Why do I get the error "unexpected end of string while parsing JSON string" when decoding a URI-encoded JSON string?

Question

I'm trying to POST some JSON data to my Perl script, but the JSON module seems to be unable to cope with this string:

[{"":"#","jednostka":"","login":"SA"}]

I used encodeURIComponent() in JavaScript, so my string actually looks like this:

[{%22%22:%22#%22,%22jednostka%22:%22%22,%22login%22:%22SA%22}]

Error log:

JSON::PP::decode_error('unexpected end of string while parsing JSON string') called at C:\strawberry\perl\lib/JSON/PP.pm line 837
|   JSON::PP::string() called at C:\strawberry\perl\lib/JSON/PP.pm line 960
|   JSON::PP::object() called at C:\strawberry\perl\lib/JSON/PP.pm line 724
|   JSON::PP::value() called at C:\strawberry\perl\lib/JSON/PP.pm line 907
|   JSON::PP::array() called at C:\strawberry\perl\lib/JSON/PP.pm line 725
|   JSON::PP::value() called at C:\strawberry\perl\lib/JSON/PP.pm line 688
|   JSON::PP::PP_decode_json('JSON::PP=HASH(0xd0c2534)', '[{%22%22:%22#%22,%22jednostka%22:%22%22,%22login%22:%22SA%22}]', 0) called at C:\strawberry\perl\lib/JSON/PP.pm line 148

Answer 1

Do you realise that you ned to escape the data only for GET requests? That's why the function is called encodeURIComponent, because the resulting string is for use within a URL. In POST requests the data is passed in the message body, not in the URL

I see that you're using the JSON::PP module, which works fine with the simple JSON string that you show. Here's an example program that shows the resulting data structure dumped using Data::Dump

Acccording to the error log you're encoding the JSON data when you shouldn't be. If I replace the JSON data below with encodeURIComponent then I get the error message

unexpected end of string while parsing JSON string, at character offset 3 (before "22%22:%22#%22,%22jed...")

which is as you described, and what the error log confirms

use strict;
use warnings 'all';

use JSON::PP;
use Data::Dump;

my $json = '[{"":"#","jednostka":"","login":"SA"}]';

my $data = JSON::PP::decode_json($json);

dd $data;

output

[{ "" => "#", "jednostka" => "", "login" => "SA" }]