UpstreamMessage.php

<?php
namespace HMS\PushKit;

use InvalidArgumentException;
use stdClass;

/**
 * Class HMS PushKit Upstream Message
 *
 * @link https://developer.huawei.com/consumer/en/doc/development/HMSCore-References/https-uplink-api-0000001050170915
 * @author Martin Zeitler
 */
class UpstreamMessage {

    private const ENV_VAR_HUAWEI_HMAC_VERIFICATION_KEY = 'Variable ENV_VAR_HUAWEI_HMAC_VERIFICATION_KEY is not set.';

    private string|null $raw_body = null;
    private string|null $hmac_verification_key;
    private string|null $sender_token  = null;
    private string|null $package_name  = null;
    private string|null $message_id    = null;
    private string|false $message_data = false;

    /** Constructor */
    public function __construct( string|null $key ) {
        if ($key == null) {
            throw new InvalidArgumentException(self::ENV_VAR_HUAWEI_HMAC_VERIFICATION_KEY );
        }
        $this->hmac_verification_key = $key;
        // $this->parse_request_body();
    }

    public function getRawBody(): string|null {
        return $this->raw_body;
    }

    public function getSenderToken(): string|null {
        return $this->sender_token;
    }

    public function getPackageName(): string|null {
        return $this->package_name;
    }

    public function getMessageId(): string|null {
        return $this->message_id;
    }

    public function getMessageData(): string|null {
        return $this->message_data;
    }

    /**
     * @param string $from       Token of the app that sends uplink messages.
     * @param string $category   Package name of the app that sends uplink messages.
     * @param string $message_id Unique ID generated by the app for a message.
     * @param string $data       Valid key-value pairs contained in the message.
     *                           The parameter value needs to be encoded using Base64.
     */
    private function parse_request_body(): bool {
        if (isset($_SERVER['X-HW-SIGNATURE']) && !empty($_SERVER['X-HW-SIGNATURE'])) {
            $this->raw_body = stream_get_contents(STDIN);
            if ($this->hmac_verify( $this->raw_body, $_SERVER['X-HW-SIGNATURE'] )) {
                $payload = json_decode( $this->raw_body );
                $this->sender_token = $payload->from;
                $this->package_name = $payload->category;
                $this->message_id   = $payload->message_id;
                $this->message_data = base64_decode($payload->data);
                return true;
            }
        }
        return false;
    }

    /** Concatenate the input string, generate HMAC hash with SHA256 algorithm, then encode as base64. */
    private function generate_signature( int $timestamp, string $nonce, string $data_str ): string {
        $input = $timestamp.$nonce.$data_str;
        $hmac = hash_hmac( 'sha256', $input, $this->hmac_verification_key );
        return base64_encode( $hmac );
    }

    /** Convert the received signature string to object. */
    private function parse_signature( string $signature ): stdClass {
        $input = str_getcsv( $signature, '; ' );
        $data = new stdClass();
        $data->timestamp = (int) str_replace('timestamp=', '', $input[0]);
        $data->nonce  = (string) str_replace(   ' nonce=', '', $input[1]);
        $data->value  = (string) str_replace(   ' value=', '', $input[2]);
        return $data;
    }

    public function hmac_verify( string|null $raw_body, string $signature ): bool {

        if ($raw_body == null) {return false;}

        /* Extract data-string from the raw body. */
        $payload = json_decode( $raw_body );
        $data_str = base64_decode( $payload->data );

        /* Convert the received signature string to object. */
        $signature = $this->parse_signature( $signature );

        /* Generate a signature which to compare to. */
        $generated = $this->generate_signature( $signature->timestamp, $signature->nonce, $data_str );

        /* Compare the generated with the received signature. */
        return $generated === $signature->value;
    }

    public function asObject(): object {
        return (object) [
            'sender_token' => $this->sender_token,
            'package_name' => $this->package_name,
            'message_id'   => $this->message_id,
            'message_data' => $this->message_data
        ];
    }
}