[mojo-edk] Add support for transferring mach ports.

mojo/edk/system/mach_port_relay.h

Index: mojo/edk/system/mach_port_relay.h
diff --git a/mojo/edk/system/mach_port_relay.h b/mojo/edk/system/mach_port_relay.h
new file mode 100644
index 0000000000000000000000000000000000000000..87bc56cf5bb31e81451f01e131889ec60f67e48e
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+++ b/mojo/edk/system/mach_port_relay.h
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+// 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.
+
+#ifndef MOJO_EDK_SYSTEM_MACH_PORT_RELAY_H_
+#define MOJO_EDK_SYSTEM_MACH_PORT_RELAY_H_
+
+#include <set>
+
+#include "base/macros.h"
+#include "base/process/port_provider_mac.h"
+#include "base/synchronization/lock.h"
+#include "mojo/edk/embedder/scoped_platform_handle.h"
+#include "mojo/edk/system/channel.h"
+
+namespace mojo {
+namespace edk {
+
+// The MachPortRelay is used by a privileged process, usually the root process,
+// to manipulate Mach ports in a child process. Ports can be added to and
+// extracted from a child process that has registered itself with the
+// |base::PortProvider| used by this class.
+class MachPortRelay : public base::PortProvider::Observer {
+ public:
+  class Observer {
+   public:
+    // Called by the MachPortRelay to notify observers that a new process is
+    // ready for Mach ports to be sent/received. There are no guarantees about
+    // the thread this is called on, including the presence of a MessageLoop.
+    // Implementations must not call AddObserver() or RemoveObserver() during
+    // this function, as doing so will deadlock.
+    virtual void OnProcessReady(base::ProcessHandle process) = 0;
+  };
+
+  // Used by a child process to receive Mach ports from a sender (privileged)
+  // process. Each Mach port in |handles| is interpreted as an intermediate Mach
+  // port. It replaces each Mach port with the final Mach port received from the
+  // intermediate port. This method takes ownership of the intermediate Mach
+  // port and gives ownership of the final Mach port to the caller. Any handles
+  // that are not Mach ports will remain unchanged, and the number and ordering
+  // of handles is preserved.
+  // Returns |false| on failure and there is no guarantee about whether a Mach
+  // port is intermediate or final.
+  //
+  // See SendPortsToProcess() for the definition of intermediate and final Mach
+  // ports.
+  static bool ReceivePorts(PlatformHandleVector* handles);
+
+  explicit MachPortRelay(base::PortProvider* port_provider);
+  ~MachPortRelay() override;
+
+  // Sends the Mach ports attached to |message| to |process|.
+  // For each Mach port attached to |message|, a new Mach port, the intermediate
+  // port, is created in |process|. The message's Mach port is then sent over
+  // this intermediate port and the message is modified to refer to the name of
+  // the intermediate port. The Mach port received over the intermediate port in
+  // the child is referred to as the final Mach port.
+  // Returns |false| on failure and |message| may contain a mix of actual Mach
+  // ports and names.
+  bool SendPortsToProcess(Channel::Message* message,
+                          base::ProcessHandle process);
+
+  // Extracts the Mach ports attached to |message| from |process|.
+  // Any Mach ports attached to |message| are names and not actual Mach ports
+  // that are valid in this process. For each of those Mach port names, a send
+  // right is extracted from |process| and the port name is replaced with the
+  // send right.
+  // Returns |false| on failure and |message| may contain a mix of actual Mach
+  // ports and names.
+  bool ExtractPortRights(Channel::Message* message,
+                         base::ProcessHandle process);
+
+  // Observer interface.
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
+  base::PortProvider* port_provider() const { return port_provider_; }
+
+ private:
+  // base::PortProvider::Observer implementation.
+  void OnReceivedTaskPort(base::ProcessHandle process) override;
+
+  base::PortProvider* const port_provider_;
+
+  base::Lock observers_lock_;
+  std::set<Observer*> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(MachPortRelay);
+};
+
+}  // namespace edk
+}  // namespace mojo
+
+#endif  // MOJO_EDK_SYSTEM_MACH_PORT_RELAY_H_