feat(core,host): Wake-on-LAN sender + host MAC advertisement

Add a runtime-free Wake-on-LAN sender in punktfunk-core (per-interface subnet-directed broadcast + 255.255.255.255 on ports 9/7, repeated, optional last-known-IP unicast) exposed both as a Rust fn and a punktfunk_wake_on_lan C-ABI (ABI v3), plus a parse_mac helper. The host enumerates its wake-capable NIC MAC(s) and advertises them in a new mDNS `mac` TXT record (routed NIC first), and best-effort detects & warns (never modifies) when the NIC isn't armed for WoL.

MAC delivery is via the unauthenticated mDNS TXT rather than the connection handshake by design: a spoofed MAC only makes a wake fail (the packet is inert; the cert fingerprint still gates the connection), and it avoids threading through the hot connect path.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-core/Cargo.toml

@@ -38,6 +38,10 @@ thiserror = "2"
 tracing = { version = "0.1", default-features = false, features = ["std"] }
 rand = "0.9"
 zeroize = "1"
+# Interface enumeration for Wake-on-LAN: computes each NIC's subnet-directed broadcast so a
+# magic packet reaches the host's L2 segment on multi-homed clients (VPN/docker/multiple LANs),
+# not just the default route. Tiny, cross-platform (getifaddrs / GetAdaptersAddresses), no cmake.
+if-addrs = "0.13"
 
 quinn = { version = "0.11", optional = true }
 rustls = { version = "0.23", optional = true, default-features = false, features = ["ring", "std"] }

crates/punktfunk-core/src/abi.rs

@@ -183,6 +183,60 @@ pub extern "C" fn punktfunk_abi_version() -> u32 {
     crate::ABI_VERSION
 }
 
+/// Send a Wake-on-LAN magic packet to wake sleeping host NIC(s).
+///
+/// `macs` points to `mac_count` contiguous 6-byte MAC addresses (`mac_count * 6` bytes total) —
+/// a host may report several NICs; all are woken. `last_known_ip`, if non-NULL, is an IPv4
+/// dotted-quad string additionally targeted by unicast (pass NULL to skip). The packet is
+/// broadcast to every local interface's subnet-directed broadcast and to `255.255.255.255` on
+/// ports 9 and 7. This does NOT require an open connection and is not part of the QUIC surface.
+///
+/// Returns `Ok` if at least one datagram was sent. Call off the UI thread.
+///
+/// # Safety
+/// `macs` must point to at least `mac_count * 6` readable bytes. `last_known_ip`, if non-NULL,
+/// must be a NUL-terminated string.
+#[no_mangle]
+pub unsafe extern "C" fn punktfunk_wake_on_lan(
+    macs: *const u8,
+    mac_count: usize,
+    last_known_ip: *const c_char,
+) -> PunktfunkStatus {
+    guard(|| {
+        if macs.is_null() {
+            return PunktfunkStatus::NullPointer;
+        }
+        if mac_count == 0 {
+            return PunktfunkStatus::InvalidArg;
+        }
+        let bytes = unsafe { std::slice::from_raw_parts(macs, mac_count * 6) };
+        let mac_vec: Vec<crate::wol::Mac> = bytes
+            .chunks_exact(6)
+            .map(|c| {
+                let mut m = [0u8; 6];
+                m.copy_from_slice(c);
+                m
+            })
+            .collect();
+        let ip = if last_known_ip.is_null() {
+            None
+        } else {
+            match unsafe { CStr::from_ptr(last_known_ip) }
+                .to_str()
+                .ok()
+                .and_then(|s| s.parse::<std::net::Ipv4Addr>().ok())
+            {
+                Some(ip) => Some(ip),
+                None => return PunktfunkStatus::InvalidArg,
+            }
+        };
+        match crate::wol::send_magic_packet(&mac_vec, ip) {
+            Ok(()) => PunktfunkStatus::Ok,
+            Err(_) => PunktfunkStatus::Io,
+        }
+    })
+}
+
 /// Create a session over a real UDP transport (`local`/`peer` are `host:port` strings).
 /// Returns NULL on error.
 ///

crates/punktfunk-core/src/lib.rs

@@ -39,6 +39,7 @@ pub mod quic;
 pub mod session;
 pub mod stats;
 pub mod transport;
+pub mod wol;
 
