Add functions to get/set rtp header extension by id.

webrtc/modules/rtp_rtcp/source/rtp_packet.h

 /*
  *  Copyright (c) 2016 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_MODULES_RTP_RTCP_SOURCE_RTP_PACKET_H_
@@ skipping 77 matching lines @@
 
   template <typename Extension, typename... Values>
   bool GetExtension(Values...) const;
 
   template <typename Extension, typename... Values>
   bool SetExtension(Values...);
 
   template <typename Extension>
   bool ReserveExtension();
 
+  bool HasRawExtension(int id) const;

[nisse-webrtc, 2017/04/03 09:38:00]

|id| is the numerical value used on the wire (and associated with an uri via the
extensions map)? Doesn't seem entirely obvious from context, so I think it
deserves either a comment or a more verbose argument name.

In other places, in particular, RtpHeaderExtensionMap, we use the uint8_t for
the id. But RtpExtension uses an int. Can we get any consistency?

[danilchap, 2017/04/03 10:57:00]

Failed to find verbose enough argument name, so added a comment.
Moving towards |int|, specially for parameters.
uint8_t is not a good type for this value since it is not one-byte value on the
wire (it takes half-byte). Style recommend int for this kind of generic case
with run-time range checks.

+
+  // Returns place where extension with |id| is stored.
+  // Returns empty arrayview if extension is not present.

[nisse-webrtc, 2017/04/03 09:38:00]

The return convention makes sense, assuming that no valid extension can have
zero length. Is ArrayView used in this way elsewhere in the code?

[danilchap, 2017/04/03 10:57:00]

Yes, extension is not allowed to have 0 length.
Not right now: I try to use ArrayView more often though.
When return value can't be empty, then plan to use same convention, (i.e.
treating empty arrayview as a nullptr pointer.)

+  rtc::ArrayView<const uint8_t> GetRawExtension(int id) const;
+
+  // Allocates and store header extension. Returns true on success.
+  bool SetRawExtension(int id, rtc::ArrayView<const uint8_t> data);
+
+  // Allocates and returns place to store rtp header extension.
+  // Returns empty arrayview on failure.
+  rtc::ArrayView<uint8_t> AllocateRawExtension(int id, size_t length);
+
   // Reserve size_bytes for payload. Returns nullptr on failure.
   uint8_t* SetPayloadSize(size_t size_bytes);
   // Same as SetPayloadSize but doesn't guarantee to keep current payload.
   uint8_t* AllocatePayload(size_t size_bytes);
   bool SetPadding(uint8_t size_bytes, Random* random);
 
  protected:
   // |extensions| required for SetExtension/ReserveExtension functions during
   // packet creating and used if available in Parse function.
   // Adding and getting extensions will fail until |extensions| is
@@ skipping 79 matching lines @@
   uint16_t offset = 0;
   if (!AllocateExtension(Extension::kId, Extension::kValueSizeBytes, &offset))
     return false;
   memset(WriteAt(offset), 0, Extension::kValueSizeBytes);
   return true;
 }
 }  // namespace rtp
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_RTP_PACKET_H_