Re: g_log_structured() and introspection

[Ray Strode <halfline gmail com>]

Hey,

> During the talk on GLib's new structured logging API at GUADEC today,
> it was pointed out that g_log_structured() (and the rest of the
> interesting bits of the new structured logging API) are not
> introspectable.
>
> I'm not sure what we can do about this. The API is based around
> GLogField, which is basically a pointer and a length, and hence is not
> introspectable:
>
>     struct _GLogField
>     {
>       const gchar *key;
>       gconstpointer value;
>       gssize length;
>     };

One idea:

1) g_log_variant (GLogLevelFlags log_level, GVariant *variant);

The variant would have to be of type G_VARIANT_TYPE_VARDICT

In javascript for instance it could look like this:

fields = { 'MESSAGE': new GLib.Variant('s', 'checking for optional
sweep modulation'),
              'GLIB_DOMAIN': new GLib.Variant('s', 'Foo'),
              'FOO_STATE': new GLib.Variant('s', JSON.stringify(fooState)),
              'FOO_AGE': new GLib.Variant('u', 3) };

GLib.log_variant(GLib.LogLevelFlags.level_debug, new
GLib.Variant('a{sv}', fields))

which is a little wordy, but not more awful than how dbus is done.
Then Gjs could ship a string only convenience
api like g_log_structured by doing:

GLib.log_structured = function(logDomain, logLevel, stringFields) = {
   fields = {};
   for (let key in stringFields) {
     fields[key] = new GLib.Variant('s', stringFields[key]);
   }
   fields['GLIB_DOMAIN'] = new GLib.Variant('s', logDomain);

   GLib.log_variant(logLevel, new GLib.Variant('a{sv}', fields);
}

then the javascript would be:

GLib.log_structured(GLib.LogLevelFlags.level_debug,
                             { 'MESSAGE': 'checking for optional sweep
modulation',
                               'FOO_STATE': JSON.stringify(fooState)});

(or it could make it variadic like g_log_structured, but that's less
idiomatic for our brand of javascript)

One complication with g_log_variant, is figuring out how to send the
variant off to journald. If you just use g_variant_print, you'll end
up putting quotes around all the strings, which is probably wrong.
It's probably have to unpack the variant manually, with fall back to
g_variant_print

anyway, just an idea.