Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1179 insertions, 0 deletions

diff --git a/third_party/rust/neqo-transport/src/tparams.rs b/third_party/rust/neqo-transport/src/tparams.rs
new file mode 100644
index 0000000000..862a74cecf
--- /dev/null
+++ b/third_party/rust/neqo-transport/src/tparams.rs
@@ -0,0 +1,1179 @@
+// 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.
+
+// Transport parameters. See -transport section 7.3.
+
+use crate::cid::{
+    ConnectionId, ConnectionIdEntry, CONNECTION_ID_SEQNO_PREFERRED, MAX_CONNECTION_ID_LEN,
+};
+use crate::version::{Version, VersionConfig, WireVersion};
+use crate::{Error, Res};
+
+use neqo_common::{hex, qdebug, qinfo, qtrace, Decoder, Encoder, Role};
+use neqo_crypto::constants::{TLS_HS_CLIENT_HELLO, TLS_HS_ENCRYPTED_EXTENSIONS};
+use neqo_crypto::ext::{ExtensionHandler, ExtensionHandlerResult, ExtensionWriterResult};
+use neqo_crypto::{random, HandshakeMessage, ZeroRttCheckResult, ZeroRttChecker};
+
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::convert::TryFrom;
+use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};
+use std::rc::Rc;
+
+pub type TransportParameterId = u64;
+macro_rules! tpids {
+        { $($n:ident = $v:expr),+ $(,)? } => {
+            $(pub const $n: TransportParameterId = $v as TransportParameterId;)+
+
+            /// A complete list of internal transport parameters.
+            #[cfg(not(test))]
+            pub(crate) const INTERNAL_TRANSPORT_PARAMETERS: &[TransportParameterId] = &[ $($n),+ ];
+        };
+    }
+tpids! {
+    ORIGINAL_DESTINATION_CONNECTION_ID = 0x00,
+    IDLE_TIMEOUT = 0x01,
+    STATELESS_RESET_TOKEN = 0x02,
+    MAX_UDP_PAYLOAD_SIZE = 0x03,
+    INITIAL_MAX_DATA = 0x04,
+    INITIAL_MAX_STREAM_DATA_BIDI_LOCAL = 0x05,
+    INITIAL_MAX_STREAM_DATA_BIDI_REMOTE = 0x06,
+    INITIAL_MAX_STREAM_DATA_UNI = 0x07,
+    INITIAL_MAX_STREAMS_BIDI = 0x08,
+    INITIAL_MAX_STREAMS_UNI = 0x09,
+    ACK_DELAY_EXPONENT = 0x0a,
+    MAX_ACK_DELAY = 0x0b,
+    DISABLE_MIGRATION = 0x0c,
+    PREFERRED_ADDRESS = 0x0d,
+    ACTIVE_CONNECTION_ID_LIMIT = 0x0e,
+    INITIAL_SOURCE_CONNECTION_ID = 0x0f,
+    RETRY_SOURCE_CONNECTION_ID = 0x10,
+    GREASE_QUIC_BIT = 0x2ab2,
+    MIN_ACK_DELAY = 0xff02_de1a,
+    MAX_DATAGRAM_FRAME_SIZE = 0x0020,
+    VERSION_NEGOTIATION = 0xff73db,
+}
+
+#[derive(Clone, Debug, Copy)]
+pub struct PreferredAddress {
+    v4: Option<SocketAddr>,
+    v6: Option<SocketAddr>,
+}
+
+impl PreferredAddress {
+    /// Make a new preferred address configuration.
+    ///
+    /// # Panics
+    /// If neither address is provided, or if either address is of the wrong type.
