Updated

local modem = peripheral.find("modem")
local tape = peripheral.find("tape_drive")
local endPos = 1
local control = {1200,1500,1800}
local blockSize = 32768
local state = {0,0}
for k,v in pairs(control) do
  modem.open(v)
end

local function backSeek()
    tape.seek(-tape.getPosition())
end



local function Write(url)
    state[2] = 1
    backSeek()
    local reply = http.get(url, nil, true)
    repeat
        local bytes = {}
        for i=1, blockSize do
            local byte = reply.read()
            if not byte then
                break
            else
                bytes[#bytes+1] = byte
            end
        end
        if #bytes > 0  then
            for i=1, #bytes do
                tape.write(bytes[i])
            end
            sleep(0)
        end
    until not bytes or #bytes <= 0
    endPos = tape.getPosition()
    backSeek()
    state[2] = 0
end

local function stop()
  print("Stopping")
  tape.stop()
end

local function play(A,T)
  print(T.." - "..A)
  tape.play()
  state[1] = 1
end

local function fin()
  print("Awaiting song..")
  tape.stop()
  modem.transmit(control[3],control[3],"ready")
end

local function sync()
  modem.transmit(control[3],control[3],"sync")
end

local function main()
    sync()
  while true do
    local evnt, side, sChan, rChan, msg, dist = os.pullEvent("modem_message")
    local tbl = textutils.unserialize(msg)
    if tbl ~= nil and tbl["URL"] ~= nil then
      local URL = tbl["URL"]
      local Artist = tbl["Artist"]
      local Title = tbl["Title"]
      if rChan == control[1] and string.find(URL,".dfpwm") then
        backSeek()
        Write(URL)
        play(Artist,Title)
      elseif rChan == control[2] and msg == "stop" then
        stop()
      elseif rChan == control[3] and state[1] ~= 1 then
        backSeek()
        Write(URL)
        play(Artist,Title)
      end
      end
    end
end

local function secondary()
  while true do
    if tape.getPosition() >= endPos and state[1] == 1 and state[2] ~= 1 then
      fin()
      backSeek()
    end
    sleep(0.5)
  end
end
parallel.waitForAny(main,secondary)