Quelle cid.rs
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Representation and management of connection IDs.
use std::{
borrow::Borrow,
cell::{Ref, RefCell},
cmp::{max, min},
ops::Deref,
rc::Rc,
};
use neqo_common::{hex, hex_with_len, qdebug, qinfo, Decoder, Encoder};
use neqo_crypto::{random, randomize};
use smallvec::{smallvec, SmallVec};
use crate::{
frame::FRAME_TYPE_NEW_CONNECTION_ID, packet::PacketBuilder, recovery::RecoveryToke n,
stats::FrameStats, Error, Res,
};
pub const MAX_CONNECTION_ID_LEN: usize = 20;
pub const LOCAL_ACTIVE_CID_LIMIT: usize = 8;
pub const CONNECTION_ID_SEQNO_INITIAL: u64 = 0;
pub const CONNECTION_ID_SEQNO_PREFERRED: u64 = 1;
/// A special value. See `ConnectionIdManager::add_odcid`.
const CONNECTION_ID_SEQNO_ODCID: u64 = u64::MAX;
/// A special value. See `ConnectionIdEntry::empty_remote`.
const CONNECTION_ID_SEQNO_EMPTY: u64 = u64::MAX - 1;
#[derive(Clone, Default, Eq, Hash, PartialEq)]
pub struct ConnectionId {
pub(crate) cid: SmallVec<[u8; MAX_CONNECTION_ID_LEN]>,
}
impl ConnectionId {
/// # Panics
/// When `len` is larger than `MAX_CONNECTION_ID_LEN`.
#[must_use]
pub fn generate(len: usize) -> Self {
assert!(matches!(len, 0..=MAX_CONNECTION_ID_LEN));
let mut cid = smallvec![0; len];
randomize(&mut cid);
Self { cid }
}
// Apply a wee bit of greasing here in picking a length between 8 and 20 bytes long.
#[must_use]
pub fn generate_initial() -> Self {
let v = random::<1>()[0];
// Bias selection toward picking 8 (>50% of the time).
let len: usize = max(8, 5 + (v & (v >> 4))).into();
Self::generate(len)
}
#[must_use]
pub fn as_cid_ref(&self) -> ConnectionIdRef {
ConnectionIdRef::from(&self.cid[..])
}
}
impl AsRef<[u8]> for ConnectionId {
fn as_ref(&self) -> &[u8] {
self.borrow()
}
}
impl Borrow<[u8]> for ConnectionId {
fn borrow(&self) -> &[u8] {
&self.cid
}
}
impl From<SmallVec<[u8; MAX_CONNECTION_ID_LEN]>> for ConnectionId {
fn from(cid: SmallVec<[u8; MAX_CONNECTION_ID_LEN]>) -> Self {
Self { cid }
}
}
impl<T: AsRef<[u8]> + ?Sized> From<&T> for ConnectionId {
fn from(buf: &T) -> Self {
Self::from(SmallVec::from(buf.as_ref()))
}
}
impl<'a> From<ConnectionIdRef<'a>> for ConnectionId {
fn from(cidref: ConnectionIdRef<'a>) -> Self {
Self::from(SmallVec::from(cidref.cid))
}
}
impl std::ops::Deref for ConnectionId {
type Target = [u8];
fn deref(&self) -> &Self::Target {
&self.cid
}
}
impl ::std::fmt::Debug for ConnectionId {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
write!(f, "CID {}", hex_with_len(&self.cid))
}
}
impl ::std::fmt::Display for ConnectionId {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
write!(f, "{}", hex(&self.cid))
}
}
impl<'a> PartialEq<ConnectionIdRef<'a>> for ConnectionId {
fn eq(&self, other: &ConnectionIdRef<'a>) -> bool {
&self.cid[..] == other.cid
}
}
#[derive(Hash, Eq, PartialEq, Clone, Copy)]
pub struct ConnectionIdRef<'a> {
cid: &'a [u8],
}
impl ::std::fmt::Debug for ConnectionIdRef<'_> {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
write!(f, "CID {}", hex_with_len(self.cid))
}
}
impl ::std::fmt::Display for ConnectionIdRef<'_> {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
write!(f, "{}", hex(self.cid))
}
}
impl<'a, T: AsRef<[u8]> + ?Sized> From<&'a T> for ConnectionIdRef<'a> {
fn from(cid: &'a T) -> Self {
Self { cid: cid.as_ref() }
}
}
impl std::ops::Deref for ConnectionIdRef<'_> {
type Target = [u8];
fn deref(&self) -> &Self::Target {
self.cid
}
}
impl PartialEq<ConnectionId> for ConnectionIdRef<'_> {
fn eq(&self, other: &ConnectionId) -> bool {
self.cid == &other.cid[..]
