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use std::collections::{HashSet, VecDeque};
use std::net::SocketAddr;
use std::time::{Duration, Instant};
use rand::random;
use crate::io::{DatagramRecv, Receive, Transmit, DATAGRAM_MTU};
use crate::io::{Id, DATAGRAM_MTU_WARN};
use crate::io::{StunMessage, TransId, STUN_TIMEOUT};
use super::candidate::{Candidate, CandidateKind};
use super::pair::{CandidatePair, CheckState, PairId};
/// Timing advance (Ta) value.
///
/// ICE agents SHOULD use a default Ta value, 50 ms, but MAY use another
/// value based on the characteristics of the associated data.
const TIMING_ADVANCE: Duration = Duration::from_millis(50);
#[derive(Debug)]
pub struct IceAgent {
/// Last time handle_timeout run (paced by timing_advance).
///
/// This drives the state forward.
last_now: Option<Instant>,
/// Whether this agent is operating as ice-lite.
/// ice-lite is a minimal version of the ICE specification, intended for servers
/// running on a public IP address. ice-lite requires the media server to only answer
/// incoming STUN binding requests and acting as a controlled entity in the ICE
/// process itself.
ice_lite: bool,
// The default limit of candidate pairs for the checklist set is 100,
// but the value MUST be configurable.
max_candidate_pairs: Option<usize>,
/// Credentials for this side. Set on init and ice-restart.
local_credentials: IceCreds,
/// Credentials for the remote side. Set when we learn about it.
remote_credentials: Option<IceCreds>,
/// If this side is controlling or controlled.
controlling: bool,
/// Number used in STUN attribute ICE-CONTROLLING and ICE-CONTROLLED.
/// An ICE agent MUST use the same number for all Binding requests,
/// for all streams, within an ICE session
control_tie_breaker: u64,
/// Current state of the agent.
state: IceConnectionState,
/// All local candidates, in the order they are "discovered" (either by
/// adding explicitly using add_candidate, or via binding/allocation
/// requests.
local_candidates: Vec<Candidate>,
/// All remote candidates, in the order we get to know them.
remote_candidates: Vec<Candidate>,
/// The candidate pairs.
candidate_pairs: Vec<CandidatePair>,
/// Transmit packet ready to be polled by poll_transmit.
transmit: VecDeque<Transmit>,
/// Events ready to be polled by poll_event.
events: VecDeque<IceAgentEvent>,
/// Queue of incoming STUN requests we might have to queue up before we receive
/// the remote_credentials.
stun_server_queue: VecDeque<StunRequest>,
/// Remote addresses we have seen traffic appear from. This is used
/// to dedupe [`IceAgentEvent::DiscoveredRecv`].
discovered_recv: HashSet<SocketAddr>,
/// Currently nominated pair for sending. This is used to evalulate
/// if we get a better candidate for [`IceAgentEvent::NominatedSend`].
nominated_send: Option<PairId>,
/// Statistics counter for the agent.
stats: IceAgentStats,
}
#[derive(Debug)]
struct StunRequest {
now: Instant,
source: SocketAddr,
destination: SocketAddr,
trans_id: TransId,
prio: u32,
use_candidate: bool,
remote_ufrag: String,
}
const REMOTE_PEER_REFLEXIVE_TEMP_FOUNDATION: &str = "tmp_prflx";
/// States the ICE connection can be in.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum IceConnectionState {
/// The ICE agent is gathering addresses.
New,
/// The ICE agent is checking pairs of local and remote candidates against one
/// another to try to find a compatible match, but has not yet found a pair
/// which will allow the peer connection to be made. It is possible that
/// gathering of candidates is also still underway.
Checking,
/// A usable pairing of local and remote candidates has been found, and the
/// connection has been established. The agent is not in `Completed` because
/// it is still gathering candidates or is still checking candidates against
/// one another looking for a better connection to use.
Connected,
/// The ICE agent has finished gathering candidates, has checked all pairs
/// against one another, and has found a working connection.
Completed,
/// Connection failed. This is a less stringent test than `failed` and may trigger
/// intermittently and resolve just as spontaneously on less reliable networks,
/// or during temporary disconnections. When the problem resolves, the connection
/// may return to the connected state.
Disconnected,
//
// NB: The failed and closed state doesn't really have a mapping in this implementation.
// We never end trickle ice and it's always possible to "come back" if more remote
// candidates are added.
//
// The ICE candidate has checked all candidates pairs against one another and has
// failed to find compatible matches.
// Failed,
// The ICE agent has shut down and is no longer handling requests.
// Closed,
}
impl IceConnectionState {
/// Tells if this state is a connected state.
pub fn is_connected(&self) -> bool {
use IceConnectionState::*;
matches!(self, Connected | Completed)
}
/// Tells if this state is a disconnected state.
pub fn is_disconnected(&self) -> bool {
*self == IceConnectionState::Disconnected
}
}
/// Credentials for STUN packages.
///
/// By matching IceCreds in STUN to SDP, we know which STUN belongs to which Peer.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct IceCreds {
// From a=ice-ufrag
pub ufrag: String,
// From a=ice-pwd
pub pass: String,
}
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub struct IceAgentStats {
pub bind_request_sent: u64,
pub bind_success_recv: u64,
pub bind_request_recv: u64,
pub discovered_recv_count: u64,
pub nomination_send_count: u64,
}
/// Events from an [`IceAgent`].
#[derive(Debug, PartialEq, Eq)]
pub enum IceAgentEvent {
/// The agent resarted (or started).
IceRestart(IceCreds),
/// Connection state changed.
///
/// This is mostly for show since the actual addresses to use will be
/// communicated in `PossibleRemote` and `NominatedLocal`.
IceConnectionStateChange(IceConnectionState),
/// A possible remote socket for the peer.
///
/// The application should associate this with the peer. There will
/// be more than one of these, and traffic might eventually come in
/// on any of them.
///
/// For each ICE restart, the app will only receive unique addresses once.
