Json_encode is crazy

Wildhoney · 01-18-2008, 05:00 PM

To cut a long story short, I'm wanting to check the return value of the json_encode function - therefore if its false I can throw an exception. What do I find? The lovely json_encode returns false as a string if it fails!

php Code:

$aJson = json_encode($szContent);

if(!$aJson)
{
    throw new Exception('Badly formatted JSON returned');
}

That won't work because it's a string, and I can't typecast it using (bool) because the string will be seen as a true value. Here's the result from var_dump when json_encode fails:

Quote:

string(5) "false"

Does anybody have any idea? I don't want to just do it like the following as that would be very silly indeed.

php Code:

if($aJson == 'false')
{
    
}

Salathe · 01-18-2008, 05:05 PM

What's the $szContent that you're failing to encode? I might be having an attack of the dumbass (lack of caffeine, honestly) but the only time json_encode returns "false" is with a boolean false. I think.

Orc · 01-18-2008, 05:15 PM

What is $szContent?

xenon · 01-18-2008, 05:22 PM

So check it against the string 'false'...

Code:

if( $content === 'false' )
{
    // do ya thang :D
}

Wildhoney · 01-18-2008, 05:34 PM

Yes, $szContent would be false as I've omitted the exception above it to test what happens. So am I okay then? If $szContent is anything but false - which it won't be because it would execute the exception above it, then it WILL return false as a boolean?

Salathe · 01-18-2008, 05:50 PM

json_encode will never return a boolean. If you previously check that the $szContent cannot be FALSE then you might consider it ok to check to see if json_encode returns string "false".

However, if you pass in a non-encodable value (e.g. a resource) the return string won't be "false" but will instead be (string) "null" with an E_WARNING error ([json] (json_encode_r) type is unsupported, encoded as null.).

Depending on your specific scenario, simply checking for string "false" might suffice.

Wildhoney · 01-18-2008, 06:00 PM

Is there a valid reason for it returning a string and not a boolean?

Salathe · 01-18-2008, 06:04 PM

Yep, the reasoning is:

Return as binary string, since the result is 99% likely to be just echo'ed out and we want to avoid overhead of double conversion.

From PHP source for json_encode function

Wildhoney · 01-18-2008, 06:18 PM

What's wrong with NULL?

Salathe · 01-18-2008, 06:47 PM

Well, json_encode will only return "null" in two cases:

If the argument passed in was NULL.
If the argument passed is not JSON encodable.

Therefore, a quick check for errors might be something along the lines of the following :

PHP Code:


			


    // Suppress E_WARNING error if any. 

    $szJson = @json_encode($szContent);



    // If the encoded string is "null" but we didn't pass in NULL

    // then throw the exception.

    if ($szJson === 'null' AND $szContent !== NULL)

    {

        throw new Exception(sprintf(

            'Unable to encode "%s" into JSON format.',

            gettype($szContent)

        ));

    }