[mojo-edk] Support transferring null Mach ports.

mojo/edk/system/channel_posix.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/edk/system/channel.h"
 
 #include <errno.h>
 #include <sys/uio.h>
 
 #include <algorithm>
@@ skipping 122 matching lines @@
   }
 
   ScopedPlatformHandleVectorPtr GetReadPlatformHandles(
       size_t num_handles,
       const void* extra_header,
       size_t extra_header_size) override {
 #if defined(OS_MACOSX) && !defined(OS_IOS)
     // On OSX, we can have mach ports which are located in the extra header
     // section.
     using MachPortsEntry = Channel::Message::MachPortsEntry;
-    CHECK(extra_header_size >= num_handles * sizeof(MachPortsEntry));
-    size_t num_mach_ports = 0;
-    const MachPortsEntry* mach_ports =
-        reinterpret_cast<const MachPortsEntry*>(extra_header);
-    for (size_t i = 0; i < num_handles; i++) {
-      if (mach_ports[i].mach_port != MACH_PORT_NULL)
-        num_mach_ports++;
-    }
+    using MachPortsExtraHeader = Channel::Message::MachPortsExtraHeader;
+    CHECK(extra_header_size >=
+          sizeof(MachPortsExtraHeader) + num_handles * sizeof(MachPortsEntry));
+    const MachPortsExtraHeader* mach_ports_header =
+        reinterpret_cast<const MachPortsExtraHeader*>(extra_header);
+    size_t num_mach_ports = mach_ports_header->num_ports;
     CHECK(num_mach_ports <= num_handles);
     if (incoming_platform_handles_.size() + num_mach_ports < num_handles)
       return nullptr;
 
     ScopedPlatformHandleVectorPtr handles(
         new PlatformHandleVector(num_handles));
+    const MachPortsEntry* mach_ports = mach_ports_header->entries;
     for (size_t i = 0, mach_port_index = 0; i < num_handles; ++i) {
       if (mach_port_index < num_mach_ports &&
           mach_ports[mach_port_index].index == i) {
         (*handles)[i] = PlatformHandle(
             static_cast<mach_port_t>(mach_ports[mach_port_index].mach_port));
         CHECK((*handles)[i].type == PlatformHandle::Type::MACH);
         // These are actually just Mach port names until they're resolved from
         // the remote process.
         (*handles)[i].type = PlatformHandle::Type::MACH_NAME;
         mach_port_index++;
@@ skipping 319 matching lines @@
 // static
 scoped_refptr<Channel> Channel::Create(
     Delegate* delegate,
     ScopedPlatformHandle platform_handle,
     scoped_refptr<base::TaskRunner> io_task_runner) {
   return new ChannelPosix(delegate, std::move(platform_handle), io_task_runner);
 }
 
 }  // namespace edk
 }  // namespace mojo