In Conduit responses, assert that Phabricator supports a "gzip" capability

Summary: Ref T13507. If we believe the server can accept "Content-Encoding: gzip" requests, make the claim in an "X-Conduit-Capabilities" header in responses. Clients can use request compression on subsequent requests.

Test Plan: See D21119 for the client piece.

Maniphest Tasks: T13507

Differential Revision: https://secure.phabricator.com/D21120

src/aphront/requeststream/AphrontRequestStream.php

···
 
     $filters = stream_get_filters();
     foreach ($filters as $filter) {
-      if (preg_match('/^zlib\\./', $filter)) {
+      if (!strncasecmp($filter, 'zlib.', strlen('zlib.'))) {
         $has_zlib = true;
+        break;
       }
     }
 

src/aphront/response/AphrontJSONResponse.php

···
   }
 
   public function getHeaders() {
-    $headers = array(
-      array('Content-Type', 'application/json'),
-    );
-    $headers = array_merge(parent::getHeaders(), $headers);
+    $headers = parent::getHeaders();
+
+    $headers[] = array('Content-Type', 'application/json');
+
     return $headers;
   }
 

src/aphront/response/AphrontResponse.php

···
   private $contentSecurityPolicyURIs;
   private $disableContentSecurityPolicy;
   protected $frameable;
-
+  private $headers = array();
 
   public function setRequest($request) {
     $this->request = $request;
···
 
   final public function setDisableContentSecurityPolicy($disable) {
     $this->disableContentSecurityPolicy = $disable;
+    return $this;
+  }
+
+  final public function addHeader($key, $value) {
+    $this->headers[] = array($key, $value);
     return $this;
   }
 
···
     }
 
     $headers[] = array('Referrer-Policy', 'no-referrer');
+
+    foreach ($this->headers as $header) {
+      $headers[] = $header;
+    }
 
     return $headers;
   }

src/applications/conduit/controller/PhabricatorConduitAPIController.php

···
           $method_implementation);
       case 'json':
       default:
-        return id(new AphrontJSONResponse())
+        $response = id(new AphrontJSONResponse())
           ->setAddJSONShield(false)
           ->setContent($response->toDictionary());
+
+        $capabilities = $this->getConduitCapabilities();
+        if ($capabilities) {
+          $capabilities = implode(' ', $capabilities);
+          $response->addHeader('X-Conduit-Capabilities', $capabilities);
+        }
+
+        return $response;
     }
   }
 
···
     return false;
   }
 
+  private function getConduitCapabilities() {
+    $capabilities = array();
+
+    if (AphrontRequestStream::supportsGzip()) {
+      $capabilities[] = 'gzip';
+    }
+
+    return $capabilities;
+  }
 
 }