Bug 1443942 - Fix dom/media/test/midflight-redirect.sjs. r=jya

Problems here:
* The variable `to` is undefined for byte range requests to the end of
the resource, making the math fail. Firefox normally makes ranges requests like
this.
* The bytes.length/4 calculation may not be a whole number, so can
result in a byte range header part of the way between two bytes. We need to
round the length off.
* Instead of re-calculating the contentLength, we can just use the length of
the actual byterange substring being returned. That's clearer.
* test_midflight_redirect_blocked needs the redirect to happen
before metadata has completed loading, but other tests require the redirect to
happen *after* metadata is loaded. So add a redirectAt query parameter for the
requester to control when to redirect.

MozReview-Commit-ID: I6n1NqK0Uze

--HG--
extra : rebase_source : a6bd68fe75cfd4c46f63ca815c5a4e9390bd671a

dom/media/test/midflight-redirect.sjs

@@ -48,16 +48,21 @@ function handleRequest(request, response)
     return;
   }
 
-  if (from == 0 && !redirected) {
-    to = Math.min(bytes.length / 4, 200);
-  } else {
-    to = to || Math.max(from, bytes.length - 1);
+  if (isNaN(to)) {
+    to = bytes.length - 1;
   }
 
+  if (from == 0 && !redirected) {
+    to = parseInt(parseQuery(query, "redirectAt")) || Math.floor(bytes.length / 4);
+  }
+  to = Math.min(to, bytes.length - 1);
+
+  // Note: 'to' is the first index *excluded*, so we need (to + 1)
+  // in the substring end here.
   byterange = bytes.substring(from, to + 1);
 
   let contentRange = "bytes " + from + "-" + to + "/" + bytes.length;
-  let contentLength = (to - from + 1).toString();
+  let contentLength = byterange.length.toString();
 
   response.setStatusLine(request.httpVersion, 206, "Partial Content");
   response.setHeader("Content-Range", contentRange);

dom/media/test/test_midflight_redirect_blocked.html

@@ -42,10 +42,12 @@
           }, false);
 
           var noise = Math.floor(Math.random() * 100000000);
+          // Note: request redirect before the end of metadata, otherwise we won't
+          // error before metadata has loaded if mixed origins are allowed.
           element.src = "midflight-redirect.sjs?resource=" + test.name
                       + (useCors ? "&cors" : "")
                       + "&type=" + test.type
-                      + "&noise=" + noise;
+                      + "&redirectAt=200";
           element.preload = "metadata";
           document.body.appendChild(element);
           element.load()

dom/media/test/test_mixed_principals.html

@@ -43,13 +43,11 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=489415
       return new Promise(function (resolve, reject) {
         // Load will redirect mid-flight, which will be detected and should error,
         // and we should no longer be able to readback.
-        var noise = Math.floor(Math.random() * 100000000);
         var video = document.createElement("video");
         video.preload = "metadata";
         video.controls = true;
-        var url = "http://" + origin + "/tests/dom/media/test/midflight-redirect.sjs?key="
-                  + noise + "&resource=pixel_aspect_ratio.mp4"
-                  + "&type=video/mp4";
+        var url = "http://" + origin + "/tests/dom/media/test/midflight-redirect.sjs"
+                  + "?resource=pixel_aspect_ratio.mp4&type=video/mp4";
         SimpleTest.info("Loading from " + url);
         video.src = url;
         document.body.appendChild(video);