ServiceWorkerLifetimeExtension.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_serviceworkerlifetimeextension_h

#define mozilla_dom_serviceworkerlifetimeextension_h

#include "mozilla/TimeStamp.h"

#include "mozilla/Variant.h"

namespace mozilla::dom {

// Do not extend the ServiceWorker's lifetime.  This should only be used for

// special internal cases like sending a termination op.  If you are thinking

// of using this for other purposes, you probably should not be using the

// ServiceWorkerOp mechanism.

struct NoLifetimeExtension {};

// Propagated lifetime extension allows us to ensure that a ServiceWorker

// using ServiceWorker.postMessage to contact another ServiceWorker cannot

// extend the lifetime of the recipient ServiceWorker beyond the lifetime of

// the sender.

struct PropagatedLifetimeExtension {

  // We propagate the lifetime as a timestamp-as-deadline rather than a

  // duration because a duration is effectively frozen in time until it is

  // applied, providing potential for abuse due to the inherently async nature

  // of the events involved.

//

  // It is possible for this value to be in the past by the time it is

  // processed.  It is also possible for this value to be null because of

  // async delays between the transmission of a message from one ServiceWorker

  // (in the content process) and the time it is received in the parent

  // process and/or because the sending ServiceWorker has reached its deadline

  // but is in its "grace period".  We do not attempt to normalize these cases

  // into `NoLifetimeExtension`.

  TimeStamp mDeadline;

};

// For functional events that are initiated by window clients or very specific

// APIs like the Push API where care has been taken to ensure that Service

// Workers can only run without having a tab open under very specific

// circumstances that have been extensively discussed with the standards,

// privacy, and security teams.

struct FullLifetimeExtension {};

/**

 * Conveys how events dispatched at a Service Worker global should impact its

 * lifetime.

*/

struct ServiceWorkerLifetimeExtension

    : public Variant<NoLifetimeExtension, PropagatedLifetimeExtension,

                     FullLifetimeExtension> {

 public:

  explicit ServiceWorkerLifetimeExtension(NoLifetimeExtension aExt)

      : Variant(AsVariant(std::move(aExt))) {}

  explicit ServiceWorkerLifetimeExtension(PropagatedLifetimeExtension aExt)

      : Variant(AsVariant(std::move(aExt))) {}

  explicit ServiceWorkerLifetimeExtension(FullLifetimeExtension aExt)

      : Variant(AsVariant(std::move(aExt))) {}

  // Check whether this lifetime extends at least the provided number of

  // seconds into the future.  This is for use in situations where we might

  // freshly spawn a new ServiceWorker like `SpawnWorkerIfNeeded`.  This helps

  // compensate for the fixed costs to spawning a ServiceWorker as well as the

  // assumption that a ServiceWorker needs at least a minimum amount of run time

  // to accomplish something.  Note that a spawned ServiceWorker will still

  // potentially be able to leverage the

  // "dom.serviceWorkers.idle_extended_timeout" grace period, which with current

  // pref values means an extra 30 seconds of potential execution time.  (But

  // the grace period never counts for propagated deadline purposes.)

  bool LifetimeExtendsIntoTheFuture(uint32_t aRequiredSecs = 5) const;

};

}  // namespace mozilla::dom

#endif  // mozilla_dom_serviceworkerlifetimeextension_h