[Extensions] Extension Port Ids and Initialization 2.0

extensions/common/api/messaging/port_id.h

Index: extensions/common/api/messaging/port_id.h
diff --git a/extensions/common/api/messaging/port_id.h b/extensions/common/api/messaging/port_id.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 EXTENSIONS_COMMON_API_MESSAGING_PORT_ID_H_
+#define EXTENSIONS_COMMON_API_MESSAGING_PORT_ID_H_
+
+#include <utility>
+
+#include "base/unguessable_token.h"
+
+namespace extensions {
+
+// A unique identifier for the Channel a port is on; i.e., the two-way
+// communication between opener and receiver(s). We can use the pair of
+// <context_id, port_number> which is the same between opener and receivers
+// but unique amongst all other connections.
+using ChannelId = std::pair<base::UnguessableToken, int>;
+
+// A unique identifier for an extension port. The id is composed of three parts:
+// - context_id: An UnguessableToken that uniquely identifies the creation
+//               context of the port.
+// - port_number: A simple identifer that uniquely identifies the port *within
+//                the creation context*. That is, each creation context may
+//                have a port with number '1', but there should only be a single
+//                port with the number '1' in each.
+// - is_opener: Whether or not this port id is for the opener port (false
+//              indicating it is the receiver port).
+// A few more notes:
+// - There should only be a single existent opener port. That is, in all the
+//   contexts, there should only be one with a given context_id, port_number,
+//   and is_opener set to true. However, each port can have multiple receivers,
+//   thus there may be multiple ports with a given context_id, port_number, and
+//   is_opener set to false.
+// - The context_id and port_number refer to the values at *creation*, and are
+//   conceptually immutable. Receiver ports will always have a context id other
+//   than the one they are hosted in (since we don't dispatch messages to the
+//   same context). Only in the case of opener ports do these identify the
+//   current context.
+// - Context id and port number are set in the renderer process. Theoretically,
+//   this means that multiple contexts could have the same id. However, GUIDs
+//   are sufficiently random as to be globally unique in practice (the chance
+//   of a duplicate is about the same as the sun exploding right now).
+struct PortId {
+  // See class comments for the description of these fields.
+  base::UnguessableToken context_id;
+  int port_number = 0;
+  bool is_opener = false;
+
+  PortId();
+  PortId(const base::UnguessableToken& context_id,
+         int port_number,
+         bool is_opener);
+  ~PortId();
+  PortId(PortId&& other);
+  PortId(const PortId& other);
+  PortId& operator=(const PortId& other);
+
+  ChannelId GetChannelId() const {
+    return std::make_pair(context_id, port_number);
+  }
+
+  // Returns the identifier for the opposite port(s). That is, a call on a
+  // receiver port returns the ID of the opener, and a call on the opener port
+  // returns the ID of all receivers.
+  PortId GetOppositePortId() const {
+    return PortId(context_id, port_number, !is_opener);
+  }
+
+  bool operator==(const PortId& other) const;
+  bool operator<(const PortId& other) const;
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_COMMON_API_MESSAGING_PORT_ID_H_