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Fix ICE failures by replacing mDNS .local addresses with real peer IPs

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Modern browsers obfuscate local IP addresses with mDNS hostnames
(e.g. abcdef12-3456.local) for privacy. When mDNS resolution is
unavailable on the LAN, WebRTC ICE candidates cannot be resolved
and the peer connection fails.

This fix makes the signaling server extract each client's real IP
from the TCP connection and share it via Welcome/PeerJoined messages.
The client then replaces any .local mDNS addresses in SDP offers,
answers, and trickle ICE candidates with the peer's actual IP address,
enabling direct IP connectivity without relying on mDNS.

https://claude.ai/code/session_01EZrFdyAR35RLwRdHUA9zPJ
This commit is contained in:
Claude 2026-02-09 07:38:49 +00:00
parent accbfdb1ea
commit cc57356a53
No known key found for this signature in database
2 changed files with 78 additions and 33 deletions
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30
lanshare/src/main.rs
View file

@ -1,5 +1,6 @@
use axum::{
extract::{
connect_info::ConnectInfo,
ws::{Message, WebSocket, WebSocketUpgrade},
State,
},
@ -63,6 +64,7 @@ enum SignalMessage {
/// Server assigns an ID to a new peer
Welcome {
peer_id: String,
ip: String,
peers: Vec<PeerInfo>,
},
/// Peer announces themselves (with optional name)
@ -73,6 +75,7 @@ enum SignalMessage {
PeerJoined {
peer_id: String,
name: String,
ip: String,
},
/// Broadcast: a peer left
PeerLeft {
@ -120,6 +123,7 @@ enum SignalMessage {
struct PeerInfo {
peer_id: String,
name: String,
ip: String,
is_sharing: bool,
has_audio: bool,
}
@ -127,6 +131,7 @@ struct PeerInfo {
/// State for a connected peer
struct PeerState {
name: String,
ip: String,
is_sharing: bool,
has_audio: bool,
tx: broadcast::Sender<SignalMessage>,
@ -150,6 +155,7 @@ impl AppState {
.map(|entry| PeerInfo {
peer_id: entry.key().clone(),
name: entry.value().name.clone(),
ip: entry.value().ip.clone(),
is_sharing: entry.value().is_sharing,
has_audio: entry.value().has_audio,
})
@ -216,19 +222,27 @@ async fn main() {
let config = RustlsConfig::from_pem_file(args.certificate, args.key).await.unwrap();
axum_server::bind_rustls(addr, config).serve(app.into_make_service()).await.unwrap();
axum_server::bind_rustls(addr, config)
.serve(app.into_make_service_with_connect_info::<SocketAddr>())
.await
.unwrap();
}
async fn serve_index() -> impl IntoResponse {
Html(include_str!("../static/index.html"))
}
async fn ws_handler(ws: WebSocketUpgrade, State(state): State<Arc<AppState>>) -> impl IntoResponse {
ws.on_upgrade(move |socket| handle_socket(socket, state))
async fn ws_handler(
ws: WebSocketUpgrade,
ConnectInfo(addr): ConnectInfo<SocketAddr>,
State(state): State<Arc<AppState>>,
) -> impl IntoResponse {
ws.on_upgrade(move |socket| handle_socket(socket, state, addr))
}
async fn handle_socket(socket: WebSocket, state: Arc<AppState>) {
async fn handle_socket(socket: WebSocket, state: Arc<AppState>, addr: SocketAddr) {
let peer_id = Uuid::new_v4().to_string();
let peer_ip = addr.ip().to_string();
let (tx, _) = broadcast::channel::<SignalMessage>(64);
// Add peer to state with default name
@ -236,6 +250,7 @@ async fn handle_socket(socket: WebSocket, state: Arc<AppState>) {
peer_id.clone(),
PeerState {
name: format!("Peer {}", &peer_id[..8]),
ip: peer_ip.clone(),
is_sharing: false,
has_audio: false,
tx: tx.clone(),
@ -250,6 +265,7 @@ async fn handle_socket(socket: WebSocket, state: Arc<AppState>) {
// Send welcome message with current peer list
let welcome = SignalMessage::Welcome {
peer_id: peer_id.clone(),
ip: peer_ip,
peers: peers.into_iter().filter(|p| p.peer_id != peer_id).collect(),
};
@ -319,6 +335,11 @@ async fn handle_socket(socket: WebSocket, state: Arc<AppState>) {
async fn handle_signal(state: &AppState, from_peer: &str, signal: SignalMessage) {
match signal {
SignalMessage::Announce { name } => {
let ip = state
.peers
.get(from_peer)
.map(|p| p.ip.clone())
.unwrap_or_default();
if let Some(mut peer) = state.peers.get_mut(from_peer) {
peer.name = name.clone();
}
@ -326,6 +347,7 @@ async fn handle_signal(state: &AppState, from_peer: &str, signal: SignalMessage)
SignalMessage::PeerJoined {
peer_id: from_peer.to_string(),
name,
ip,
},
Some(from_peer),
);

