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Copied from wiki.php.net, last synchronized Oct 13, 2026 11:54 UTC
If the name of the function needs to be change, I will change it; the functionality is the important thing here
This RFC introduces a new function called is_json() to validate if an string contains a valid json.
Most userland implementations to achieve this are done using json_decode() which by design generates an object/array while parsing the string, ergo using memory and processing, that could be save.
is_json(string $json, int $depth = 512, int $flags = 0): bool
json
The json string being analyzed.
This function only works with UTF-8 encoded strings.
Note:
PHP implements a superset of JSON as specified in the original » RFC 7159.
depth
Maximum nesting depth of the structure being decoded.
flags
Bitmask of JSON_INVALID_UTF8_IGNORE, JSON_THROW_ON_ERROR. The behavior of these constants is described on the JSON constants page.
Function description, examples, technical strategy, current JSON parser, etc.
Returns true if the string passed contains a valid json, otherwise returns false.
-
-
By design, json_decode() generates an object/array while parsing the string, ergo using memory and processing for it, that is not needed if the only thing to discover is if a string contains a valid json.
Using a regex for this task forces different, error-prone, hard to maintain, implementations.
In the “References” section, there is a list of major open-source php projects needing this feature; also in th mntioned section can find a link to one of the most popular StackOverflow questions, which somehow reflects the need from our developers to have a feature like this included.
At the moment, there is a JSON parser in the core, used by json_decode to do its job, so there is no need to write a new JSON parser for this RFC; the proposed function will use the existing JSON parser exclusively to parse an string without generating any object/array in memory for it.
None, as this is a new function only.
is_json will no longer be available as a function name, could break potential userland implementations.
next PHP 8.x
This RFC has no impact on SAPIs, existing extensions, Opcache, etc.
- No open issues
- (To be defined)
- (To be defined)
- (To be done later after pushing to github)
class JsonValidator extends ConstraintValidator
public function validateJson($attribute, $value)
{
if (is_array($value)) {
return false;
}
if (! is_scalar($value) && ! is_null($value) && ! method_exists($value, '__toString')) {
return false;
}
json_decode($value);
return json_last_error() === JSON_ERROR_NONE;
}
public static function isJson($value)
{
private function getJSONString($input)
{
$output = json_decode($input);
return $output ? $this->_jsonEncoder->encode($output) : '{}';
}
protected function isValidJsonValue($value)
{
if (in_array($value, ['null', 'false', '0', '""', '[]'])
|| (json_decode($value) !== null && json_last_error() === JSON_ERROR_NONE)
) {
return true;
}
//JSON last error reset
json_encode([]);
return false;
}
public function isValid($string)
{
if ($string !== false && $string !== null && $string !== '') {
json_decode($string);
if (json_last_error() === JSON_ERROR_NONE) {
return true;
}
}
return false;
}
public static function validateJson($value, $params)
{
return (bool) (@json_decode($value));
}
public function getPrettyJson()
{
$decoded = json_decode($this->getContent()); //<------ here
return \JSON_ERROR_NONE === json_last_error() ? json_encode($decoded, \JSON_PRETTY_PRINT) : null;
}
final class Json extends AbstractRule
{
/**
* {@inheritDoc}
*/
public function validate($input): bool
{
if (!is_string($input) || $input === '') {
return false;
}
json_decode($input);
return json_last_error() === JSON_ERROR_NONE;
}
}
final class Json extends AbstractRule
{
/**
* {@inheritDoc}
*/
public function validate($input): bool
{
if (!is_string($input) || $input === '') {
return false;
}
json_decode($input);
return json_last_error() === JSON_ERROR_NONE;
}
}
public function actionIndex()
{
Yii::$app->response->statusCode = 204;
if(!SecuritySettings::isReportingEnabled()) {
return;
}
$json_data = file_get_contents('php://input');
if ($json_data = json_decode($json_data)) { //<----- json_decode() just to check if is valid json-string only
$json_data = json_encode($json_data, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);
$json_data = preg_replace('/\'nonce-[^\']*\'/', "'nonce-xxxxxxxxxxxxxxxxxxxxxxxx'", $json_data);
Yii::error($json_data, 'web.security');
}
}
public static function isJson($string)
{
json_decode($string);
return json_last_error() == JSON_ERROR_NONE;
}
function is_json( $argument, $ignore_scalars = true ) {
if ( ! is_string( $argument ) || '' === $argument ) {
return false;
}
if ( $ignore_scalars && ! in_array( $argument[0], [ '{', '[' ], true ) ) {
return false;
}
json_decode( $argument, $assoc = true );
return json_last_error() === JSON_ERROR_NONE;
}
if (\is_string($value)) {
json_decode($value); //<------ HERE
// Check if value is a valid JSON string.
if ($value !== '' && json_last_error() !== JSON_ERROR_NONE) {
/**
* If the value is not empty and is not a valid JSON string,
* it is most likely a custom field created in Joomla 3 and
* the value is a string that contains the file name.
*/
if (is_file(JPATH_ROOT . '/' . $value)) {
$value = '{"imagefile":"' . $value . '","alt_text":""}';
} else {
$value = '';
}
}
In PHP, this question is one of the most high ranked questions related to json && php in stackoverflow, “Fastest way to check if a string is JSON in PHP?”. The question
Viewed 484k times. The ranking
Person asking how to do exactly this, also providing a real use case; eventhough in python, the programming language is not important. In Python
Someone has also doing exactly this , in JAVA. In Java
- No rejected features currently.