Bug 1767514 - Part 2: Increase the attached handle limit for IPC Messages, r=ipc-reviewers,jld

This is made possible by part 1, which made it possible to send more messages
using IPC::Channel. A limit is still in place, however it is now substantially
higher, hopefully making it effectively unlimited for practical purposes.

Differential Revision: https://phabricator.services.mozilla.com/D145392

ipc/chromium/src/chrome/common/ipc_message.h

@@ -93,9 +93,8 @@ class Message : public mojo::core::ports::UserMessage, public Pickle {
     REPLY = 1,
   };
 
-  // Mac and Linux both limit the number of file descriptors per message to
-  // slightly more than 250.
-  enum { MAX_DESCRIPTORS_PER_MESSAGE = 200 };
+  // The hard limit of handles or file descriptors allowed in a single message.
+  static constexpr size_t MAX_DESCRIPTORS_PER_MESSAGE = 32767;
 
   class HeaderFlags {
     friend class Message;

ipc/ipdl/test/gtest/PTestManyHandles.ipdl

@@ -0,0 +1,15 @@
+/* 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/. */
+
+namespace mozilla {
+namespace _ipdltest {
+
+[ParentImpl=virtual, ChildImpl=virtual]
+async protocol PTestManyHandles {
+child:
+    async ManyHandles(FileDescriptor[] descrs);
+};
+
+} // namespace _ipdltest
+} // namespace mozilla

ipc/ipdl/test/gtest/TestManyHandles.cpp

@@ -0,0 +1,72 @@
+/* -*- 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 "gtest/gtest.h"
+
+#include "mozilla/_ipdltest/IPDLUnitTest.h"
+#include "mozilla/_ipdltest/PTestManyHandlesChild.h"
+#include "mozilla/_ipdltest/PTestManyHandlesParent.h"
+
+using namespace mozilla::ipc;
+
+namespace mozilla::_ipdltest {
+
+class TestManyHandlesChild : public PTestManyHandlesChild {
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(TestManyHandlesChild, override)
+
+ public:
+  IPCResult RecvManyHandles(nsTArray<FileDescriptor>&& aDescrs) override {
+    EXPECT_EQ(aDescrs.Length(), 500u);
+    for (int i = 0; i < static_cast<int>(aDescrs.Length()); ++i) {
+      UniqueFileHandle handle = aDescrs[i].TakePlatformHandle();
+      int value;
+      const int size = sizeof(value);
+#ifdef XP_WIN
+      EXPECT_TRUE(::ReadFile(handle.get(), &value, size, nullptr, nullptr));
+#else
+      EXPECT_EQ(read(handle.get(), &value, size), size);
+#endif
+      EXPECT_EQ(value, i);
+    }
+    Close();
+    return IPC_OK();
+  }
+
+ private:
+  ~TestManyHandlesChild() = default;
+};
+
+class TestManyHandlesParent : public PTestManyHandlesParent {
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(TestManyHandlesParent, override)
+
+ private:
+  ~TestManyHandlesParent() = default;
+};
+
+IPDL_TEST(TestManyHandles) {
+  nsTArray<FileDescriptor> descrs;
+  for (int i = 0; i < 500; ++i) {
+    const int size = sizeof(i);
+    UniqueFileHandle readPipe;
+    UniqueFileHandle writePipe;
+#ifdef XP_WIN
+    ASSERT_TRUE(::CreatePipe(getter_Transfers(readPipe),
+                             getter_Transfers(writePipe), nullptr, size));
+    ASSERT_TRUE(::WriteFile(writePipe.get(), &i, size, nullptr, nullptr));
+#else
+    int fds[2];
+    ASSERT_EQ(pipe(fds), 0);
+    readPipe.reset(fds[0]);
+    writePipe.reset(fds[1]);
+    ASSERT_EQ(write(writePipe.get(), &i, size), size);
+#endif
+    descrs.AppendElement(FileDescriptor(std::move(readPipe)));
+  }
+  bool ok = mActor->SendManyHandles(descrs);
+  ASSERT_TRUE(ok);
+}
+
+}  // namespace mozilla::_ipdltest

ipc/ipdl/test/gtest/moz.build

@@ -17,11 +17,13 @@ EXPORTS.mozilla._ipdltest += [
 SOURCES += [
     "IPDLUnitTest.cpp",
     "TestBasic.cpp",
+    "TestManyHandles.cpp",
 ]
 
 IPDL_SOURCES += [
     "PIPDLUnitTest.ipdl",
     "PTestBasic.ipdl",
+    "PTestManyHandles.ipdl",
 ]
 
 include("/ipc/chromium/chromium-config.mozbuild")