Support ServiceWorkerAutoPreload behavior

Author: sisidovski

docs/index.bs

@@ -3228,6 +3228,7 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
       1. Let |shouldSoftUpdate| be true if any of the following are true, and false otherwise:
           * |request| is a [=non-subresource request=].
           * |request| is a [=subresource request=] and |registration| is [=stale=].
+      1. Let |raceResponse| be null.
       1. If |activeWorker|'s [=service worker/list of router rules=] [=list/is not empty=]:
           1. Set |timingInfo|’s [=service worker timing info/worker router evaluation start=] to the [=coarsened shared current time=] given |useHighResPerformanceTimers|.
           1. Let |source| be the result of running the [=Get Router Source=] algorithm with |registration|'s <a>active worker</a> and |request|.
@@ -3287,29 +3288,43 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
                   1. Set |routedResponse|'s [=service worker timing info=]'s [=service worker timing info/worker final router source=] be set to |result|'s [=race result/used route=].
                   1. Return |routedResponse|.
               1. Assert: |source| is "{{RouterSourceEnum/fetch-event}}"
-      1. If |request| is a [=navigation request=], |registration|'s [=navigation preload enabled flag=] is set, |request|'s [=request/method=] is \`<code>GET</code>\`, |registration|'s [=active worker=]'s [=set of event types to handle=] [=set/contains=] <code>fetch</code>, and |registration|'s [=active worker=]'s [=all fetch listeners are empty flag=] is not set then:
-
-          Note: If the above is true except |registration|'s [=active worker=]'s <a>set of event types to handle</a> **does not** contain <code>fetch</code>, then the user agent may wish to show a console warning, as the developer's intent isn't clear.
-
-          1. Let |preloadRequest| be the result of [=request/cloning=] the request |request|.
-          1. Let |preloadRequestHeaders| be |preloadRequest|'s [=request/header list=].
-          1. Let |preloadResponseObject| be a new {{Response}} object associated with a new {{Headers}} object whose [=guard=] is "`immutable`".
-          1. [=header list/Append=] to |preloadRequestHeaders| a new [=header=] whose [=header/name=] is \`<code>Service-Worker-Navigation-Preload</code>\` and [=header/value=] is |registration|'s [=navigation preload header value=].
-          1. Set |preloadRequest|'s [=service-workers mode=] to "`none`".
-          1. Let |preloadFetchController| be null.
-          1. Run the following substeps [=in parallel=], but [=abort when=] |fetchController|'s [=fetch controller/state=] is "<code>terminated</code>" or "<code>aborted</code>":
-              1. Set |preloadFetchController| to the result of [=Fetch|fetching=] |preloadRequest|.
-
-                  To [=fetch/processResponse=] for |navigationPreloadResponse|, run these substeps:
-
-                  1. If |navigationPreloadResponse|'s [=response/type=] is "`error`", reject |preloadResponse| with a `TypeError` and terminate these substeps.
-                  1. Associate |preloadResponseObject| with |navigationPreloadResponse|.
-                  1. Resolve |preloadResponse| with |preloadResponseObject|.
-          1. [=If aborted=], then:
-              1. Let |deserializedError| be the result of [=deserialize a serialized abort reason=] given null and |workerRealm|.
-              1. [=fetch controller/Abort=] |preloadFetchController| with |deserializedError|.
+      1. If |request| is a [=navigation request=], |request|'s [=request/method=] is \`<code>GET</code>\`, |registration|'s [=active worker=]'s [=set of event types to handle=] [=set/contains=] <code>fetch</code>, and |registration|'s [=active worker=]'s [=all fetch listeners are empty flag=] is not set then:
+          1. If |registration|'s [=navigation preload enabled flag=] is set then: 
+
+              Note: If the above is true except |registration|'s [=active worker=]'s <a>set of event types to handle</a> **does not** contain <code>fetch</code>, then the user agent may wish to show a console warning, as the developer's intent isn't clear.
+
+              1. Let |preloadRequest| be the result of [=request/cloning=] the request |request|.
+              1. Let |preloadRequestHeaders| be |preloadRequest|'s [=request/header list=].
+              1. Let |preloadResponseObject| be a new {{Response}} object associated with a new {{Headers}} object whose [=guard=] is "`immutable`".
+              1. [=header list/Append=] to |preloadRequestHeaders| a new [=header=] whose [=header/name=] is \`<code>Service-Worker-Navigation-Preload</code>\` and [=header/value=] is |registration|'s [=navigation preload header value=].
+              1. Set |preloadRequest|'s [=service-workers mode=] to "`none`".
+              1. Let |preloadFetchController| be null.
+              1. Run the following substeps [=in parallel=], but [=abort when=] |fetchController|'s [=fetch controller/state=] is "<code>terminated</code>" or "<code>aborted</code>":
+                  1. Set |preloadFetchController| to the result of [=Fetch|fetching=] |preloadRequest|.
+
+                      To [=fetch/processResponse=] for |navigationPreloadResponse|, run these substeps:
+
+                      1. If |navigationPreloadResponse|'s [=response/type=] is "`error`", reject |preloadResponse| with a `TypeError` and terminate these substeps.
+                      1. Associate |preloadResponseObject| with |navigationPreloadResponse|.
+                      1. Resolve |preloadResponse| with |preloadResponseObject|.
+              1. [=If aborted=], then:
+                  1. Let |deserializedError| be the result of [=deserialize a serialized abort reason=] given null and |workerRealm|.
+                  1. [=fetch controller/Abort=] |preloadFetchController| with |deserializedError|.
+          1. Else, a user agent may run the following substeps:
+
+              Note: A user agent may speculatively dispatch a network request in parallel with creating a fetch event in order to minimize the bootstrap cost.
+
+              1. Let |autoPreloadFetchController| be null.
+              1. Set |raceResponse| to be a [=race response=] whose [=race response/value=] is "<code>pending</code>".
+              1. Run the following substeps [=in parallel=], but [=abort when=] |fetchController|'s [=fetch controller/state=] is "<code>terminated</code>" or "<code>aborted</code>":
+                  1. Set |autoPreloadFetchController| to the result of calling [=fetch=] given |request|, with [=fetch/processResponse=] set to the following steps given a [=/response=] |autoPreloadRequestResponse|:
+                  1. If |autoPreloadRequestResponse|'s [=response/status=] is [=ok status=], set |raceResponse|'s [=race response/value=] to |autoPreloadRequestResponse|.
+              1. [=If aborted=] and |autoPreloadFetchController| is not null, then:
+                  1. [=fetch controller/Abort=] |autoPreloadFetchController|.
+                  1. Set |raceResponse| to a [=race response=] whose [=race response/value=] is null.
+              1. Resolve |preloadResponse| with undefined.
       1. Else, resolve |preloadResponse| with undefined.
-      1. Let |fetchResult| be the result of [=Create Fetch Event and Dispatch=] with |request|, |registration|, |useHighResPerformanceTimers|, |timingInfo|, |workerRealm|, |reservedClient|, |preloadResponse|, and null.
+      1. Let |fetchResult| be the result of [=Create Fetch Event and Dispatch=] with |request|, |registration|, |useHighResPerformanceTimers|, |timingInfo|, |workerRealm|, |reservedClient|, |preloadResponse|, and |raceResponse|.
       1. If |timingInfo|'s [=service worker timing info/worker final router source=] is not an empty string:
           1. Assert |timingInfo|'s [=service worker timing info/worker final router source=] is {{RouterSourceEnum/"network"}}.
           1. If |fetchResult| is null, then return |timingInfo|.