Make Client.postMessage to unloaded client not throw (#1293)

cf834f0 clarified the target object can be null, and it must throw in that case. But #1291 pointed out that we cannot implement that behavior without blocking the service worker process in multi-process browser architectures. This change makes the control return right away if the target client has been unloaded. Fixes #1291.
w3c · May 28, 2019 · 86d9414 · 86d9414
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diff --git a/docs/index.bs b/docs/index.bs
@@ -1071,19 +1071,23 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
 
       The <dfn method for="Client"><code>postMessage(|message|, |options|)</code></dfn> method *must* run these steps:
 
-        1. Let |sourceSettings| be the <a>context object</a>'s <a>relevant settings object</a>.
-        1. Let |destination| be the {{ServiceWorkerContainer}} object whose [=ServiceWorkerContainer/service worker client=] is the <a>context object</a>'s [=Client/service worker client=], or null if no match is found.
-        1. If |destination| is null, <a>throw</a> an "{{InvalidStateError}}" {{DOMException}}.
+        1. Let |sourceSettings| be the [=context object=]'s [=relevant settings object=].
         1. Let |serializeWithTransferResult| be <a abstract-op>StructuredSerializeWithTransfer</a>(|message|, |options|.transfer). Rethrow any exceptions.
-        1. Add a <a>task</a> that runs the following steps to |destination|'s [=ServiceWorkerContainer/client message queue=]:
-            1. Let |origin| be the [=Unicode serialization of an origin|Unicode serialization=] of |sourceSettings|'s [=environment settings object/origin=].
-            1. Let |source| be a {{ServiceWorker}} object, which represents the [=ServiceWorkerGlobalScope/service worker=] associated with |sourceSettings|'s [=environment settings object/global object=].
-            1. Let |deserializeRecord| be <a abstract-op>StructuredDeserializeWithTransfer</a>(|serializeWithTransferResult|, |destination|'s [=relevant Realm=]).
-
-                If this throws an exception, catch it, [=fire an event=] named {{messageerror!!event}} at |destination|, using {{MessageEvent}}, with the {{MessageEvent/origin}} attribute initialized to |origin| and the {{MessageEvent/source}} attribute initialized to |source|, and then abort these steps.
-            1. Let |messageClone| be |deserializeRecord|.\[[Deserialized]].
-            1. Let |newPorts| be a new [=frozen array type|frozen array=] consisting of all {{MessagePort}} objects in |deserializeRecord|.\[[TransferredValues]], if any.
-            1. [=Dispatch|Dispatch an event=] named {{Window/message!!event}} at |destination|, using {{MessageEvent}}, with the {{MessageEvent/origin}} attribute initialized to |origin|, the {{MessageEvent/source}} attribute initialized to |source|, the {{MessageEvent/data}} attribute initialized to |messageClone|, and the {{MessageEvent/ports}} attribute initialized to |newPorts|.
+        1. Run the following steps [=in parallel=]:
+            1. Let |targetClient| be null.
+            1. For each [=/service worker client=] |client|:
+                1. If |client| is the [=context object=]'s [=Client/service worker client=], set |targetClient| to |client|, and [=break=].
+            1. If |targetClient| is null, return.
+            1. Let |destination| be the {{ServiceWorkerContainer}} object whose associated [=ServiceWorkerContainer/service worker client=] is |targetClient|.
+            1. Add a [=task=] that runs the following steps to |destination|'s [=ServiceWorkerContainer/client message queue=]:
+                1. Let |origin| be the [=Unicode serialization of an origin|Unicode serialization=] of |sourceSettings|'s [=environment settings object/origin=].
+                1. Let |source| be a {{ServiceWorker}} object, which represents the [=ServiceWorkerGlobalScope/service worker=] associated with |sourceSettings|'s [=environment settings object/global object=].
+                1. Let |deserializeRecord| be <a abstract-op>StructuredDeserializeWithTransfer</a>(|serializeWithTransferResult|, |destination|'s [=relevant Realm=]).
+
+                    If this throws an exception, catch it, [=fire an event=] named {{messageerror!!event}} at |destination|, using {{MessageEvent}}, with the {{MessageEvent/origin}} attribute initialized to |origin| and the {{MessageEvent/source}} attribute initialized to |source|, and then abort these steps.
+                1. Let |messageClone| be |deserializeRecord|.\[[Deserialized]].
+                1. Let |newPorts| be a new [=frozen array type|frozen array=] consisting of all {{MessagePort}} objects in |deserializeRecord|.\[[TransferredValues]], if any.
+                1. [=Dispatch|Dispatch an event=] named {{Window/message!!event}} at |destination|, using {{MessageEvent}}, with the {{MessageEvent/origin}} attribute initialized to |origin|, the {{MessageEvent/source}} attribute initialized to |source|, the {{MessageEvent/data}} attribute initialized to |messageClone|, and the {{MessageEvent/ports}} attribute initialized to |newPorts|.
     </section>
 