DiscoveredRecv {
/// The remote socket to look out for.
source: SocketAddr,
},
/// A nominated local and remote socket for sending data.
///
/// As opposed to the ICE spec, we can send this multiple times without
/// requiring an ICE restart. The application should always use the values
/// of the last emitted event to send data.
NominatedSend {
/// The local socket address to send datagrams from.
///
/// This will correspond to some local address added to
/// [`IceAgent::add_local_candidate`].
source: SocketAddr,
/// The remote address to send datagrams to.
destination: SocketAddr,
},
}
impl IceCreds {
pub fn new() -> Self {
// Username Fragment and Password: Values used to perform connectivity
// checks. The values MUST be unguessable, with at least 128 bits of
// random number generator output used to generate the password, and
// at least 24 bits of output to generate the username fragment.
//
// Chrome demands lengths for ufrag 4 and pass 22.
let ufrag = Id::<4>::random().to_string();
let pass = Id::<22>::random().to_string();
IceCreds { ufrag, pass }
}
}
impl IceAgent {
pub fn new() -> Self {
IceAgent {
last_now: None,
ice_lite: false,
max_candidate_pairs: None,
local_credentials: IceCreds::new(),
remote_credentials: None,
controlling: false,
control_tie_breaker: random(),
state: IceConnectionState::New,
local_candidates: vec![],
remote_candidates: vec![],
candidate_pairs: vec![],
transmit: VecDeque::new(),
events: VecDeque::new(),
stun_server_queue: VecDeque::new(),
discovered_recv: HashSet::new(),
nominated_send: None,
stats: IceAgentStats::default(),
}
}
/// Enable or disable ice_lite.
///
/// Default is disabled.
pub fn set_ice_lite(&mut self, enabled: bool) {
self.ice_lite = enabled;
}
/// Local ice credentials.
pub fn local_credentials(&self) -> &IceCreds {
&self.local_credentials
}
/// Local ice candidates.
pub fn local_candidates(&self) -> &[Candidate] {
&self.local_candidates
}
/// Sets the remote ice credentials.
pub fn set_remote_credentials(&mut self, r: IceCreds) {
if self.remote_credentials.as_ref() != Some(&r) {
info!("Set remote credentials: {:?}", r);
self.remote_credentials = Some(r);
}
}
/// Credentials for STUN.
///
/// The username for the credential is formed by concatenating the
/// username fragment provided by the peer with the username fragment of
/// the ICE agent sending the request, separated by a colon (":").
///
/// The password is equal to the password provided by the peer.
///
/// The responses utilize the same usernames and passwords as the requests
/// (note that the USERNAME attribute is not present in the response).
///
/// ### Panics
///
/// Panics if there are no remote credentials set.
fn stun_credentials(&self, reply: bool) -> (String, String) {
let local = &self.local_credentials;
let (left, right, peer_pass) = if reply {
("not_used", "not_used", "not_used")
} else {
let peer = self
.remote_credentials
.as_ref()
.expect("Remote ICE credentials");
(&peer.ufrag[..], &local.ufrag[..], &peer.pass[..])
};
let username = format!("{left}:{right}");
let password = if reply {
local.pass.clone()
} else {
peer_pass.into()
};
(username, password)
}
/// Whether this side is controlling or controlled.
#[allow(unused)]
pub fn controlling(&self) -> bool {
self.controlling
}
/// Set whether we are the controlling side.
///
/// ### Panics
///
/// Panics if we have started running the ice agent.
pub fn set_controlling(&mut self, v: bool) {
self.controlling = v;
}
/// Current ice agent state.
pub fn state(&self) -> IceConnectionState {
self.state
}
/// Stats for the agent.
///
/// Resets on ICE restart.
#[allow(unused)]
pub fn stats(&self) -> IceAgentStats {
self.stats
}
/// Adds a local candidate.
///
/// Returns `false` if the candidate was not added because it is redundant.
/// Adding loopback addresses or multicast/broadcast addresses causes
/// an error.
pub fn add_local_candidate(&mut self, mut c: Candidate) -> bool {
info!("Add local candidate: {:?}", c);
let ip = c.addr().ip();
if self.ice_lite {
// Reject all non-host candidates.
if c.kind() != CandidateKind::Host {
debug!("Reject non-host candidate due to ice-lite mode: {:?}", c);
return false;
}
}
// https://datatracker.ietf.org/doc/html/rfc8445#section-5.1.2.1
// The local preference MUST be an integer from 0 (lowest preference) to
// 65535 (highest preference) inclusive. When there is only a single IP
// address, this value SHOULD be set to 65535. If there are multiple
// candidates for a particular component for a particular data stream
// that have the same type, the local preference MUST be unique for each
// one.
// ...
// If an ICE agent is multihomed and has multiple IP addresses, the
// recommendations in [RFC8421] SHOULD be followed. If multiple TURN
// servers are used, local priorities for the candidates obtained from
// the TURN servers are chosen in a similar fashion as for multihomed
// local candidates: the local preference value is used to indicate a
// preference among different servers, but the preference MUST be unique
// for each one.
// ================
//
// The above presupposes that we know all the candidates when we start
// the ice agent. That doesn't work for us, so we deliberately do not
// follow spec. We assign the following intervals for the different
// types of candidates:
//
// 0 - 16384 => relay
// 16384 - 32768 => srflx
// 32768 - 49152 => prflx
// 49152 - 65536 => host
//
// And furthermore we subdivide these to interleave IPv6 with IPv4
// so that odd numbers are ipv6 and even are ipv4.
