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diff --git a/dom/workers/loader/WorkerLoadContext.h b/dom/workers/loader/WorkerLoadContext.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_WorkerLoadContext_h__
+#define mozilla_dom_workers_WorkerLoadContext_h__
+
+#include "nsIChannel.h"
+#include "nsIInputStream.h"
+#include "nsIRequest.h"
+#include "mozilla/CORSMode.h"
+#include "mozilla/dom/Promise.h"
+#include "js/loader/ScriptKind.h"
+#include "js/loader/ScriptLoadRequest.h"
+#include "js/loader/LoadContextBase.h"
+
+class nsIReferrerInfo;
+class nsIURI;
+
+namespace mozilla::dom {
+
+class ClientInfo;
+class WorkerPrivate;
+
+namespace workerinternals::loader {
+class CacheCreator;
+class ScriptLoaderRunnable;
+}  // namespace workerinternals::loader
+
+/*
+ * WorkerLoadContext (for all workers)
+ *
+ * LoadContexts augment the loading of a ScriptLoadRequest. They
+ * describe how a ScriptLoadRequests loading and evaluation needs to be
+ * augmented, based on the information provided by the loading context. The
+ * WorkerLoadContext has the following generic fields applied to all worker
+ * ScriptLoadRequests (and primarily used for error handling):
+ *
+ *    * mMutedErrorFlag
+ *        Set when we finish loading a script, and used to determine whether a
+ *        given error is thrown or muted.
+ *    * mLoadResult
+ *        In order to report errors correctly in the worker thread, we need to
+ *        move them from the main thread to the worker. This field records the
+ *        load error, for throwing when we return to the worker thread.
+ *    * mKind
+ *        See documentation of WorkerLoadContext::Kind.
+ *    * mClientInfo
+ *        A snapshot of a global living in the system (see documentation for
+ *        ClientInfo). In worker loading, this field is important for CSP
+ *        information and knowing what to intercept for Service Worker
+ *        interception.
+ *    * mChannel
+ *        The channel used by this request for it's load. Used for cancellation,
+ *        in order to cancel the stream.
+ *
+ * The rest of the fields on this class focus on enabling the ServiceWorker
+ * usecase, in particular -- using the Cache API to store the worker so that
+ * in the case of (for example) a page refresh, the service worker itself is
+ * persisted so that it can do other work. For more details see the
+ * CacheLoadHandler.h file.
+ *
+ */
+
+class WorkerLoadContext : public JS::loader::LoadContextBase {
+ public:
+  /* Worker Load Context Kinds
+   *
+   * A script that is loaded and run as a worker can be one of several species.
+   * Each may have slightly different behavior, but they fall into roughly two
+   * categories: the Main Worker Script (the script that triggers the first
+   * load) and scripts that are attached to this main worker script.
+   *
+   * In the specification, the Main Worker Script is referred to as the "top
+   * level script" and is defined here:
+   * https://html.spec.whatwg.org/multipage/webappapis.html#fetching-scripts-is-top-level
+   */
+
+  enum Kind {
+    // Indicates that the is-top-level bit is true. This may be a Classic script
+    // or a Module script.
+    MainScript,
+    // We are importing a script from the worker via ImportScript. This may only
+    // be a Classic script.
+    ImportScript,
+    // We have an attached debugger, and these should be treated specially and
+    // not like a main script (regardless of their type). This is not part of
+    // the specification.
+    DebuggerScript
+  };
+
+  explicit WorkerLoadContext(Kind aKind, const Maybe<ClientInfo>& aClientInfo);
+
+  // Used to detect if the `is top-level` bit is set on a given module.
+  bool IsTopLevel() {
+    return mRequest->IsTopLevel() && (mKind == Kind::MainScript);
+  };
+
+  static Kind GetKind(bool isMainScript, bool isDebuggerScript) {
+    if (isDebuggerScript) {
+      return Kind::DebuggerScript;
+    }
+    if (isMainScript) {
+      return Kind::MainScript;
+    }
+    return Kind::ImportScript;
+  };
+
+  /* These fields are used by all workers */
+  Maybe<bool> mMutedErrorFlag;
+  nsresult mLoadResult = NS_ERROR_NOT_INITIALIZED;
+  bool mLoadingFinished = false;
+  bool mIsTopLevel = true;
+  Kind mKind;
+  Maybe<ClientInfo> mClientInfo;
+  nsCOMPtr<nsIChannel> mChannel;
+
+  /* These fields are only used by service workers */
+  /* TODO: Split out a ServiceWorkerLoadContext */
+  // This full URL string is populated only if this object is used in a
+  // ServiceWorker.
+  nsString mFullURL;
+
+  // This promise is set only when the script is for a ServiceWorker but
+  // it's not in the cache yet. The promise is resolved when the full body is
+  // stored into the cache.  mCachePromise will be set to nullptr after
+  // resolution.
+  RefPtr<Promise> mCachePromise;
+
+  // The reader stream the cache entry should be filled from, for those cases
+  // when we're going to have an mCachePromise.
+  nsCOMPtr<nsIInputStream> mCacheReadStream;
+
+  enum CacheStatus {
+    // By default a normal script is just loaded from the network. But for
+    // ServiceWorkers, we have to check if the cache contains the script and
+    // load it from the cache.
+    Uncached,
+
+    WritingToCache,
+
+    ReadingFromCache,
+
+    // This script has been loaded from the ServiceWorker cache.
+    Cached,
+
+    // This script must be stored in the ServiceWorker cache.
+    ToBeCached,
+
+    // Something went wrong or the worker went away.
+    Cancel
+  };
+
+  CacheStatus mCacheStatus = Uncached;
+
+  bool IsAwaitingPromise() const { return bool(mCachePromise); }
+};
+
+class ThreadSafeRequestHandle final {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadSafeRequestHandle)
+
+  ThreadSafeRequestHandle(JS::loader::ScriptLoadRequest* aRequest,
+                          nsISerialEventTarget* aSyncTarget);
+
+  JS::loader::ScriptLoadRequest* GetRequest() const { return mRequest; }
+
+  WorkerLoadContext* GetContext() { return mRequest->GetWorkerLoadContext(); }
+
+  bool IsEmpty() { return !mRequest; }
+
+  // Runnable controls
+  nsresult OnStreamComplete(nsresult aStatus);
+
+  void LoadingFinished(nsresult aRv);
+
+  void MaybeExecuteFinishedScripts();
+
+  bool IsCancelled();
+
+  bool Finished() {
+    return GetContext()->mLoadingFinished && !GetContext()->IsAwaitingPromise();
+  }
+
+  nsresult GetCancelResult();
+
+  already_AddRefed<JS::loader::ScriptLoadRequest> ReleaseRequest();
+
+  workerinternals::loader::CacheCreator* GetCacheCreator();
+
+  RefPtr<workerinternals::loader::ScriptLoaderRunnable> mRunnable;
+
+  bool mExecutionScheduled = false;
+
+ private:
+  ~ThreadSafeRequestHandle();
+
+  RefPtr<JS::loader::ScriptLoadRequest> mRequest;
+  nsCOMPtr<nsISerialEventTarget> mOwningEventTarget;
+};
+
+}  // namespace mozilla::dom
+#endif /* mozilla_dom_workers_WorkerLoadContext_h__ */