     <section>

diff --git a/docs/v1/index.bs b/docs/v1/index.bs
@@ -983,19 +983,23 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
 
       The <dfn method for="Client"><code>postMessage(|message|, |transfer|)</code></dfn> method *must* run these steps:
 
-        1. Let |sourceSettings| be the <a>context object</a>'s <a>relevant settings object</a>.
-        1. Let |destination| be the {{ServiceWorkerContainer}} object whose [=ServiceWorkerContainer/service worker client=] is the <a>context object</a>'s [=Client/service worker client=], or null if no match is found.
-        1. If |destination| is null, <a>throw</a> an "{{InvalidStateError}}" {{DOMException}}.
+        1. Let |sourceSettings| be the [=context object=]'s [=relevant settings object=].
         1. Let |serializeWithTransferResult| be <a abstract-op>StructuredSerializeWithTransfer</a>(|message|, |transfer|). Rethrow any exceptions.
-        1. Add a <a>task</a> that runs the following steps to |destination|'s [=ServiceWorkerContainer/client message queue=]:
-            1. Let |origin| be the [=Unicode serialization of an origin|Unicode serialization=] of |sourceSettings|'s [=environment settings object/origin=].
-            1. Let |source| be a {{ServiceWorker}} object, which represents the [=ServiceWorkerGlobalScope/service worker=] associated with |sourceSettings|'s [=environment settings object/global object=].
-            1. Let |deserializeRecord| be <a abstract-op>StructuredDeserializeWithTransfer</a>(|serializeWithTransferResult|, |destination|'s [=relevant Realm=]).
-
-                If this throws an exception, catch it, [=fire an event=] named {{messageerror!!event}} at |destination|, using {{MessageEvent}}, with the {{MessageEvent/origin}} attribute initialized to |origin| and the {{MessageEvent/source}} attribute initialized to |source|, and then abort these steps.
-            1. Let |messageClone| be |deserializeRecord|.\[[Deserialized]].
-            1. Let |newPorts| be a new [=frozen array type|frozen array=] consisting of all {{MessagePort}} objects in |deserializeRecord|.\[[TransferredValues]], if any.
-            1. [=Dispatch|Dispatch an event=] named {{Window/message!!event}} at |destination|, using {{MessageEvent}}, with the {{MessageEvent/origin}} attribute initialized to |origin|, the {{MessageEvent/source}} attribute initialized to |source|, the {{MessageEvent/data}} attribute initialized to |messageClone|, and the {{MessageEvent/ports}} attribute initialized to |newPorts|.
+        1. Run the following steps [=in parallel=]:
+            1. Let |targetClient| be null.
+            1. For each [=/service worker client=] |client|:
+                1. If |client| is the [=context object=]'s [=Client/service worker client=], set |targetClient| to |client|, and [=break=].
+            1. If |targetClient| is null, return.
+            1. Let |destination| be the {{ServiceWorkerContainer}} object whose associated [=ServiceWorkerContainer/service worker client=] is |targetClient|.
+            1. Add a [=task=] that runs the following steps to |destination|'s [=ServiceWorkerContainer/client message queue=]:
+                1. Let |origin| be the [=Unicode serialization of an origin|Unicode serialization=] of |sourceSettings|'s [=environment settings object/origin=].
+                1. Let |source| be a {{ServiceWorker}} object, which represents the [=ServiceWorkerGlobalScope/service worker=] associated with |sourceSettings|'s [=environment settings object/global object=].
+                1. Let |deserializeRecord| be <a abstract-op>StructuredDeserializeWithTransfer</a>(|serializeWithTransferResult|, |destination|'s [=relevant Realm=]).
+
+                    If this throws an exception, catch it, [=fire an event=] named {{messageerror!!event}} at |destination|, using {{MessageEvent}}, with the {{MessageEvent/origin}} attribute initialized to |origin| and the {{MessageEvent/source}} attribute initialized to |source|, and then abort these steps.
+                1. Let |messageClone| be |deserializeRecord|.\[[Deserialized]].
+                1. Let |newPorts| be a new [=frozen array type|frozen array=] consisting of all {{MessagePort}} objects in |deserializeRecord|.\[[TransferredValues]], if any.
+                1. [=Dispatch|Dispatch an event=] named {{Window/message!!event}} at |destination|, using {{MessageEvent}}, with the {{MessageEvent/origin}} attribute initialized to |origin|, the {{MessageEvent/source}} attribute initialized to |source|, the {{MessageEvent/data}} attribute initialized to |messageClone|, and the {{MessageEvent/ports}} attribute initialized to |newPorts|.
     </section>
 
     <section>