Add SdpHelper for more reliable codec configuration in WebrtcTransport.

remoting/protocol/sdp_helper.h

+// Find the line in form of "a=rtpmap:<payload_type> <codec>/.." with the
+// specified |codec|. Sets |line_num| to line number and |payload_type| to the
+// payload type from that line. Returns false if the codec wasn't found.
+// 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 REMOTING_PROTOCOL_SDP_HELPER_H_
+#define REMOTING_PROTOCOL_SDP_HELPER_H_
+
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+
+namespace remoting {
+namespace protocol {
+
+// SdpHelper is used to process SDP session descriptions generated by WebRTC,

[Jamie, 2016/11/28 21:02:52]

Maybe define SDP the first time you use it.

[Sergey Ulanov, 2016/11/28 22:45:08]

Done.

+// and particularly to configure desired video and audio codecs.
+//
+// It also normalizes the SDP message to make sure the text used for HMAC
+// signatures verifications is the same that was signed on the sending side.

[Jamie, 2016/11/28 21:02:52]

s/signatures verifications/signature verification/

[Sergey Ulanov, 2016/11/28 22:45:08]

Done.

+// This is necessary because WebRTC generates SDP with CRLF line endings which
+// are sometimes converted to LF after passing the signaling channel.
+class SdpHelper {

[Jamie, 2016/11/28 21:02:52]

*Helper is a bit generic as a name. If this encapsulates an SDP message, maybe
SdpMessage would be better?

[Sergey Ulanov, 2016/11/28 22:45:09]

Done.

+ public:
+  explicit SdpHelper(const std::string& sdp);
+  ~SdpHelper();
+
+  bool has_audio() const { return has_audio_; }
+  bool has_video() const { return has_video_; }
+
+  // Returns string representation of the SDP. The result always has

[Jamie, 2016/11/28 21:02:52]

s/SDP/SDP message/

[Sergey Ulanov, 2016/11/28 22:45:08]

Done.

+  // line-endings normalized and empty lines removed.

[Jamie, 2016/11/28 21:02:52]

Be specific about what the normalized line-endings are. Looking at the code, it
seems that we're normalizing on \n. If this class is always used, it shouldn't
make any difference to our code, so I wonder if it would make more sense to
normalize on on CRLF for consistency?

[Sergey Ulanov, 2016/11/28 22:45:08]

The client normalizes with LF, so changing it to CRLF would break compatibility
with the client.

+  std::string ToString() const;
+
+  // Adds specified parameters for the |codec|. Returns false if the |codec| is
+  // not listed anywhere in SDP.

[Jamie, 2016/11/28 21:02:52]

s/SDP/the SDP message/

[Sergey Ulanov, 2016/11/28 22:45:09]

Done.

+  bool AddCodecParameter(const std::string& codec,
+                         const std::string& parameters_to_add);
+
+ private:
+  // Find the line in form of "a=rtpmap:<payload_type> <codec>/.." with the

[Jamie, 2016/11/28 21:02:52]

s/in form of/of the form/

[Sergey Ulanov, 2016/11/28 22:45:08]

Done.

+  // specified |codec|. Sets |line_num| to line number and |payload_type| to the
+  // payload type from that line. Returns false if the codec wasn't found.
+  bool FindCodec(const std::string& codec,
+                 int* line_num,
+                 std::string* payload_type) const;
+
+  std::vector<std::string> sdp_lines_;
+
+  bool has_audio_ = false;
+  bool has_video_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(SdpHelper);
+};
+
+}  // namespace protocol
+}  // namespace remoting
+
+#endif  // REMOTING_PROTOCOL_SDP_HELPER_H_