//
// For host candidates this means:
// 65535 - first ipv6
// 65534 - first ipv4
// 65533 - second ipv6
// 65432 - second ipv4
let counter_start: u32 = {
use CandidateKind::*;
let x = match c.kind() {
Host => 65_535,
PeerReflexive => 49_151,
ServerReflexive => 32_767,
Relayed => 16_383,
};
x - if ip.is_ipv6() { 0 } else { 1 }
};
// Count the number of existing candidates of the same kind.
let same_kind = self
.local_candidates
.iter()
.filter(|v| v.kind() == c.kind())
.filter(|v| v.addr().is_ipv6() == ip.is_ipv6())
.count() as u32;
let pref = counter_start - same_kind * 2;
trace!("Calculated local preference: {}", pref);
c.set_local_preference(pref);
// A candidate is redundant if and only if its transport address and base equal those
// of another candidate. The agent SHOULD eliminate the redundant
// candidate with the lower priority.
//
// NB this must be done _after_ set_local_prefrence(), since the prio() used in the
// elimination is calculated from that preference.
if let Some((idx, other)) = self
.local_candidates
.iter_mut()
.enumerate()
.find(|(_, v)| v.addr() == c.addr() && v.base() == c.base())
{
if c.prio() < other.prio() {
// The new candidate is not better than what we already got.
debug!(
"Reject redundant candidate, current: {:?} rejected: {:?}",
other, c
);
return false;
} else {
// Stop using the current candidate in favor of the new one.
debug!(
"Replace redundant candidate, current: {:?} replaced with: {:?}",
other, c
);
other.set_discarded();
self.discard_candidate_pairs(idx);
}
}
// Tie this ufrag to this ICE-session.
c.set_ufrag(&self.local_credentials.ufrag);
// These are the indexes of the remote candidates this candidate should be paired with.
let remote_idxs: Vec<_> = self
.remote_candidates
.iter()
.enumerate()
.filter(|(_, v)| !v.discarded() && v.addr().is_ipv4() == ip.is_ipv4())
.map(|(i, _)| i)
.collect();
self.local_candidates.push(c);
let local_idxs = [self.local_candidates.len() - 1];
// We always run in trickle ice mode.
//
// https://www.rfc-editor.org/rfc/rfc8838.html#section-10
// A Trickle ICE agent MUST NOT pair a local candidate until it has been trickled
// to the remote party.
//
// TODO: The trickle ice spec is strange. What does it mean "has been trickled to the
// remote party"? Since we don't get a confirmation that the candidate has been received
// by the remote party, whether we form local pairs directly or later seems irrelevant.
self.form_pairs(&local_idxs, &remote_idxs);
true
}
/// Adds a local candidate.
///
/// Returns `false` if the candidate was not added because it is redundant.
/// Adding loopback addresses or multicast/broadcast addresses causes
/// an error.
pub fn add_remote_candidate(&mut self, c: Candidate) {
info!("Add remote candidate: {:?}", c);
// This is a a:rtcp-mux-only implementation. The only component
// we accept is 1 for RTP.
if c.component_id() != 1 {
debug!("Reject candidate for component other than 1: {:?}", c);
return;
}
if let Some(creds) = &self.remote_credentials {
if let Some(ufrag) = c.ufrag() {
if ufrag != creds.ufrag {
debug!(
"Reject candidate with ufrag mismatch: {} != {}",
ufrag, creds.ufrag
);
return;
}
}
}
let existing_prflx = self
.remote_candidates
.iter_mut()
.enumerate()
.find(|(_, v)| {
v.foundation() == REMOTE_PEER_REFLEXIVE_TEMP_FOUNDATION
&& v.kind() == CandidateKind::PeerReflexive
&& v.addr() == c.addr()
});
let ipv4 = c.addr().is_ipv4();
let remote_idx = if let Some((idx, existing)) = existing_prflx {
// If any subsequent candidate exchanges contain this peer-reflexive
// candidate, it will signal the actual foundation for the candidate.
info!(
"Replace peer reflexive candidate, current: {:?} replaced with: {:?}",
existing, c
);
*existing = c;
idx
} else {
self.remote_candidates.push(c);
self.remote_candidates.len() - 1
};
// These are the indexes of the local candidates this candidate should be paired with.
let local_idxs: Vec<_> = self
.local_candidates
.iter()
.enumerate()
.filter(|(_, v)| !v.discarded() && v.addr().is_ipv4() == ipv4)
.map(|(i, _)| i)
.collect();
let remote_idxs = [remote_idx];
self.form_pairs(&local_idxs, &remote_idxs);
}
/// Form pairs given two slices of indexes into the local_candidates and remote_candidates.
fn form_pairs(&mut self, local_idxs: &[usize], remote_idxs: &[usize]) {
for local_idx in local_idxs {
'outer: for remote_idx in remote_idxs {
let local = &self.local_candidates[*local_idx];
let remote = &self.remote_candidates[*remote_idx];
let prio =
CandidatePair::calculate_prio(self.controlling, remote.prio(), local.prio());
let mut pair = CandidatePair::new(*local_idx, *remote_idx, prio);
trace!("Form pair local: {:?} remote: {:?}", local, remote);
// The agent prunes each checklist. This is done by removing a
// candidate pair if it is redundant with a higher-priority candidate
// pair in the same checklist. Two candidate pairs are redundant if
// their local candidates have the same base and their remote candidates
// are identical.
for (check_idx, check) in self.candidate_pairs.iter().enumerate() {
let check_local = check.local_candidate(&self.local_candidates);
let check_remote = check.remote_candidate(&self.remote_candidates);
let redundant =
local.base() == check_local.base() && remote.addr() == check_remote.addr();
if redundant {
if check.prio() >= pair.prio() {
// skip this new pair since there is a redundant pair already in the
// list with higher/equal prio.
debug!(
"Reject redundant pair, current: {:?} rejected: {:?}",
check, pair
);
} else {
// replace the existing candidate pair, since the new one got a higher prio.
debug!(
"Replace redundant pair, current: {:?} replaced with: {:?}",
check, pair
);
let was_nominated = self.candidate_pairs[check_idx].is_nominated();
pair.nominate(was_nominated);
self.candidate_pairs[check_idx] = pair;
}
// There can only be one candidate pair per local base / remote addr.
