Simple Quake 3 "Update" (MOTD) Server Implementation

luaq3update.lua

--------------------------------------------------
-- Simple Quake 3 Update Server Implementation
-- Author: Dion Williams
-- Copyright: 2013 Dion Williams
-- Licence: MIT/X11; Please see README.md
-- Requires: LuaSocket, LuaLogging
--------------------------------------------------

local _VERSION = "LuaQ3Update r2"

-- CONFIGURATION
local hostname = "*" -- "*" means any interface
local port = 29061

-- Load library namespaces
local logging = require("logging")
local socket = require("socket")

local logger = require("logging.console")("%date [%level] %message\n")
logger:setLevel(logging.DEBUG)

-- Setup the local UDP server socket
local function setupSocket()
  if mysock ~= nil then
    -- Release the socket and binding immediately instead of waiting for GC
    mysock:close()
    mysock = nil
  end
  mysock = assert( socket.udp() )
  assert( mysock:setsockname(hostname, port) )
  assert( mysock:settimeout(1) )
  logger:info("Listening socket established on " .. hostname .. ":" .. port)
end

-- Initialize the psuedo-random number generator
local function setupRNG()
  math.randomseed(os.time())
end

-- Return a table of tokens for the given Q3 command string
local function cmdTokenize(text)
  local i = 1
  local t = {}
  while true do
    -- Skip white-space
    i = text:find("%S", i)
    -- If end is reached, return the table
    if i == nil then
      return t
    end
    -- Check if this is a quoted argument
    local thisarg = text:match("^\"[^\"]*\"?", i)
    if thisarg ~= nil then
      i = i + thisarg:len()
      -- Strip the quotes from the argument
      table.insert(t, (thisarg:gsub("[\"]", "")))
    else
      -- Else try to parse an unquoted argument
      thisarg = text:match("[^\"%s]+", i)
      if thisarg ~= nil then
        i = i + thisarg:len()
        table.insert(t, thisarg)
      end
    end
  end
end

-- Command Tokenizer tests
local function testCmdTokenize()
  local cmds = cmdTokenize("foo bar \"abc\" \"test test\" \"herp\"derp \"one\"\"two\" \"broccoli")
  assert(cmds[1] == "foo",        "TEST #1: Unquoted argument")
  assert(cmds[2] == "bar",        "TEST #2: Unquoted argument")
  assert(cmds[3] == "abc",        "TEST #3: Quoted non-spaced argument")
  assert(cmds[4] == "test test",  "TEST #4: Quoted spaced argument")
  assert(cmds[5] == "herp",       "TEST #5: Quoted argument joined to unquoted argument")
  assert(cmds[6] == "derp",       "TEST #6: Unquoted argument joined to quoted argument")
  assert(cmds[7] == "one",        "TEST #7: Quoted argument joined to quoted argument")
  assert(cmds[8] == "two",        "TEST #8: Quoted argument joined to quoted argument")
  assert(cmds[9] == "broccoli",   "TEST #9: Semi-quoted argument cut-off at the end")
  print("Command Tokenizer tests completed")
end

-- Return the key/value pairs of an Info String as a table
local function infoStringToTable(text)
  local i = 1
  local t = {}
  while true do
    -- Seek to the first backslash
    i = text:find("\\", i)
    -- If end is reached, return the table
    if i == nil then
      return t
    end
    -- Read in this key
    local key = text:match("^\\[^\\]*", i)
    if key ~= nil then
      i = i + key:len()
      -- Strip the preceding backslash
      key = key:sub(2)
      
      -- Now read the value for this key
      local value = text:match("^\\[^\\]*", i)
      if value ~= nil then
        i = i + value:len()
        -- Strip the preceding backslash
        value = value:sub(2)
        -- Add it into the table
        t[key] = value
      else
        -- Malformed sequence, return nil
        return nil
      end
    else
      -- Malformed sequence, return nil
      return nil
    end
  end
end

-- Info Table tests
local function testInfoStringToTable()
  local t = infoStringToTable("\\a_key\\a_value")
  assert(t["a_key"] ~= nil,       "TEST #1: a_key doesn't exist")
  assert(t["a_key"] == "a_value", "TEST #2: a_key's value isn't \"a_value\"")
  
  t = infoStringToTable("\\\\test")
  assert(t[""] ~= nil,            "TEST #3: Empty key doesn't exist")
  assert(t[""] == "test",         "TEST #4: Empty key's value isn't \"test\"")
  
  t = infoStringToTable("\\foo\\")
  assert(t["foo"] ~= nil,         "TEST #3: foo doesn't exist")
  assert(t["foo"] == "",          "TEST #4: foo's value isn't \"\"")
  
  t = infoStringToTable("\\k1\\v1\\k2")
  assert(t == nil,                "TEST #7: Orphaned key didn't abort parsing")
  
  t = infoStringToTable("")
  assert(t ~= nil,                "TEST #8: Empty info string didn't return empty table")
  
  print("Info Table tests completed")
end

-- Print keys/values of a table with fixed columns
local function printTable(t)
  local biglen = 0
  if t ~= nil then
    for k,v in pairs(t) do
      if biglen < string.len(k) then
        biglen = string.len(k)
      end
    end
    
    biglen = biglen + 4
    
    for k,v in pairs(t) do
      local len = string.len(k)
      local line = k .. string.rep(" ", biglen-len) .. v
      print(line)
    end
  else
    print("nil")
  end
end

-- Read a line of packet text
local function parseMsgLine(msg, i)
  i = i or 1
  local line = msg:match("^[^%z\255\n]*", i)
  if line ~= nil then
    -- Replace all '%' characters with '.' (only because JKA does this)
    line = line:gsub("[%%]", ".")
    return line
  else
    return nil
  end
end

-- Handle incoming getmotd request packets from clients
local function incomingGetMotd(cmd, fromaddr, fromport)
  if #cmd < 2 then
    return
  end
  
  local infotable = infoStringToTable(cmd[2])
  if infotable == nil then
    return
  end
  
  if infotable["challenge"] == nil then
    logger:debug(fromaddr .. ":" .. fromport .. " GETMOTD, no challenge given")
  else
    logger:debug(fromaddr .. ":" .. fromport .. " GETMOTD, challenge = '" .. infotable["challenge"] .. "'")
    mysock:sendto("\255\255\255\255motd \"\\challenge\\" .. infotable["challenge"] .. "\\motd\\Source FAQ & Interesting Article - JKHub.org\"", fromaddr, fromport)
  end
end

local function main()
  logger:info(_VERSION .. " starting up...")
  setupRNG()
  setupSocket()
  
  while true do
    local msg,fromaddr,fromport = mysock:receivefrom()
    -- Ignore any errors/timeouts
    if msg ~= nil then
      -- Ensure packet begins with \255\255\255\255 and at least one more letter,
      -- and doesn't contain a NUL character
      if msg:find("^\255\255\255\255%a") and not msg:find("%z") then
        --print("Valid packet from " .. fromaddr .. ":" .. fromport .. ", Length: " .. msg:len())
        msg = msg:sub(5)
        -- Parse the first line as a command string
        local line = parseMsgLine(msg)
        if line ~= nil then
          local cmd = cmdTokenize(line)
          if #cmd >= 1 then
            if cmd[1]:lower() == "getmotd" then
              incomingGetMotd(cmd, fromaddr, fromport)
            end
          end
        end
      end
    end
  end
end

-- Run!
main()