Multinet

function split(str, pat)
    local t = {}  -- NOTE: use {n = 0} in Lua-5.0
    if str ~= nil then
       local fpat = "(.-)" .. pat
       local last_end = 1
       local s, e, cap = str:find(fpat, 1)
       while s do
          if s ~= 1 or cap ~= "" then
         table.insert(t,cap)
          end
          last_end = e+1
          s, e, cap = str:find(fpat, last_end)
       end
       if last_end <= #str then
          cap = str:sub(last_end)
          table.insert(t, cap)
       end
    else
        print("##ERROR failed to split ["..str.."] by:"..pat)
    end
    return t
end

local function getTableSize(table)
    local sz = 0
    for k,v in pairs(table) do
        sz = sz + 1
    end
    return sz
end

function unformatTable(string, join)
    return split(string, join)
end

function formatTable(table, join, start)
    if start == nil then start = 1 end
    local str = ""
    for i=start,#table do
        if i == start then str = table[i] else str = str..join..table[i] end
    end
    return str
end

function formatComplexTable(table, join, op)
    local str = ""
    for k,v in pairs(table) do
        if type(v) ~= "function" and type(v) ~= "nil" then
            if str == "" then
                str = k..op..v
            else
                str = str..join..k..op..v
            end
        end
    end
    return str
end

function unformatComplexTable(string, join, op)
    local table = split(string, join)
    local ntable = {}
    for i=1,#table do
        local splt = split(table[i], op)
        if splt[1] ~= nil then
            ntable[splt[1]] = splt[2]
        end
    end
    return ntable
end

function createServer(sname, sid)
    local server = {
        name = sname,
        id = sid,
        users = { },
        data = { },
        getPlayerList = function(self)
            local list = {}
            for k,v in pairs(self.users) do
                list[#list + 1] = k
            end
            return list
        end,
        sendPlayerList = function(self, player)
            local p = self.users[player]
            if p ~= nil then
                rednet.send(p[1], formatTable(self:getPlayerList(), "#@#"))
            end
        end,
        getUsers = function(self)
            return self.users
        end,
        addPlayer = function(self, player, id, data)
            self:getUsers()[player] = {id, data}
        end,
        removePlayer = function(self, player)
            local users = self.users
            if users == nil then users = {} end
            users[player] = nil
            self.users = users
        end,
        addSData = function(self, name, info)
            local data = self.data
            if data == nil then data = {} end
            data[name] = info
            self.data = data
        end,
        getSData = function(self)
            local val = self.data
            if val ~= nil then
                val = formatComplexTable(val, "#@#", "#=#")
                return val
            end
            return nil
        end,
        getPlayer = function(self, id)
            local users = self.users
            if users == nil then users = {} end
            for k,v in pairs(users) do
                if v[1] == id then return k end
            end
            self.users = users
            return nil
        end,
        getID = function(self, player)
            local users = self.users
            if users == nil then users = {} end
            local p = users[player]
            if p ~= nil then return p[1] else
                return nil
            end
            self.users = users
        end,
        getData = function(self, player)
            local users = self.users
            if users == nil then users = {} end
            local p = users[player]
            if p ~= nil then return p[2] else
                return data
            end
            self.users = users
        end,
        setData = function(self, player, data)
            local users = self.users
            if users == nil then users = {} end
            local p = users[player]
            if p ~= nil then
                p[2] = data
            end
            self.users = users
        end,
        pingUsers = function(self, info)
            local users = self.users
            if users == nil then users = {} end
            for k,v in pairs(users) do
                rednet.send(v[1], info)
            end
            self.users = users
        end,
        waitForCommand = function(self)
            local id, message, distance = rednet.receive()
            local users = self.users
            if users == nil then users = {} end
            local data = self.data
            if data == nil then data = {} end

