docshell/base/SyncedContext.h
author Nika Layzell <nika@thelayzells.com>
Wed, 16 Sep 2020 20:47:55 +0000
changeset 549331 ab7d302fd3186b10ada9264528c80f6840e44571
parent 546314 a31a710e76e421ea1a97e66bd2b3fd69e69d4c47
permissions -rw-r--r--
Bug 1659696 - Check PendingInitialization before targeting in window.open, r=kmag This requires adding the flag as a synced field on the BrowsingContext, and checking it in a few more places. Attempts to open a new window in this racy manner will now raise an exception. This should avoid the issue from bug 1658854 by blocking the buggy attempts to load before the nested event loop has been exited. Differential Revision: https://phabricator.services.mozilla.com/D87927

/* -*- 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_SyncedContext_h
#define mozilla_dom_SyncedContext_h

#include "mozilla/EnumSet.h"
#include "mozilla/Maybe.h"
#include "mozilla/RefPtr.h"
#include "mozilla/Tuple.h"
#include <utility>

class PickleIterator;

namespace IPC {
class Message;
}  // namespace IPC

namespace mozilla {
namespace ipc {
class IProtocol;
class IPCResult;
template <typename T>
struct IPDLParamTraits;
}  // namespace ipc

namespace dom {
class ContentParent;
class ContentChild;

namespace syncedcontext {

template <size_t I>
using Index = typename std::integral_constant<size_t, I>;

using IndexSet = EnumSet<size_t, uint64_t>;

template <typename Context>
class Transaction {
 public:
  // Set a field at the given index in this `Transaction`. Creating a
  // `Transaction` object and setting multiple fields on it allows for
  // multiple mutations to be performed atomically.
  template <size_t I, typename U>
  void Set(U&& aValue) {
    mValues.Get(Index<I>{}) = std::forward<U>(aValue);
    mModified += I;
  }

  // Apply the changes from this transaction to the specified Context in all
  // processes. This method will call the correct `CanSet` and `DidSet` methods,
  // as well as move the value.
  //
  // If the target has been discarded, changes will be ignored.
  //
  // NOTE: This method mutates `this`, clearing the modified field set.
  MOZ_MUST_USE nsresult Commit(Context* aOwner);

  // Called from `ContentParent` in response to a transaction from content.
  mozilla::ipc::IPCResult CommitFromIPC(const MaybeDiscarded<Context>& aOwner,
                                        ContentParent* aSource);

  // Called from `ContentChild` in response to a transaction from the parent.
  mozilla::ipc::IPCResult CommitFromIPC(const MaybeDiscarded<Context>& aOwner,
                                        uint64_t aEpoch, ContentChild* aSource);

 private:
  friend struct mozilla::ipc::IPDLParamTraits<Transaction<Context>>;

  void Write(IPC::Message* aMsg, mozilla::ipc::IProtocol* aActor) const;
  bool Read(const IPC::Message* aMsg, PickleIterator* aIter,
            mozilla::ipc::IProtocol* aActor);

  // You probably don't want to directly call this method - instead call
  // `Commit`, which will perform the necessary synchronization.
  //
  // `Validate` must be called before calling this method.
  void Apply(Context* aOwner);

  // Returns the set of fields which failed to validate, or an empty set if
  // there were no validation errors.
  IndexSet Validate(Context* aOwner, ContentParent* aSource);

  template <typename F>
  static void EachIndex(F&& aCallback) {
    Context::FieldValues::EachIndex(aCallback);
  }

  template <size_t I>
  static uint64_t& FieldEpoch(Index<I>, Context* aContext) {
    return std::get<I>(aContext->mFields.mEpochs);
  }

  typename Context::FieldValues mValues;
  IndexSet mModified;
};

template <typename Base, size_t Count>
class FieldValues : public Base {
 public:
  // The number of fields stored by this type.
  static constexpr size_t count = Count;
  static_assert(count < 64,
                "At most 64 synced fields are supported. Please file a bug if "
                "you need additional fields.");

  // The base type will define a series of `Get` methods for looking up a field
  // by its field index.
  using Base::Get;