}
}
pub trait ConnectionIdDecoder {
/// Decodes a connection ID from the provided decoder.
fn decode_cid<'a>(&self, dec: &mut Decoder<'a>) -> Option<ConnectionIdRef<'a>>;
}
pub trait ConnectionIdGenerator: ConnectionIdDecoder {
/// Generates a connection ID. This can return `None` if the generator
/// is exhausted.
fn generate_cid(&mut self) -> Option<ConnectionId>;
/// Indicates whether the connection IDs are zero-length.
/// If this returns true, `generate_cid` must always produce an empty value
/// and never `None`.
/// If this returns false, `generate_cid` must never produce an empty value,
/// though it can return `None`.
///
/// You should not need to implement this: if you want zero-length connection IDs,
/// use `EmptyConnectionIdGenerator` instead.
fn generates_empty_cids(&self) -> bool {
false
}
fn as_decoder(&self) -> &dyn ConnectionIdDecoder;
}
/// An `EmptyConnectionIdGenerator` generates empty connection IDs.
#[derive(Default)]
pub struct EmptyConnectionIdGenerator {}
impl ConnectionIdDecoder for EmptyConnectionIdGenerator {
fn decode_cid<'a>(&self, _: &mut Decoder<'a>) -> Option<ConnectionIdRef<'a>> {
Some(ConnectionIdRef::from(&[]))
}
}
impl ConnectionIdGenerator for EmptyConnectionIdGenerator {
fn generate_cid(&mut self) -> Option<ConnectionId> {
Some(ConnectionId::from(&[]))
}
fn as_decoder(&self) -> &dyn ConnectionIdDecoder {
self
}
fn generates_empty_cids(&self) -> bool {
true
}
}
/// An `RandomConnectionIdGenerator` produces connection IDs of
/// a fixed length and random content. No effort is made to
/// prevent collisions.
pub struct RandomConnectionIdGenerator {
len: usize,
}
impl RandomConnectionIdGenerator {
#[must_use]
pub const fn new(len: usize) -> Self {
Self { len }
}
}
impl ConnectionIdDecoder for RandomConnectionIdGenerator {
fn decode_cid<'a>(&self, dec: &mut Decoder<'a>) -> Option<ConnectionIdRef<'a>> {
dec.decode(self.len).map(ConnectionIdRef::from)
}
}
impl ConnectionIdGenerator for RandomConnectionIdGenerator {
fn generate_cid(&mut self) -> Option<ConnectionId> {
let mut buf = smallvec![0; self.len];
randomize(&mut buf);
Some(ConnectionId::from(buf))
}
fn as_decoder(&self) -> &dyn ConnectionIdDecoder {
self
}
fn generates_empty_cids(&self) -> bool {
self.len == 0
}
}
/// A single connection ID, as saved from `NEW_CONNECTION_ID`.
/// This is templated so that the connection ID entries from a peer can be
/// saved with a stateless reset token. Local entries don't need that.
#[derive(Debug, PartialEq, Eq, Clone)]
pub struct ConnectionIdEntry<SRT: Clone + PartialEq> {
/// The sequence number.
seqno: u64,
/// The connection ID.
cid: ConnectionId,
/// The corresponding stateless reset token.
srt: SRT,
}
impl ConnectionIdEntry<[u8; 16]> {
/// Create a random stateless reset token so that it is hard to guess the correct
/// value and reset the connection.
pub fn random_srt() -> [u8; 16] {
random::<16>()
}
/// Create the first entry, which won't have a stateless reset token.
pub fn initial_remote(cid: ConnectionId) -> Self {
Self::new(CONNECTION_ID_SEQNO_INITIAL, cid, Self::random_srt())
}
/// Create an empty for when the peer chooses empty connection IDs.