// Since we found that redundant entry, there's no point in checking further
// candidate pairs.
continue 'outer;
}
}
debug!("Add new pair {:?}", pair);
// This is not a redundant pair, add it.
self.candidate_pairs.push(pair);
}
}
// NB it would be nicer to have BTreeSet, but that makes it impossible to
// get mut references to the elements in the list.
self.candidate_pairs.sort();
// an ICE agent MUST limit the total number of connectivity checks
// the agent performs across all checklists in the checklist set.
// This is done by limiting the total number of candidate pairs in the
// checklist set. The default limit of candidate pairs for the checklist
// set is 100, but the value MUST be configurable.
//
// TODO: How does this work with trickle ice?
let max = self.max_candidate_pairs.unwrap_or(100);
while self.candidate_pairs.len() > max {
let pair = self.candidate_pairs.pop();
debug!("Remove overflow pair {:?}", pair);
}
}
/// Invalidate a candidate and remove it from the connection.
///
/// This is done for host candidates disappearing due to changes in the network
/// interfaces like a WiFi disconnecting or changing IPs.
///
/// Returns `true` if the candidate was found and invalidated.
#[allow(unused)]
pub fn invalidate_candidate(&mut self, c: &Candidate) -> bool {
info!("Invalidate candidate: {:?}", c);
if let Some((idx, other)) =
self.local_candidates.iter_mut().enumerate().find(|(_, v)| {
v.addr() == c.addr() && v.base() == c.base() && v.raddr() == c.raddr()
})
{
if !other.discarded() {
debug!("Local candidate to discard {:?}", other);
other.set_discarded();
self.discard_candidate_pairs(idx);
return true;
}
}
debug!("Candidate to discard not found: {:?}", c);
false
}
/// Restart ICE.
///
/// This is useful when detecting a change in network interfaces, such as
/// current session running off a 4G, and we connect to a WiFi. The session
/// should continue sending data over the 4G until we redone the ICE gathering
/// process.
#[allow(unused)]
pub fn ice_restart(&mut self) {
// An ICE agent MAY restart ICE for existing data streams. An ICE
// restart causes all previous states of the data streams, excluding the
// roles of the agents, to be flushed. The only difference between an
// ICE restart and a brand new data session is that during the restart,
// data can continue to be sent using existing data sessions, and a new
// data session always requires the roles to be determined.
self.local_credentials = IceCreds::new();
self.remote_credentials = None;
self.local_candidates.clear();
self.remote_candidates.clear();
self.candidate_pairs.clear();
self.transmit.clear();
self.events.clear();
self.discovered_recv.clear();
self.emit_event(IceAgentEvent::IceRestart(self.local_credentials.clone()));
self.set_connection_state(IceConnectionState::Checking, "ice restart");
}
/// Discard candidate pairs that contain the candidate identified by a local index.
fn discard_candidate_pairs(&mut self, local_idx: usize) {
trace!("Discard pairs for local candidate index: {:?}", local_idx);
self.candidate_pairs.retain(|c| c.local_idx() != local_idx);
}
/// Tells whether the message is for this agent instance.
///
/// This is used to multiplex multiple ice agents on a server sharing the same UDP socket.
/// For this to work, the server should operate in ice-lite mode and not initiate any
/// binding requests itself.
///
/// If no remote credentials have been set using `set_remote_credentials`, the remote
/// ufrag is not checked.
pub fn accepts_message(&self, message: &StunMessage<'_>) -> bool {
trace!("Check if accepts message: {:?}", message);
// The username for the credential is formed by concatenating the
// username fragment provided by the peer with the username fragment of
// the ICE agent sending the request, separated by a colon (":").
if message.is_binding_request() {
// The existence of USERNAME is checked in the STUN parser.
let (local, remote) = message.split_username().unwrap();
let local_creds = self.local_credentials();
if local != local_creds.ufrag {
trace!(
"Message rejected, local user mismatch: {} != {}",
local,
local_creds.ufrag
);
return false;
}
if let Some(remote_creds) = &self.remote_credentials {
if remote != remote_creds.ufrag {
trace!(
"Message rejected, remote user mismatch: {} != {}",
remote,
remote_creds.ufrag
);
return false;
}
}
}
let (_, password) = self.stun_credentials(!message.is_response());
if !message.check_integrity(&password) {
trace!("Message rejected, integrity check failed");
return false;
}
trace!("Message accepted");
true
}
/// Handles an incoming STUN message.
///
/// Will not be used if [`IceAgent::accepts_message`] returns false.
pub fn handle_receive(&mut self, now: Instant, r: Receive) {
trace!("Handle receive: {:?}", r);
let message = match r.contents {
DatagramRecv::Stun(v) => v,
_ => {
trace!("Receive rejected, not STUN");
return;
}
};
// Regardless of whether we have remote_creds at this point, we can
// at least check the message integrity.
if !self.accepts_message(&message) {
debug!("Message not accepted");
return;
}
if message.is_binding_request() {
self.stun_server_handle_message(now, r.source, r.destination, message);
} else if message.is_successful_binding_response() {
self.stun_client_handle_response(now, message);
}
self.emit_event(IceAgentEvent::DiscoveredRecv { source: r.source });
// TODO handle unsuccessful responses.
