ServiceWorker polyfill Fetch implementation.

Source/modules/serviceworkers/polyfills/fetchPolyfill.js

Index: Source/modules/serviceworkers/polyfills/fetchPolyfill.js
diff --git a/public/web/WebHeap.h b/Source/modules/serviceworkers/polyfills/fetchPolyfill.js
similarity index 59%
copy from public/web/WebHeap.h
copy to Source/modules/serviceworkers/polyfills/fetchPolyfill.js
index 6f23c21fa6ccd2c0295675af185352924173a73b..3d40cd650a724c5c52a479b6fc5a4be5e5bb86ca 100644
--- a/public/web/WebHeap.h
+++ b/Source/modules/serviceworkers/polyfills/fetchPolyfill.js
@@ -28,36 +28,41 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef WebHeap_h
-#define WebHeap_h
+// A simple, incomplete implementation of Fetch, intended to facilitate end

[jsbell, 2014/06/05 17:48:03]

Add link to spec in comment.

http://fetch.spec.whatwg.org/#fetch-method

[gavinp, 2014/06/06 16:43:14]

Done.

+// to end serviceworker testing.
 
-#include "public/platform/WebCommon.h"
-
-namespace blink {
-
-class WebHeap {
-public:
-    // Attach thread to the garbage collector managed heap. Thread can
-    // allocate or use garbage collector managed objects only while it is
-    // attached.
-    BLINK_EXPORT static void attachThread();
+function Fetch(request) {

[jsbell, 2014/06/05 17:48:03]

Function name is lower case in spec: "fetch"

Is making it uppercase intentional?

[jsbell, 2014/06/05 23:06:44]

FYI, the fetch spec's API has changed slightly - it's now fetch(DOMString or
Request, Dictionary), which matches the spec's Request constructor.

At the Monday SW sync we decided to track the SW spec for now - it's older, but
not a moving target. So no change needed here.

[gavinp, 2014/06/06 16:43:14]

No. Fixed.

+    function _castToRequest(item) {
+        if (typeof item == "string") {

[jsbell, 2014/06/05 17:48:03]

Nit: Be consistent with == vs. === (latter is preferred)
Nit: Prefer ' to "

(And this is fine for a temporary polyfill, but to match ES/bindings more
precisely by detecting if item is a Request, and otherwise using  String(item).
Detecting if item is a Request is a pain due to different "realms" which can
make instanceof fail, so this is probably fine.)

[gavinp, 2014/06/06 16:43:14]

Done.

+            item = new Request({
+                url: item
+            });
+        }
+        return item;
+    };
 
-    // Detach thread from the garbage collector managed heap. Thread can
-    // no longer allocate or use garbage collector managed objects.
-    BLINK_EXPORT static void detachThread();
+    request = _castToRequest(request);
 
-    // While this object is active on the stack current thread is marked as
-    // being at safepoint. It can't manipulate garbage collector managed objects
-    // until it leaves safepoint, but it can block indefinitely.
-    // When thread is not at safe-point it must not block indefinitely because
-    // garbage collector might want to stop it.
-    class SafePointScope {
-    public:
-        BLINK_EXPORT SafePointScope();
-        BLINK_EXPORT ~SafePointScope();
-    };
-};
+    return new Promise(function(resolve, reject) {
+        var xhr = new XMLHttpRequest();
+        xhr.open(request.method, request.url, true);

[jsbell, 2014/06/05 17:48:02]

Document the async flag, e.g. true /*async*/

[jsbell, 2014/06/05 17:48:02]

Add extra request headers (or FIXME to do so) via xhr.setRequestHeader()

[gavinp, 2014/06/06 16:43:14]

Done.

[gavinp, 2014/06/06 16:43:14]

Done.

+        xhr.send(null);
+        xhr.onreadystatechange = function() {
+            if (xhr.readyState !== 4) return;
 
-} // namespace blink
+            var response = new Response({
+                status: xhr.status,
+                statusText: xhr.statusText,
+                method: request.method,

[jsbell, 2014/06/05 23:06:44]

Looks like method is NYI in our Response impl.

[gavinp, 2014/06/06 16:43:14]

Whoops. The cachePolyfill needs updating on this, too.

+                // FIXME: Implement a hack for the response headers.
+                // FIXME: Implement body once Response has it.

[jsbell, 2014/06/05 23:06:44]

Add FIXME for url once Response has it.

[gavinp, 2014/06/06 16:43:14]

Done.

+            });
 
-#endif
+            if (xhr.status === 200) {
+                resolve(response);
+            } else {
+                reject(response);

[jsbell, 2014/06/05 23:06:44]

So far as I can tell from http://fetch.spec.whatwg.org/#fetch-method and
http://fetch.spec.whatwg.org/#concept-network-error if xhr.status === 0 then we
should reject(TypeError("network error")) instead. 

(The SW spec suggests using a DOMException/"NetworkError" but that's harder to
polyfill.)

+            }
+        };
+    });
+}

[jsbell, 2014/06/05 17:48:03]

A good way to structure polyfills is to wrap everything in an IIFE and pass in
the global and conditionally assign the polyfills into it, e.g.:

(function(global) {

  // helper functions, constants, etc can go here

  function fetch() { ... }

  // use native implementation if available:
  global.fetch = global.fetch || fetch;

}(self)); // window or worker global scope

[gavinp, 2014/06/06 16:43:14]

Done.