41
lanshare/static/index.html
View file

@ -428,8 +428,9 @@
// ==================== State ====================
const state = {
peerId: null,
peerIp: null, // Our own IP as seen by the server
peerName: localStorage.getItem('lanshare_name') || null,
peers: new Map(), // peer_id -> { name, isSharing, hasAudio, stream, peerConnection }
peers: new Map(), // peer_id -> { name, ip, isSharing, hasAudio, stream, peerConnection }
localStream: null,
isSharing: false,
includeAudio: true,
@ -456,6 +457,14 @@
return candidates;
}
// Replace mDNS .local addresses with a real IP.
// Modern browsers obfuscate local IPs as UUIDs ending in .local for privacy,
// which breaks direct LAN connections when mDNS resolution isn't available.
function replaceMdnsWithIp(str, realIp) {
if (!str || !realIp) return str;
return str.replace(/[a-f0-9-]+\.local/gi, realIp);
}
console.log(`ICE mode: ${USE_TRICKLE_ICE ? 'TRICKLE' : 'BUNDLED'}`);
// ==================== DOM Elements ====================
@ -537,6 +546,8 @@
switch (msg.type) {
case 'welcome':
state.peerId = msg.peer_id;
state.peerIp = msg.ip;
console.log(`Our IP as seen by server: ${msg.ip}`);
connectingOverlay.style.display = 'none';
updateConnectionStatus(true);
@ -550,7 +561,7 @@
// Add existing peers
for (const peer of msg.peers) {
addPeer(peer.peer_id, peer.name, peer.is_sharing, peer.has_audio);
addPeer(peer.peer_id, peer.name, peer.ip, peer.is_sharing, peer.has_audio);
// Request stream from peers that are already sharing
if (peer.is_sharing) {
requestStreamFrom(peer.peer_id);
@ -560,7 +571,7 @@
break;
case 'peer_joined':
addPeer(msg.peer_id, msg.name, false, false);
addPeer(msg.peer_id, msg.name, msg.ip, false, false);
// If we're sharing, proactively send an offer to the new peer
if (state.isSharing && state.localStream) {
await sendOfferTo(msg.peer_id);
@ -607,7 +618,7 @@
if (state.isSharing && state.localStream) {
// Ensure we have this peer in our state (handles race condition)
if (!state.peers.has(msg.from)) {
addPeer(msg.from, `Peer ${msg.from.slice(0, 4)}`, false, false);
addPeer(msg.from, `Peer ${msg.from.slice(0, 4)}`, null, false, false);
}
await sendOfferTo(msg.from);
}
@ -628,11 +639,12 @@
}
// ==================== Peer Management ====================
function addPeer(peerId, name, isSharing, hasAudio) {
function addPeer(peerId, name, ip, isSharing, hasAudio) {
if (peerId === state.peerId) return;
state.peers.set(peerId, {
name,
ip,
isSharing,
hasAudio,
stream: null,
@ -683,11 +695,14 @@
console.log(` → type: ${c.type}, protocol: ${c.protocol}, address: ${c.address}, port: ${c.port}`);
if (USE_TRICKLE_ICE) {
// Replace mDNS .local addresses with our real IP for direct LAN connectivity
const candidateObj = event.candidate.toJSON();