}
pub fn handle_timeout(&mut self, now: Instant) {
// The generation of ordinary and triggered connectivity checks is
// governed by timer Ta.
if let Some(last_now) = self.last_now {
let min_step = last_now + TIMING_ADVANCE;
if now < min_step {
return;
}
}
// This happens exactly once because evaluate_state() below will
// switch away from New -> Checking.
if self.state == IceConnectionState::New {
self.emit_event(IceAgentEvent::IceRestart(self.local_credentials.clone()));
}
self.evaluate_state(now);
// First we try to empty the queue of saved STUN requests.
if self.remote_credentials.is_some() {
let queue = &mut self.stun_server_queue;
// No need hanging on to very old requests.
while let Some(peek) = queue.front() {
if now - peek.now >= STUN_TIMEOUT {
let r = queue.pop_front();
trace!("Drop too old enqueued STUN request: {:?}", r.unwrap());
} else {
break;
}
}
if let Some(req) = self.stun_server_queue.pop_front() {
debug!("Handle enqueued STUN request: {:?}", req);
self.stun_server_handle_request(req);
return;
}
}
self.last_now = Some(now);
self.evaluate_nomination();
// prune failed candidates.
let mut any_pruned = false;
self.candidate_pairs.retain(|p| {
let keep = p.is_still_possible(now, self.ice_lite);
if !keep {
debug!("Remove failed pair: {:?}", p);
any_pruned = true;
}
keep
});
if any_pruned {
self.evaluate_nomination();
self.evaluate_state(now);
}
if self.remote_credentials.is_none() {
trace!("Stop timeout due to missing remote credentials");
return;
}
if self.ice_lite {
// Remote binding request time is the timestamp in the CandidatePair that
// is used to decide whether something is timed out or not. We need all
// pairs to have this time set, so that pairs that don't receive any
// STUN binding requests eventually times out.
for p in &mut self.candidate_pairs {
if p.remote_binding_request_time().is_none() {
p.increase_remote_binding_requests(now);
}
}
trace!("Stop timeout since ice-lite do no checks");
return;
}
// when do we need to handle the next candidate pair?
let next = self
.candidate_pairs
.iter_mut()
.enumerate()
.map(|(i, c)| (i, c.next_binding_attempt(now)))
.min_by_key(|(_, t)| *t);
if let Some((idx, deadline)) = next {
if now >= deadline {
let pair = &self.candidate_pairs[idx];
trace!("Handle next triggered pair: {:?}", pair);
self.stun_client_binding_request(now, idx);
} else {
trace!("Next triggered pair is in the future: {:?}", deadline - now);
}
}
}
/// Poll for the next datagram to send.
pub fn poll_transmit(&mut self) -> Option<Transmit> {
let x = self.transmit.pop_front();
if let Some(x) = &x {
if x.contents.len() > DATAGRAM_MTU_WARN {
warn!("ICE above MTU {}: {}", DATAGRAM_MTU_WARN, x.contents.len());
}
trace!("Poll transmit: {:?}", x);
}
x
}
/// Poll for the next time to call [`IceAgent::handle_timeout`].
///
/// Returns `None` until the first ever `handle_timeout` is called.
pub fn poll_timeout(&mut self) -> Option<Instant> {
// if we never called handle_timeout, there will be no current time.
let last_now = self.last_now?;
// We must empty the queued replies as soon as possible.
if !self.stun_server_queue.is_empty() {
return Some(last_now + TIMING_ADVANCE);
}
// when do we need to handle the next candidate pair?
let maybe_next = if self.ice_lite {
// ice-lite doesn't do checks.
None
} else {
self.candidate_pairs
.iter_mut()
.map(|c| c.next_binding_attempt(last_now))
.min()
};
// Time must advance with at least Ta.
let next = if let Some(next) = maybe_next {
if next < last_now + TIMING_ADVANCE {
last_now + TIMING_ADVANCE
} else {
next
}
} else {
// IDLE for a while.
last_now + Duration::from_secs(3)
};
Some(next)
}
fn emit_event(&mut self, event: IceAgentEvent) {
if let IceAgentEvent::DiscoveredRecv { source } = event {
if !self.discovered_recv.insert(source) {
// we already dispatched this discovered
return;
}
self.stats.discovered_recv_count += 1;
} else if matches!(event, IceAgentEvent::NominatedSend { .. }) {
self.stats.nomination_send_count += 1;
}
trace!("Enqueueing event: {:?}", event);
self.events.push_back(event);
}
pub fn poll_event(&mut self) -> Option<IceAgentEvent> {
let x = self.events.pop_front();
if x.is_some() {
trace!("Poll event: {:?}", x);
}
x
}
fn stun_server_handle_message(
&mut self,
now: Instant,
source: SocketAddr,
destination: SocketAddr,
message: StunMessage,
) {
let prio = message
.prio()
// this should be guarded in the parsing
.expect("STUN request prio");
let use_candidate = message.use_candidate();
if use_candidate {
trace!("Binding request sent USE-CANDIDATE");
}
let trans_id = message.trans_id();
// The existence of USERNAME is checked by the STUN parser.
let (_, remote_ufrag) = message.split_username().unwrap();
// Because we might have to delay stun requests until we receive the remote
// credentials, we extract all relevant bits of information so it can be owned.
let req = StunRequest {
now,
source,
destination,
trans_id,
prio,
use_candidate,
remote_ufrag: remote_ufrag.into(),
};
if self.remote_credentials.is_some() {
self.stun_server_handle_request(req);
} else {
debug!(
"Enqueue STUN request due to missing remote credentials: {:?}",
req
);
let queue = &mut self.stun_server_queue;
// It is possible (and in fact very likely) that the
// initiating agent will receive a Binding request prior to receiving
// the candidates from its peer.
queue.push_back(req);
// This is some denial-of-service attack protection.
while queue.len() > 100 {
let r = queue.pop_front();
debug!("Remove overflow STUN request {:?}", r);
}
// If this happens, the agent MUST
// immediately generate a response. The agent has sufficient
// information at this point to generate the response; the password from
// the peer is not required.
// TODO: The spec seems to indicate we can generate a reply, but that seems
// to fly in the face of logic. A reply requires a fingerprint message integrity
// and we can't construct that until we get the remote password.
