FTP

-----------------------------
--[   Global varibales    ]--
-----------------------------
local protocolRequest = "FTP_request"
local protocolData = "FTP_data"
local protocolArrived = "FTP_arrived"
local messageContinue = "continue"
local messageStop = "stop"

local args = {...}
local debug = true
local modemSide

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--[   Utility Functions   ]--
-----------------------------
local function getWirelessModemSide()
  local sides = rs.getSides()
  local side = nil

  for i = 1, #sides do
    if peripheral.getType(sides[i]) == "modem" then
      if peripheral.wrap(sides[i]).isWireless() then
        side = sides[i]
      end
    end
  end

  return side
end

-----------------------------
--[    Main Functions     ]--
-----------------------------
local function send(targetID, filePath, code)
  -- Checks the targetID variable
  if tonumber(targetID) == nil then
    if debug then print("The ID argument must be a number.") end
    return
  else
    if tonumber(targetID) < 0 then
      if debug then print("The ID argument cannot be lower than 0.") end
      return
    end
  end

  -- Checks the filePath variable
  if not fs.exists(filePath) then
    if debug then print("The file path you specified does not exist.") end
    return
  end
  local file = fs.open(filePath, "r")
  local fileContent = file.readAll()
  file.close()

  -- Sends a request and waits for confirmation of arrival
  local senderID, message, protocol = nil
  local i = 0
  while senderID == nil and i < 10 do
    rednet.send(tonumber(targetID), code, protocolRequest)
    senderID, message, protocol = rednet.receive(protocolArrived, 1)
    i = i + 1
  end
  if senderID == nil and i == 10 then
    if debug then print("We didn't receive a response, not sending any data.") end
    return
  elseif message == messageStop then
    if debug then print("The codes didn't match, not sending any data.") end
    return
  end

  -- Sends the file content and waits for confirmation of arrival
  local senderID, message, protocol = nil
  local i = 0
  while senderID == nil and i < 10 do
    rednet.send(tonumber(targetID), fileContent, protocolData)
    senderID, message, protocol = rednet.receive(protocolArrived, 1)
    i = i + 1
  end
  if i == 10 then
    if debug then print("We didn't receive a response, the data may have not arrived.") end
    return
  end
end
local function receive(time, code)
  -- Checks the time variable
  if tonumber(time) == nil then
    if debug then print("The time argument must be a number.") end
    return
  else
    if tonumber(time) < 0 then
      if debug then print("The time argument cannot be lower than 0.") end
      return
    end
  end

  -- Starts the timer
  local timerID
  if tonumber(time) > 0 then
    timerID = os.startTimer(tonumber(time))
  end

  local fileCount = 0
  while true do
    -- Waits for the next event
    local event, p1, p2, p3 = os.pullEvent()

    if event == "rednet_message" and p3 == protocolRequest then
      if p2 == code then
        -- Sends a message to confirm arrival
        rednet.send(p1, messageContinue, protocolArrived)

        -- Waits for the file content, saves it to a file (if the codes match) and sends a message to confirm arrival
        local senderID, message, protocol = rednet.receive(protocolData, 10)
        rednet.send(senderID, messageStop, protocolArrived)

        local file = fs.open("download" .. fileCount, "w")
        file.write(message)
        file.close()

        if debug then print("A file from computer " .. senderID .. " arrived and was saved in the path \"download" .. fileCount .. "\".") end

        fileCount = fileCount + 1
      else
        -- Sends a message to confirm arrival
        rednet.send(p1, messageStop, protocolArrived)

        if debug then print("A file from computer " .. p1 .. " arrived and was discarded, because the codes didn't match.") end
      end
    elseif event == "key" then
      -- Stops receiving files if the user presses any button
      if debug then print("The user pressed a key, stopped receiving files.") end
      return
    elseif event == "timer" and p1 == timerID then
      -- Stops receiving files if the timer went off
      if debug then print("The time has passed, stopped receiving files.") end
      return
    end
  end
end

-----------------------------
--[        Program        ]--
-----------------------------
-- Opens a wireless modem
modemSide = getWirelessModemSide()
if modemSide == nil then
  if debug then print("Please attach a wireless modem to this computer.") end
  return
else
  rednet.open(modemSide)
end

-- Runs main program
if args[1] == "send" and args[2] ~= nil and args[3] ~= nil and args[4] ~= nil then
  send(args[2], args[3], args[4])
elseif args[1] == "send" and args[2] ~= nil and args[3] ~= nil then
  send(args[2], args[3], "")
elseif args[1] == "receive" and args[2] ~= nil and args[3] ~= nil then
  receive(args[2], args[3])
elseif args[1] == "receive" and args[2] ~= nil then
  receive(args[2], "")
else
  print("Usage (<> required, [] optional):")
  print("  FTP send <ID> <file path> [code]")
  print("    sends <file path> to <ID> (with [code])")
  print("  FTP receive <time> [code]")
  print("    receives files for <time> in seconds and saves")
  print("    them (if they are sent with the right [code])")
  print("    (set <time> to 0 for indefinite file receiving)")
end

-- Closes the wireless modem
rednet.close(modemSide)