candidateObj.candidate = replaceMdnsWithIp(candidateObj.candidate, state.peerIp);
send({
type: 'ice_candidate',
from: state.peerId,
to: peerId,
candidate: JSON.stringify(event.candidate),
candidate: JSON.stringify(candidateObj),
});
}
} else {
@ -784,7 +799,8 @@
await waitForIceGathering(pc, peerId);
}
const sdpToSend = pc.localDescription;
// Replace mDNS .local addresses with our real IP for direct LAN connectivity
const sdpToSend = { type: pc.localDescription.type, sdp: replaceMdnsWithIp(pc.localDescription.sdp, state.peerIp) };
const candidates = extractCandidatesFromSDP(sdpToSend.sdp);
console.log(`[${peerId.slice(0,8)}] Sending offer with ${candidates.length} candidates in SDP`);
@ -799,7 +815,7 @@
async function handleOffer(fromPeerId, sdpJson) {
// Ensure we have this peer in state
if (!state.peers.has(fromPeerId)) {
addPeer(fromPeerId, `Peer ${fromPeerId.slice(0, 4)}`, true, false);
addPeer(fromPeerId, `Peer ${fromPeerId.slice(0, 4)}`, null, true, false);
}
const peer = state.peers.get(fromPeerId);
@ -813,7 +829,9 @@
const pc = createPeerConnection(fromPeerId);
peer.peerConnection = pc;
// Replace any mDNS .local addresses in the remote SDP with the peer's real IP
const sdp = JSON.parse(sdpJson);
sdp.sdp = replaceMdnsWithIp(sdp.sdp, peer.ip);
const remoteCandidates = extractCandidatesFromSDP(sdp.sdp);
console.log(`[${fromPeerId.slice(0,8)}] Received offer with ${remoteCandidates.length} candidates in SDP:`);
remoteCandidates.forEach(c => console.log(` ${c}`));
@ -828,7 +846,8 @@
await waitForIceGathering(pc, fromPeerId);
}
const sdpToSend = pc.localDescription;
// Replace mDNS .local addresses with our real IP for direct LAN connectivity
const sdpToSend = { type: pc.localDescription.type, sdp: replaceMdnsWithIp(pc.localDescription.sdp, state.peerIp) };
const localCandidates = extractCandidatesFromSDP(sdpToSend.sdp);
console.log(`[${fromPeerId.slice(0,8)}] Sending answer with ${localCandidates.length} candidates in SDP`);
@ -853,7 +872,9 @@
return;
}
// Replace any mDNS .local addresses in the remote SDP with the peer's real IP
const sdp = JSON.parse(sdpJson);
sdp.sdp = replaceMdnsWithIp(sdp.sdp, peer.ip);
const remoteCandidates = extractCandidatesFromSDP(sdp.sdp);
console.log(`[${fromPeerId.slice(0,8)}] Received answer with ${remoteCandidates.length} candidates in SDP:`);
remoteCandidates.forEach(c => console.log(` ${c}`));
@ -869,7 +890,9 @@
return;
}
// Replace any mDNS .local addresses with the peer's real IP
const candidate = JSON.parse(candidateJson);
candidate.candidate = replaceMdnsWithIp(candidate.candidate, peer.ip);
console.log(`[${fromPeerId.slice(0,8)}] Remote candidate: ${candidate.candidate}`);
peer.peerConnection.addIceCandidate(new RTCIceCandidate(candidate))