Add read support of RtpStreamId/RepairedRtpStreamId header extensions.

webrtc/common_types.h

Index: webrtc/common_types.h
diff --git a/webrtc/common_types.h b/webrtc/common_types.h
index e1a4c77d37adf184bb43b0fd87070d635f54d917..c4e32083868011cb59c71f858facb4d63fdbc0ba 100644
--- a/webrtc/common_types.h
+++ b/webrtc/common_types.h
@@ -717,6 +717,16 @@ struct RTPHeaderExtension {
   VideoRotation videoRotation;
 
   PlayoutDelay playout_delay = {-1, -1};
+
+  // For identification of a stream when ssrc is not signaled. See
+  // https://tools.ietf.org/html/draft-ietf-avtext-rid-09
+  // TODO(danilchap): Update url from draft to release version.
+  // Stream id is limited to 16 bytes because it is the maximum length
+  // that can be encoded with one-byte header extensions.
+  size_t stream_id_size = 0;
+  char stream_id[16];

[nisse-webrtc, 2017/04/10 07:15:27]

This is intended as an arbitrary octet string, which could include nul bytes?
And the octet strings "foo", "foo\0", "foo\0\0" must be treated as distinct?

Then it seems uint8_t would be more appropriate than char, and that would also
signal that str* functions aren't appropriate. (And std::basic_string<uint8_t>
instead of std::string where a string class is wanted).

[danilchap, 2017/04/10 08:39:41]

according to spec valid characters are [0-9A-Za-z], so "foo\0" is an invalid
value.
This check is not enforced during parsing for simplicity:
It makes sense to validate the configured rsid, then invalid rsid would never
match valid one.

[nisse-webrtc, 2017/04/10 09:18:33]

Then one alternative would be to always zero-pad the values to 16 bytes, and
then drop the *_size members?

That would make things look simpler here, and comparisons could be done with
memcmp(stream_id, ..., sizeof(stream_id)). Might make things complex elsewhere,
though, depending on how this is used. This option is similar to the arcane unix
strncpy semantics.

Or make it 17 bytes and always nul-terminated (and if needed to avoid false
matches, reject received ids including nul characters).

I don't have a strong opinion here, but I think it would be nice if the
representation could be simplified.

[danilchap, 2017/04/10 11:44:16]

I've created a dedicated class StreamId and moved all complexity there. This way
it become easy to remove size property and make rest of the code simpler.

+  size_t repaired_stream_id_size = 0;
+  char repaired_stream_id[16];
 };
 
 struct RTPHeader {