Allow instantiation with existing PDOs

src/DriverFactory.php

@@ -21,4 +21,19 @@ class DriverFactory
             return null;
         }
     }
+
+    public static function factoryFromPDO(\PDO &$pdo, string $type = null) : ?Drivers\DSODriverInterface
+    {
+        if (!$type) {
+            $type = $pdo->getAttribute(\PDO::ATTR_DRIVER_NAME);
+        }
+        $type = strtolower($type);
+        if ($class = @static::$map[$type]) {
+            $f = new $class();
+            $f->pdo($pdo);
+            return $f;
+        } else {
+            return null;
+        }
+    }
 }

src/Drivers/AbstractDriver.php

@@ -12,11 +12,22 @@ abstract class AbstractDriver implements DSODriverInterface
     public $pdo;
     const EXTENSIBLE_VIRTUAL_COLUMNS = true;
 
-    public function __construct(string $dsn, string $username=null, string $password=null, array $options=null)
+    public function __construct(string $dsn=null, string $username=null, string $password=null, array $options=null)
     {
-        if (!$this->pdo = new \PDO($dsn, $username, $password, $options)) {
+        if ($dsn) {
+            if (!($pdo = new \PDO($dsn, $username, $password, $options))) {
                 throw new \Exception("Error creating PDO connection");
             }
+            $this->pdo($pdo);
+        }
+    }
+
+    public function &pdo(\PDO &$pdo=null) : ?\PDO
+    {
+        if ($pdo) {
+            $this->pdo = $pdo;
+        }
+        return $this->pdo;
     }
 
     protected function expandPaths($value)

src/Drivers/DSODriverInterface.php

@@ -7,7 +7,8 @@ use Destructr\Search;
 
 interface DSODriverInterface
 {
-    public function __construct(string $dsn, string $username=null, string $password=null, array $options=null);
+    public function __construct(string $dsn=null, string $username=null, string $password=null, array $options=null);
+    public function &pdo(\PDO &$pdo=null) : ?\PDO;
 
     public function createTable(string $table, array $virtualColumns) : bool;
     public function select(string $table, Search $search, array $params);

src/LegacyDrivers/SQLiteDriver.php

@@ -16,9 +16,10 @@ use Destructr\Factory;
  */
 class SQLiteDriver extends AbstractLegacyDriver
 {
-    public function __construct(string $dsn, string $username=null, string $password=null, array $options=null)
+    public function &pdo(\PDO &$pdo=null) : ?\PDO
     {
-        parent::__construct($dsn, $username, $password, $options);
+        if ($pdo) {
+            $this->pdo = $pdo;
             /*
             What we're doing here is adding a custom function to SQLite so that it
             can extract JSON values. It's not fast, but it does let us use JSON
@@ -30,6 +31,8 @@ class SQLiteDriver extends AbstractLegacyDriver
                 2
             );
         }
+        return $this->pdo;
+    }
 
     public static function JSON_EXTRACT($json, $path)
     {