Regarding your question about extracting fields from the XML string. I don't know.

There are perl modules for sure such as XML::Parser.

But for JSON it is that simple from cpan's JSON page and this http://www.perlmonks.org/?node_id=1138138 for utf8-related problems:

use warnings;
use utf8;

binmode STDOUT, ":utf8";

use JSON;
use MIME::Base64;
use Data::Dumper;

die("exactly 1 param is needed.") unless scalar(@ARGV) == 1;

my $params_str_base64 = $ARGV[0];
my $json_str = MIME::Base64::decode_base64($params_str_base64);
my $params_as_perl = JSON::from_json($json_str);

print Dumper($params_as_perl);
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