More JSON handling routines in LMS builds?

[Paul Webster]

Philippe's recent post about Crypto reminded me of this.

I'd like something that would allow me to specify json in a similar way to how XPath does for XML.
I think this would allow me to remove code I have that checks for certain elements being present in a received JSON document and instead move it out to a configuration file that checks an XPath-like definition.

In my messy code I have a bunch of if/then/else statements testing the received json from various radio stations to determine which format it is in so that I can subsequently parse it correctly.
I have made the subsequent parsing code simpler than it used to be by having song & programme field names in a config file per station group.

I could put real Perl code in the config files and then eval it but I don't think that is a good way of doing things.

If I could put a XPath like statement in there as well then I could simplify things further.

Perhaps JSON::Path ... it looks to me like it has a lot of dependencies that are currently not met in standard LMS installation and I think some are not pure Perl so would mean compiling and packaging binaries for the various platforms which is something I don't really want to get into.

[mherger]

> I'd like something that would allow me to specify json in a similar way
> to how XPath does for XML.

I'm not familiar with XPath. Can you elaborate what you're trying to do?

[Paul Webster]

I would like to replace lots of bits of code that are variants on

if (ref($perl_data) ne "ARRAY" && 
    exists $perl_data->{"data"} && 
      exists $perl_data->{"data"}->{"TitleDiffusions"} && ref($perl_data->{"data"}->{"TitleDiffusions"}) eq "ARRAY" )

with something in my config file that results in something like
my @paths = [ '$root/TitleDiffusions[0]' ];


Then the if statement becomes something like ...

my $matched = true;
foreach my $path ( @paths ){
    my $jpath = JSON::Path->new($path);
    

    $matched = false  if $jpath->values($perl_data) == 0;

}

if ( $matched ){
 // process it
etc
etc
}

Another "if" looks like this ...

if (ref($perl_data) ne "ARRAY" && 
			  exists $perl_data->{"id_playlst"} && exists $perl_data->{"update_tm"} && 
			  exists $perl_data->{"itms"} && ref($perl_data->{"itms"}) eq "ARRAY" )

which would become

$paths = [
                '$root/id_playlst',
                '$root/update_tm',
                '$root/itms[0]',
              ];

[mherger]

Ah, ok, that makes a lot of sense. I've been thinking about how to
simplify this, too. But I was looking at it from a JS perspective, where
lodash is a very popular library (see eg.
https://lodash.com/docs/4.17.15#get). The problem I'm seeing with this
approach is that a user would have to have the latest LMS in order to
run your plugin.

[Paul Webster]

I could make my own mini-parser that only handles the specifics that I care about rather than using an all encompassing one.
Then I could have my own syntax and possibly include an OR operator which I could make use of but would not get from the module I referred to.

So ignore this for now and I'll experiment.