Define Stream base classes

webrtc/stream.h

+/*
+ *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#ifndef WEBRTC_STREAM_H_
+#define WEBRTC_STREAM_H_
+
+#include "webrtc/common_types.h"
+
+namespace webrtc {
+
+enum NetworkState {
+  kNetworkUp,
+  kNetworkDown,
+};
+
+// Common base class for streams.
+class Stream {
+ public:
+  // Starts stream activity.
+  // When a stream is active, it can receive, process and deliver samples.

[pbos-webrtc, 2015/07/15 13:06:53]

s/samples/packets/

[Jelena, 2015/07/15 14:21:45]

Done.

+  virtual void Start() = 0;
+  // Stops stream activity.
+  // When a stream is stopped, it can't receive, process or deliver samples.
+  virtual void Stop() = 0;
+  // Called to notify that network state has changed.

[pbos-webrtc, 2015/07/15 13:06:53]

Used to stop encoding and sending data while the network is down.

+  virtual void SignalNetworkState(NetworkState state) = 0;
+  // Called when a RTCP packet is received.
+  virtual bool DeliverRtcp(const uint8_t* packet, size_t length) = 0;
+
+ protected:
+  virtual ~Stream() {}
+};
+
+// Common base class for receive streams.
+class ReceiveStream : public Stream {
+ public:
+  // Called when a RTP packet is received.
+  virtual bool DeliverRtp(const uint8_t* packet, size_t length) = 0;
+};
+
+// Common base class for send streams.
+// A tag class that represents send stream concept and serves as a placeholder
+// for future functionality.

[pbos-webrtc, 2015/07/15 13:06:53]

Remove the "serves as a placeholder..", we don't add placeholders if there's no
clear functionality that will definitely be added.

Imo, do "typedef Stream SendStream;" to show that it's just for symmetry with
ReceiveStream. If we want to add stuff to it, we'll do it then.

[Jelena, 2015/07/15 14:21:45]

I agree that at a first glance, having an empty class looks unnecessary.
However, having a class instead of a typedef here, tells both a human and a
compiler that SendStream is -not- the same as Stream. Consider this:

VideoReceiveStream* receive_stream = ...;
SendStream* send_stream = static_cast<SendStream*>(receive_stream);

If SendStream is defined like this:
class SendStream : public Stream {};
the compiler catches this error.
If SendStream is defined like this:
typedef Stream SendStream;
the erroneous code gets compiled and possibly a strange bug is introduced.

+class SendStream : public Stream {};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_STREAM_H_