1347146 - devtools network monitor counts service worker cached responses against "transferred"

Status: RESOLVED FIXED

(DevTools :: Netmonitor, defect, P3)

Description

[Ben Kelly [:bkelly, not reviewing]]

Attachment: Screenshot 2017-03-14 09.34.43.png

Its great that devtools network monitor now shows a separate "transferred" size, but I don't think its quite handling service workers correctly.  In general we should not count responses returned from a service worker as transferred.

If the service worker actually got the response from the network it will show up as its own line in the netmonitor with cause "fetch".  That line should count towards the transfer total, but not then counted again when returned from the service worker.

For example, see the attached screenshot.  Here most of the resources are offline cached by the service worker and should not be counted at all.  The "/" resource does do a network revalidation, but otherwise the site does not use the network at all.  Devtools shows that 480kb were transferred, when it should be close to zero.

Comment 1

[Ben Kelly [:bkelly, not reviewing]]

Looks like the devtools change landed in FF54, so we should try to fix it there.

Comment 2

[Julian Descottes [:jdescottes]]

Interesting to note that if the service worker redirects to another file, the transferred size will be 0, as expected.

eg page requests "foo.css", serviceworker fetches "bar.css" and returns the response for "bar.css", transferred size will show 0.
It seems that when the cache is hit for a different URL than the one requested initially, the onProgress (nsIProgressEventSink) callback for our NetworkResponseListener is never triggered.

Regardless of this, we have a clear flag for requests which were transferred to a serviceworker (httpActivity.fromServiceWorker) so we should be able to handle this in DevTools and set a transferred size of 0.

Alternatively if we could APIs on the channel or the request to get the size information (header size, transferred size etc...), I feel like this could be more reliable than our current implementation?

Comment 3

[Hubert Boma Manilla (:bomsy)]

Attachment: Bug 1347146 - [devtools] Make sure that the total transferred size does not include service worker requests r=#devtools-reviewers

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/9ea04a2cc829
[devtools] Make sure that the total transferred size does not include service worker requests r=devtools-reviewers,nchevobbe

Comment 5

[Iulian Moraru]

https://hg.mozilla.org/mozilla-central/rev/9ea04a2cc829