gpstools/endpoint.php

<?php

require_once("config.php");

if (isset($_GET["lat"]) && preg_match("/^-?\d+\.\d+$/", $_GET["lat"]) && isset($_GET["lon"]) && preg_match("/^-?\d+\.\d+$/", $_GET["lon"]) && isset($_GET["device"]) ) {

    $conn = new mysqli($servername, $username, $password, $dbname);

    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    }

    $sql = "INSERT INTO tracker (device, lat, lon) VALUES ('" . mysqli_real_escape_string($conn, $_GET['device']) . "', " . mysqli_real_escape_string($conn, $_GET['lat']) . ", " . mysqli_real_escape_string($conn, $_GET['lon']) . ");";

    if (!mysqli_query($conn, $sql)) {
        die('Error: ' . mysqli_error($conn));
    }

    mysqli_close($conn);

    echo "OK";

} elseif (isset($_GET["tracker"])) {

    echo "OK";

} else {

    header('HTTP/1.0 400 Bad Request');
    echo 'This is an endpoint for compatible GPS trackers only.';

}