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Improve download progress firing algorithm
Closes #41.
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Diff for: ‎index.bs

+120-110
Original file line numberDiff line numberDiff line change
@@ -861,127 +861,137 @@ enum AIRewriterLength { "as-is", "shorter", "longer" };
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1. Wait for the total number of bytes to be downloaded to become determined, and let that number be |totalBytes|.
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This number must be equal to the number of bytes that the user agent needs to download at the present time, not including any that have already been downloaded.
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<div class="note">
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<p>For example, if another tab has started the download and it is 90% finished, and the user agent is planning to share the model across all tabs, then |totalBytes| will be 10% of the size of the model, not 100% of the size of the model.
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<p>This prevents the web developer-perceived progress from suddenly jumping from 0% to 90%, and then taking a long time to go from 90% to 100%. It also provides some protection against the (admittedly not very powerful) fingerprinting vector of measuring the current download progress across multiple sites.
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</div>
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1. Let |lastProgressFraction| be 0.
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1. Let |lastProgressTime| be the [=monotonic clock=]'s [=monotonic clock/unsafe current time=].
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1. Perform |fireProgressEvent| given 0.
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1. While true:
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1. If one or more bytes have been downloaded, then:
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1. If the [=monotonic clock=]'s [=monotonic clock/unsafe current time=] minus |lastProgressTime| is greater than 50 ms, then:
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1. Let |bytesSoFar| be the number of bytes downloaded so far.
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1. [=Assert=]: |bytesSoFar| is greater than 0 and less than or equal to |totalBytes|.
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1. Let |rawProgressFraction| be |bytesSoFar| divided by |totalBytes|.
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1. Let |progressFraction| be [$floor$](|rawProgressFraction| &times; 65,536) &divide; 65,536.
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1. Perform |fireProgressEvent| given |progressFraction|.
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<div class="note">
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<p>We use a fraction, instead of firing a progress event with the number of bytes downloaded, to avoid giving precise information about the size of the model or other material being downloaded.</p>
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<p>|progressFraction| is calculated from |rawProgressFraction| to give a precision of one part in 2<sup>16</sup>. This ensures that over most internet speeds and with most model sizes, the {{ProgressEvent/loaded}} value will be different from the previous one that was fired ~50 milliseconds ago.</p>
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<details>
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<summary>Full calculation</summary>
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<p>Assume a 5 GiB download size, and a 20 Mbps download speed (chosen as a number on the lower range from [this source](https://worldpopulationreview.com/country-rankings/internet-speeds-by-country)). Then, downloading 5 GiB will take:</p>
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<math style="display:block math">
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<mtable>
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<mtr>
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<mtd></mtd>
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<mtd style="text-align: left">
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<mn>5</mn>
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<mtext>&nbsp;GiB</mtext>
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<mo>×</mo>
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<mfrac>
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<mrow>
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<msup>
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<mn>2</mn>
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<mn>30</mn>
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</msup>
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<mtext>&nbsp;bytes</mtext>
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</mrow>
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<mtext>GiB</mtext>
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</mfrac>
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<mo>×</mo>
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<mfrac>
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<mrow>
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<mn>8</mn>
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<mtext>&nbsp;bits</mtext>
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</mrow>
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<mtext>bytes</mtext>
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</mfrac>
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<mo>÷</mo>
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<mfrac>
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<mrow>
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<mn>20</mn>
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<mo>×</mo>
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<msup>
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<mn>10</mn>
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<mn>6</mn>
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</msup>
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<mtext>&nbsp;bits</mtext>
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</mrow>
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<mtext>s</mtext>
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</mfrac>
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<mo>×</mo>
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<mfrac>
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<mrow>
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<mn>1000</mn>
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<mtext>&nbsp;ms</mtext>
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</mrow>
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<mtext>s</mtext>
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</mfrac>
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<mo>÷</mo>
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<mfrac>
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<mrow>
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<mn>50</mn>
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<mtext>&nbsp;ms</mtext>
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</mrow>
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<mtext>interval</mtext>
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</mfrac>
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</mtd>
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</mtr>
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<mtr>
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<mtd>
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<mo>=</mo>
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</mtd>
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<mtd style="text-align: left">
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<mn>49,950</mn>
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<mtext>&nbsp;intervals</mtext>
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</mtd>
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</mtr>
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</mtable>
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</math>
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Rounding up to the nearest power of two gives a conservative estimate of 65,536 fifty millisecond intervals, so we want to give progress to 1 part in 2<sup>16</sup>.
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</details>
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</div>
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1. If |bytesSoFar| equals |totalBytes|, then [=iteration/break=].