  // Calls a generic lambda with an `Index<I>` for each index less than the
  // field count.
  template <typename F>
  static void EachIndex(F&& aCallback) {
    EachIndexInner(std::make_index_sequence<count>(),
                   std::forward<F>(aCallback));
  }

 private:
  friend struct mozilla::ipc::IPDLParamTraits<FieldValues<Base, Count>>;

  void Write(IPC::Message* aMsg, mozilla::ipc::IProtocol* aActor) const;
  bool Read(const IPC::Message* aMsg, PickleIterator* aIter,
            mozilla::ipc::IProtocol* aActor);

  template <typename F, size_t... Indexes>
  static void EachIndexInner(std::index_sequence<Indexes...> aIndexes,
                             F&& aCallback) {
    (aCallback(Index<Indexes>()), ...);
  }
};

// Storage related to synchronized context fields. Contains both a tuple of
// individual field values, and epoch information for field synchronization.
template <typename Values>
class FieldStorage {
 public:
  // Unsafely grab a reference directly to the internal values structure which
  // can be modified without telling other processes about the change.
  //
  // This is only sound in specific code which is already messaging other
  // processes, and doesn't need to worry about epochs or other properties of
  // field synchronization.
  Values& RawValues() { return mValues; }
  const Values& RawValues() const { return mValues; }

  // Get an individual field by index.
  template <size_t I>
  const auto& Get() const {
    return RawValues().Get(Index<I>{});
  }

  // Set the value of a field without telling other processes about the change.
  //
  // This is only sound in specific code which is already messaging other
  // processes, and doesn't need to worry about epochs or other properties of
  // field synchronization.
  template <size_t I, typename U>
  void SetWithoutSyncing(U&& aValue) {
    GetNonSyncingReference<I>() = std::move(aValue);
  }

  // Get a reference to a field that can modify without telling other
  // processes about the change.
  //
  // This is only sound in specific code which is already messaging other
  // processes, and doesn't need to worry about epochs or other properties of
  // field synchronization.
  template <size_t I>
  auto& GetNonSyncingReference() {
    return RawValues().Get(Index<I>{});
  }

  FieldStorage() = default;
  explicit FieldStorage(Values&& aInit) : mValues(std::move(aInit)) {}

 private:
  template <typename Context>
  friend class Transaction;

  // Data Members
  std::array<uint64_t, Values::count> mEpochs{};
  Values mValues;
};

// Helper type traits to use concrete types rather than generic forwarding
// references for the `SetXXX` methods defined on the synced context type.
//
// This helps avoid potential issues where someone accidentally declares an
// overload of these methods with slightly different types and different
// behaviours. See bug 1659520.
template <typename T>
struct GetFieldSetterType {
  using SetterArg = T;
};
template <>
struct GetFieldSetterType<nsString> {
  using SetterArg = const nsAString&;
};
template <>
struct GetFieldSetterType<nsCString> {
  using SetterArg = const nsACString&;
};
template <typename T>
using FieldSetterType = typename GetFieldSetterType<T>::SetterArg;

#define MOZ_DECL_SYNCED_CONTEXT_FIELD_INDEX(name, type) IDX_##name,
#define MOZ_DECL_SYNCED_CONTEXT_FIELDS_DECL(name, type)             \
  /* index based field lookup */                                    \
  type& Get(FieldIndex<IDX_##name>) { return m##name; }             \
  const type& Get(FieldIndex<IDX_##name>) const { return m##name; } \
                                                                    \
  /* storage for the field */                                       \
  type m##name{};
#define MOZ_DECL_SYNCED_CONTEXT_FIELD_GETSET(name, type)                       \
  const type& Get##name() const { return mFields.template Get<IDX_##name>(); } \
                                                                               \
  MOZ_MUST_USE nsresult Set##name(                                             \
      ::mozilla::dom::syncedcontext::FieldSetterType<type> aValue) {           \
    Transaction txn;                                                           \
    txn.template Set<IDX_##name>(std::move(aValue));                           \
    return txn.Commit(this);                                                   \
  }                                                                            \
  void Set##name(::mozilla::dom::syncedcontext::FieldSetterType<type> aValue,  \
                 ErrorResult& aRv) {                                           \
    nsresult rv = this->Set##name(std::move(aValue));                          \
    if (NS_FAILED(rv)) {                                                       \
      aRv.ThrowInvalidStateError("cannot set synced field '" #name             \
                                 "': context is discarded");                   \
    }                                                                          \
  }

