Perl -- 'Not a HASH reference' error when using JSON::RPC::Client - perl

Question

I'm a newbie in Perl.
I have a JSON-RPC server running at http://localhost:19000 and I need to call checkEmail() method.
use JSON::RPC::Client;
my $client = new JSON::RPC::Client;
my $url = 'http://localhost:19000';
my $callobj = {
method => 'checkEmail',
params => [ 'rprikhodchenko#gmail.com' ],
};
my $res = $client->call($url, $callobj);
if($res) {
if ($res->is_error) {
print "Error : ", $res->error_message;
}
else {
print $res->result;
}
}
else {
print $client->status_line;
}
When I try to launch it it tells following:
perl ./check_ac.pl
Not a HASH reference at /usr/local/share/perl/5.10.1/JSON/RPC/Client.pm line 193.
UPD:
Full stack-trace:
perl -MCarp::Always ./check_ac.pl
Not a HASH reference at /usr/local/share/perl/5.10.1/JSON/RPC/Client.pm line 193
JSON::RPC::ReturnObject::new('JSON::RPC::ReturnObject', 'HTTP::Response=HASH(0x9938d48)', 'JSON=SCALAR(0x96f1518)') called at /usr/local/share/perl/5.10.1/JSON/RPC/Client.pm line 118
JSON::RPC::Client::call('JSON::RPC::Client=HASH(0x944a818)', 'http://localhost:19000', 'HASH(0x96f1578)') called at ./check_ac.pl line 11

Answer 1

This error means that your JSON-RPC server is not actually one, inasmuch as it does not satisfy requirement 7.3. The error is triggered when JSON::RPC::Client assumes the document returned by the JSON-RPC service is well-formed (i.e., a JSON Object), and this assumptions turns out to have been in error. A bug report to the author of JSON::RPC::Client would be an appropriate way to request better error messaging.
I would attack this sort of problem by finding out what the server was returning that was causing JSON::RPC::Client to choke. Unfortunately, JRC fails to provide adequate hookpoints for finding this out, so you'll have to be a little bit tricky.
I don't like editing external libraries, so I recommend an extend-and-override approach to instrumenting traffic with the JSON-RPC server. Something like this (in check_ac.pl):
use Data::Dumper qw();
package JSON::RPC::InstrumentedClient;
use base 'JSON::RPC::Client';
# This would be better done with Module::Install, but I'm limiting dependencies today.
sub _get {
my ($self, #args) = #_;
return $self->_dump_response($self->SUPER::_get(#args));
}
sub _post {
my ($self, #args) = #_;
return $self->_dump_response($self->SUPER::_post(#args));
}
sub _dump_response {
my ($self, $response) = #_;
warn Data::Dumper::Dump([$response->decoded_content], [qw(content)]);
return $response;
}
package main;
my $client = JSON::RPC::InstrumentedClient->new();
my $url = 'http://localhost:19000';
... # rest of check_ac.pl
This wraps the calls to _get and _post that JSON::RPC::Client makes internally in such a way as to let you examine what the web server actually said in response to the request we made. The above code dumps the text content of the page; this might not be the right thing in your case and will blow up if an error is encountered. It's a debugging aid only, to help you figure out from the client code side what is wrong with the server.
That's enough caveats for now, I think. Good luck.

Answer 2

It seems to be a bug in method new of JSON::RPC::ReturnObject.
sub new {
my ($class, $obj, $json) = #_;
my $content = ( $json || JSON->new->utf8 )->decode( $obj->content );
#...
# line 193
$content->{error} ? $self->is_success(0) : $self->is_success(1);
#...
}
$content's value will be something returned from a JSON::decode() call. But looking at the documentation, it seems that JSON->decode() returns a scalar which could be a number, a string, an array reference, or a hash reference.
Unfortunately, JSON::RPC::ReturnObject->new() doesn't check what sort of thing JSON->decode() returned before trying to access it as a hashref. Given your error, I'm going to go ahead and assume what it got in your case was not one. :-)
I don't know if there's a way to force a fix from your code. I'd recommend contacting the author and letting him know about the issue, and/or filing a bug.