Re: g_log_structured() and introspection

[Philip Withnall <philip tecnocode co uk>]

Hey,

On Sat, 2016-08-13 at 01:49 -0400, Ray Strode wrote:
> > 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)});

Seems reasonable to me. pygobject, gjs people: how does that look to
you?

> 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

Yeah, the conversion from each a{sv} value to a GLogField value would
be the least satisfying part: I guess we'd do something like:
  if it's a string: use the string directly
  if it's a byte array ('ay'): use the byte array with its length
  if it's anything else: g_variant_print() and hope it looks reasonable

Philip

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