/// This uses a special sequence number just because it can.
pub fn empty_remote() -> Self {
Self::new(
CONNECTION_ID_SEQNO_EMPTY,
ConnectionId::from(&[]),
Self::random_srt(),
)
}
fn token_equal(a: &[u8; 16], b: &[u8; 16]) -> bool {
// rustc might decide to optimize this and make this non-constant-time
// with respect to `t`, but it doesn't appear to currently.
let mut c = 0;
for (&a, &b) in a.iter().zip(b) {
c |= a ^ b;
}
c == 0
}
/// Determine whether this is a valid stateless reset.
pub fn is_stateless_reset(&self, token: &[u8; 16]) -> bool {
// A sequence number of 2^62 or more has no corresponding stateless reset token.
(self.seqno < (1 << 62)) && Self::token_equal(&self.srt, token)
}
/// Return true if the two contain any equal parts.
fn any_part_equal(&self, other: &Self) -> bool {
self.seqno == other.seqno || self.cid == other.cid || self.srt == other.srt
}
/// The sequence number of this entry.
pub const fn sequence_number(&self) -> u64 {
self.seqno
}
/// Write the entry out in a `NEW_CONNECTION_ID` frame.
/// Returns `true` if the frame was written, `false` if there is insufficient space.
pub fn write(&self, builder: &mut PacketBuilder, stats: &mut FrameStats) -> bool {
let len = 1 + Encoder::varint_len(self.seqno) + 1 + 1 + self.cid.len() + 16;
if builder.remaining() < len {
return false;
}
builder.encode_varint(FRAME_TYPE_NEW_CONNECTION_ID);
builder.encode_varint(self.seqno);
builder.encode_varint(0u64);
builder.encode_vec(1, &self.cid);
builder.encode(&self.srt);
stats.new_connection_id += 1;
true
}
pub fn is_empty(&self) -> bool {
self.seqno == CONNECTION_ID_SEQNO_EMPTY || self.cid.is_empty()
}
}
impl ConnectionIdEntry<()> {
/// Create an initial entry.
pub const fn initial_local(cid: ConnectionId) -> Self {
Self::new(0, cid, ())
}
}
impl<SRT: Clone + PartialEq> ConnectionIdEntry<SRT> {
pub const fn new(seqno: u64, cid: ConnectionId, srt: SRT) -> Self {
Self { seqno, cid, srt }
}
/// Update the stateless reset token. This panics if the sequence number is non-zero.
pub fn set_stateless_reset_token(&mut self, srt: SRT) {
assert_eq!(self.seqno, CONNECTION_ID_SEQNO_INITIAL);
self.srt = srt;
}
/// Replace the connection ID. This panics if the sequence number is non-zero.
pub fn update_cid(&mut self, cid: ConnectionId) {
assert_eq!(self.seqno, CONNECTION_ID_SEQNO_INITIAL);
self.cid = cid;
}
pub const fn connection_id(&self) -> &ConnectionId {
&self.cid
}
pub const fn reset_token(&self) -> &SRT {
&self.srt
}
}
pub type RemoteConnectionIdEntry = ConnectionIdEntry<[u8; 16]>;
/// A collection of connection IDs that are indexed by a sequence number.
/// Used to store connection IDs that are provided by a peer.
#[derive(Debug, Default)]
pub struct ConnectionIdStore<SRT: Clone + PartialEq> {
cids: SmallVec<[ConnectionIdEntry<SRT>; 8]>,
}
impl<SRT: Clone + PartialEq> ConnectionIdStore<SRT> {
pub fn retire(&mut self, seqno: u64) {
self.cids.retain(|c| c.seqno != seqno);
}
pub fn contains(&self, cid: ConnectionIdRef) -> bool {
self.cids.iter().any(|c| c.cid == cid)
}
pub fn next(&mut self) -> Option<ConnectionIdEntry<SRT>> {
if self.cids.is_empty() {
None
} else {
Some(self.cids.remove(0))
}
}
pub fn len(&self) -> usize {
self.cids.len()
}
}
impl ConnectionIdStore<[u8; 16]> {
pub fn add_remote(&mut self, entry: ConnectionIdEntry<[u8; 16]>) -> Res<()> {
// It's OK if this perfectly matches an existing entry.
