json_decode returns NULL for a string variable

Question

I met a really weird problem on json_decode, with this code:

$url="http://localhost:8983/solr/db/select?wt=json&rows=1&q=94305";
$string=file_get_contents($url);
echo $string; echo '<br><br>';
$json=json_decode($string);
var_dump($json);

I got the following result:

{"responseHeader":{"status":0,"QTime":0,"params":{"q":"94305","wt":"json","rows":"1"}},"response":{"numFound":165,"start":0,"docs":[{"price":"","tags":"ATMs","phone_n":"","location":"37.42409897,-122.1709976 ","store":"Discover ATM","store_id":"478602","state":"CA","latitude":"37.42409897","address":"459 LAGUNITA","zipcode_n":"94305","longitude":"-122.1709976\r","url":"Discover_ATM_459_LAGUNITA_Stanford_CA_94305","city":"Stanford","category":"ATMs","text":["","CA","459 LAGUNITA","94305","Stanford"],"spell":["Discover ATM"]}]}}

NULL

It seems that I cannot json_decode this string. However, when I do like this (copy the output of the string above and put it to $string directly):

$string='{"responseHeader":{"status":0,"QTime":0,"params":{"q":"94305","wt":"json","rows":"1"}},"response":{"numFound":165,"start":0,"docs":[{"price":"","tags":"ATMs","phone_n":"","location":"37.42409897,-122.1709976 ","store":"Discover ATM","store_id":"478602","state":"CA","latitude":"37.42409897","address":"459 LAGUNITA","zipcode_n":"94305","longitude":"-122.1709976\r","url":"Discover_ATM_459_LAGUNITA_Stanford_CA_94305","city":"Stanford","category":"ATMs","text":["","CA","459 LAGUNITA","94305","Stanford"],"spell":["Discover ATM"]}]}}';
$json=json_decode($string);
var_dump($json);

json_decode works. Why json_decode get NULL at the first part while works properly here?

First check if error occurred in parsing the json data with the code i posted in the answer. Where is the data coming from exactly? — Navneet Singh
– Navneet Singh, Commented Dec 19, 2012 at 8:02
I already checked the BOM before I post this. print_r prints the exact same thing with echo. — user570494
– user570494, Commented Dec 19, 2012 at 8:13

Ja͢ck · Accepted Answer · 2012-12-19 09:00:45Z

4

Your code looks okay, so let's take one step closer and investigate what $output really is. It helps to choose a representation that can handle ASCII ranges that you can't see.

echo bin2hex($output);

That will give a huge string, but you'll be mostly interested in the front and back of the string.

If that seems kosher, you can create an in-between representation:

echo preg_replace('@[\x00-\x1f\x7f-\xff]@e', '" (0x" . dechex(ord("\\0")) . ") "', $output);

It replaces any character in the lower or higher ASCII range with a hexadecimal representation, making it somewhat easier to spot them :)

Update

From your investigation based on the above, your string seems to contain a carriage return - \r - somewhere in the middle.

"CA","latitude":"37.42409897","
                            ^

You can remove those with a preg_replace() if it can't be solved in another way.

preg_replace("/\r(?!\n)/", '', $output);

That removes any \r not followed by a \n.

edited Dec 19, 2012 at 9:00

answered Dec 19, 2012 at 8:39

Ja͢ck

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4 Comments

user570494 Over a year ago

There is some difference in the middle: 370d222c vs 3720222c

Ja͢ck Over a year ago

@user570494 Not sure why you have a carriage return in the middle there, but it might be causing issues ... I've updated my answer with a hackish solution .. it's better to know why solr gives you that result in the first place.

user570494 Over a year ago

preg_replace("/\r(?!\n)/", '', $output); works! Thank you so much!

Ja͢ck Over a year ago

@user570494 Seriously weird! :) I would do some more thorough research on why solr would give you those results ;-)

Navneet Singh · Accepted Answer · 2012-12-19 08:26:28Z

3

There may be some NULL bytes in the string

Remove it using

$string = trim($string, "\x0");
$json=json_decode($string);
var_dump($json);

Change the Content type to json on this page http://localhost:8983/solr/db/select?wt=json&rows=1&q=94305

header('Content-type:application/json; charset=utf-8');

Remove BOM (Byte Order mark)

if (substr($string, 0,3) == pack("CCC",0xef,0xbb,0xbf)) { 
$string = substr($string, 3); 
}

Check if error occurred in parsing the json data

   $json_errors = array(
         JSON_ERROR_NONE => 'No error has occurred',
         JSON_ERROR_DEPTH => 'The maximum stack depth has been exceeded',
         JSON_ERROR_CTRL_CHAR => 'Control character error, possibly incorrectly encoded',
         JSON_ERROR_SYNTAX => 'Syntax error',
        );
        echo 'Last error : ',

 $json_errors[json_last_error()], PHP_EOL, PHP_EOL;

edited Dec 19, 2012 at 8:26

answered Dec 19, 2012 at 8:04

Navneet Singh

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8 Comments

user570494 Over a year ago

Tried $string = trim($string, "\x0");, no luck.

user570494 Over a year ago

I tried it on another server, it got " Last error : Syntax error "

user570494 Over a year ago

The content type is set as json.

user570494 Over a year ago

No luck with removing BOM. (there is no BOM).

Navneet Singh Over a year ago

then the last thing you can do is by matching the bin2hex of received json string with bin2hex of actual json string , Check this function

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