use closeCursor()

api/persistency.php

 <?php
-$pdo = null;
-$cost = ["cost" => 12];
+$PDO = null;
+$COST = ["cost" => 12];
 
 /**
  * @return void
  */
 function initialize_db(): void
 {
-    global $pdo;
-    $pdo = new PDO('sqlite:_286827163ab1.db');
-    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
+    global $PDO;
+    $PDO = new PDO('sqlite:_286827163ab1.db');
+    $PDO->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
 
     $q = "CREATE TABLE IF NOT EXISTS users("
         . "email TEXT PRIMARY KEY NOT NULL, "
@@ -17,7 +17,7 @@ function initialize_db(): void
         . "firstname TEXT NOT NULL, lastname TEXT NOT NULL, "
         . "is_active INTEGER DEFAULT 0 NOT NULL, "
         . "password TEXT NOT NULL, public_key TEXT)";
-    $pdo->exec($q);
+    $PDO->exec($q);
 }
 
 /**
@@ -35,11 +35,11 @@ function create_user(array $data): array
         delete_user($email);
 
         // create user
-        global $pdo;
+        global $PDO;
 
         $uuid = uuid_v4();
         /** @var PDOStatement $stm */
-        $stm = $pdo->prepare('INSERT INTO users(user_id, email, firstname, lastname, password) ' .
+        $stm = $PDO->prepare('INSERT INTO users(user_id, email, firstname, lastname, password) ' .
             'VALUES(:uuid, :email, :firstname, :lastname, :password)');
         $stm->bindValue(':uuid', $uuid);
         $stm->bindValue(':email', $data['email']);
@@ -48,6 +48,7 @@ function create_user(array $data): array
         $stm->bindValue(':password', password_hash($data['password'],
             PASSWORD_DEFAULT, ["cost" => 12]));
         $stm->execute();
+        $stm->closeCursor();
 
         // prepare register email
         $registration = "https://" . $_SERVER['HTTP_HOST'] . "/app?register&uuid=" . $uuid;
@@ -70,12 +71,15 @@ function create_user(array $data): array
  */
 function get_user_by_uuid($uuid): mixed
 {
-    global $pdo;
+    global $PDO;
     /** @var PDOStatement $stm */
-    $stm = $pdo->prepare('SELECT * FROM users WHERE user_id = :uuid');
+    $stm = $PDO->prepare('SELECT * FROM users WHERE user_id = :uuid');
     $stm->bindValue(':uuid', $uuid);
     $stm->execute();
-    return $stm->fetch(PDO::FETCH_ASSOC);
+    $data = $stm->fetch(PDO::FETCH_ASSOC);
+    $stm->closeCursor();
+
+    return $data;
 }
 
 /**
@@ -85,13 +89,16 @@ function get_user_by_uuid($uuid): mixed
  */
 function get_user($email, $is_active): mixed
 {
-    global $pdo;
+    global $PDO;
     /** @var PDOStatement $stm */
-    $stm = $pdo->prepare('SELECT * FROM users WHERE email = :email AND is_active = :is_active');
+    $stm = $PDO->prepare('SELECT * FROM users WHERE email = :email AND is_active = :is_active');
     $stm->bindValue(':email', $email);
     $stm->bindValue(':is_active', $is_active);
     $stm->execute();
-    return $stm->fetch(PDO::FETCH_ASSOC);
+    $data = $stm->fetch(PDO::FETCH_ASSOC);
+    $stm->closeCursor();
+
+    return $data;
 }
 
 /**
@@ -124,8 +131,8 @@ function login_user(array $data): array
     }
 
     if ($success) {
-        global $cost;
-        if (password_needs_rehash($user['password'], PASSWORD_DEFAULT, $cost)) {
+        global $COST;
+        if (password_needs_rehash($user['password'], PASSWORD_DEFAULT, $COST)) {
             password_change($email, $data);
         }
         user_to_token($user);
@@ -149,14 +156,15 @@ function update_user($email, array $data): array
 
     $user = get_user($email, 1);
     if ($user) {
-        global $pdo;
+        global $PDO;
         /** @var PDOStatement $stm */
-        $stm = $pdo->prepare('UPDATE users ' .
+        $stm = $PDO->prepare('UPDATE users ' .
             'SET firstname = :firstname, lastname = :lastname WHERE email = :email');
         $stm->bindValue(':email', $email);
         $stm->bindValue(':firstname', $data['firstname']);
         $stm->bindValue(':lastname', $data['lastname']);
         $stm->execute();
+        $stm->closeCursor();
     } else {
         $result['status'] = 404;
         $result['error'] = "User does not exist or is not registered.";
@@ -181,13 +189,14 @@ function password_change($email, array $data): array
     $password = $data['password'];
     $user = get_user($email, 1);
     if ($user) {
-        global $pdo;
-        global $cost;
+        global $PDO;
+        global $COST;
         /** @var PDOStatement $stm */
-        $stm = $pdo->prepare('UPDATE users SET password = :password WHERE email = :email');
+        $stm = $PDO->prepare('UPDATE users SET password = :password WHERE email = :email');
         $stm->bindValue(':email', $email);
-        $stm->bindValue(':password', password_hash($password, PASSWORD_DEFAULT, $cost));
+        $stm->bindValue(':password', password_hash($password, PASSWORD_DEFAULT, $COST));
         $stm->execute();
+        $stm->closeCursor();
     } else {
         $result['status'] = 404;
         $result['error'] = "User does not exist or is not registered.";
@@ -203,12 +212,13 @@ function delete_user($email): array
 {
     $result = base_result();
 
-    global $pdo;
+    global $PDO;
 
     /** @var PDOStatement $stm */
-    $stm = $pdo->prepare('DELETE FROM users WHERE email = :email');
+    $stm = $PDO->prepare('DELETE FROM users WHERE email = :email');
     $stm->bindValue(':email', $email);
     $stm->execute();
+    $stm->closeCursor();
 
     return $result;
 }
@@ -223,12 +233,13 @@ function register_user($uuid): array
     $result = base_result();
     $user = get_user_by_uuid($uuid, 0);
     if ($user && ($user['is_active'] == 0)) {
-        global $pdo;
+        global $PDO;
 
         /** @var PDOStatement $stm */
-        $stm = $pdo->prepare('UPDATE users SET is_active = 1 WHERE user_id = :uuid');
+        $stm = $PDO->prepare('UPDATE users SET is_active = 1 WHERE user_id = :uuid');
         $stm->bindValue(':uuid', $uuid);
         $stm->execute();
+        $stm->closeCursor();
 
         user_to_token($user);
     } else {