 pub use config::{CompositorPref, Config, FecConfig, FecScheme, Mode, ProtocolPhase, Role};
 pub use error::{PunktfunkError, PunktfunkStatus, Result};
@@ -50,4 +51,6 @@ pub use stats::Stats;
 ///
 /// v2: `punktfunk_connect` gained `client_cert_pem`/`client_key_pem` (pairing identities);
 /// added `punktfunk_pair` / `punktfunk_generate_identity` / `punktfunk_connection_request_mode`.
-pub const ABI_VERSION: u32 = 2;
+/// v3: added `punktfunk_wake_on_lan` (Wake-on-LAN magic packet; the host's wake MAC(s) reach
+/// clients out-of-band via the mDNS `mac` TXT record, so no connection is required to wake).
+pub const ABI_VERSION: u32 = 3;

crates/punktfunk-core/src/wol.rs

@@ -0,0 +1,182 @@
+//! Wake-on-LAN: magic-packet builder + broadcast sender.
+//!
+//! Runtime-free by design — a magic packet is one fire-and-forget UDP datagram, so this needs
+//! neither the `quic` feature nor an async runtime and links into every client (including the
+//! QUIC-less builds). The Rust clients (linux/windows/android) call these `pub fn`s directly;
+//! Swift/iOS reach them through the `punktfunk_wake_on_lan` C-ABI wrapper in [`crate::abi`].
+//!
+//! Reliability (this is the whole point — a sleeping host has no ARP entry, so a plain unicast
+//! can't wake it, and `255.255.255.255` alone leaves only via the default route). For each
+//! known host MAC we send the 102-byte packet to:
+//!   * every non-loopback IPv4 interface's **subnet-directed broadcast** (routes to that NIC's
+//!     segment — this is what covers multi-homed clients on VPN/docker/multiple LANs), and
+//!   * the **limited broadcast** `255.255.255.255`, and
+//!   * optionally a **unicast** to the host's last-known IP (covers the brief window where the
+//!     host is reachable but hasn't re-advertised, and NICs that wake on a directed unicast),
+//! on the two conventional WoL ports (9 and 7), repeated a few times to survive UDP loss.
+
+use std::io;
+use std::net::{Ipv4Addr, SocketAddr, SocketAddrV4, UdpSocket};
+
+/// A MAC address (EUI-48), the 6 bytes a magic packet targets.
+pub type Mac = [u8; 6];
+
+/// Conventional Wake-on-LAN UDP ports. 9 (discard) is by far the most common; 7 (echo) is a
+/// historical alternative some NICs also listen on. Sending to both is free insurance.
+const WOL_PORTS: [u16; 2] = [9, 7];
+
+/// Times each packet is re-sent per call. UDP is lossy and this is fire-and-forget; a small
+/// burst costs microseconds and materially improves the odds a waking NIC catches one. The
+/// caller's connect-retry loop provides the longer-spaced re-attempts.
+const BURST: usize = 3;
+
+/// Parse a MAC string — `aa:bb:cc:dd:ee:ff` or `aa-bb-...`, case-insensitive — into 6 bytes.
+/// Returns `None` for anything that isn't exactly six hex octets. Shared by the Rust clients
+/// (linux/windows) so MAC parsing lives in one place; the Swift/Apple client parses its own.
+pub fn parse_mac(s: &str) -> Option<Mac> {
+    let mut m = [0u8; 6];
+    let mut n = 0;
+    for part in s.split(|c| c == ':' || c == '-') {
+        if n == 6 {
+            return None; // too many octets
+        }
+        m[n] = u8::from_str_radix(part.trim(), 16).ok()?;
+        n += 1;
+    }
+    (n == 6).then_some(m)
+}
+
+/// The 102-byte magic packet for `mac`: 6×`0xFF` followed by the MAC repeated 16 times.
+pub fn build_magic_packet(mac: Mac) -> [u8; 102] {
+    let mut pkt = [0xFFu8; 102];
+    for i in 0..16 {
+        let off = 6 + i * 6;
+        pkt[off..off + 6].copy_from_slice(&mac);
+    }
+    pkt
+}
+
+/// Broadcast a wake for every MAC in `macs`. `last_known_ip`, when set, is additionally
+/// targeted by unicast.
+///
+/// Returns `Ok` if at least one datagram was sent, so a single unreachable target (e.g. a
+/// directed broadcast with no route) doesn't fail the whole wake. Errors only if no socket
+/// could be opened or nothing could be sent at all.
+pub fn send_magic_packet(macs: &[Mac], last_known_ip: Option<Ipv4Addr>) -> io::Result<()> {
+    if macs.is_empty() {
+        return Err(io::Error::new(io::ErrorKind::InvalidInput, "no MAC addresses"));
+    }
+