if self.cids.iter().any(|c| c == &entry) {
return Ok(());
}
// It's not OK if any individual piece matches though.
if self.cids.iter().any(|c| c.any_part_equal(&entry)) {
qinfo!("ConnectionIdStore found reused part in NEW_CONNECTION_ID");
return Err(Error::ProtocolViolation);
}
// Insert in order so that we use them in order where possible.
if let Err(idx) = self.cids.binary_search_by_key(&entry.seqno, |e| e.seqno) {
self.cids.insert(idx, entry);
Ok(())
} else {
Err(Error::ProtocolViolation)
}
}
// Retire connection IDs and return the sequence numbers of those that were retired.
pub fn retire_prior_to(&mut self, retire_prior: u64) -> Vec<u64> {
let mut retired = Vec::new();
self.cids.retain(|e| {
if !e.is_empty() && e.seqno < retire_prior {
retired.push(e.seqno);
false
} else {
true
}
});
retired
}
}
impl ConnectionIdStore<()> {
fn add_local(&mut self, entry: ConnectionIdEntry<()>) {
self.cids.push(entry);
}
}
pub struct ConnectionIdDecoderRef<'a> {
generator: Ref<'a, dyn ConnectionIdGenerator>,
}
// Ideally this would be an implementation of `Deref`, but it doesn't
// seem to be possible to convince the compiler to build anything useful.
impl<'a: 'b, 'b> ConnectionIdDecoderRef<'a> {
pub fn as_ref(&'a self) -> &'b dyn ConnectionIdDecoder {
self.generator.as_decoder()
}
}
/// A connection ID manager looks after the generation of connection IDs,
/// the set of connection IDs that are valid for the connection, and the
/// generation of `NEW_CONNECTION_ID` frames.
pub struct ConnectionIdManager {
/// The `ConnectionIdGenerator` instance that is used to create connection IDs.
generator: Rc<RefCell<dyn ConnectionIdGenerator>>,
/// The connection IDs that we will accept.
/// This includes any we advertise in `NEW_CONNECTION_ID` that haven't been bound to a path
/// yet. During the handshake at the server, it also includes the randomized DCID pick by
/// the client.
connection_ids: ConnectionIdStore<()>,
/// The maximum number of connection IDs this will accept. This is at least 2 and won't
/// be more than `LOCAL_ACTIVE_CID_LIMIT`.
limit: usize,
/// The next sequence number that will be used for sending `NEW_CONNECTION_ID` frames.
next_seqno: u64,
/// Outstanding, but lost `NEW_CONNECTION_ID` frames will be stored here.
lost_new_connection_id: Vec<ConnectionIdEntry<[u8; 16]>>,
}
impl ConnectionIdManager {
pub fn new(generator: Rc<RefCell<dyn ConnectionIdGenerator>>, initial: ConnectionId) -> Self {
let mut connection_ids = ConnectionIdStore::default();
connection_ids.add_local(ConnectionIdEntry::initial_local(initial));
Self {
generator,
connection_ids,
// A note about initializing the limit to 2.
// For a server, the number of connection IDs that are tracked at the point that
// it is first possible to send `NEW_CONNECTION_ID` is 2. One is the client-generated
// destination connection (stored with a sequence number of `HANDSHAKE_SEQNO`); the
// other being the handshake value (seqno 0). As a result, `NEW_CONNECTION_ID`
// won't be sent until until after the handshake completes, because this initial
// value remains until the connection completes and transport parameters are handled.
limit: 2,
next_seqno: 1,
lost_new_connection_id: Vec::new(),
}
}
pub fn generator(&self) -> Rc<RefCell<dyn ConnectionIdGenerator>> {
Rc::clone(&self.generator)
}
pub fn decoder(&self) -> ConnectionIdDecoderRef {
ConnectionIdDecoderRef {
generator: self.generator.deref().borrow(),
}
}
/// Generate a connection ID and stateless reset token for a preferred address.
