E-invoicing

// The same document, in three formats.
$serializer = new Serializer();
$xml  = $serializer->serialize($quotation, 'xml');    // the official UBL XML
$json = $serializer->serialize($quotation, 'json');   // the "UBL JSON Alternative Representation" of OASIS
$yaml = $serializer->serialize($quotation, 'yaml');   // the same data, in YAML

// And back. The XML does not say which UBL version it is, so you choose it
// (the default is 2.1):
$deserializer = new Deserializer();
$quotation = $deserializer->deserialize($xml, 'xml', ['version' => '2.3']);

// Validate it while it is read, against the official schemas:
$quotation = $deserializer->deserialize($json, 'json', ['validate' => true]);

// Or validate an XML on its own. If it is not valid, it throws a ValidationException
// with the errors that libxml reported.
try {
    (new XmlSchemaValidator())->validate($xml);
} catch (ValidationException $e) {
    foreach ($e->getErrors() as $error) {
        printf("Line %d: %s\n", $error->line, trim($error->message));
    }
}

// XML to a PHP array and back. Attributes go in "@attributes" and the text in "@value".
$document = new XmlDocument();
$document->loadXml($xml);

$array = (new XmlDecoder())->decode($document);
$xml   = (new XmlEncoder())->encode($array)->saveXml();

// Or read the document without converting it, with XPath and with types.
// The text is '0021': the typed reads say what you want it to be.
$reader = $document->getReader();
$reader->requireString('//seller/name');   // 'Seller name'
$reader->getAsInt('//info/number');        // 21
$reader->getString('//info/number');       // '0021'

// The package also validates a document with an XSD, with the errors of libxml
// explained and translated, and gives the canonical XML (C14N).

$loader = new CertificateLoader();
$certificate = $loader->loadFromFile('/path/to/certificate.p12', 'password');

$certificate->getId();               // The identity, for example "12345678-9".
$certificate->getName();
$certificate->getEmail();
$certificate->isActive();            // It is not expired.
$certificate->getExpirationDays();

// Check that it has an ID, in the format that you expect (a regular expression).
// If it does not, it throws a CertificateException that says why.
(new CertificateValidator('/^\d+-[\dK]$/'))->validate($certificate);

// For tests, you can make a self-signed certificate instead of asking for one.
$selfSigned = new SelfSignedCertificate();
$certificate = $loader->loadFromArray($selfSigned->toArray());

// Sign the whole XML, or only the element that has a given ID.
$signedXml = $signatureService->signXml($xml, $certificate);
$signedXml = $signatureService->signXml($xml, $certificate, 'elementId');

// Validate a signed XML. You get one result for each signature in the document, and
// you check each one. It throws a SignatureException only if the XML is malformed
// or if it has no signature at all.
foreach ($signatureService->validateXml($signedXml) as $signature) {
    if (!$signature->isValid()) {
        echo $signature->getError()?->getMessage();
    }
}

// The XML signature is an enveloped signature, with canonical XML 1.0, RSA-SHA1
// and a SHA1 digest. The certificate goes inside the signature.

// Plain data can be signed too, with any algorithm that OpenSSL offers.
$signature = $signatureService->sign($data, $privateKey, OPENSSL_ALGO_SHA256);
$valid = $signatureService->validate($data, $signature, $publicKey, OPENSSL_ALGO_SHA256);