feat(rust-proxy-engine): add a Rust SIP proxy engine with shared SIP and codec libraries

rust/crates/proxy-engine/src/rtp.rs

@@ -0,0 +1,158 @@
+//! RTP port pool and media forwarding.
+//!
+//! Manages a pool of even-numbered UDP ports for RTP media.
+//! Each port gets a bound tokio UdpSocket. Supports:
+//! - Direct forwarding (SIP-to-SIP, no transcoding)
+//! - Transcoding forwarding (via codec-lib, e.g. G.722 ↔ Opus)
+//! - Silence generation
+//! - NAT priming
+//!
+//! Ported from ts/call/rtp-port-pool.ts + sip-leg.ts RTP handling.
+
+use std::collections::HashMap;
+use std::net::SocketAddr;
+use std::sync::Arc;
+use tokio::net::UdpSocket;
+
+/// A single RTP port allocation.
+pub struct RtpAllocation {
+    pub port: u16,
+    pub socket: Arc<UdpSocket>,
+}
+
+/// RTP port pool — allocates even-numbered UDP ports.
+pub struct RtpPortPool {
+    min: u16,
+    max: u16,
+    allocated: HashMap<u16, Arc<UdpSocket>>,
+}
+
+impl RtpPortPool {
+    pub fn new(min: u16, max: u16) -> Self {
+        let min = if min % 2 == 0 { min } else { min + 1 };
+        Self {
+            min,
+            max,
+            allocated: HashMap::new(),
+        }
+    }
+
+    /// Allocate an even-numbered port and bind a UDP socket.
+    pub async fn allocate(&mut self) -> Option<RtpAllocation> {
+        let mut port = self.min;
+        while port < self.max {
+            if !self.allocated.contains_key(&port) {
+                match UdpSocket::bind(format!("0.0.0.0:{port}")).await {
+                    Ok(sock) => {
+                        let sock = Arc::new(sock);
+                        self.allocated.insert(port, sock.clone());
+                        return Some(RtpAllocation { port, socket: sock });
+                    }
+                    Err(_) => {
+                        // Port in use, try next.
+                    }
+                }
+            }
+            port += 2;
+        }
+        None // Pool exhausted.
+    }
+
+    /// Release a port back to the pool.
+    pub fn release(&mut self, port: u16) {
+        self.allocated.remove(&port);
+        // Socket is dropped when the last Arc reference goes away.
+    }
+
+    pub fn size(&self) -> usize {
+        self.allocated.len()
+    }
+
+    pub fn capacity(&self) -> usize {
+        ((self.max - self.min) / 2) as usize
+    }
+}
+
+/// An active RTP relay between two endpoints.
+/// Receives on `local_socket` and forwards to `remote_addr`.
+pub struct RtpRelay {
+    pub local_port: u16,
+    pub local_socket: Arc<UdpSocket>,
+    pub remote_addr: Option<SocketAddr>,
+    /// If set, transcode packets using this codec session before forwarding.
+    pub transcode: Option<TranscodeConfig>,
+    /// Packets received counter.
+    pub pkt_received: u64,
+    /// Packets sent counter.
+    pub pkt_sent: u64,
+}
+
+pub struct TranscodeConfig {
+    pub from_pt: u8,
+    pub to_pt: u8,
+    pub session_id: String,
+}
+
+impl RtpRelay {
+    pub fn new(port: u16, socket: Arc<UdpSocket>) -> Self {
+        Self {
+            local_port: port,
+            local_socket: socket,
+            remote_addr: None,
+            transcode: None,
+            pkt_received: 0,
+            pkt_sent: 0,
+        }
+    }
+
+    pub fn set_remote(&mut self, addr: SocketAddr) {
+        self.remote_addr = Some(addr);
+    }
+}
+
+/// Send a 1-byte NAT priming packet to open a pinhole.
+pub async fn prime_nat(socket: &UdpSocket, remote: SocketAddr) {
+    let _ = socket.send_to(&[0u8], remote).await;
+}
+
+/// Build an RTP silence frame for PCMU (payload type 0).
+pub fn silence_frame_pcmu() -> Vec<u8> {
+    // 12-byte RTP header + 160 bytes of µ-law silence (0xFF)
+    let mut frame = vec![0u8; 172];
+    frame[0] = 0x80; // V=2
+    frame[1] = 0; // PT=0 (PCMU)
+    // seq, timestamp, ssrc left as 0 — caller should set these
+    frame[12..].fill(0xFF); // µ-law silence
+    frame
+}
+
+/// Build an RTP silence frame for G.722 (payload type 9).
+pub fn silence_frame_g722() -> Vec<u8> {
+    // 12-byte RTP header + 160 bytes of G.722 silence
+    let mut frame = vec![0u8; 172];
+    frame[0] = 0x80; // V=2
+    frame[1] = 9; // PT=9 (G.722)
+    // G.722 silence: all zeros is valid silence
+    frame
+}
+
+/// Build an RTP header with the given parameters.
+pub fn build_rtp_header(pt: u8, seq: u16, timestamp: u32, ssrc: u32) -> [u8; 12] {
+    let mut header = [0u8; 12];
+    header[0] = 0x80; // V=2
+    header[1] = pt & 0x7F;
+    header[2..4].copy_from_slice(&seq.to_be_bytes());
+    header[4..8].copy_from_slice(&timestamp.to_be_bytes());
+    header[8..12].copy_from_slice(&ssrc.to_be_bytes());
+    header
+}
+
+/// Get the RTP clock increment per 20ms frame for a payload type.
+pub fn rtp_clock_increment(pt: u8) -> u32 {
+    match pt {
+        9 => 160,   // G.722: 8000 Hz clock rate (despite 16kHz audio) × 0.02s
+        0 | 8 => 160, // PCMU/PCMA: 8000 × 0.02
+        111 => 960, // Opus: 48000 × 0.02
+        _ => 160,
+    }
+}