local function record_session() 
    recording_dir = '/tmp/'
    filename = freeswitch_call_uuid .. '.wav'
    recording_filename = string.format('%s%s', recording_dir, filename)
    recording_filename_str = string.format('%s%s', recording_dir, filename)
    if session:ready() then
		session:setInputCallback('onInputCBF', '')
		max_len_secs = 240
		silence_threshold = 500
		silence_secs = 3
		recording_file = session:recordFile(recording_filename, max_len_secs, silence_threshold, silence_secs);
		recording_ended = os.time()
      currently_recording_session = false
  end
end

function onInputCBF(s, _type, obj, arg)
    local k, v = nil, nil
    local _debug = true
    if _debug then
        for k, v in pairs(obj) do
            printSessionFunctions(obj)
            print(string.format('obj k-> %s v->%s\n', tostring(k), tostring(v)))
        end
        if _type == 'table' then
            for k, v in pairs(_type) do
                print(string.format('_type k-> %s v->%s\n', tostring(k), tostring(v)))
            end
        end
        print(string.format('\n(%s == dtmf) and (obj.digit [%s])\n', _type, obj.digit))
    end
    if (_type == "dtmf") then
        return 'break'
    else
        return ''
    end
end

Dial string is :         <action application="bridge" data="{record_waste_resources=true,ignore_early_media=true}sofia/external/${fwdno}"/>