[asterisk-dev] [Code Review] 3763: media formats: Fix appending of compatible formats

[Matt Jordan]

> On July 12, 2014, 10:32 p.m., Matt Jordan wrote:
> > I'm not sure I understand the problem for your issue description:
> > 
> > "When ast_format_cap_append was replaced with ast_format_cap_append_from_cap, the behavior of the original function was not preserved. This change introduces ast_format_cap_append_compatible_from_cap which reproduces the original behavior of ast_format_cap_append and alters the original users of ast_format_cap_append to use ast_format_cap_append_compatible_from_cap."
> > 
> > What behavioural difference was changed? Why do we need to switch it back? What is the intent of ast_format_cap_append_compatible_from_cap? And why wouldn't you just use ast_format_cap_get_compatible?
> > 
> >
> 
> opticron wrote:
>     The difference in behavior is that ast_format_cap_append_from_cap appends unconditionally from the source format capability while ast_format_cap_append checks for compatibility with ast_format_cap_iscompatible before appending from the source format capability.
>     
>     Without switching it back, chan_pjsip now offers codecs to the endpoint that are not configured in its codec definition and causes one-way audio where it otherwise would have declined the INVITE.
>     
>     It appears that this could be accomplished using ast_format_cap_get_compatible, ast_format_cap_append_from_cap, and the allocation of another format cap for each instance.
> 
> opticron wrote:
>     I could also add an ast_media_type parameter to ast_format_cap_get_compatible to obtain equivalent functionality:
>     ast_format_cap_get_compatible(cap1, cap2, cap2, type);

ast_format_cap_append doesn't check for compatibility. In fact, ast_format_cap_append_from_cap calls ast_format_cap_append when it copies the formats over; there's really not difference between the two.

Compatibility is determined only via ast_format_cap_iscompatible_format and ast_format_cap_get_compatible. The latter will take two format compatibility structures and compute their joint capabilities. I don't see why ast_format_cap_get_compatible can't be used.

As for needing one that takes in a type as well, I don't think that will necessarily be needed. IIRC, PJSIP already maintains its formats for different media streams in different compatibility structures; other channel drivers (such as chan_sip) should already have code that pulls the formats of a particular type out of their joint capability structure.


- Matt


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On July 12, 2014, 9:19 p.m., opticron wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviewboard.asterisk.org/r/3763/
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> 
> (Updated July 12, 2014, 9:19 p.m.)
> 
> 
> Review request for Asterisk Developers, Corey Farrell and Matt Jordan.
> 
> 
> Repository: Asterisk
> 
> 
> Description
> -------
> 
> When ast_format_cap_append was replaced with ast_format_cap_append_from_cap, the behavior of the original function was not preserved. This change introduces ast_format_cap_append_compatible_from_cap which reproduces the original behavior of ast_format_cap_append and alters the original users of ast_format_cap_append to use ast_format_cap_append_compatible_from_cap.
> 
> The primary difference in behavior is that ast_format_cap_append_from_cap appends unconditionally from the source format capability while ast_format_cap_append checks for compatibility with ast_format_cap_iscompatible.
> 
> 
> Diffs
> -----
> 
>   team/group/media_formats-reviewed-trunk/res/res_pjsip_session.c 418441 
>   team/group/media_formats-reviewed-trunk/res/res_pjsip_sdp_rtp.c 418441 
>   team/group/media_formats-reviewed-trunk/main/format_cap.c 418441 
>   team/group/media_formats-reviewed-trunk/include/asterisk/format_cap.h 418441 
>   team/group/media_formats-reviewed-trunk/channels/chan_sip.c 418441 
>   team/group/media_formats-reviewed-trunk/addons/chan_ooh323.c 418441 
> 
> Diff: https://reviewboard.asterisk.org/r/3763/diff/
> 
> 
> Testing
> -------
> 
> Ensured that calling a channel via Dial() produced the same behavior as trunk.
> 
> 
> Thanks,
> 
> opticron
> 
>

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