is received, do exist on the client.
--This is NOT PVS related, there are cases with 'usermessage' when the object that's created is too far and it is,
--But not in this case, the object can be created on the server BEFORE the server sends out the net-msg,
--And at-least 1 frame before the client receives the usermessage telling it that this entity has been created,
--The 'net' library has already received, and handled it's message, this creates problems like:

--1) You will have to use timer.Simple(0, function() end) needlessy throughout your script when sending information
--  about a new entity over the network via the 'net' library. (And even this isn't reliable w/ the net library, umsg guarentees delivery order.)
--2) All source-object related networking functions don't guarentee that the client has knowledge of this object existing
--  before handling the received 'net' msg that contains info about said object.

if SERVER then
    hook.Add("PlayerSpawn", "NETMSGSUCKS::PlayerSpawn", function(player)
        local ent = ents.Create("prop_physics")
        ent:SetModel("models/error.mdl")
        ent:SetPos(player:GetPos())
        ent:Spawn()
        net.Start("test")
            net.WriteEntity(ent)
        net.Send(player)
        umsg.Start("test", player)
            umsg.Entity(ent)
        umsg.End()
    end)
end

if CLIENT then
    net.Receive("test", function(len)
        print("Net: " .. tostring(IsValid(net.ReadEntity))
    end)

    umsg.Hook("test", function(msg) --msg being our bf_read object. (Part of source engine.)
        print("Umsg: "tostring(msg:ReadEntity()))
    end)
ebd