[sr-dev] adding ice attributes to sdp parser

[Ovidiu Sas]

On Sat, Dec 29, 2012 at 2:51 AM, Juha Heinanen <jh at tutpro.com> wrote:
> Ovidiu Sas writes:
>
>> The right place to add them would be sdp_stream_cell (those attributes
>> are stream attributes)
>
> ovidiu,
>
> my goal is to be able to figure out in rtpproxy/force_rtp_proxy function
> if a=candidate relay attribute(s) should be added when the function
> alters ip address and port of a media stream.
>
> the terms are a bit confusing here.  ice rfc 5245 uses terms session
> (stuff that follows s= line) and media stream (stuff that follows m=
> line).

When the sdp is parsed:
 - for each s line an sdp_session_cell is created;
 - for each m line an sdp_stream_cell is created;
 - for each codec identified by a payload in m line an
sdp_payload_attr is created.

If an SDP is received with two streams (one for audio and one for
video), we will have two m lines and therefore two sdp_stream_cell(s).
Each stream will have it's own ICE attributes.

> anyway, if media stream contains a a=candidate line with component-id 1
> (= rtp) or 2 (= rtcp), i would like to add a corresponding a=candidate
> relay line.
>
> for example, if media stream contains line
>
> a=candidate:c0626422 1 UDP 2113932031 192.98.102.1 18380 typ host
>
> i would like to add (for example) a line:
>
> a=candidate:r6ba1155 1 UDP 16777215 192.98.102.10 51345 typ relay
>
> where 192.98.102.10 and 50345 are ip and port of the media relay.
>
>> The only thing is how to organize them:
>>  - a list of all attributes
>>  - several lists based on candidate-type or component-id or something else.
>> It all depends on what do we want to access.
>
> the only thing i care about a a=candidate line is if a line with given
> type (1 or 2) exists.  i don't care how many such lines exists.  the
> other thing is that i need to know a place in sdp where the new
> a=candidate line can be added (it can be anywhere among the a= lines of
> the media stream).
>
> so i thought to add these two fields to typedef struct sdp_stream_cell:
>
>         char *first_rtp_candidate;
>              /**< RFC5245: pointer to first rtp candidate (if any) */
>         char *first_rtpc_candidate;
>              /**< RFC5245: pointer to first rtpc candidate (if any) */
>
> does this sound reasonable to you?

I think it would make sense to create a list of ice attributes so we
can add the new attribute to the proper location.  Just like we add
sdp_payload_attr to each stream we should add ice attributes to each
stream.
This will make the retrieval of each attribute fast and adding a new
ice attribute in proper place will be easier (as we would have proper
pointers to where to insert the lumps).

The ice attributes management should be very similar to
sdp_payload_attr management.

typedef struct sdp_ice_attr {
    struct sdp_ice_attr *next;
    str foundation;
    str component_id;
    str transport;
    str connection_addr
    str port;
    str candidate_type;
    int candidateType; /* ICE_HOST/ICE_SRFLX/ICE_PRFLX/ICE_RELAY/ICE_UNKNOWN */
} sdp_ice_attr_t;

and inside the sdp_stream_cell we add:
    int ice_attrs_num; /**< number of ICE attrs inside a stream */
    struct sdp_ice_attr **p_sdp_ice_attr; /**< fast access pointers to
ice attrs */
    struct sdp_ice_attr *ice_attr;


Let me know what do you think?

-ovidiu