Web Performance WG Teleconference #33 Agenda 2011-05-18 -- 18 May 2011

<scribe> scribe: JatinderMann

move to agenda 1

Jatinder: Per last week’s action items, Resource Timing Section 4.1 has been updated with reference to SVG, Section 4.2 now refers to “in-memory browser cache, Section 4.3 definitions of redirectStart and redirectEnd have been updated to refer to Timing-Allow-Origin, step 5 of the processing model has been updated to refer to Timing-Allow-Origin.

close ACTION-27

<trackbot> ACTION-27 Update the first example in Section 4.2 to make the cache item clear. closed

close ACTION-28

<trackbot> ACTION-28 Add SVG to Section 4.1 closed

close ACTION-29

<trackbot> ACTION-29 Update Section 4.3 and Processing Model to refer to Timing-Allow-Origin header section. closed

Jatinder: I have also updated Section 1 Introduction. Is there any feedback on these changes?

Chrisitian: Should assign a function directly instead of an anonymous function.

Jatinder: Let’s review Tony’s Resource Timing feedback: http://lists.w3.org/Archives/Public/public-web-perf/2011May/0078.html

Tony: Let's call out DataURI out in the example as not being reported.

Nic: Agreed, that's what we were thinking too.

<tonyg> http://dev.w3.org/html5/spec/Overview.html#fetch

Tony: I feel that the processing model should call out which resources should or shouldn't be included. Like the HTML5 Fetch spec.

ACTION Jatinder to update the processing model to make it more clear which resources are included or not included.

<trackbot> Created ACTION-30 - Update the processing model to make it more clear which resources are included or not included. [on Jatinder Mann - due 2011-05-25].

Tony: For examples, plugins aren't clear in the spec whether they do include resources or not.

Jatinder: We can update the spec around plugins to make it more clear.

Tony: What is the rationale for basing the type attribute on the initiator element rather than content-type of the resource?

Nic: If you only know the content type, it may not be clear where the resource came from. For example, XHR may cause a fetch of various types of resources. Without the intiator type, it may not be clear where the resources came from.

Christian: With images the content-type could be misleading.

Nic: Content-type is not available to script at all today. Not sure what the security background here is.

Tony: It makes sense to have the intiator type, based on this conversation.

Nic: We will send an email to the thread to make this point clear.

Tony: Video can add a resource with two ways, via the poster or source. Maybe it maybe fine to have both come from video intiator.
... While we are fetching a resource that has a redirect, we could begin populating the attributes, but after the redirect occurs we would go back and make changes. It could be weird if someone would reference that in the meanwhile. For NT, javascript doesn't have a chance to observe things until the end. We should carefully think about when we want to populate things.
... Another thing to consider, we may or may not want this interface to be abused as a download progress API

Nic: Our two options are to either add the attribute values after the download occurs at the end of the array, or write '0' values and then expose it in the very end.

Tony: There could be a usecase where a resource fails to download, and you would like to see which phase does the resource fail at.

Jatinder: Sounds like a good use case.

Zhiheng: If the download takes too long and fetchStart has started, but there is no fetchEnd, what should we see?

Nic: Either '0's or no values.

Jatinder: I like the '0's because it implies something is outstanding.

Zhiheng: That feels good to me.

Tony: I don't feel strongly. If something is in the array, they should be accurate when written. The way our network works, we fill in things as they occur anyway.

Christian: We should keep an integer, like zero, there as a return value.

Chrisitan: What about using something like -1?

Jatinder: Since 0 collides with the cross domain case, we should either use something clearly undefined, like -1, or do not add until we are done.

Tony: Since the data is defined as unsigned, maybe that means we should stick with not adding until we are done.

Nic: That will make the processing model easier too.

Jatinder: We can take a stab at this in our processing model action item, and discuss this further on the mailing list.

Zhiheng: resourceStart starts when the resources has been queued to download.

Jatinder: We can update the text here.
... Let's discuss the onbufferful attribute. Tony mentioned whether we need this handler. Considering user agents can change the default size, a web developer may find this event useful. Otherwise, the web developer will need to explicitly set the maximum buffer size.

Tony: I'm not clear if the buffer is defined as a circular buffer or are resources dropped once it is filled.

Nic: We have defined this not as a circular buffer. Resources get dropped once the buffer is full.

Tony: One usecase could be setting the buffer to size 1, and then use the onbufferful event to know when the resources are getting downloaded.

Jatinder: We will update the spec with the rest of the smaller feedback points.

move to agenda 2

Jatinder: Let’s review Tony’s User Timing feedback: http://lists.w3.org/Archives/Public/public-web-perf/2011May/0081.html
... Considering we plan to go to FPWD for Resource Timing by next Wednesday, we will aim to have these changes made available this week.

move to agenda 3

Jatinder: I have made updates to the Page Visibility spec, per my mail on the mailing list: http://lists.w3.org/Archives/Public/public-web-perf/2011May/0063.html
... Let’s discuss Page Visibility privacy concerns

Page Visibility Privacy Concerns

Jatinder: To recap, the privacy concern is that web applications can better deterministically know whether you are viewing their content then they could have done before.
... Using window.onfocus and window.onblur already gives a website a good indication of the user presence. Page Visibility will give a more accurate indication of user presence; Page Visibility will correctly return the User agent is visible in the case that it is not minimized and another application is in focus, whereas onfocus and onblur won’t.
... Our options are as so: (1) Determine that Page Visibility doesn’t significantly increase the privacy issue that is already present, (2) Allow User agents to specify a setting to disable Page Visibility APIs, (3) Page Visibility should be limited to same-origin unless specified via a meta-tag, (4) a combination of options 2 and 3.
... I would argue against option 3. The convention is to allow scripts added to a page to have full access to properties on window/document; they are treated as if they were same origin scripts. For example, today a x-domain script added to a page has access to window.onfocus and window.onblur. We shouldn’t change this behavior.
... Let's follow up on the mailing list with these two proposals and close on the list, as we don't have all concerned parties here.

move to agenda 4

Jatinder: As we have been evaluating this spec, the concept of a window.animationStartTime seems like a very reasonable property to standardize. This property will allow all animations to have the same starting point. Without standardizing this property, web developers will be forced to Date.now().
... We think that both window.animationStartTime and the requestAnimationFrame() callback timestamp should be implemented as monotonically increasing clocks, in UTC format with millisecond resolution.

http://www.w3.org/2010/webperf/track/actions

Action Cameron to consider including window.animationStartTime and the requestAnimationFrame() callback timestamp as monotonically increasing clocks, in UTC format with millisecond resolution.

<trackbot> Created ACTION-31 - Consider including window.animationStartTime and the requestAnimationFrame() callback timestamp as monotonically increasing clocks, in UTC format with millisecond resolution. [on Cameron McCormack - due 2011-05-25].

- DRAFT -

Web Performance WG Teleconference #33 Agenda 2011-05-18

18 May 2011

Attendees

Contents

Page Visibility Privacy Concerns

Summary of Action Items

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