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Spot
Spot

Reputation: 8155

How to determine whether a string is valid JSON?

Does anyone know of a robust (and bullet proof) is_JSON function snippet for PHP? I (obviously) have a situation where I need to know if a string is JSON or not.

Hmm, perhaps run it through a JSONLint request/response, but that seems a bit overkill.

Upvotes: 48

Views: 93696

Answers (8)

jcmargentina
jcmargentina

Reputation: 321

json_validate() is available since PHP 8.3.

Upvotes: 1

COil
COil

Reputation: 7606

Finally! As of PHP 8.3 one can use the new json_validate() function:

$fixtures = [
    // Not valid
    'foo',
    '{foo: bar}',
    "'{'foo': 'bar'}",
    '{...}',

    // Valid
    '"foo"',
    '1',
    '{"foo": "bar"}',
];

foreach ($fixtures as $string) {
    if (json_validate($string)) {
        echo sprintf('YES, >%s< is a valid JSON string', $string).PHP_EOL;
        echo 'decoded: '. var_export(json_decode($string), true).PHP_EOL;
    } else {
        echo sprintf('NO, >%s< is NOT a valid JSON string: %s', $string, json_last_error_msg()). PHP_EOL;
    }
}

This function only accepts a string as the first argument: output of this snippet

Upvotes: 0

Mohsin Hassan
Mohsin Hassan

Reputation: 81

This is the best and efficient way 

function isJson($string) {
    return (json_decode($string) == null) ? false : true;
}

Upvotes: 4

Daff
Daff

Reputation: 44215

If you are using the built in json_decode PHP function, json_last_error returns the last error (e.g. JSON_ERROR_SYNTAX when your string wasn't JSON).

Usually json_decode returns null anyway.

Upvotes: 70

cgaldiolo
cgaldiolo

Reputation: 3867

For my projects I use this function (please read the "Note" on the json_decode() docs).

Passing the same arguments you would pass to json_decode() you can detect specific application "errors" (e.g. depth errors)

With PHP >= 5.6

// PHP >= 5.6
function is_JSON(...$args) {
    json_decode(...$args);
    return (json_last_error()===JSON_ERROR_NONE);
}

With PHP >= 5.3

// PHP >= 5.3
function is_JSON() {
    call_user_func_array('json_decode',func_get_args());
    return (json_last_error()===JSON_ERROR_NONE);
}

Usage example:

$mystring = '{"param":"value"}';
if (is_JSON($mystring)) {
    echo "Valid JSON string";
} else {
    $error = json_last_error_msg();
    echo "Not valid JSON string ($error)";
}

Upvotes: 21

Kitson
Kitson

Reputation: 1678

Doesn't json_decode() with a json_last_error() work for you? Are you looking for just a method to say "does this look like JSON" or actually validate it? json_decode() would be the only way to effectively validate it within PHP.

Upvotes: 4

McNally Paulo
McNally Paulo

Reputation: 191

$this->post_data = json_decode( stripslashes( $post_data ) );
  if( $this->post_data === NULL )
   {
   die( '{"status":false,"msg":"The post_data parameter must be valid JSON"}' );
   }

Upvotes: 2

Pascal MARTIN
Pascal MARTIN

Reputation: 401182

What about using json_decode, which should return null if the given string was not valid JSON-encoded data ?

See example 3 on the manual page :

// the following strings are valid JavaScript but not valid JSON

// the name and value must be enclosed in double quotes
// single quotes are not valid 
$bad_json = "{ 'bar': 'baz' }";
json_decode($bad_json); // null

// the name must be enclosed in double quotes
$bad_json = '{ bar: "baz" }';
json_decode($bad_json); // null

// trailing commas are not allowed
$bad_json = '{ bar: "baz", }';
json_decode($bad_json); // null

Upvotes: 17

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