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

How are you parsing the JSON? Have you tried JSON.parse('[{"":"#","jednostka":"","login":"SA"}]') ? — Krishnakumar_Muraleedharan
– Krishnakumar_Muraleedharan, Commented Jul 12, 2016 at 5:58
I'm not sure why you need the encodeURIComponent(). doesn't it work without it? and shouldn't you do decode on the other side? — Ronen Ness
– Ronen Ness, Commented Jul 12, 2016 at 6:14
I can't reproduce the problem, you need to provide an minimal reproducible example — Quentin
– Quentin, Commented Jul 12, 2016 at 6:54

Borodin · Accepted Answer · 2016-07-12 07:06:02Z

3

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" }]

edited Jul 12, 2016 at 7:06

answered Jul 12, 2016 at 6:50

Borodin

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3 Comments

Piotr Bielski Over a year ago

Someone fuction after Encoding change " to %22 that was problem. I need to change value="VALUE " to value='Value'. End no change " to %22 in html.

Piotr Bielski Over a year ago

Other option is replace " to &qout;

Timo Over a year ago

My error was in the text element: I had a return inside the string and after removing the invisible return, the unexpected end of string went.

Trutane · Accepted Answer · 2020-01-25 00:29:58Z

0

Another way to get the "unexpected end of string while parsing JSON string" from Perl's JSON::decode_json() function, is if your JSON file contains trailing commas, like this:

{"widget": {
    "debug": "on",
    "window": {
        "title": "Sample Konfabulator Widget",
        "name": "main_window",
        "width": 500,
        "height": 500,
    }  }}

The JSON specification does not allow a trailing comma (this is unrelated to URI-encoding, btw). You should be able to catch such JSON format violations using JSON::Parse::valid_json().

answered Jan 25, 2020 at 0:29

Trutane

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Comments

raduation · Accepted Answer · 2016-07-12 06:06:24Z

-2

It looks like you're decoding it in Perl, but attempting to decode an empty variable name. Give the first variable a name.

answered Jul 12, 2016 at 6:06

raduation

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