Bug 1839319 - Add fetchpriority support for fetch() API. r=valentin,necko-reviewers,webidl,saschanaz,fredw

This is to add basic fetch priority support. It introduces preference of
fetch priority adjustment as per to recent discussions. We need to refine the
fetchpriority mapping taking into account of destination, which will be
addressed in Bug 1881040.

In addition, this changes the relervant prefs type to atomic type to accommodate
the access of the prefs off the main thread in the worker case.

Differential Revision: https://phabricator.services.mozilla.com/D200778

dom/fetch/FetchDriver.cpp

@@ -9,6 +9,7 @@
 #include "mozilla/TaskQueue.h"
 #include "mozilla/dom/FetchDriver.h"
 
+#include "mozilla/dom/FetchPriority.h"
 #include "mozilla/dom/ReferrerInfo.h"
 #include "nsIAsyncVerifyRedirectCallback.h"
 #include "mozilla/dom/Document.h"
@@ -840,11 +841,20 @@ nsresult FetchDriver::HttpFetch(
                        nsIClassOfService::Tail);
   }
 
-  if (mIsTrackingFetch &&
+  if (nsCOMPtr<nsISupportsPriority> p = do_QueryInterface(chan)) {
-      StaticPrefs::privacy_trackingprotection_lower_network_priority()) {
+    if (mIsTrackingFetch &&
-    nsCOMPtr<nsISupportsPriority> p = do_QueryInterface(chan);
+        StaticPrefs::privacy_trackingprotection_lower_network_priority()) {
-    if (p) {
       p->SetPriority(nsISupportsPriority::PRIORITY_LOWEST);
+    } else if (StaticPrefs::network_fetchpriority_enabled()) {
+      // TODO: Bug 1881040 - we need to take into account of destination for the
+      // fetchpriority mapping.
+      const auto fetchPriority = ToFetchPriority(mRequest->GetPriorityMode());
+      // The spec defines the priority to be set in an implementation defined
+      // manner (<https://fetch.spec.whatwg.org/#concept-fetch>, step 15.
+      // See corresponding preferences in StaticPrefList.yaml for more context.
+      const int32_t supportsPriorityDelta =
+          FETCH_PRIORITY_ADJUSTMENT_FOR(global_fetch_api, fetchPriority);
+      p->AdjustPriority(supportsPriorityDelta);
     }
   }
 

dom/fetch/InternalRequest.cpp

@@ -49,6 +49,7 @@ SafeRefPtr<InternalRequest> InternalRequest::GetRequestConstructorCopy(
   copy->mCredentialsMode = mCredentialsMode;
   copy->mCacheMode = mCacheMode;
   copy->mRedirectMode = mRedirectMode;
+  copy->mPriorityMode = mPriorityMode;
   copy->mContentPolicyTypeOverridden = mContentPolicyTypeOverridden;
 
   copy->mPreferredAlternativeDataType = mPreferredAlternativeDataType;
@@ -91,7 +92,8 @@ InternalRequest::InternalRequest(const nsACString& aURL,
       mMode(RequestMode::No_cors),
       mCredentialsMode(RequestCredentials::Omit),
       mCacheMode(RequestCache::Default),
-      mRedirectMode(RequestRedirect::Follow) {
+      mRedirectMode(RequestRedirect::Follow),
+      mPriorityMode(RequestPriority::Auto) {
   MOZ_ASSERT(!aURL.IsEmpty());
   AddURL(aURL, aFragment);
 }
@@ -101,7 +103,8 @@ InternalRequest::InternalRequest(
     RequestCache aCacheMode, RequestMode aMode,
     RequestRedirect aRequestRedirect, RequestCredentials aRequestCredentials,
     const nsAString& aReferrer, ReferrerPolicy aReferrerPolicy,
-    nsContentPolicyType aContentPolicyType, const nsAString& aIntegrity)
+    RequestPriority aPriority, nsContentPolicyType aContentPolicyType,
+    const nsAString& aIntegrity)
     : mMethod(aMethod),
       mHeaders(aHeaders),
       mBodyLength(InternalResponse::UNKNOWN_BODY_SIZE),
@@ -113,6 +116,7 @@ InternalRequest::InternalRequest(
       mCredentialsMode(aRequestCredentials),
       mCacheMode(aCacheMode),
       mRedirectMode(aRequestRedirect),
+      mPriorityMode(aPriority),
       mIntegrity(aIntegrity) {
   MOZ_ASSERT(!aURL.IsEmpty());
   AddURL(aURL, aFragment);
@@ -132,6 +136,7 @@ InternalRequest::InternalRequest(const InternalRequest& aOther,
       mResponseTainting(aOther.mResponseTainting),
       mCacheMode(aOther.mCacheMode),
       mRedirectMode(aOther.mRedirectMode),
+      mPriorityMode(aOther.mPriorityMode),
       mIntegrity(aOther.mIntegrity),
       mMozErrors(aOther.mMozErrors),
       mFragment(aOther.mFragment),

dom/fetch/InternalRequest.h

@@ -93,6 +93,7 @@ class InternalRequest final : public AtomicSafeRefCounted<InternalRequest> {
                   RequestRedirect aRequestRedirect,
                   RequestCredentials aRequestCredentials,
                   const nsAString& aReferrer, ReferrerPolicy aReferrerPolicy,
+                  RequestPriority aPriority,
                   nsContentPolicyType aContentPolicyType,
                   const nsAString& aIntegrity);
 
@@ -250,6 +251,12 @@ class InternalRequest final : public AtomicSafeRefCounted<InternalRequest> {
     mRedirectMode = aRedirectMode;
   }
 
