[FEATURE] extend rtpengine module to support lists and dictionaries in 'ng' protocol

[jpyle490]

This is for the rtpengine module.

The rtpengine daemon supports lists and dictionaries over the 'ng' protocol. These are required to access some features. From the doc page:

Lists and dictionaries are supported in this format using square brackets [ ], for example:

{ "rtpp_flags": "via-branch=auto-next OSRTP=[accept] codec=[transcode=[PCMA PCMU] accept=[AMR-WB AMR] strip=[EVS]]" }

One such command is sdp-media-remove, which requires a list. In Kamailio invokes it like this to remove the video, message and image streams from the SDP:

rtpengine_offer("sdp-media-remove=[video message image]")

Can we adopt the same syntax in OpenSIPS as well?

[github-actions]

Any updates here? No progress has been made in the last 15 days, marking as stale. Will close this issue if no further updates are made in the next 30 days.

[NormB]

Implementation

PR #3818 adds bracket syntax to the rtpengine module, enabling the list and dictionary features of the ng protocol from OpenSIPS script. The syntax matches the format described in the rtpengine ng protocol documentation and is compatible with how Kamailio exposes this.

Usage

# Remove media streams — sdp-media-remove expects a list
rtpengine_offer("sdp-media-remove=[video message image]");

# Codec manipulation — codec expects a dictionary with list values
rtpengine_offer("codec=[transcode=[PCMA PCMU] accept=[AMR-WB AMR] strip=[EVS]]");

# SDP attribute manipulation with escape sequences
# '..' → space, '--' → equals
rtpengine_offer("sdp-attr=[audio=[add=[fmtp:96..useinbandfec--1]]]");

# Brackets can be mixed with regular flags in the same call
rtpengine_offer("trust-address replace-origin ICE=remove codec=[transcode=[PCMA]]");

How it works

A value enclosed in [...] is parsed module-side into a native bencode list (space-separated items) or dictionary (if any top-level item contains =). Brackets can be nested for multi-level structures like codec=[transcode=[PCMA PCMU] strip=[EVS]]. The resulting bencode structures are sent to the rtpengine daemon as standard bencode — no daemon-side changes required, compatible with all daemon versions that support the underlying features.

The tokenizer in parse_flags() was extended to track bracket nesting depth when scanning values, so expressions like codec=[transcode=[PCMA PCMU]] are correctly consumed as a single value rather than being split on the inner space.

Security

• Nesting depth limited to 8 levels
• Input length limited to 4096 bytes per bracket value
• Bracket balance validated in both tokenizer and parser
• All allocations NULL-checked

Backward compatibility

Fully backward compatible. Existing flag strings are parsed identically — the bracket path is only entered when =[ is encountered. Legacy prefix-style codec flags (transcode-CODEC, codec-strip-CODEC, etc.) continue to work unchanged.

Testing

53 unit tests covering lists, dictionaries, nesting, security edge cases (depth overflow, length overflow, unmatched brackets, empty keys/values, NULL buffer), and escape sequences.