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RE: Cross Origin and Resource Timing

From: Alois Reitbauer <alois.reitbauer@dynatrace.com>
Date: Thu, 16 Feb 2012 10:26:35 +0000
To: "public-web-perf@w3.org" <public-web-perf@w3.org>
Message-ID: <A8638EB8DF9DE24D8C1E12D326D97AC399B976@ATEX01.dynatrace.local>
I am convinced that if we do not get an overall timing for third party resources it has very hard to understand their performance impact on the page. Our analysis shows that a lot of today's pages spend more than two thirds of their time with Third Party resources.

Getting these timings is also possible today. It requires a couple of hacks;  but works. We implemented it for our own monitoring, would however prefer if there is a better way to do this.  Following the principle that we expose the same information that people get today this information therefore can be exposed without adding an additional security hole. It will just be easier to access it and collecting this information and have less effect on page performance as it might have today.

// Alois

From: Jatinder Mann [mailto:jmann@microsoft.com]
Sent: Wednesday, February 15, 2012 8:54 PM
To: Alois Reitbauer; public-web-perf@w3.org
Subject: RE: Cross Origin and Resource Timing

Initially, I had thought that we had zero'd out the respondEnd attribute in error in the cross-origin restrictions section and that our intention was to give durations for even cross-origin resources.

However, while looking at the Resource Timing Processing Model in more detail, I see that we had added the following clause:

If the last non-redirected fetch<http://www.w3.org/TR/html5/fetching-resources.html#fetch> of the resource is not the same origin as the current document and the Timing-Allow-Origin<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#timing-allow-origin> HTTP response header does not apply, the user agent must set redirectStart<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#redirect-start>, redirectEnd<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#redirect-end>, domainLookupStart<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#domainlookup-start>, domainLookupEnd<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#domainlookup-end>, connectStart<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#connect-start>, connectEnd<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#connect-end>, requestStart<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#request-start>, responseStart<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#response-start>, responseEnd<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#response-end>, and duration<https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html#duration-attribute> to zero and abort the remaining steps.

Not only is the duration explicitly set to zero, but steps to include this resource in the buffer are skipped. I believe the motivation here was that cross-origin resources should be explicitly not included in the PerformanceResourceTiming buffer. However, if someone were to look at the entire performance timeline, they could deduce that the gap was due to a cross-origin resource.

An alternate proposal could be to provide the end to end time (fetchStart to responseEnd), but zero out the individual attributes.

Does the working group recall why we went with the former approach?

Thanks,
Jatinder

From: Alois Reitbauer [mailto:alois.reitbauer@dynatrace.com]<mailto:[mailto:alois.reitbauer@dynatrace.com]>
Sent: Wednesday, February 15, 2012 12:06 AM
To: public-web-perf@w3.org<mailto:public-web-perf@w3.org>
Subject: Cross Origin and Resource Timing

As far as I can remember the final decision was that for cross origin resources which do not have the allow origin header set no detailed timings but the total time to download the resources is shown. I checked again with the latest version of the spec and it says

, these attributes must be set to zero: redirectStart<http://w3c-test.org/webperf/specs/ResourceTiming/#redirect-start>, redirectEnd<http://w3c-test.org/webperf/specs/ResourceTiming/#redirect-end>, domainLookupStart<http://w3c-test.org/webperf/specs/ResourceTiming/#domainlookup-start>, domainLookupEnd<http://w3c-test.org/webperf/specs/ResourceTiming/#domainlookup-end>, connectStart<http://w3c-test.org/webperf/specs/ResourceTiming/#connect-start>, connectEnd<http://w3c-test.org/webperf/specs/ResourceTiming/#connect-end>, requestStart<http://w3c-test.org/webperf/specs/ResourceTiming/#request-start>, responseStart<http://w3c-test.org/webperf/specs/ResourceTiming/#response-start>, and responseEnd<http://w3c-test.org/webperf/specs/ResourceTiming/#response-end>.

This would mean that one only gets the fetchStart time which means that we only know when the download started but not when it is finished.

Did I miss anything here?

// Alois
Received on Thursday, 16 February 2012 10:27:11 GMT

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