Minimal WebRTC sender client with WHIP, DTLS via NWConnection, and SRTP

[Copilot]

From-scratch WebRTC send-only client: single outgoing stream (H.264 video + Opus audio), WHIP signaling, local ICE candidates only. No incoming streams, no data channels, no WHEP, no STUN/TURN.

DTLS uses NWConnection with NWParameters(dtls:udp:) rather than a custom protocol implementation — Apple handles the handshake natively.

New files (Moblin/Media/HaishinKit/WebRtc/)

• RtpPacket.swift — RTP header encode/decode, sequencer with SSRC/timestamp management
• StunMessage.swift — STUN binding request/response (RFC 5389) for ICE connectivity checks
• SdpMessage.swift — SDP offer/answer generation and parsing; sendonly, BUNDLE, rtcp-mux
• IceAgent.swift — Host candidate gathering via getifaddrs() (IPv4 only)
• WhipSession.swift — WHIP client: POST offer → parse answer → DELETE teardown; whip:// → https://
• DtlsSession.swift — NWConnection-based DTLS 1.2 session with self-signed EC P-256 certificate, SHA-256 fingerprint for SDP, SRTP keying material export via SSLExportKeyingMaterial
• SrtpSession.swift — SRTP key derivation (RFC 3711), AES-128-CTR payload encryption, HMAC-SHA1 auth tags
• WebRtcStream.swift — Top-level stream wiring WHIP → ICE → DTLS → SRTP → encoder pipeline

DTLS approach

let params = NWParameters(dtls: tlsOptions, udp: .init())
connection = NWConnection(host: nwHost, port: nwPort, using: params)
// NWConnection.State.ready = DTLS handshake complete
// SRTP keys extracted via sec_protocol_metadata_access_handle

Self-signed cert created via keychain (SecIdentity), fingerprint derived from DER data, keychain entries cleaned up immediately after identity creation.

Integration

• SettingsStreamProtocol — added .webRtc
• SettingsStream.getProtocol() — maps whip:// scheme → .webRtc
• Media.swift — webRtcStream lifecycle, WebRtcStreamDelegate conformance
• ModelStream.swift — .webRtc case in start/stop stream
• Validate.swift — whip recognized as valid URL scheme

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