Changed ConnectionContext::retryAsync to accept generator function.

To reducer boilerplate in async connectors, we now only accept a Closure
that returns a Generator, instead of any callable. We cannot accept a
Promise because it would most likely be a Coroutine that cannot be
cloned because it wraps a generator that cannot be cloned.

Author: Bilge

composer.json

@@ -11,7 +11,7 @@
   "require": {
     "php": "^7.1",
     "scriptfusion/static-class": "^1",
-    "scriptfusion/retry": "^1.2",
+    "scriptfusion/retry": "^2",
     "scriptfusion/retry-exception-handlers": "^1.1",
     "amphp/amp": "^2",
     "psr/container": "^1",

src/Connector/ConnectionContext.php

@@ -1,6 +1,7 @@
 <?php
 namespace ScriptFUSION\Porter\Connector;
 
+use Amp\Coroutine;
 use Amp\Promise;
 use ScriptFUSION\Porter\Connector\FetchExceptionHandler\FetchExceptionHandler;
 use ScriptFUSION\Porter\Connector\FetchExceptionHandler\StatelessFetchExceptionHandler;
@@ -46,8 +47,8 @@ public function mustCache(): bool
     }
 
     /**
-     * Retries the specified callback a predefined number of times with the specified resource fetch exception handler,
-     * if set, and then the predefined fetch exception handler.
+     * Retries the specified callback up to a predefined number of times. If it throws a recoverable exception, the
+     * resource fetch exception handler is invoked, if set, and then the predefined fetch exception handler.
      *
      * @param callable $callback Callback.
      *
@@ -63,16 +64,21 @@ public function retry(callable $callback)
     }
 
     /**
-     * Retries the specified callback asynchronously a predefined number of times with the specified resource fetch
-     * exception handler, if set, and then the predefined fetch exception handler.
+     * Closes over the specified async generator function with a static factory method that invokes it as a coroutine
+     * and retries it up to the predefined number of fetch attempts. If it throws a recoverable exception, the resource
+     * fetch exception handler is invoked, if set, and then the predefined fetch exception handler.
      *
-     * @param callable $callback
+     * @param \Closure $asyncGenerator Async generator function.
+     *
+     * @return Promise The result returned by the async function.
      */
-    public function retryAsync(callable $callback): Promise
+    public function retryAsync(\Closure $asyncGenerator): Promise
     {
         return \ScriptFUSION\Retry\retryAsync(
             $this->maxFetchAttempts,
-            $callback,
+            static function () use ($asyncGenerator): Coroutine {
+                return new Coroutine($asyncGenerator());
+            },
             $this->createExceptionHandler()
         );
     }
@@ -81,7 +87,7 @@ private function createExceptionHandler(): \Closure
     {
         $userHandlerCloned = $providerHandlerCloned = false;
 
-        return function (\Exception $exception) use (&$userHandlerCloned, &$providerHandlerCloned) {
+        return function (\Exception $exception) use (&$userHandlerCloned, &$providerHandlerCloned): void {
             // Throw exception instead of retrying, if unrecoverable.
             if (!$exception instanceof RecoverableConnectorException) {
                 throw $exception;