I need to convert some node.js code to work with PHP. I know there are pack() and unpack() functions and I think they may do the job but I don't know the correct way to do it in PHP. I got this code from https://web-push-book.gauntface.com/ and trying to do this in PHP.
const keyLabel = new Buffer('P-256\0', 'utf8');
// Convert subscription public key into a buffer.
const subscriptionPubKey = new Buffer(subscription.keys.p256dh, 'base64');
const subscriptionPubKeyLength = new Uint8Array(2);
subscriptionPubKeyLength[0] = 0;
subscriptionPubKeyLength[1] = subscriptionPubKey.length;
const localPublicKeyLength = new Uint8Array(2);
subscriptionPubKeyLength[0] = 0;
subscriptionPubKeyLength[1] = localPublicKey.length;
const contextBuffer = Buffer.concat([
keyLabel,
subscriptionPubKeyLength.buffer,
subscriptionPubKey,
localPublicKeyLength.buffer,
localPublicKey,
]);
const nonceEncBuffer = new Buffer('Content-Encoding: nonce\0', 'utf8');
const nonceInfo = Buffer.concat([nonceEncBuffer, contextBuffer]);
const cekEncBuffer = new Buffer('Content-Encoding: aesgcm\0');
const cekInfo = Buffer.concat([cekEncBuffer, contextBuffer]);