            local typ = nil
            if id ~= nil then
                if message:sub(1, 5) == "JOIN " then
                    local splt = split(message, " ")
                    local name = formatTable(splt, " ", 2)
                    users[name] = { id, {} }
                    typ = 1
                elseif message == "LEAVE" then
                    self:removePlayer(self:getPlayer(id))
                    typ = 2
                elseif message == "GET_DATA" then
                    if self:getPlayer(id) ~= nil then
                        local player = self:getPlayer(id)
                        local dat = self:getData(player)
                        if dat ~= nil then
                            rednet.send(id, formatTable(dat, "#@#"))
                            typ = 3
                        end
                    end
                elseif message:sub(1, string.len("SET_DATA ")) == "SET_DATA " then
                    local type = 11
                    if self:getPlayer(id) ~= nil then
                        local splt = split(message, " ")
                        local ftabl = formatTable(splt, " ", 2)
                        local table = unformatTable(ftabl, "#@#")
                        if table ~= nil then
                            self.setData(self, self:getPlayer(id), table)
                            typ = 8
                        end
                    end
                elseif message == "GET_PLAYERLIST" then
                    if self:getPlayer(id) ~= nil then
                        local fmt = formatTable(self:getPlayerList(), "#@#")
                        rednet.send(id, "PLS::"..fmt)
                        typ = 4
                    end
                elseif message == "@#@GET_NAME@#@" then
                    rednet.send(id, "~S~"..self.name)
                    typ = 5
                elseif message == "GET_SERVER_DATA" then
                    if self:getPlayer(id) ~= nil then
                        rednet.send(id, self:getSData())
                        typ = 6
                    end
                elseif message:sub(1, string.len("SET_SERVER_DATA@#@")) == "SET_SERVER_DATA@#@" then
                    if self:getPlayer(id) ~= nil then
                        local splt = split(message, "@#@")
                        local piece = splt[3]
                        local name = splt[2]
                        if name == "#LEN#" then name = #data end
                        if name == "#LEN+#" then name = #data + 1 end
                        self:addSData(name, piece)
                        typ = 7
                    end
                end
            end
            if typ ~= nil then
                return tonumber(typ)
            else
                return "INVALID"
            end
            self.users = users
            self.data = data
        end,
    }
    return server
end

function createUser(uname, sname, uid, sid)
    local user = {
        name = uname,
        id = uid,
        server_name = sname,
        server_id = sid,
        joinServer = function(self)
            rednet.send(self.server_id, "JOIN "..self.name)
        end,
        leaveServer = function(self)
            rednet.send(self.server_id, "LEAVE")
        end,
        getPlayerList = function(self)
            rednet.send(self.server_id, "GET_PLAYERLIST")
            local id, message, distance = rednet.receive()
            local typ = string.sub(message, 1, 5)
            message = message:sub(6, -1)
            local n = 1
            while id ~= self.server_id and typ ~= "PLS::" and n < 20 do
                id, message, distance = rednet.receive()
                typ = string.sub(message, 1, 5)
                message = message:sub(6, -1)
                n = n + 1
            end
            if n < 20 then
                return unformatTable(message, "#@#")
            end
            return nil
        end,
        getData = function(self)
            rednet.send(self.server_id, "GET_DATA")
            local id, message, distance = rednet.receive()
            if id == self.server_id then
                return unformatTable(message, "#@#")
            end
            return nil
        end,
        setData = function(self, table)
            rednet.send(self.server_id, "SET_DATA "..formatTable(table, "#@#", 1))
        end,
        getSData = function(self)
            rednet.send(self.server_id, "GET_SERVER_DATA")
            local id, message, distance = rednet.receive()
            if id == self.server_id then
                return unformatComplexTable(message, "#@#", "#=#")
            end
            return nil
        end,
        setSData = function(self, name, piece)
            rednet.send(self.server_id, "SET_SERVER_DATA@#@"..name.."@#@"..piece)
        end,
        waitForPing = function(self)
            local id, message, distance = rednet.receive()
            if id ~= nil and id == self.server_id then
                return message
            end
            return nil
        end,
        isFromServer = function(self, id)
            return id == self.server_id
        end,
    }
    return user
end

function getServers()
    local servers = {}
    local n = 0
    local i = 0
    local ok = true
    rednet.broadcast("@#@GET_NAME@#@")
    while ok and i < 500 do
        local id, message, distance = rednet.receive(2)
        if id ~= nil then
            local str = message:sub(1, 3)
            if str == "~S~" then
                local sname = message:sub(4, -1)
                servers[sname] = id
                n = 0
            else
                n = n + 1
                if n > 5 then ok = false end
            end
        else
            ok = false
        end
        i = i + 1
    end
    return servers
end