}
}
fn stun_server_handle_request(&mut self, req: StunRequest) {
let remote_creds = self.remote_credentials.as_ref().expect("Remote ICE creds");
if req.remote_ufrag != remote_creds.ufrag {
// this check can be delayed due to receiving STUN bind requests before we
// get the exchange on the signal level.
debug!(
"STUN request rejected, remote user mismatch (enqueued): {} != {}",
req.remote_ufrag, remote_creds.ufrag
);
return;
}
if req.use_candidate && self.controlling {
// the other side is not controlling, and it sent USE-CANDIDATE. that's wrong.
debug!("STUN request rejected, USE-CANDIDATE when local is controlling");
return;
}
self.stats.bind_request_recv += 1;
// If the source transport address of the request does not match any
// existing remote candidates, it represents a new peer-reflexive remote
// candidate.
let found_in_remote = self
.remote_candidates
.iter()
.enumerate()
.find(|(_, c)| !c.discarded() && c.addr() == req.source);
let remote_idx = if let Some((idx, _)) = found_in_remote {
trace!("Remote candidate for STUN request found");
idx
} else {
// o The priority is the value of the PRIORITY attribute in the Binding
// request.
//
// o The foundation is an arbitrary value, different from the
// foundations of all other remote candidates. If any subsequent
// candidate exchanges contain this peer-reflexive candidate, it will
// signal the actual foundation for the candidate.
let c = Candidate::peer_reflexive(
req.source,
req.source,
req.prio,
// TODO: REMOTE_PEER_REFLEXIVE_TEMP_FOUNDATION should probably have
// a counter to really make it "different from the foundations of
// all other remote candidates".
// In practice it might no matter since we don't do the frozen-waiting
// dance for candidate pairs.
Some(REMOTE_PEER_REFLEXIVE_TEMP_FOUNDATION.into()),
self.local_credentials.ufrag.clone(),
);
info!(
"Created peer reflexive remote candidate from STUN request: {:?}",
c
);
// This candidate is added to the list of remote candidates. However,
// the ICE agent does not pair this candidate with any local candidates.
self.remote_candidates.push(c);
self.remote_candidates.len() - 1
};
let local_idx = self
.local_candidates
.iter()
.enumerate()
.find(|(_, v)| {
// The local candidate will be
// either a host candidate (for cases where the request was not received
// through a relay) or a relayed candidate (for cases where it is
// received through a relay). The local candidate can never be a
// server-reflexive candidate.
matches!(v.kind(), CandidateKind::Host | CandidateKind::Relayed)
&& v.addr() == req.destination
})
// Receiving traffic for an IP address that neither is a HOST nor RELAY is a configuration
// fault. We need to be aware of the interfaces that the ice agent is connected to.
.expect(
"STUN request for socket that is neither a host nor a relay candidate. This is a config error.",
)
.0;
let maybe_pair = self
.candidate_pairs
.iter_mut()
.find(|p| p.local_idx() == local_idx && p.remote_idx() == remote_idx);
if let Some(pair) = maybe_pair {
// When the pair is already on the checklist:
trace!("Found existing pair for STUN request: {:?}", pair);
// TODO: The spec has all these ideas about resetting to Waiting state
// for the candidate pair. I think that's to do speeding up the triggered
// checks if a nomination comes through. It doesn't seem to make much
// sense in this implementation, where a nomination jumps the queue.
// https://datatracker.ietf.org/doc/html/rfc8445#section-7.3.1.4
} else {
// If the pair is not already on the checklist:
let local = &self.local_candidates[local_idx];
let remote = &self.remote_candidates[remote_idx];
let prio = CandidatePair::calculate_prio(self.controlling, remote.prio(), local.prio());
// * Its state is set to Waiting. (this is the default)
// * The pair is inserted into the checklist based on its priority.
// * The pair is enqueued into the triggered-check queue.
let pair = CandidatePair::new(local_idx, remote_idx, prio);
debug!("Created new pair for STUN request: {:?}", pair);
self.candidate_pairs.push(pair);
self.candidate_pairs.sort();
}
let pair = self
.candidate_pairs
.iter_mut()
.find(|p| p.local_idx() == local_idx && p.remote_idx() == remote_idx)
// unwrap is fine since we have inserted a pair if it was missing.
.unwrap();
let local = pair.local_candidate(&self.local_candidates);
let local_addr = local.base();
let remote = pair.remote_candidate(&self.remote_candidates);
let remote_addr = remote.addr();
pair.increase_remote_binding_requests(req.now);
if !self.controlling && !pair.is_nominated() && req.use_candidate {
// We need to answer a nomination request with a binding request
// in the other direction.
//
// If this is ice-lite, we make it successful straight away.
pair.nominate(self.ice_lite);
}
if self.controlling && pair.state() == CheckState::Succeeded {
// See if we can nominate something now.
self.evaluate_nomination();
}
let (_, password) = self.stun_credentials(true);
let reply = StunMessage::reply(req.trans_id, req.source);
debug!(
"Send STUN reply: {} -> {} {:?}",
local_addr, remote_addr, reply
);
let mut buf = vec![0_u8; DATAGRAM_MTU];
let n = reply
.to_bytes(&password, &mut buf)
.expect("IO error writing STUN reply");
buf.truncate(n);
let trans = Transmit {
source: local_addr,
destination: remote_addr,
contents: buf.into(),
};
self.transmit.push_back(trans);
}
fn stun_client_binding_request(&mut self, now: Instant, pair_idx: usize) {
let (username, password) = self.stun_credentials(false);
let pair = &mut self.candidate_pairs[pair_idx];
let local = pair.local_candidate(&self.local_candidates);
let remote = pair.remote_candidate(&self.remote_candidates);
let prio = local.prio_prflx();
// Only the controlling side sends USE-CANDIDATE.
let use_candidate = self.controlling && pair.is_nominated();
let trans_id = pair.new_attempt(now);
self.stats.bind_request_sent += 1;
let binding = StunMessage::binding_request(
&username,
trans_id,
self.controlling,
self.control_tie_breaker,
prio,
use_candidate,
);
debug!(
"Send STUN request: {} -> {} {:?}",
local.base(),
remote.addr(),
binding
);
let mut buf = vec![0_u8; DATAGRAM_MTU];
let n = binding
.to_bytes(&password, &mut buf)
.expect("IO error writing STUN reply");
buf.truncate(n);
let trans = Transmit {
source: local.base(),
destination: remote.addr(),
contents: buf.into(),
};
self.transmit.push_back(trans);
}
fn stun_client_handle_response(&mut self, now: Instant, message: StunMessage<'_>) {
// Find the candidate pair that this trans_id was sent for.
let trans_id = message.trans_id();
let maybe_pair = self
.candidate_pairs
.iter_mut()
.find(|p| p.has_binding_attempt(trans_id));
self.stats.bind_success_recv += 1;
let pair = match maybe_pair {
Some(v) => v,
// Not finding the candidate pair is fine. That might mean the
// binding response came in "too late", after we discarded the
// pair for some reason.
