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Invalid data when a timer is equal to startTime (with rounding) #8

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cvazac opened this issue Feb 28, 2017 · 0 comments
Open

Invalid data when a timer is equal to startTime (with rounding) #8

cvazac opened this issue Feb 28, 2017 · 0 comments

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@cvazac
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cvazac commented Feb 28, 2017 •
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The timing data for this PerformanceResourceTiming entry:

{
  connectEnd: 914.7050000000002,
  connectStart: 777.1100000000001,
  decodedBodySize: 23612,
  domainLookupEnd: 777.1100000000001,
  domainLookupStart: 777.1100000000001,
  encodedBodySize: 23612,
  fetchStart: 776.7700000000001,
  initiatorType: "css",
  redirectEnd: 0,
  redirectStart: 0,
  requestStart: 914.8750000000001,
  responseEnd: 1055.345,
  responseStart: 1052.2450000000001,
  secureConnectionStart: 830.8850000000001,
  startTime: 776.7700000000001,
  transferSize: 24261,
}

compresses to:

4ll,7q,7n,3u,3u,1i*1i7w,i1

which decompresses to:

{
  connectEnd: 915,
  connectStart: 0,
  decodedBodySize: 23612,
  domainLookupEnd: 0,
  domainLookupStart: 0,
  duration: 278,
  encodedBodySize: 23612,
  fetchStart: 777,
  initiatorType: "css",
  redirectStart: 0,
  requestStart: 915,
  responseEnd: 1055,
  responseStart: 1052,
  secureConnectionStart: 831
  startTime: 777,
  transferSize: 24261,
}

connectStart gets decompressed to 0 instead of 777, which would lead a consumer of the decompressed data to think that it took (915-0=915)ms to connect, whereas it was actually (915-777=138)ms. "In the wild" I have seen this with connectStart/connectEnd as well as domainLookupStart/domainLookupEnd.

I think the breakdown occurs because a 0 in the compressed data can either mean that the timestamp was actually 0 (cross-origin) or was equal (with rounding) to startTime.
@nicjansma nicjansma changed the title invalid data when a timer is equal to startTime (with rounding) Invalid data when a timer is equal to startTime (with rounding) Sep 27, 2018
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