Re: [Tarantool-patches] [PATCH 2/3] lua/log: allow to use json formatter early

[Oleg Babin <olegrok@tarantool.org>]

Hi! Thanks for your answers.

On 02/07/2020 10:27, Cyrill Gorcunov wrote:
> On Wed, Jul 01, 2020 at 01:01:43PM +0300, Oleg Babin wrote:
>> tarantool> log.cfg{log = ' syslog:identity=test', format = 'json'}
>> IllegalParams: expecting a file name or a prefix, such as '|', 'pipe:',
>> 'syslog:'
>> failed to initialize logging subsystem
>>
>> ```
> File a bug please. Lets be clear -- our config parsing code is
> far from being user friendly, hopefully we will make it more
> convenient with time. I'm pretty sure that using lua language
> for parsing config params was wrong from the very beginning
> (especially when we start to allow config procedure via
> modules and to sync data between box config and module config
> we've to provide some internal "api", this is utter crap but
> imposible to fix without remake of the whole config engine.
> I expect we will do so eventually).
https://github.com/tarantool/tarantool/issues/5130
>> It should be a simple error but not panic. I've just add a space in log
>> parameter.
>>
>> At the same time:
>>
>> ```
>>
>> tarantool> box.cfg{log = ' syslog:'}
>> ---
>> - error: 'Incorrect value for option ''log'': expecting a file name or a
>> prefix, such
>>      as ''|'', ''pipe:'', ''syslog:'''
>> ...
>>
>> ```
> Yup.
>
>>> @@ -459,13 +459,13 @@ local function prepare_cfg(cfg, default_cfg, template_cfg,
>>>                                module_cfg[k], modify_cfg[k], readable_name)
>>>            elseif template_cfg[k] == 'module' then
>>>                local old_value = module_cfg[k].cfg_get(k, v)
>>> -            module_cfg_backup[k] = old_value
>>> +            module_cfg_backup[k] = old_value or box.NULL
>> Could you please clarify this change? I see below you check "value ==
>> box.NULL" but if value is simple nil then such condition is true.
>>
>> ```
> The key moment is that Lua treats box.NULL in a special way.
>
> tarantool> a={log=box.NULL}
> ---
> ...
>
> tarantool> a
> ---
> - log: null
> ...
>
> tarantool> a={log=nil}
> ---
> ...
>
> tarantool> a
> ---
> - []
> ...
>
>
> IOW, when you set up some key to nil it gets vanished.
> But when configuration fails I need to restore log=nil
> if it were so (because setting cfg entries doesn't go
> in one pass but instead one by one). Thus imagine we
> set up log="syslog:" and made some mistake in format
> key, I need to walk over backed up values and setup
> them back.
Thanks for the explanation.