None => {
debug!("No pair found for STUN response: {:?}", message);
return;
}
};
// The ICE agent MUST check the mapped address from the STUN response.
// If the transport address does not match any of the local candidates
// that the agent knows about, the mapped address represents a new
// candidate: a peer-reflexive candidate.
let mapped_address = message
.mapped_address()
// This should be caught in the parsing.
.expect("Mapped address in STUN response");
let found_in_local = self
.local_candidates
.iter()
.enumerate()
.find(|(_, c)| c.addr() == mapped_address);
let (pair, valid_idx) = if let Some((valid_idx, _)) = found_in_local {
// Note, the valid_idx might not be the same as the local_idx that we
// sent the request from. This might happen for hosts with asymmetric
// routing, traffic leaving on one interface and responses coming back
// on another.
trace!(
"Found local candidate for mapped address: {}",
mapped_address
);
(pair, valid_idx)
} else {
let local_sent_from = pair.local_candidate(&self.local_candidates);
// Like other candidates, a peer-reflexive candidate has a type, base, priority,
// and foundation. They are computed as follows:
// o The priority is the value of the PRIORITY attribute in the Binding
// request.
//
// The PRIORITY attribute MUST be included in a Binding request and be
// set to the value computed by the algorithm in Section 5.1.2 for the
// local candidate, but with the candidate type preference of peer-
// reflexive candidates.
let prio = local_sent_from.prio_prflx();
// o The base is the local candidate of the candidate pair from which
// the Binding request was sent.
let base = local_sent_from.base();
// o The type is peer reflexive.
let candidate = Candidate::peer_reflexive(
mapped_address,
base,
prio,
None,
self.local_credentials.ufrag.clone(),
);
debug!(
"Created local peer reflexive candidate for mapped address: {}",
mapped_address
);
// The ICE agent does not need to pair the peer-reflexive candidate with
// remote candidates.
// If an agent wishes to pair the peer-reflexive candidate with remote
// candidates other than the one in the valid pair that will be generated,
// the agent MAY provide updated candidate information to the peer that includes
// the peer-reflexive candidate. This will cause the peer-reflexive candidate
// to be paired with all other remote candidates.
// For now we do not tell the other side about discovered peer-reflexive candidates.
// We just include it in our list of local candidates and use it for the "valid pair".
self.local_candidates.push(candidate);
let idx = self.local_candidates.len() - 1;
(pair, idx)
};
pair.record_binding_response(now, trans_id, valid_idx);
if self.controlling {
self.evaluate_nomination();
}
// State might change when we get a response.
self.evaluate_state(now);
}
fn evaluate_nomination(&mut self) {
let best = if self.controlling {
// For controlling agents, we pick the best candidate pair using
// this strategy.
self.candidate_pairs
.iter()
.filter(|p| p.state() == CheckState::Succeeded && p.remote_binding_requests() > 0)
.max_by_key(|p| p.prio())
.map(|p| p.id())
} else {
// For controlled agents, we pick the best pair from what the controlling
// agent has indicated with USE-CANDIDATE stun attribute.
self.candidate_pairs
.iter()
.filter(|p| p.is_nominated())
.max_by_key(|p| p.prio())
.map(|p| p.id())
};
if let Some(best) = best {
if let Some(current_best) = self.nominated_send {
if best == current_best {
// The best is also the current best.
return;
} else {
trace!("Found better nomination than current");
}
} else {
trace!("Nominating best candidate");
}
let pair = self
.candidate_pairs
.iter_mut()
.find(|p| p.id() == best)
// above logic means this can't fail
.unwrap();
if !pair.is_nominated() && (self.controlling || self.ice_lite) {
// ice lite progresses pair to success straight away.
pair.nominate(self.ice_lite);
}
let local = pair.local_candidate(&self.local_candidates);
let remote = pair.remote_candidate(&self.remote_candidates);
self.nominated_send = Some(best);
self.emit_event(IceAgentEvent::NominatedSend {
source: local.base(),
destination: remote.addr(),
})
}
}
fn set_connection_state(&mut self, state: IceConnectionState, reason: &'static str) {
if self.state != state {
info!("State change ({}): {:?} -> {:?}", reason, self.state, state);
self.state = state;
self.emit_event(IceAgentEvent::IceConnectionStateChange(state));
}
}
fn evaluate_state(&mut self, now: Instant) {
use IceConnectionState::*;
let mut any_nomination = false;
let mut any_still_possible = false;
for p in &self.candidate_pairs {
if p.is_nominated() {
any_nomination = true;
} else if p.is_still_possible(now, self.ice_lite) {
any_still_possible = true;
}
}
// As a special case, before the ice agent has received any add_remote_candidate() or
// discovered a peer reflexive via a STUN message, the agent is still viable. This is
// also the case for ice_restart.