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<p class="note">Since this is the only exit condition for the loop, we are guaranteed to fire a {{AICreateMonitor/downloadprogress}} event for the 100% mark.</p>
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1. Set |lastProgressTime| to the [=monotonic clock=]'s [=monotonic clock/unsafe current time=].
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1. Otherwise, if downloading has failed and cannot continue, then:
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1. If downloading has failed, then:
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1. [=Queue a global task=] on the [=AI task source=] given |realm|'s [=realm/global object=] to [=reject=] |promise| with a "{{NetworkError}}" {{DOMException}}.
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1. Abort these steps.
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1. Let |bytesSoFar| be the number of bytes downloaded so far.
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1. [=Assert=]: |bytesSoFar| is greater than or equal to 0, and less than or equal to |totalBytes|.
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1. If the [=monotonic clock=]'s [=monotonic clock/unsafe current time=] minus |lastProgressTime| is greater than 50 ms, or |bytesSoFar| equals |totalBytes|, then:
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1. Let |rawProgressFraction| be |bytesSoFar| divided by |totalBytes|.
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1. Let |progressFraction| be [$floor$](|rawProgressFraction| &times; 65,536) &divide; 65,536.
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<div class="note">
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<p>We use a fraction, instead of firing a progress event with the number of bytes downloaded, to avoid giving precise information about the size of the model or other material being downloaded.</p>
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<p>|progressFraction| is calculated from |rawProgressFraction| to give a precision of one part in 2<sup>16</sup>. This ensures that over most internet speeds and with most model sizes, the {{ProgressEvent/loaded}} value will be different from the previous one that was fired ~50 milliseconds ago.</p>
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<details>
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<summary>Full calculation</summary>
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<p>Assume a 5 GiB download size, and a 20 Mbps download speed (chosen as a number on the lower range from [this source](https://worldpopulationreview.com/country-rankings/internet-speeds-by-country)). Then, downloading 5 GiB will take:</p>
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<math style="display:block math">
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<mtable>
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<mtr>
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<mtd></mtd>
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<mtd style="text-align: left">
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<mn>5</mn>
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<mtext>&nbsp;GiB</mtext>
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<mo>×</mo>
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<mfrac>
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<mrow>
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<msup>
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<mn>2</mn>
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<mn>30</mn>
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</msup>
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<mtext>&nbsp;bytes</mtext>
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</mrow>
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<mtext>GiB</mtext>
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</mfrac>
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<mo>×</mo>
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<mfrac>
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<mrow>
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<mn>8</mn>
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<mtext>&nbsp;bits</mtext>
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</mrow>
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<mtext>bytes</mtext>
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</mfrac>
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<mo>÷</mo>
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<mfrac>
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<mrow>
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<mn>20</mn>
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<mo>×</mo>
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<msup>
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<mn>10</mn>
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<mn>6</mn>
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</msup>
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<mtext>&nbsp;bits</mtext>
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</mrow>
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<mtext>s</mtext>
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</mfrac>
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<mo>×</mo>
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<mfrac>
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<mrow>
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<mn>1000</mn>
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<mtext>&nbsp;ms</mtext>
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</mrow>
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<mtext>s</mtext>
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</mfrac>
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<mo>÷</mo>
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<mfrac>
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<mrow>
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<mn>50</mn>
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<mtext>&nbsp;ms</mtext>
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</mrow>
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<mtext>interval</mtext>
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</mfrac>
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</mtd>
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</mtr>
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<mtr>
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<mtd>
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<mo>=</mo>
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</mtd>
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<mtd style="text-align: left">
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<mn>49,950</mn>
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<mtext>&nbsp;intervals</mtext>
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</mtd>
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</mtr>
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</mtable>
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</math>
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Rounding up to the nearest power of two gives a conservative estimate of 65,536 fifty millisecond intervals, so we want to give progress to 1 part in 2<sup>16</sup>.
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</details>
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</div>
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1. If |progressFraction| is not equal to |lastProgressFraction|, then perform |fireProgressEvent| given |progressFraction|.
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1. If |bytesSoFar| equals |totalBytes|, then [=iteration/break=].
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<p class="note">Since this is the only non-failure exit condition for the loop, we will never miss firing a {{AICreateMonitor/downloadprogress}} event for the 100% mark.</p>
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1. Set |lastProgressFraction| to |progressFraction|.
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1. Set |lastProgressTime| to the [=monotonic clock=]'s [=monotonic clock/unsafe current time=].
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1. [=If aborted=], then:
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1. [=Queue a global task=] on the [=AI task source=] given |realm|'s [=realm/global object=] to perform the following steps:

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