Bug 1704658: Implement ParamTraits for RefPtr<nsAtom> r=nika

Serialization for both nsStaticAtoms and nsDynamicAtoms.

Differential Revision: https://phabricator.services.mozilla.com/D112433

ipc/glue/IPCMessageUtilsSpecializations.cpp

@@ -0,0 +1,67 @@
+/* -*- 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/. */
+
+#include "IPCMessageUtilsSpecializations.h"
+#include "nsGkAtoms.h"
+
+namespace IPC {
+
+static const uint16_t kDynamicAtomToken = 0xffff;
+static const uint16_t kAtomsCount =
+    static_cast<uint16_t>(mozilla::detail::GkAtoms::Atoms::AtomsCount);
+
+static_assert(static_cast<size_t>(
+                  mozilla::detail::GkAtoms::Atoms::AtomsCount) == kAtomsCount,
+              "Number of static atoms must fit in a uint16_t");
+
+static_assert(kDynamicAtomToken >= kAtomsCount,
+              "Exceeded supported number of static atoms");
+
+/* static */
+void ParamTraits<nsAtom*>::Write(Message* aMsg, const nsAtom* aParam) {
+  MOZ_ASSERT(aParam);
+
+  if (aParam->IsStatic()) {
+    const nsStaticAtom* atom = aParam->AsStatic();
+    uint16_t index = static_cast<uint16_t>(nsGkAtoms::IndexOf(atom));
+    MOZ_ASSERT(index < kAtomsCount);
+    WriteParam(aMsg, index);
+    return;
+  }
+  WriteParam(aMsg, kDynamicAtomToken);
+  nsDependentAtomString atomStr(aParam);
+  // nsDependentAtomString is serialized as its base, nsString, but we
+  // can be explicit about it.
+  nsString& str = atomStr;
+  WriteParam(aMsg, str);
+}
+
+/* static */
+bool ParamTraits<nsAtom*>::Read(const Message* aMsg, PickleIterator* aIter,
+                                RefPtr<nsAtom>* aResult) {
+  uint16_t token;
+  if (!ReadParam(aMsg, aIter, &token)) {
+    return false;
+  }
+  if (token != kDynamicAtomToken) {
+    if (token >= kAtomsCount) {
+      return false;
+    }
+    *aResult = nsGkAtoms::GetAtomByIndex(token);
+    return true;
+  }
+
+  nsAutoString str;
+  if (!ReadParam(aMsg, aIter, static_cast<nsString*>(&str))) {
+    return false;
+  }
+
+  *aResult = NS_Atomize(str);
+  MOZ_ASSERT(*aResult);
+  return true;
+}
+
+}  // namespace IPC

ipc/glue/IPCMessageUtilsSpecializations.h

@@ -68,6 +68,8 @@ template <typename T>
 class Optional;
 }
 
+class nsAtom;
+
 namespace IPC {
 
 template <>
@@ -887,6 +889,15 @@ struct ParamTraits<mozilla::dom::Optional<T>> {
   }
 };
 
+template <>
+struct ParamTraits<nsAtom*> {
+  typedef nsAtom paramType;
+
+  static void Write(Message* aMsg, const paramType* aParam);
+  static bool Read(const Message* aMsg, PickleIterator* aIter,
+                   RefPtr<paramType>* aResult);
+};
+
 struct CrossOriginOpenerPolicyValidator {
   using IntegralType =
       std::underlying_type_t<nsILoadInfo::CrossOriginOpenerPolicy>;

ipc/glue/moz.build

@@ -160,6 +160,7 @@ UNIFIED_SOURCES += [
     "IdleSchedulerParent.cpp",
     "InputStreamUtils.cpp",
     "IPCMessageUtils.cpp",
+    "IPCMessageUtilsSpecializations.cpp",
     "IPCStreamChild.cpp",
     "IPCStreamDestination.cpp",
     "IPCStreamParent.cpp",

xpcom/ds/nsGkAtoms.h

@@ -149,6 +149,13 @@ class nsGkAtoms {
     return const_cast<nsStaticAtom*>(&sAtoms[aIndex]);
   }
 
+  static size_t IndexOf(const nsStaticAtom* atom) {
+    nsStaticAtom* firstAtom = GetAtomByIndex(0);
+    size_t ret = atom - firstAtom;
+    MOZ_ASSERT(ret < sAtomsLen);
+    return ret;
+  }
+
 // The definition of the pointer to each static atom.
 //
 // These types are not `static constexpr <type>* const` -- even though these