fix guzzle promise handling

src/Instrumentation/Guzzle/src/GuzzleInstrumentation.php

@@ -7,6 +7,7 @@
 use function get_cfg_var;
 use GuzzleHttp\Client;
 use GuzzleHttp\Exception\BadResponseException;
+use GuzzleHttp\Promise\Is;
 use GuzzleHttp\Promise\PromiseInterface;
 use OpenTelemetry\API\Globals;
 use OpenTelemetry\API\Instrumentation\CachedInstrumentation;
@@ -101,7 +102,7 @@ public static function register(): void
                     $span->end();
                 }
 
-                $promise->then(
+                $p = $promise->then(
                     onFulfilled: function (ResponseInterface $response) use ($span) {
                         $span->setAttribute(TraceAttributes::HTTP_RESPONSE_STATUS_CODE, $response->getStatusCode());
                         $span->setAttribute(TraceAttributes::NETWORK_PROTOCOL_VERSION, $response->getProtocolVersion());
@@ -117,8 +118,6 @@ public static function register(): void
                             $span->setStatus(StatusCode::STATUS_ERROR);
                         }
                         $span->end();
-
-                        return $response;
                     },
                     onRejected: function (\Throwable $t) use ($span) {
                         if ($t instanceof BadResponseException && $t->hasResponse()) {
@@ -130,10 +129,13 @@ public static function register(): void
                         $span->recordException($t);
                         $span->setStatus(StatusCode::STATUS_ERROR, $t->getMessage());
                         $span->end();
-
-                        throw $t;
                     }
                 );
+
+                //if the original promise is already settled, force our additional promise to execute immediately
+                if (Is::settled($promise)) {
+                    $p->wait();
+                }
             }
         );
     }

src/Instrumentation/Guzzle/tests/Integration/GuzzleInstrumentationTest.php

@@ -9,12 +9,15 @@
 use GuzzleHttp\Exception\ConnectException;
 use GuzzleHttp\Handler\MockHandler;
 use GuzzleHttp\HandlerStack;
+use GuzzleHttp\Promise\FulfilledPromise;
 use GuzzleHttp\Promise\PromiseInterface;
+use GuzzleHttp\Promise\RejectedPromise;
 use GuzzleHttp\Promise\Utils;
 use Nyholm\Psr7\Request;
 use Nyholm\Psr7\Response;
 use OpenTelemetry\API\Instrumentation\Configurator;
 use OpenTelemetry\API\Trace\Propagation\TraceContextPropagator;
+use OpenTelemetry\API\Trace\StatusCode;
 use OpenTelemetry\Context\ScopeInterface;
 use OpenTelemetry\SDK\Trace\ImmutableSpan;
 use OpenTelemetry\SDK\Trace\SpanExporter\InMemoryExporter;
@@ -164,7 +167,58 @@ public function test_headers_propagation(): void
 
         $this->mock->append(new Response());
         $this->client->get('/');
+    }
+
+    /**
+     * @dataProvider promiseProvider
+     * @link https://github.com/open-telemetry/opentelemetry-php/issues/1623
+     */
+    public function test_transfer_promises_execute_for_sync_requests(PromiseInterface $promise, bool $expectedException): void
+    {
+        /**
+         * Approximate the Curl handler's behaviour of returning a FulfilledPromise without any
+         * additional promise chaining, so that post hook receives a FulfilledPromise.
+         */
+        $handler = function () use ($promise): PromiseInterface {
+            return $promise;
+        };
+        $handlerStack = HandlerStack::create($handler);
+
+        $client = new Client([
+            'handler' => $handlerStack,
+            'base_uri' => 'https://example.com/',
+            'http_errors' => false,
+            'allow_redirects' => false,
+        ]);
+        $this->assertCount(0, $this->storage);
+
+        $request = new Request('GET', 'https://example.com/foo');
 
+        try {
+            $client->send($request);
+        } catch (\Throwable $e) {
+            if (!$expectedException) {
+                throw $e;
+            }
+        }
+
+        $this->assertCount(1, $this->storage);
+        $span = $this->storage->offsetGet(0);
+        assert($span instanceof ImmutableSpan);
+        if ($expectedException) {
+            $this->assertSame(StatusCode::STATUS_ERROR, $span->getStatus()->getCode());
+            $this->assertSame('Test exception', $span->getStatus()->getDescription());
+        } else {
+            $this->assertSame(201, $span->getAttributes()->get(TraceAttributes::HTTP_RESPONSE_STATUS_CODE));
+        }
+    }
+
+    public static function promiseProvider(): array
+    {
+        return [
+            'fulfilled' => [new FulfilledPromise(new Response(201)), false],
+            'rejected' => [new RejectedPromise(new \RuntimeException('Test exception')), true],
+        ];
     }
 
     /**