September 18, 2026 — Pluggable VoIP media backend

Features

Pluggable media backend behind a neutral contract (#1509) The call flow (signaling, facade, CallHandle, registry) and the media engine (wacore::voip::CallEngine) are now separated by a neutral trait contract, whatsapp_rust::voip_control. The registry stores an Arc<dyn VoipMediaSession> and never names an engine type. That opens two new build shapes:

voip-control — compiles the whole call flow with no media engine linked. A voip-control-only build with no backend injected fails each media start with the typed MediaSetupError::NoBackend, never a panic or silent no-op.
voip-engine-wacore — the resident backend that implements the contract on top of wacore::voip::CallEngine. Composed automatically by every codec profile (voip-mlow, voip-libopus, voip), so existing VoIP clients ship the engine as their default backend with no code changes.

Install a foreign backend on the builder:

use whatsapp_rust::voip_control::{VoipMediaBackend, VoipMediaSession};

let client = Client::builder()
    // ...
    .with_voip_media_backend(MyBackend::new())
    .build()
    .await?;

whatsapp_rust::voip_control re-exports every trait, command, event, spec, and port a backend implementation names, so an external backend crate imports only from whatsapp_rust::voip_control and does not need wacore in its dependency tree. Calling with_voip_media_backend twice, or overriding the default resident backend with another, returns ClientBuilderError::VoipMediaBackendAlreadyInstalled. voip-runtime now means the composition of voip-control + voip-engine-wacore — every voip-* codec feature already includes both, so a Cargo.toml that names one of the codec features (or the voip aggregate) needs no update. Observable behavior for existing VoIP users does not change: the engine is constructed with the same config, driven by the same run_call, and events reach CallHandle::events() on the same stream, with the same pairing. Relay-connect failures surface as CallError::Connect (through the new MediaSetupError::Connect) and everything else as CallError::Setup. See VoIP Calls — Pluggable media backend for the full walkthrough and the updated Feature flags table.

​Features

Features