Do you mean mime sniffing the service worker script type? I think that shouldn't be done. The spec requires an explicit content-type.

Thanks! I misunderstood the expectation message.
https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/virtual/service-worker-servicification/http/tests/serviceworker/register-error-messages-expected.txt

Probably the problem is opposite. The response shouldn't be sniffed but it is. It's because RenderProcessHost::CreateURLLoader() routes the network request to the ResourceDispatcherHostImpl, which internally has MimeSniffingResourceHandler.

Good catch. It's important to fix this because requiring Content-Type is a security mitigation to prevent users from, e.g, using a site's image upload feature to upload JavaScript and registering a service worker for the site.

Is there a way to stop the sniffing by RDHI?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/34ab40ca0d0be59f87fb068151b34a8386f0d416

commit 34ab40ca0d0be59f87fb068151b34a8386f0d416
Author: Makoto Shimazu <shimazu@chromium.org>
Date: Thu Aug 23 04:32:03 2018

Use network::mojom::kURLLoadOptionSniffMimeType everywhere

This CL is to reflect kURLLoadOptionSniffMimeType when making
ResourceHandlers. If there is no option to request mime sniffing, it won't
create MimeSniffingResourceHandler. ServiceWorkerNewScriptLoader removes the
mime sniffing option, so requests for service worker scripts can skip mime
sniffing in RDHI.

Context of this CL:
Before NetS13nServiceWorker, network requests for service worker scripts is handled
by ServiceWorkerWriteToCacheJob, and it rejects responses without mime type. It
results in network error and none of ResourceHandlers handle the response.
After NetS13nServiceWorker, network requests coming from the renderer reach
ServiceWorkerNewScriptLoader first, and eventually they are routed to
ResourceDispatcherHostImpl. It means that ResourceDispatcherHostImpl works as
usual and MimeSniffingResourceHandler in RDHI handles the response.
This CL helps to avoid the script response is handled by
MimeSniffingResourceHandler.


Bug:  871654 
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: Ia7c7885157029be16a3a4669cf204ac85232f1b6
Reviewed-on: https://chromium-review.googlesource.com/1179482
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585398}
[modify] https://crrev.com/34ab40ca0d0be59f87fb068151b34a8386f0d416/content/browser/loader/navigation_url_loader_impl.cc
[modify] https://crrev.com/34ab40ca0d0be59f87fb068151b34a8386f0d416/content/browser/loader/resource_dispatcher_host_impl.cc
[modify] https://crrev.com/34ab40ca0d0be59f87fb068151b34a8386f0d416/content/browser/loader/resource_dispatcher_host_impl.h
[modify] https://crrev.com/34ab40ca0d0be59f87fb068151b34a8386f0d416/content/browser/loader/resource_dispatcher_host_unittest.cc
[modify] https://crrev.com/34ab40ca0d0be59f87fb068151b34a8386f0d416/content/browser/loader/url_loader_factory_impl_unittest.cc
[modify] https://crrev.com/34ab40ca0d0be59f87fb068151b34a8386f0d416/content/renderer/loader/resource_dispatcher.cc
[modify] https://crrev.com/34ab40ca0d0be59f87fb068151b34a8386f0d416/services/network/public/mojom/url_loader_factory.mojom
[delete] https://crrev.com/b9501577665f81d4ed981186d7494af921f2d424/third_party/WebKit/LayoutTests/virtual/service-worker-servicification/http/tests/serviceworker/register-error-messages-expected.txt

re c#4: sorry for my slow reply. MimeSniffingResourceHandler was originally always created, so I added the way to skipt it at c#6.