wikimedia / json-codec
Interfaces to serialize and deserialize PHP objects to/from JSON
Requires
- php: >=7.4.3
- psr/container: ^1.1.2|^2.0.2
- symfony/polyfill-php81: ^1.27.0
Requires (Dev)
- mediawiki/mediawiki-codesniffer: 43.0.0
- mediawiki/mediawiki-phan-config: 0.14.0
- mediawiki/minus-x: 1.1.1
- ockcyp/covers-validator: 1.6.0
- php-parallel-lint/php-console-highlighter: 1.0.0
- php-parallel-lint/php-parallel-lint: 1.4.0
- phpunit/phpunit: 9.6.16
- wikimedia/assert: ^0.5.1
- wikimedia/update-history: 1.0.1
README
JsonCodec
Interfaces to serialize and deserialize PHP objects to/from JSON.
Additional documentation about this library can be found on mediawiki.org.
Usage
To make an object serializable/deserializable to/from JSON, the
simplest way is to use the JsonCodecableTrait
and implement two
methods in your class, toJsonArray()
and the static method
newFromJsonArray()
:
use Wikimedia\JsonCodec\JsonCodecable; class SampleObject implements JsonCodecable { use JsonCodecableTrait; /** @var string */ public string $property; // .... // Implement JsonCodecable using the JsonCodecableTrait /** @inheritDoc */ public function toJsonArray(): array { return [ 'property' => $this->property, ]; } /** @inheritDoc */ public static function newFromJsonArray( array $json ): SampleObject { return new SampleObject( $json['property'] ); } }
A slightly more complicated version of this example can be found in
tests/SampleObject.php
.
If your class requires explicit management -- for example, object
instances need to be created using a factory service, you can
implement JsonCodecable
directly:
use Wikimedia\JsonCodec\JsonCodecable; class ManagedObject implements JsonCodecable { public static function jsonClassCodec( ContainerInterface $serviceContainer ) { $factory = $serviceContainer->get( 'MyObjectFactory' ); return new class( $factory ) implements JsonClassCodec { // ... public function toJsonArray( $obj ): array { // ... } public function newFromJsonArray( string $className, array $json ): ManagedObject { return $this->factory->create( $json[....] ); } }; } }
A full example can be found in
tests/ManagedObject.php
.
Note that array returned by toJsonArray()
can include other
JsonCodecable
objects, which will be recursively serialized.
When newFromJsonArray
is called during deserialization, all
of these recursively included objects will already have been
deserialized back into objects.
To serialize an object to JSON, use JsonCodec
:
use Wikimedia\JsonCodec\JsonCodec; $services = ... your global services object, or null ...; $codec = new JsonCodec( $services ); $string_result = $codec->toJsonString( $someComplexValue ); $someComplexValue = $codec->newFromJsonString( $string_result );
In some cases you want to embed this output into another context,
or to pretty-print the output using non-default json_encode
options.
In these cases it can be useful to have access to methods which
return or accept the array form of the encoding, just before
json encoding/decoding:
$array_result = $codec->toJsonArray( $someComplexValue ); var_export($array_result); // pretty-print $request->jsonResponse( [ 'error': false, 'embedded': $array_result ] ); $someComplexValue = $codec->fromJsonArray( $data['embedded'] );
Handling "non-codecable" objects
In some cases you want to be able to serialize/deserialize third-party
objects which don't implement JsonCodecable. This can be done using
the JsonCodec method ::addCodecFor()
which allows the creator of
the JsonCodec
instance to specify a JsonClassCodec
to use for
an arbitrary class name. For example:
use Wikimedia\JsonCodec\JsonCodec; $codec = new JsonCodec( ...optional services object... ); $codec->addCodecFor( \DocumentFragment::class, new MyDOMSerializer() ); $string_result = $codec->toJsonString( $someComplexValue );
This is done by default to provide a serializer for stdClass
objects.
If adding class codecs one-by-one is not sufficient, for example if
you wish to add support for all objects implementing some
alternate serialization interface, you can subclass JsonCodec
and
override the protected JsonCodec::codecFor()
method to return
an appropriate codec. Your code should look like this:
class MyCustomJsonCodec extends JsonCodec { protected function codecFor( string $className ): ?JsonClassCodec { $codec = parent::codecFor( $className ); if ($codec === null && is_a($className, MyOwnSerializationType::class, true)) { $codec = new MyCustomSerializer(); // Cache this for future use $this->addCodecFor( $className, $codec ); } return $codec; } }
A full example can be found in
tests/AlternateCodec.php
.