if self.remote_candidates.is_empty() {
any_still_possible = true;
}
match self.state {
New => {
self.set_connection_state(Checking, "new connection");
}
Checking | Disconnected => {
if any_nomination {
if any_still_possible {
self.set_connection_state(Connected, "got nomination, still trying others");
} else {
self.set_connection_state(Completed, "got nomination, no others to try");
}
} else if !any_still_possible {
self.set_connection_state(Disconnected, "no possible pairs");
}
}
Connected => {
if any_nomination {
if !any_still_possible {
self.set_connection_state(Completed, "no more possible to try");
}
} else {
self.set_connection_state(Disconnected, "none nominated");
}
}
Completed => {
if any_nomination {
if any_still_possible {
self.set_connection_state(Connected, "got new possible");
}
} else {
self.set_connection_state(Disconnected, "none nominated");
}
}
}
}
}
#[cfg(test)]
mod test {
use super::*;
use std::net::SocketAddr;
impl IceAgent {
fn pair_indexes(&self) -> Vec<(usize, usize)> {
self.candidate_pairs
.iter()
.map(|c| (c.local_idx(), c.remote_idx()))
.collect()
}
}
fn ipv4_1() -> SocketAddr {
"1.2.3.4:5000".parse().unwrap()
}
fn ipv4_2() -> SocketAddr {
"2.3.4.5:5000".parse().unwrap()
}
fn ipv4_3() -> SocketAddr {
"3.4.5.6:5000".parse().unwrap()
}
fn ipv4_4() -> SocketAddr {
"4.5.6.7:5000".parse().unwrap()
}
fn ipv6_1() -> SocketAddr {
"[1001::]:5000".parse().unwrap()
}
fn ipv6_2() -> SocketAddr {
"[1002::]:5000".parse().unwrap()
}
#[test]
fn local_preference_host() {
let mut agent = IceAgent::new();
agent.add_local_candidate(Candidate::host(ipv4_1()).unwrap());
agent.add_local_candidate(Candidate::host(ipv6_1()).unwrap());
agent.add_local_candidate(Candidate::host(ipv6_2()).unwrap());
agent.add_local_candidate(Candidate::host(ipv4_2()).unwrap());
let v: Vec<_> = agent
.local_candidates
.iter()
.map(|c| c.local_preference())
.collect();
assert_eq!(v, vec![65534, 65535, 65533, 65532]);
}
#[test]
fn discard_adding_redundant() {
let mut agent = IceAgent::new();
// Frequently, a server-reflexive candidate and a host candidate will be
// redundant when the agent is not behind a NAT.
let x2 = agent.add_local_candidate(Candidate::host(ipv4_1()).unwrap());
assert!(x2);
// this is redundant given we have the direct host candidate above.
let x1 = agent.add_local_candidate(Candidate::test_peer_rflx(ipv4_1(), ipv4_1()));
assert!(!x1);
}
#[test]
fn discard_already_added_redundant() {
let mut agent = IceAgent::new();
// Frequently, a server-reflexive candidate and a host candidate will be
// redundant when the agent is not behind a NAT.
// this is contrived, but it is redundant when we add the host candidate below.
let x1 = agent.add_local_candidate(Candidate::test_peer_rflx(ipv4_1(), ipv4_1()));
assert!(x1);
let x2 = agent.add_local_candidate(Candidate::host(ipv4_1()).unwrap());
assert!(x2);
let v: Vec<_> = agent
.local_candidates
.iter()
.map(|v| v.discarded())
.collect();
assert_eq!(v, vec![true, false]);
}
#[test]
fn form_pairs() {
let mut agent = IceAgent::new();
// local 0
agent.add_local_candidate(Candidate::host(ipv4_1()).unwrap());
// local 1
agent.add_local_candidate(Candidate::test_peer_rflx(ipv4_4(), ipv4_2()));
// remote 0
agent.add_remote_candidate(Candidate::test_peer_rflx(ipv4_4(), ipv4_3()));
// remote 1
agent.add_remote_candidate(Candidate::host(ipv4_3()).unwrap());
// we expect:
// (host host) - (0, 1)
// (host rflx) - (0, 1)
// (rflx host) - (1, 1)
// (rflx rflx) - (1, 0)
assert_eq!(agent.pair_indexes(), [(0, 1), (0, 0), (1, 1), (1, 0)]);
}
#[test]
fn form_pairs_skip_redundant() {
let mut agent = IceAgent::new();
agent.add_remote_candidate(Candidate::host(ipv4_3()).unwrap());
agent.add_local_candidate(Candidate::host(ipv4_1()).unwrap());
assert_eq!(agent.pair_indexes(), [(0, 0)]);
// this local candidate is redundant an won't form a new pair.
agent.add_local_candidate(Candidate::test_peer_rflx(ipv4_2(), ipv4_1()));
assert_eq!(agent.pair_indexes(), [(0, 0)]);
}
#[test]
fn form_pairs_replace_redundant() {
let mut agent = IceAgent::new();
agent.add_remote_candidate(Candidate::host(ipv4_3()).unwrap());
agent.add_local_candidate(Candidate::test_peer_rflx(ipv4_2(), ipv4_1()));
assert_eq!(agent.pair_indexes(), [(0, 0)]);
// this local candidate is redundant, but has higher prio than then existing pair.
// it replaces the existing pair.
agent.add_local_candidate(Candidate::host(ipv4_1()).unwrap());
assert_eq!(agent.pair_indexes(), [(1, 0)]);
}
#[test]
fn poll_time_must_timing_advance() {
let mut agent = IceAgent::new();
agent.add_local_candidate(Candidate::host(ipv4_1()).unwrap());
agent.add_remote_candidate(Candidate::host(ipv4_3()).unwrap());
let now1 = Instant::now();
agent.handle_timeout(now1);
let now2 = agent.poll_timeout().unwrap();
assert!(now2 - now1 == TIMING_ADVANCE);
}
#[test]
fn no_disconnect_before_remote_candidates() {
let mut agent = IceAgent::new();
let now = Instant::now();
agent.handle_timeout(now);
while let Some(ev) = agent.poll_event() {
if let IceAgentEvent::IceConnectionStateChange(s) = ev {
assert!(s != IceConnectionState::Disconnected);
}
}
agent.handle_timeout(now + Duration::from_millis(200));
while let Some(ev) = agent.poll_event() {
if let IceAgentEvent::IceConnectionStateChange(s) = ev {
assert!(s != IceConnectionState::Disconnected);
}
}
}
}