+    // Build the target IP set: each interface's directed broadcast, the limited broadcast, and
+    // the optional last-known unicast. Dedup so a single-NIC client doesn't send twice.
+    let mut targets = broadcast_addrs();
+    targets.push(Ipv4Addr::BROADCAST); // 255.255.255.255
+    if let Some(ip) = last_known_ip {
+        targets.push(ip);
+    }
+    targets.sort_unstable();
+    targets.dedup();
+
+    // One broadcast-enabled socket bound to all interfaces. Directed broadcasts route to the
+    // matching NIC via the routing table; the limited broadcast leaves via the default route.
+    let sock = UdpSocket::bind((Ipv4Addr::UNSPECIFIED, 0))?;
+    sock.set_broadcast(true)?;
+
+    let mut sent_any = false;
+    for _ in 0..BURST {
+        for mac in macs {
+            let pkt = build_magic_packet(*mac);
+            for ip in &targets {
+                for port in WOL_PORTS {
+                    let dst = SocketAddr::V4(SocketAddrV4::new(*ip, port));
+                    if sock.send_to(&pkt, dst).is_ok() {
+                        sent_any = true;
+                    }
+                }
+            }
+        }
+    }
+
+    if sent_any {
+        Ok(())
+    } else {
+        Err(io::Error::new(io::ErrorKind::Other, "no magic packet could be sent"))
+    }
+}
+
+/// Subnet-directed broadcast address of every non-loopback IPv4 interface (`ip | !netmask`,
+/// or the OS-provided broadcast when present). Best-effort: interface enumeration failing
+/// (permissions, exotic platform) yields an empty list, and the limited broadcast still fires.
+fn broadcast_addrs() -> Vec<Ipv4Addr> {
+    let mut out = Vec::new();
+    let ifaces = match if_addrs::get_if_addrs() {
+        Ok(i) => i,
+        Err(_) => return out,
+    };
+    for iface in ifaces {
+        if iface.is_loopback() {
+            continue;
+        }
+        if let if_addrs::IfAddr::V4(v4) = iface.addr {
+            let bcast = v4.broadcast.unwrap_or_else(|| {
+                Ipv4Addr::from(u32::from(v4.ip) | !u32::from(v4.netmask))
+            });
+            // Skip a degenerate 0.0.0.0 (unconfigured) and the all-ones limited broadcast we
+            // already add unconditionally.
+            if !bcast.is_unspecified() && bcast != Ipv4Addr::BROADCAST {
+                out.push(bcast);
+            }
+        }
+    }
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn magic_packet_layout() {
+        let mac: Mac = [0xDE, 0xAD, 0xBE, 0xEF, 0x01, 0x02];
+        let pkt = build_magic_packet(mac);
+        assert_eq!(pkt.len(), 102);
+        // 6-byte 0xFF sync stream.
+        assert_eq!(&pkt[0..6], &[0xFF; 6]);
+        // MAC repeated exactly 16 times.
+        for i in 0..16 {
+            let off = 6 + i * 6;
+            assert_eq!(&pkt[off..off + 6], &mac, "repetition {i} mismatch");
+        }
+    }
+
+    #[test]
+    fn empty_macs_is_error() {
+        assert!(send_magic_packet(&[], None).is_err());
+    }
+
+    #[test]
+    fn parse_mac_forms() {
+        assert_eq!(parse_mac("aa:bb:cc:dd:ee:ff"), Some([0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff]));
+        assert_eq!(parse_mac("AA-BB-CC-DD-EE-FF"), Some([0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff]));
+        assert_eq!(parse_mac("01:02:03:04:05:06"), Some([1, 2, 3, 4, 5, 6]));
+        assert_eq!(parse_mac("aa:bb:cc:dd:ee"), None); // too few
+        assert_eq!(parse_mac("aa:bb:cc:dd:ee:ff:00"), None); // too many
+        assert_eq!(parse_mac("zz:bb:cc:dd:ee:ff"), None); // non-hex
+        assert_eq!(parse_mac(""), None);
+    }
+
+    #[test]
+    fn send_does_not_panic_with_a_mac() {
+        // Best-effort: binds a real socket and broadcasts on the loopback host. Must not panic
+        // and, on any machine with a usable network stack, should report success.
+        let _ = send_magic_packet(&[[0x01, 0x02, 0x03, 0x04, 0x05, 0x06]], None);
+    }
+
+    #[test]
+    fn broadcast_addrs_never_contains_limited_or_unspecified() {
+        for b in broadcast_addrs() {
+            assert_ne!(b, Ipv4Addr::BROADCAST);
+            assert!(!b.is_unspecified());
+        }
+    }
+}