logger.lua

-- We require our libraries and modules here
local component = require("component")
local modem = component.modem
local io = require("io")
local event = require("event")
local fs = require("filesystem")

-- This line will allow the user to easily specify how many
-- ports, and messages, we want to use with the program.
local ports, msgs = ...

-- This ensures that the proper amount of arguments are being used,
-- and if not, will display proper usage of running the program
if #({...}) ~= 2 then
  error("Usage: Logger (# of ports to listen to, starting at 1) (# of messages to write to file before program ends.", 0)
  return
end

-- You can ignore this snippet of code, unless you're
-- ping. Or unless you really want to wait half an hour
-- for all ports to open. Luckily if you're running this
-- on a Minecraft server, you will only need to do this once,
-- so long as you set a high enough message count.
if ports == "potato" then
  ports = 65535
end

-- This is to check whether or not the argument being passed
-- as ports is actually a number, and not words or symbols.
if not tonumber(ports) then
  error("The port needs to be a number!",0)
  return
end

-- Same thing as our first check, only here we're checking the
-- messages amount argument.
if not tonumber(msgs) then
  error("The amount of messages needs to be a number!", 0)
  return
end

-- Now, we have to open our ports that we want to listen to.
-- Note the maximum on our range is the variable we defined in our
-- first argument.
for prt = 1,ports do
  modem.open(prt)
end

-- This is where the magic happens. This is where we open our log file, or
-- create one if it doesn't exist, and listen for messages to write to our
-- file until we've caught enough messages to satisfy our second argument.
local h = io.open("Logs.txt", "a")
for n = 1, tonumber(msgs) do
  local _, _, from, port, _, message = event.pull("modem_message")
  print("Got a message from " .. from .. " on port " .. port .. ": " .. tostring(message))
  h:write("Got a message from " .. from .. " on port " .. port .. ": " .. tostring(message) .. "\n")
end

-- Now that we have enough messages, we can close the ports we opened earlier on.
modem.close()
-- Notice I didn't specify a port?  That's because
-- by default in OC, when a port isn't defined, all
-- ports are closed when this method is called.

-- Now we must close our log file to ensure that it saves.
h:close()

-- This lets the user know that the logs were successfully saved.
-- Huzzah!
print("Saved logs to Logs.txt.")