+  RequestPriority GetPriorityMode() const { return mPriorityMode; }
+
+  void SetPriorityMode(RequestPriority aPriorityMode) {
+    mPriorityMode = aPriorityMode;
+  }
+
   const nsString& GetIntegrity() const { return mIntegrity; }
 
   void SetIntegrity(const nsAString& aIntegrity) {
@@ -445,6 +452,7 @@ class InternalRequest final : public AtomicSafeRefCounted<InternalRequest> {
   LoadTainting mResponseTainting = LoadTainting::Basic;
   RequestCache mCacheMode;
   RequestRedirect mRedirectMode;
+  RequestPriority mPriorityMode = RequestPriority::Auto;
   nsString mIntegrity;
   bool mMozErrors = false;
   nsCString mFragment;

dom/fetch/Request.cpp

@@ -430,6 +430,13 @@ SafeRefPtr<Request> Request::Constructor(nsIGlobalObject* aGlobal,
     signal = aInit.mSignal.Value();
   }
 
+  // https://fetch.spec.whatwg.org/#dom-global-fetch
+  // https://fetch.spec.whatwg.org/#dom-request
+  // The priority of init overrides input's priority.
+  if (aInit.mPriority.WasPassed()) {
+    request->SetPriorityMode(aInit.mPriority.Value());
+  }
+
   UniquePtr<mozilla::ipc::PrincipalInfo> principalInfo;
   nsILoadInfo::CrossOriginEmbedderPolicy coep =
       nsILoadInfo::EMBEDDER_POLICY_NULL;

dom/fetch/Request.h

@@ -53,6 +53,8 @@ class Request final : public FetchBody<Request>, public nsWrapperCache {
 
   RequestRedirect Redirect() const { return mRequest->GetRedirectMode(); }
 
+  RequestPriority Priority() const { return mRequest->GetPriorityMode(); }
+
   void GetIntegrity(nsAString& aIntegrity) const {
     aIntegrity = mRequest->GetIntegrity();
   }

dom/webidl/Request.webidl

@@ -64,6 +64,9 @@ dictionary RequestInit {
 
   AbortSignal? signal;
 
+  [Pref="network.fetchpriority.enabled"]
+  RequestPriority priority;
+
   [Pref="dom.fetchObserver.enabled"]
   ObserverCallback observe;
 };

modules/libpref/init/StaticPrefList.yaml

@@ -11778,7 +11778,7 @@
 # Indicates whether the `fetchpriority` attribute for elements which support it
 # (e.g. `<script>`) is enabled.
 - name: network.fetchpriority.enabled
-  type: bool
+  type: RelaxedAtomicBool
   value: false
   mirror: always
 
@@ -11962,6 +11962,24 @@
   value: 0
   mirror: always
 
+# Adjustments to apply to the internal priority of gloable fetch API
+# for fetchpriority=low/high/auto with respect to the case when
+# network.fetchpriority is disabled.
+# - When the flag is disabled, Gecko currently sets priority to NORMAL.
+# - When the flag is enabled, it respectively maps to LOW/HIGH/NORMAL.
+- name: network.fetchpriority.adjustments.global-fetch-api.low
+  type: RelaxedAtomicInt32
+  value: 10
+  mirror: always
+- name: network.fetchpriority.adjustments.global-fetch-api.high
+  type: RelaxedAtomicInt32
+  value: -10
+  mirror: always
+- name: network.fetchpriority.adjustments.global-fetch-api.auto
+  type: RelaxedAtomicInt32
+  value: 0
+  mirror: always
+
 # Enables `<link rel="preconnect">` tag and `Link: rel=preconnect` response header
 # handling.
 - name: network.preconnect

testing/web-platform/meta/fetch/api/request/request-init-priority.any.js.ini

@@ -1,14 +1,4 @@
+prefs: [network.fetchpriority.enabled:true]
 [request-init-priority.any.html]
-  [new Request() throws a TypeError if any of RequestInit's members' values are invalid]
-    expected: FAIL
-
-  [fetch() with an invalid priority returns a rejected promise with a TypeError]
-    expected: FAIL
-
 
 [request-init-priority.any.worker.html]
-  [new Request() throws a TypeError if any of RequestInit's members' values are invalid]
-    expected: FAIL
-
-  [fetch() with an invalid priority returns a rejected promise with a TypeError]
-    expected: FAIL

testing/web-platform/mozilla/meta/fetch/fetchpriority/fetchpriority.h2.html.ini

@@ -13,8 +13,5 @@
   [image-dynamic-load.h2.html: test different 'fetchpriority' values]
     expected: FAIL
 
-  [fetch-init.h2.html: test different 'fetchpriority' values]
-    expected: FAIL
-
   [image-initial-load.h2.html: test different 'fetchpriority' values]
     expected: FAIL

testing/web-platform/mozilla/tests/fetch/fetchpriority/fetchpriority-adjustments.html

@@ -17,6 +17,7 @@
       "deferred-style": SpecialPowers.Ci.nsISupportsPriority.PRIORITY_NORMAL,
       "link-preload-style": SpecialPowers.Ci.nsISupportsPriority.PRIORITY_HIGHEST,
       "non-deferred-style": SpecialPowers.Ci.nsISupportsPriority.PRIORITY_NORMAL,
+      "global-fetch-api": SpecialPowers.Ci.nsISupportsPriority.PRIORITY_NORMAL,
   };
   for (const name in prioritiesWhenFetchpriorityDisabled) {
       let adjustments = {};