Needing to send a JSON request in perl - json

Question

I am having trouble making this work I keep getting a 400 bad request response. Any help is greatly appreciated as this is my first attempt at both coding perl and using JSON. I had to remove some of the sensitive data as this is something for work. The point of this script is to simply hit the URL sending the POST data via JSON and print the response.
#!/usr/bin/perl
use strict;
use warnings;
use LWP::UserAgent;
use HTTP::Request::Common;
use JSON;
my $ua = LWP::UserAgent->new;
my $req = POST 'URL IS HERE';
my $res = $ua->request($req);
my $json = '{"warehouseId": "ID",
"tagMap":
{"cameraId":["Name of camera"]
},
"searchStartTimeStamp": 0,
"searchEndTimeStamp": 100000000000000,
"pageSize": 1,
"client":
{"id": "username",
"type": "person"}
}';
$req->header( 'Content-Type' => 'application/json' );
$req->content( $json );
if ($res->is_success) {
print $req->content( $json );
print $res->content;
} else {
print $res->status_line . "\n";
}
exit 0;

Answer 1

You perform the request before you have fully populated it! This line does the request:
my $res = $ua->request($req);
but a few lines later, you fill some fields:
$req->header( 'Content-Type' => 'application/json' );
$req->content( $json );
Try swapping that around:
my $json = ...;
my $ua = LWP::UserAgent->new;
my $req = POST 'URL IS HERE';
$req->header( 'Content-Type' => 'application/json' );
$req->content( $json );
my $res = $ua->request($req);
Oh, never $res->content. The value of that method is not generally something usable. You always want
$res->decoded_content;