packet templates with and without lib.protocol.datagram

no_datagram.lua

local ethernet = require("lib.protocol.ethernet")

MyApp = {}

function MyApp:new ()
   local o = {}

   o.pkt = packet.allocate()

   -- create a header that points into o.pkt
   o.eth = ethernet:new_from_mem(o.pkt.data, ethernet:sizeof())
   -- initialize all static fields, unintialized fields will be garbage
   o.eth:src(ethernet:pton("42:00:00:00:00:42"))
   -- ...

   return setmetatable(o, {__index=MyApp})
end

function MyApp:echo (p_in)
   local in_eth = ethernet:new_from_mem(p_in.data, ethernet:sizeof())
   -- modify self.pkt's ethernet header based on p
   self.eth:dst(in_eth:src())
   -- copy payload to self.pkt
   self.pkt.length = ethernet:sizeof()
   packet.append(self.pkt,
                 p_in.data + ethernet:sizeof(),
                 p_in.length - ethernet:sizeof())
   -- return the packet to transmit
   return packet.clone(self.pkt)
end

with_datagram.lua

local ethernet = require("lib.protocol.ethernet")
local datagram = require("lib.protocol.datagram")

MyApp = {}

function MyApp:new ()
   local o = {}

   o.out_dgram = datagram:new() -- calls packet.allocate internally
   -- push a new header, unspecified fields have sensible defaults.
   o.out_dgram:push(ethernet:new({src=ethernet:pton("42:00:00:00:00:42")}))

   -- "reset" datagram to the beginning of our template (datagram instances
   -- have a new() method that reuses the instance)
   o.out_dgram:new(o.out_dgram:packet())
   -- so we can overlay a header into the packet
   o.out_eth = dgram:parse_match(ethernet)

   -- allocate extra datagram and ethernet header instances for parsing to
   -- avoid allocation in MyApp:echo
   o.in_dgram = datagram:new()
   packet.free(o.in_dgram:packet()) -- don't need it
   o.in_eth = ethernet:new({})

   return setmetatable(o, {__index=MyApp})
end

function MyApp:echo (p_in)
   local in_gram, in_eth = self.in_dgram, self.in_eth
   local out_gram, out_eth = self.out_dgram, self.out_eth

   -- parse
   in_dgram:new(p_in)
   in_dgram:parse_match(in_eth)

   -- copy
   out_eth:dst(in_eth:src())
   out_dgram:payload(in_dgram:data())

   return packet.clone(out_dgram:packet())
end