pub fn preferred_address_cid(&mut self) -> Res<(ConnectionId, [u8; 16])> {
if self.generator.deref().borrow().generates_empty_cids() {
return Err(Error::ConnectionIdsExhausted);
}
if let Some(cid) = self.generator.borrow_mut().generate_cid() {
assert_ne!(cid.len(), 0);
debug_assert_eq!(self.next_seqno, CONNECTION_ID_SEQNO_PREFERRED);
self.connection_ids
.add_local(ConnectionIdEntry::new(self.next_seqno, cid.clone(), ()));
self.next_seqno += 1;
let srt = ConnectionIdEntry::random_srt();
Ok((cid, srt))
} else {
Err(Error::ConnectionIdsExhausted)
}
}
pub fn is_valid(&self, cid: ConnectionIdRef) -> bool {
self.connection_ids.contains(cid)
}
pub fn retire(&mut self, seqno: u64) {
// TODO(mt) - consider keeping connection IDs around for a short while.
let empty_cid = seqno == CONNECTION_ID_SEQNO_EMPTY
|| self
.connection_ids
.cids
.iter()
.any(|c| c.seqno == seqno && c.cid.is_empty());
if empty_cid {
qdebug!("Connection ID {seqno} is zero-length, not retiring");
} else {
self.connection_ids.retire(seqno);
self.lost_new_connection_id.retain(|cid| cid.seqno != seqno);
}
}
/// During the handshake, a server needs to regard the client's choice of destination
/// connection ID as valid. This function saves it in the store in a special place.
/// Note that this is only done *after* an Initial packet from the client is
/// successfully processed.
pub fn add_odcid(&mut self, cid: ConnectionId) {
let entry = ConnectionIdEntry::new(CONNECTION_ID_SEQNO_ODCID, cid, ());
self.connection_ids.add_local(entry);
}
/// Stop treating the original destination connection ID as valid.
pub fn remove_odcid(&mut self) {
self.connection_ids.retire(CONNECTION_ID_SEQNO_ODCID);
}
pub fn set_limit(&mut self, limit: u64) {
debug_assert!(limit >= 2);
self.limit = min(
LOCAL_ACTIVE_CID_LIMIT,
usize::try_from(limit).unwrap_or(LOCAL_ACTIVE_CID_LIMIT),
);
}
pub fn write_frames(
&mut self,
builder: &mut PacketBuilder,
tokens: &mut Vec<RecoveryToken>,
stats: &mut FrameStats,
) {
if self.generator.deref().borrow().generates_empty_cids() {
debug_assert_eq!(self.generator.borrow_mut().generate_cid().unwrap().len(), 0);
return;
}
while let Some(entry) = self.lost_new_connection_id.pop() {
if entry.write(builder, stats) {
tokens.push(RecoveryToken::NewConnectionId(entry));
} else {
// This shouldn't happen often.
self.lost_new_connection_id.push(entry);
break;
}
}
// Keep writing while we have fewer than the limit of active connection IDs
// and while there is room for more. This uses the longest connection ID
// length to simplify (assuming Retire Prior To is just 1 byte).
while self.connection_ids.len() < self.limit && builder.remaining() >= 47 {
let maybe_cid = self.generator.borrow_mut().generate_cid();
if let Some(cid) = maybe_cid {
assert_ne!(cid.len(), 0);
// TODO: generate the stateless reset tokens from the connection ID and a key.
let srt = ConnectionIdEntry::random_srt();
let seqno = self.next_seqno;
self.next_seqno += 1;
self.connection_ids
.add_local(ConnectionIdEntry::new(seqno, cid.clone(), ()));
let entry = ConnectionIdEntry::new(seqno, cid, srt);
entry.write(builder, stats);
tokens.push(RecoveryToken::NewConnectionId(entry));
}
}
}
pub fn lost(&mut self, entry: &ConnectionIdEntry<[u8; 16]>) {
self.lost_new_connection_id.push(entry.clone());
}
pub fn acked(&mut self, entry: &ConnectionIdEntry<[u8; 16]>) {
self.lost_new_connection_id
.retain(|e| e.seqno != entry.seqno);
}
}
#[cfg(test)]
mod tests {
use test_fixture::fixture_init;
use crate::{cid::MAX_CONNECTION_ID_LEN, ConnectionId};
#[test]
fn generate_initial_cid() {
fixture_init();
for _ in 0..100 {
let cid = ConnectionId::generate_initial();
assert!(
matches!(cid.len(), 8..=MAX_CONNECTION_ID_LEN),
"connection ID length {cid:?}",
);
}
}
}
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2026-04-04
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