ex26.1.lua

local socket = require "socket"

local function receive (connection)
  connection:settimeout(0)
  -- do not block
  local s, status, partial = connection:receive(2^10)
  if status == "timeout" then
    coroutine.yield(connection)
  end
  return s or partial, status
end

local function download (host, file)
  local c = assert(socket.connect(host, 80))
  local count = 0 -- counts number of bytes read
  local request = string.format(
    "GET %s HTTP/1.0\r\nhost: %s\r\n\r\n", file, host)
  c:send(request)
  while true do
    local s, status = receive(c)
    count = count + #s
    if status == "closed" then break end
  end
  c:close()
  print(file, count)
end

local tasks = {} -- list of all live tasks

local function get (host, file)
  -- create coroutine for a task
  local co = coroutine.wrap(function ()
      download(host, file)
  end)
  -- insert it in the list
  table.insert(tasks, co)
end


local function dispatch ()
  local i = 1
  local timedout = {}
  while true do
    if tasks[i] == nil then
      -- no other tasks?
      if tasks[1] == nil then
        -- list is empty?
        break
        -- break the loop
      end
      i = 1
      -- else restart the loop
      timedout = {}
    end
    local res = tasks[i]()
    -- run a task
    if not res then
      -- task finished?
      table.remove(tasks, i)
    else
      -- time out
      i = i + 1
      timedout[#timedout + 1] = res
      if #timedout == #tasks then
        -- all tasks blocked?
        socket.select(timedout)
        -- wait
      end
    end
  end
end

get("www.lua.org", "/ftp/lua-5.3.1.tar.gz")
-- get("www.lua.org", "/ftp/lua-5.3.0.tar.gz")
-- get("www.lua.org", "/ftp/lua-5.2.4.tar.gz")
-- get("www.lua.org", "/ftp/lua-5.2.3.tar.gz")
-- get("www.lua.org", "/ftp/lua-5.3.2.tar.gz")

dispatch()