#define MOZ_DECL_SYNCED_CONTEXT_TRANSACTION_SET(name, type)  \
  template <typename U>                                      \
  void Set##name(U&& aValue) {                               \
    this->template Set<IDX_##name>(std::forward<U>(aValue)); \
  }
#define MOZ_DECL_SYNCED_CONTEXT_INDEX_TO_NAME(name, type) \
  case IDX_##name:                                        \
    return #name;

// Declare a type as a synced context type.
//
// clazz is the name of the type being declared, and `eachfield` is a macro
// which, when called with the name of the macro, will call that macro once for
// each field in the synced context.
#define MOZ_DECL_SYNCED_CONTEXT(clazz, eachfield)                              \
 public:                                                                       \
  /* Index constants for referring to each field in generic code */            \
  enum FieldIndexes {                                                          \
    eachfield(MOZ_DECL_SYNCED_CONTEXT_FIELD_INDEX) SYNCED_FIELD_COUNT          \
  };                                                                           \
                                                                               \
  /* Helper for overloading methods like `CanSet` and `DidSet` */              \
  template <size_t I>                                                          \
  using FieldIndex = typename ::mozilla::dom::syncedcontext::Index<I>;         \
                                                                               \
  /* Struct containing the data for all synced fields as members */            \
  struct BaseFieldValues {                                                     \
    eachfield(MOZ_DECL_SYNCED_CONTEXT_FIELDS_DECL)                             \
  };                                                                           \
  using FieldValues =                                                          \
      typename ::mozilla::dom::syncedcontext::FieldValues<BaseFieldValues,     \
                                                          SYNCED_FIELD_COUNT>; \
                                                                               \
 protected:                                                                    \
  friend class ::mozilla::dom::syncedcontext::Transaction<clazz>;              \
  ::mozilla::dom::syncedcontext::FieldStorage<FieldValues> mFields;            \
                                                                               \
 public:                                                                       \
  /* Transaction types for bulk mutations */                                   \
  using BaseTransaction = ::mozilla::dom::syncedcontext::Transaction<clazz>;   \
  class Transaction final : public BaseTransaction {                           \
   public:                                                                     \
    eachfield(MOZ_DECL_SYNCED_CONTEXT_TRANSACTION_SET)                         \
  };                                                                           \
                                                                               \
  /* Field name getter by field index */                                       \
  static const char* FieldIndexToName(size_t aIndex) {                         \
    switch (aIndex) { eachfield(MOZ_DECL_SYNCED_CONTEXT_INDEX_TO_NAME) }       \
    return "<unknown>";                                                        \
  }                                                                            \
  eachfield(MOZ_DECL_SYNCED_CONTEXT_FIELD_GETSET)

}  // namespace syncedcontext
}  // namespace dom

namespace ipc {

template <typename Context>
struct IPDLParamTraits<dom::syncedcontext::Transaction<Context>> {
  typedef dom::syncedcontext::Transaction<Context> paramType;

  static void Write(IPC::Message* aMsg, IProtocol* aActor,
                    const paramType& aParam) {
    aParam.Write(aMsg, aActor);
  }

  static bool Read(const IPC::Message* aMsg, PickleIterator* aIter,
                   IProtocol* aActor, paramType* aResult) {
    return aResult->Read(aMsg, aIter, aActor);
  }
};

template <typename Base, size_t Count>
struct IPDLParamTraits<dom::syncedcontext::FieldValues<Base, Count>> {
  typedef dom::syncedcontext::FieldValues<Base, Count> paramType;

  static void Write(IPC::Message* aMsg, IProtocol* aActor,
                    const paramType& aParam) {
    aParam.Write(aMsg, aActor);
  }

  static bool Read(const IPC::Message* aMsg, PickleIterator* aIter,
                   IProtocol* aActor, paramType* aResult) {
    return aResult->Read(aMsg, aIter, aActor);
  }
};

}  // namespace ipc
}  // namespace mozilla

#endif  // !defined(mozilla_dom_SyncedContext_h)