Calculate size in bytes of JSON payload including it in the JSON payload in PHP

Question

I have to send data using JSON in a structure like this:

$JSONDATA= 
    array(
        'response' => true, 
        'error' => null,
        'payload' => 
            array(
                'content' => $content,
                'size' => $size 
                )
        );

NOTE: the variable $content is a dynamic associative array, so its size is not constant. The JSON output is sent using the classical system:

$joutput=json_encode($JSONDATA,JSON_NUMERIC_CHECK);
echo $joutput;

The question is: how can I evaluate the variable $size dynamically and include it in the output?

You can't reliably embed the size of a string in the string as a string because that data will change the length of the string and the length of the string will change that data. Use the Content-Length: HTTP header instead. — Sammitch
– Sammitch, Commented Jan 4, 2019 at 16:09

mega6382 · Accepted Answer · 2019-01-04 16:07:40Z

9

you can use this to calculate $content's size(DEMO):

$size = strlen(json_encode($content, JSON_NUMERIC_CHECK));

This will provide you with the whole length of json_encode()d string of $content. If you want to calculate the size in bytes(if using multibyte characters), this might be more helpful(DEMO):

$size = mb_strlen(json_encode($content, JSON_NUMERIC_CHECK), '8bit');

answered Jan 4, 2019 at 16:07

mega6382

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2 Comments

Power Engineering Over a year ago

It worked fine, @mega6382 ! This is my solution: $t = mb_strlen(json_encode($JSONDATA, JSON_NUMERIC_CHECK), '8bit'); $JSONDATA['payload']['size']=$t+strlen($t); The result is perfect!

Power Engineering Over a year ago

just mentioned your great solution in my last post. Your solution is now accepted!

Power Engineering · Accepted Answer · 2019-01-04 16:26:48Z

3

I guess this will be useful for many others, so I decided to answer to my own question using @mega6382 solution:

// prepare the JSON array 
$JSONDATA= 
array(
    'response' => true, 
    'error' => null,
    'payload' => 
        array(
            'content' => $content,
            'size' => $size 
            )
    );
// evaluate the JSON output size WITHOUT accounting for the size string itself
$t = mb_strlen(json_encode($JSONDATA, JSON_NUMERIC_CHECK), '8bit');
// add the contribution of the size string and update the value
$JSONDATA['payload']['size']=$t+strlen($t);
// output the JSON data
$joutput=json_encode($JSONDATA,JSON_NUMERIC_CHECK);
echo $joutput;

answered Jan 4, 2019 at 16:26

Power Engineering

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Comments

Giorgi Lagidze · Accepted Answer · 2019-01-04 16:03:08Z

1

Part 1. If this doesn't work for you, I'll update the answer after your next error.

$test_1 = memory_get_usage();
$content = array('key'=>'value');
$size = memory_get_usage() - $test_1;

$JSONDATA= 
    array(
        'response' => true, 
        'error' => null,
        'payload' => 
            array(
                'content' => $content,
                'size' => $size 
                )
        );

answered Jan 4, 2019 at 16:03

Giorgi Lagidze

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1 Comment

Power Engineering Over a year ago

Well Giorgi, I've many thanks for your interesting reply, I've tried it and I get a result but unfortunately the numbers are wrong. In other words if I measure the output using the Chrome inspector I get 664 chars (or bytes) but using your method I get only 227 bytes...any clue?

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