added custom delay function for the retry middleware

src/AbstractClient.php

@@ -169,9 +169,9 @@ public function dontQueue()
         return $this;
     }
 
-    public function retries(int $allowed)
+    public function retries(int $allowed, callable $delay = null)
     {
-        $this->middleware['retries'] = Middleware::retries($allowed);
+        $this->middleware['retries'] = Middleware::retries($allowed, $delay);
         return $this;
     }
 

src/Middleware/Middleware.php

@@ -42,13 +42,14 @@ function (ResponseInterface $response) use ($mode) {
         );
     }
 
-    public static function retries(int $allowed)
+    public static function retries(int $allowed, callable $delay = null)
     {
         return GuzzleMiddleware::retry(
             function ($retries, $request, ResponseInterface $response) use ($allowed) {
                 return (($response->getStatusCode() >= 400)
                     && ($retries < $allowed));
-            }
+            },
+            $delay
         );
     }
 

tests/Unit/ClientTest.php

@@ -136,7 +136,7 @@ public function testItRetries()
             new Response(200, [], '{}'),
         ]);
 
-        $client->retries(7)->call();
+        $client->retries(7, function () { return 100; })->call();
     }
 
     public function testItFailsAfterRetries()
@@ -149,7 +149,7 @@ public function testItFailsAfterRetries()
             new Response(200, [], '{}'),
         ]);
 
-        $client->retries(2)->call();
+        $client->retries(2, function () { return 100; })->call();
     }
 
     /**