refactor: only accept single values in validateParameter()

this is to make handling null easier (previous Arr::wrap() approach
turned null into an empty array rather than [null] requiring two
separate null checks) and testing easier (we use empty arrays as
examples of invalid values in some tests which would previously be
accepted when passed individually as validateParameter([]) rather than
being part of a wider [something, [], ...] array)

also restrict passing null to validatePassword()

also minor grammar fix in the validateParameter() docblock

src/Database/Concerns/ValidatesDatabaseParameters.php

@@ -38,23 +38,16 @@ trait ValidatesDatabaseParameters
     public static string $allowedPasswordCharacters = ' !#$%&()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_abcdefghijklmnopqrstuvwxyz{|}~';
 
     /**
-     * Ensure that parameters (database names, usernames, etc.)
+     * Ensure that parameter (database name, username, etc.)
-     * only contain allowed characters before used in SQL statements
+     * only contains allowed characters before being used in SQL statements
      * (or paths in the case of SQLiteDatabaseManager).
      *
      * By default, only the characters in allowedParameterCharacters() are allowed.
      *
      * @throws InvalidArgumentException
      */
-    protected function validateParameter(string|array|null $parameters, string|null $allowedCharacters = null): void
+    protected function validateParameter(mixed $parameter, string|null $allowedCharacters = null): void
     {
-        if ($parameters === null) {
-            throw new InvalidArgumentException('Parameter cannot be null.');
-        }
-
-        $allowedCharacters ??= static::$allowedParameterCharacters;
-
-        foreach (Arr::wrap($parameters) as $parameter) {
         if (is_null($parameter)) {
             throw new InvalidArgumentException('Parameter cannot be null.');
         }
@@ -68,13 +61,14 @@ trait ValidatesDatabaseParameters
             throw new InvalidArgumentException('Parameter has to be a string.');
         }
 
+        $allowedCharacters ??= static::$allowedParameterCharacters;
+
         foreach (str_split($parameter) as $character) {
             if (! str_contains($allowedCharacters, $character)) {
                 throw new InvalidArgumentException("Forbidden character '{$character}' in parameter.");
             }
         }
     }
-    }
 
     /**
      * Ensure password only contains allowed characters (allowedPasswordCharacters())
@@ -87,6 +81,10 @@ trait ValidatesDatabaseParameters
      */
     protected function validatePassword(string|null $password): void
     {
+        if (is_null($password)) {
+            throw new InvalidArgumentException('Parameter cannot be null.');
+        }
+
         $this->validateParameter($password, allowedCharacters: static::$allowedPasswordCharacters);
     }
 }

src/Database/TenantDatabaseManagers/MySQLDatabaseManager.php

@@ -14,7 +14,7 @@ class MySQLDatabaseManager extends TenantDatabaseManager
         $charset = $this->connection()->getConfig('charset');
         $collation = $this->connection()->getConfig('collation');
 
-        $this->validateParameter(array_filter([$database, $charset, $collation], fn ($param) => $param !== null));
+        $this->validateParameter($database);
 
         // MySQL defaults to the server's charset and collation
         // if charset and collation are not specified.
@@ -23,10 +23,12 @@ class MySQLDatabaseManager extends TenantDatabaseManager
         $statement = "CREATE DATABASE `{$database}`";
 
         if ($charset !== null) {
+            $this->validateParameter($charset);
             $statement .= " CHARACTER SET `{$charset}`";
         }
 
         if ($collation !== null) {
+            $this->validateParameter($collation);
             $statement .= " COLLATE `{$collation}`";
         }
 

src/Database/TenantDatabaseManagers/PermissionControlledMicrosoftSQLServerDatabaseManager.php

@@ -24,7 +24,8 @@ class PermissionControlledMicrosoftSQLServerDatabaseManager extends MicrosoftSQL
         $username = $databaseConfig->getUsername();
         $password = $databaseConfig->getPassword();
 
-        $this->validateParameter([$database, $username]);
+        $this->validateParameter($database);
+        $this->validateParameter($username);
         $this->validatePassword($password);
 
         // Create login

src/Database/TenantDatabaseManagers/PermissionControlledMySQLDatabaseManager.php

@@ -25,7 +25,8 @@ class PermissionControlledMySQLDatabaseManager extends MySQLDatabaseManager impl
         $username = $databaseConfig->getUsername();
         $password = $databaseConfig->getPassword();
 
-        $this->validateParameter([$database, $username]);
+        $this->validateParameter($database);
+        $this->validateParameter($username);
         $this->validatePassword($password);
 
         $this->connection()->statement("CREATE USER `{$username}`@`%` IDENTIFIED BY '{$password}'");

src/Database/TenantDatabaseManagers/PermissionControlledPostgreSQLDatabaseManager.php

@@ -20,7 +20,9 @@ class PermissionControlledPostgreSQLDatabaseManager extends PostgreSQLDatabaseMa
         $username = $databaseConfig->getUsername();
         $schema = $databaseConfig->connection()['search_path'];
 
-        $this->validateParameter([$database, $username, $schema]);
+        $this->validateParameter($database);
+        $this->validateParameter($username);
+        $this->validateParameter($schema);
 
         // Host config
         $connectionName = $this->connection()->getConfig('name');

src/Database/TenantDatabaseManagers/PermissionControlledPostgreSQLSchemaManager.php

@@ -23,7 +23,9 @@ class PermissionControlledPostgreSQLSchemaManager extends PostgreSQLSchemaManage
         // Central database name
         $database = DB::connection(config('tenancy.database.central_connection'))->getDatabaseName();
 
-        $this->validateParameter([$username, $schema, $database]);
+        $this->validateParameter($username);
+        $this->validateParameter($schema);
+        $this->validateParameter($database);
 
         $this->connection()->statement("GRANT CONNECT ON DATABASE \"{$database}\" TO \"{$username}\"");
         $this->connection()->statement("GRANT USAGE, CREATE ON SCHEMA \"{$schema}\" TO \"{$username}\"");