Allow returning a Promise in onRejected then()

CHANGELOG.md

@@ -9,6 +9,13 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+## [2.3.0] - 2022-02-x
+
+### Changed
+
+- Enabled the `$onRejected` callback of `HttpRejectedPromise` to return a promise for implementing a retry
+  mechanism [#168](https://github.com/php-http/httplug/pull/168)
+
 ## [2.2.0] - 2020-07-13
 
 ### Changed

spec/Promise/HttpRejectedPromiseSpec.php

@@ -4,6 +4,7 @@
 
 use Http\Client\Exception;
 use Http\Client\Exception\TransferException;
+use Http\Client\Promise\HttpFulfilledPromise;
 use Http\Promise\Promise;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
@@ -87,4 +88,19 @@ function it_throws_not_http_exception()
             throw new \Exception();
         });
     }
+
+    function it_returns_a_promise_when_rejected(ResponseInterface $response)
+    {
+        $exception = new TransferException();
+        $this->beConstructedWith($exception);
+
+        $promise = $this->then(null, function (Exception $exceptionReceived) use($exception, $response) {
+            return new HttpFulfilledPromise($response->getWrappedObject());
+        });
+
+        $promise->shouldHaveType('Http\Promise\Promise');
+        $promise->shouldHaveType('Http\Client\Promise\HttpFulfilledPromise');
+        $promise->getState()->shouldReturn(Promise::FULFILLED);
+        $promise->wait()->shouldReturnAnInstanceOf('Psr\Http\Message\ResponseInterface');
+    }
 }

src/Promise/HttpRejectedPromise.php

@@ -27,7 +27,12 @@ public function then(callable $onFulfilled = null, callable $onRejected = null)
         }
 
         try {
-            return new HttpFulfilledPromise($onRejected($this->exception));
+            $result = $onRejected($this->exception);
+            if ($result instanceof Promise) {
+                return $result;
+            }
+
+            return new HttpFulfilledPromise($result);
         } catch (Exception $e) {
             return new self($e);
         }