diff -r 000000000000 -r 6474c204b198 ipc/glue/FileDescriptor.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ipc/glue/FileDescriptor.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,158 @@
+/* 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_ipc_FileDescriptor_h
+#define mozilla_ipc_FileDescriptor_h
+
+#include "base/basictypes.h"
+#include "base/process.h"
+#include "mozilla/DebugOnly.h"
+#include "nscore.h"
+
+#ifdef XP_WIN
+// Need the HANDLE typedef.
+#include <winnt.h>
+#else
+#include "base/file_descriptor_posix.h"
+#endif
+
+namespace mozilla {
+namespace ipc {
+
+// This class is used by IPDL to share file descriptors across processes. When
+// sending a FileDescriptor IPDL will first duplicate a platform-specific file
+// handle type ('PlatformHandleType') into a handle that is valid in the other
+// process. Then IPDL will convert the duplicated handle into a type suitable
+// for pickling ('PickleType') and then send that through the IPC pipe. In the
+// receiving process the pickled data is converted into a platform-specific file
+// handle and then returned to the receiver.
+//
+// To use this class add 'FileDescriptor' as an argument in the IPDL protocol
+// and then pass a file descriptor from C++ to the Call/Send method. The
+// Answer/Recv method will receive a FileDescriptor& on which PlatformHandle()
+// can be called to return the platform file handle.
+class FileDescriptor
+{
+public:
+  typedef base::ProcessHandle ProcessHandle;
+
+#ifdef XP_WIN
+  typedef HANDLE PlatformHandleType;
+  typedef HANDLE PickleType;
+#else
+  typedef int PlatformHandleType;
+  typedef base::FileDescriptor PickleType;
+#endif
+
+  // This should only ever be created by IPDL.
+  struct IPDLPrivate
+  {};
+
+  FileDescriptor();
+
+  FileDescriptor(const FileDescriptor& aOther)
+    : mHandleCreatedByOtherProcess(false),
+      mHandleCreatedByOtherProcessWasUsed(false)
+  {
+    // Don't use operator= here because that will call
+    // CloseCurrentProcessHandle() on this (uninitialized) object.
+    Assign(aOther);
+  }
+
+  FileDescriptor(PlatformHandleType aHandle);
+
+  FileDescriptor(const IPDLPrivate&, const PickleType& aPickle)
+#ifdef XP_WIN
+  : mHandle(aPickle)
+#else
+  : mHandle(aPickle.fd)
+#endif
+  , mHandleCreatedByOtherProcess(true)
+  , mHandleCreatedByOtherProcessWasUsed(false)
+  { }
+
+  ~FileDescriptor()
+  {
+    CloseCurrentProcessHandle();
+  }
+
+  FileDescriptor&
+  operator=(const FileDescriptor& aOther)
+  {
+    CloseCurrentProcessHandle();
+    Assign(aOther);
+    return *this;
+  }
+
+  // Performs platform-specific actions to duplicate mHandle in the other
+  // process (e.g. dup() on POSIX, DuplicateHandle() on Windows). Returns a
+  // pickled value that can be passed to the other process via IPC.
+  PickleType
+  ShareTo(const IPDLPrivate&, ProcessHandle aOtherProcess) const;
+
+  // Tests mHandle against a well-known invalid platform-specific file handle
+  // (e.g. -1 on POSIX, INVALID_HANDLE_VALUE on Windows).
+  bool
+  IsValid() const
+  {
+    return IsValid(mHandle);
+  }
+
+  PlatformHandleType
+  PlatformHandle() const
+  {
+    if (mHandleCreatedByOtherProcess) {
+      mHandleCreatedByOtherProcessWasUsed = true;
+    }
+    return mHandle;
+  }
+
+  bool
+  operator==(const FileDescriptor& aOther) const
+  {
+    return mHandle == aOther.mHandle;
+  }
+
+private:
+  void
+  Assign(const FileDescriptor& aOther)
+  {
+    if (aOther.mHandleCreatedByOtherProcess) {
+      mHandleCreatedByOtherProcess = true;
+      mHandleCreatedByOtherProcessWasUsed =
+        aOther.mHandleCreatedByOtherProcessWasUsed;
+      mHandle = aOther.PlatformHandle();
+    } else {
+      DuplicateInCurrentProcess(aOther.PlatformHandle());
+      mHandleCreatedByOtherProcess = false;
+      mHandleCreatedByOtherProcessWasUsed = false;
+    }
+  }
+
+  static bool
+  IsValid(PlatformHandleType aHandle);
+
+  void
+  DuplicateInCurrentProcess(PlatformHandleType aHandle);
+
+  void
+  CloseCurrentProcessHandle();
+
+  PlatformHandleType mHandle;
+
+  // If this is true then this instance is created by IPDL to ferry a handle to
+  // its eventual consumer and we never close the handle. If this is false then
+  // we are a RAII wrapper around the handle and we close the handle on
+  // destruction.
+  bool mHandleCreatedByOtherProcess;
+
+  // This is to ensure that we don't leak the handle (which is only possible
+  // when we're in the receiving process).
+  mutable DebugOnly<bool> mHandleCreatedByOtherProcessWasUsed;
+};
+
+} // namespace ipc
+} // namespace mozilla
+
+#endif // mozilla_ipc_FileDescriptor_h