More concise output
By default JsonCodec embeds the class name of the appropriate object
type into the JSON output to enable reliable deserialization. In some
applications, however, concise JSON output is desired. By providing
an optional "class hint" to the top-level call to ::toJsonArray()
and
newFromJsonArray()
and implementing the ::jsonClassHintFor()
method in your class codec you can suppress unnecessary type
information in the JSON when your provided hint matches what would
have been added. For example:
class SampleContainerObject implements JsonCodecable {
use JsonCodecableTrait;
/** @var mixed */
public $contents;
/** @var list<Foo> */
public array $foos;
// ...
// Implement JsonCodecable using the JsonCodecableTrait
/** @inheritDoc */
public function toJsonArray(): array {
return [ 'contents' => $this->contents, 'foos' => $this->foos ];
}
/** @inheritDoc */
public static function newFromJsonArray( array $json ): SampleContainerObject {
return new SampleContainerObject( $json['contents'], $json['foos'] );
}
/** @inheritDoc */
public static function jsonClassHintFor( string $keyName ) {
if ( $keyName === 'contents' ) {
// Hint that the contained value is a SampleObject. It might be!
return SampleObject::class;
} elseif ( $keyName === 'foos' ) {
// A hint with a modifier
return Hint::build( Foo::class, Hint::LIST );
}
return null;
}
}
You can then generate concise output by providing the proper hints when serializing and deserializing:
use Wikimedia\JsonCodec\JsonCodec;
$codec = new JsonCodec();
$value = new SampleContainerObject( new SampleObject( 'sample' ), ... );
$string_result = $codec->toJsonString( $value, SampleContainerObject::class );
// $string_result is now:
// {"contents":{"property":"sample"},"foos":[...]}'
// with no explicit type information.
// But we need to provide the same class hint when deserializing:
$value = $codec->newFromJsonString( $string_result, SampleContainerObject::class );
Note that the provided value is a hint. If we were to put a value
other than a SampleObject
into the SampleContainerObject
the type
of that value would be embedded into the JSON output, but it would not
break serialization/deserialization.
As illustrated with the foos
property, to indicate a homogenous list
or array of the given type, you can pass Hint::build(...., Hint::LIST)
as the class hint. A stdClass
object where properties
are values of the given type can be hinted with Hint::build(...., Hint::STDCLASS)
.
A full example can be found in
tests/SampleContainerObject.php
.
The Hint::USE_SQUARE
modifier allows ::toJsonArray()
to
return a list (see
array_is_list
)
and have that list encoded as a JSON array, with square []
brackets.
The Hint::ALLOW_OBJECT
modifier ensures that empty objects are
serialized as {}
. It has the side effect that ::toJsonArray()
may
in some cases return an object value instead of the array value
implied from the method name.
The USE_SQUARE
and ALLOW_OBJECT
hints are necessary because
normally JsonCodec
attempts to encode all object values with curly {}
brackets by inserting a _type_
property in the encoded result when
necessary to ensure that the encoded array is never a list.
PHP's json_encode
will use {}
notation for non-list arrays. If you
don't want the added _type_
property added to your encoded result,
then you need to specify whether you prefer []
notation (USE_SQUARE
)
or {}
notation (ALLOW_OBJECT
) to be used in ambiguous cases.
An example with hint modifiers can be found in
tests/SampleList.php
and its associated
test cases.
Where a superclass codec can be used to instantiate objects of
various subclasses the Hint::INHERITED
modifier can be used.
An example of this can be found in
tests/Pet.php
,
tests/Dog.php
, and
tests/Cat.php
and their associated test cases in
tests/JsonCodecTest.php
.
In some cases, ::jsonClassHintFor()
may be inadequate to describe
the implicit typing of the JSON; for example tagged union values or
implicitly-typed objects nested deeply or inside non-homogeneous
arrays. For those use cases a JsonCodecInterface
parameter is
provided to the ::jsonClassCodec()
method. This allows the
serialization/deserialization code to manually encode/decode portions
of its JSON array using an implicit type. More details can be found
in the interface documentation for
src/JsonCodecInterface.php
and a
full example can be found in
tests/TaggedValue.php
.
Further customization of the encoding of class names and class hints
is available using the protected methods JsonCodec::isArrayMarked()
,
JsonCodec::markArray()
and JsonCodec::unmarkArray()
. A full
example can be found in
tests/ReservedKeyCodec.php
.
Running tests
composer install
composer test
History
The JsonCodec concept was first introduced in MediaWiki 1.36.0 (dbdc2a3cd33). It was split out of the MediaWiki codebase and published as an independent library during the MediaWiki 1.41 development cycle, with changes to the API.