API command to fix ALPHANUMERIC source numbers received from mod_gsmopen

sms_bcd2gsm.lua

-- API command to fix ALPHANUMERIC source numbers received from mod_gsmopen
-- Usage: <action application="set" data="from=${lua(sms_bcd2gsm.lua ${from})}" />
-- !! Do not forget that for resending uses not `from` header but `from_full`.
--
-- https://github.com/moteus/lua-tpdu
--

assert(stream, 'this is API command')

local tut      = require "tpdu.utils"
local Bit7     = require "tpdu.bit7"
local Bcd      = require "tpdu.bcd"

local function split_first(str, sep, plain)
  local e, e2 = string.find(str, sep, nil, plain)
  if e then
    return string.sub(str, 1, e - 1), string.sub(str, e2 + 1)
  end
  return str
end

-- mod_gsmopen incorrectly decode ALPHANUMERIC numbers as BCD
-- so we revert it back and decode as Bit7/Gsm encoded string
local function fixup_number(number)
  -- we really can not be sure what type of number we have because we have no access
  -- to TOA structure. So we can only guess
  --
  -- 1. if string has non digit symbols
  -- 2. if string has only hex symbols
  -- 3. all symbols in string have same case
  -- 4. sting length is even
  if string.find(number,'%D')
    and string.match(number, '^%x+$')
    and ((string.upper(number) == number) or (string.lower(number) == number))
    and (#number % 2 == 0)
  then
    number = Bit7.GsmDecode ( tut.hex2bin( Bcd.Decode(number) ) )
  end
  return number
end

local function fixup_from(from)
  local user, host, proto = split_first(from, '@', true)
  proto, user = split_first(user, ':', true)
  if not user then user, proto = proto end
  user = fixup_number(user)
  if host then user = user .. '@' .. host end
  if proto then user = proto .. ':' .. user end
  return user
end

local number = assert(argv[1])
local fixed  = fixup_from(number)

freeswitch.consoleLog('debug', string.format('[sms_bcd2gsm] `%s` => `%s`\n', number, fixed))

stream:write(fixed)