wrk-script.lua

-- Global counter through the request cycle.
counter = 0

-- App key, needed for Authentication
APP_KEY="_key_"

-- A warmup needed for lua's math engine, so random can work well.
-- this is suggested by the official docs.
math.randomseed(os.time())
math.random(); math.random(); math.random()

-- We check if file exists first, and we return true here.
function file_exists(file)
  -- local is the variable definition way for scoped/private variable.
  local f = io.open(file, "rb")
  if f then f:close() end
  return f ~= nil
end

-- This is a shuffle method, it takes lines/user_ids, shuffle it and return the ids/lines back
-- lua makes shuffle so easy by just by passing same refs
-- a, b = b, a
function shuffle(user_ids)
  local j, k

  -- the # charachter before any variable gets the lengths of that variable
  -- if it's string like "ahmad" it returns 5.
  local n = #user_ids

  -- yes, foor loops here are a bit weird, but nice, eh?
  for i = 1, n do
    j, k = math.random(n), math.random(n)

    user_ids[j], user_ids[k] = user_ids[k], user_ids[j]
  end

  return user_ids
end

-- Neglect empty_lines if it ever occurs, just another way of validation.
function non_empty_lines_from(file)
  if not file_exists(file) then return {} end

  lines = {}

  for line in io.lines(file) do
    if not (line == '') then
      lines[#lines + 1] = line
    end
  end

  return shuffle(lines)
end

-- Setting the ids in a global and share it between threads
-- we still prone to errors if ids are near 2M because of limitations in luaJit DS limts.
user_ids = nil
setup = function(thread)
  if not user_ids then
    -- global variable contains All file entries.
    user_ids = non_empty_lines_from("user_ids_for_products.txt")
  end

  -- Setting the global in a setup phase and share it between other threads.
  thread:set("user_ids", user_ids)
end

-- On the stat of each thread we do on the fly calcs for the `paths`.
function init(args)
  -- Some validation.
  if #user_ids <= 0 then
    print("No user_ids found. You have to create a file user_ids.txt with one user_id per line")
    os.exit()
  end

  print("multiplepaths: Found " .. #user_ids .. " paths")
end

-- a function to increment our global counter.
function incr_counter()
  counter = counter + 1
  if counter > #user_ids then
    counter = 0
  end
end

-- a function to fetch single user_id based on the counter
function get_user_id()
  local user_id = user_ids[counter]
  if user_id == nil then
    incr_counter()
    user_id = user_ids[counter]
  end

  -- Never forget to increment.
  -- boy
  incr_counter()

  return user_id
end

-- getting multiple user_ids, based on the argument number.
function get_users_ids(ids_counter)
  -- empty array
  local u_ids  = {}

  for i = 1, ids_counter do
    table.insert(u_ids, get_user_id())
  end

  -- A bit tightly coupled to our usage, change to array of strings concatinated by ','
  local ids_string = table.concat(u_ids, ',')

 return ids_string
end

-- Main request function.
request = function()
  local id_counter = math.random(50)
  local ids = get_users_ids(id_counter)

  -- Setting the header for auth.
  wrk.headers["Current-App-Key"] = APP_KEY

  -- building the url params
  status_param = "filter[~status]=active"
  product_type_param = "filter[product_type]=premium_product"
  user_ids_param = "filter[user_id]=" .. ids

  local params = status_param .. "&" .. product_type_param .. "&" ..  user_ids_param
  local path = "/v1/products?" .. params

  return wrk.format(nil, path)
end