+    #[must_use]
+    pub fn new(v4: Option<SocketAddr>, v6: Option<SocketAddr>) -> Self {
+        assert!(v4.is_some() || v6.is_some());
+        if let Some(a) = v4 {
+            if let IpAddr::V4(addr) = a.ip() {
+                assert!(!addr.is_unspecified());
+            } else {
+                panic!("invalid address type for v4 address");
+            }
+            assert_ne!(a.port(), 0);
+        }
+        if let Some(a) = v6 {
+            if let IpAddr::V6(addr) = a.ip() {
+                assert!(!addr.is_unspecified());
+            } else {
+                panic!("invalid address type for v6 address");
+            }
+            assert_ne!(a.port(), 0);
+        }
+        Self { v4, v6 }
+    }
+
+    #[must_use]
+    pub fn ipv4(&self) -> Option<SocketAddr> {
+        self.v4
+    }
+    #[must_use]
+    pub fn ipv6(&self) -> Option<SocketAddr> {
+        self.v6
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum TransportParameter {
+    Bytes(Vec<u8>),
+    Integer(u64),
+    Empty,
+    PreferredAddress {
+        v4: Option<SocketAddr>,
+        v6: Option<SocketAddr>,
+        cid: ConnectionId,
+        srt: [u8; 16],
+    },
+    Versions {
+        current: WireVersion,
+        other: Vec<WireVersion>,
+    },
+}
+
+impl TransportParameter {
+    fn encode(&self, enc: &mut Encoder, tp: TransportParameterId) {
+        qdebug!("TP encoded; type 0x{:02x} val {:?}", tp, self);
+        enc.encode_varint(tp);
+        match self {
+            Self::Bytes(a) => {
+                enc.encode_vvec(a);
+            }
+            Self::Integer(a) => {
+                enc.encode_vvec_with(|enc_inner| {
+                    enc_inner.encode_varint(*a);
+                });
+            }
+            Self::Empty => {
+                enc.encode_varint(0_u64);
+            }
+            Self::PreferredAddress { v4, v6, cid, srt } => {
+                enc.encode_vvec_with(|enc_inner| {
+                    if let Some(v4) = v4 {
+                        debug_assert!(v4.is_ipv4());
+                        if let IpAddr::V4(a) = v4.ip() {
+                            enc_inner.encode(&a.octets()[..]);
+                        } else {
+                            unreachable!();
+                        }
+                        enc_inner.encode_uint(2, v4.port());
+                    } else {
+                        enc_inner.encode(&[0; 6]);
+                    }
+                    if let Some(v6) = v6 {
+                        debug_assert!(v6.is_ipv6());
+                        if let IpAddr::V6(a) = v6.ip() {
+                            enc_inner.encode(&a.octets()[..]);
+                        } else {
+                            unreachable!();
+                        }
+                        enc_inner.encode_uint(2, v6.port());
+                    } else {
+                        enc_inner.encode(&[0; 18]);
+                    }
+                    enc_inner.encode_vec(1, &cid[..]);
+                    enc_inner.encode(&srt[..]);
+                });
+            }
+            Self::Versions { current, other } => {
+                enc.encode_vvec_with(|enc_inner| {
+                    enc_inner.encode_uint(4, *current);
+                    for v in other {
+                        enc_inner.encode_uint(4, *v);
+                    }
+                });
+            }
+        };
+    }
+
+    fn decode_preferred_address(d: &mut Decoder) -> Res<Self> {
+        // IPv4 address (maybe)
+        let v4ip =
+            Ipv4Addr::from(<[u8; 4]>::try_from(d.decode(4).ok_or(Error::NoMoreData)?).unwrap());
+        let v4port = u16::try_from(d.decode_uint(2).ok_or(Error::NoMoreData)?).unwrap();
+        // Can't have non-zero IP and zero port, or vice versa.
+        if v4ip.is_unspecified() ^ (v4port == 0) {
+            return Err(Error::TransportParameterError);
+        }
+        let v4 = if v4port == 0 {
+            None
+        } else {
+            Some(SocketAddr::new(IpAddr::V4(v4ip), v4port))
+        };
+
+        // IPv6 address (mostly the same as v4)
+        let v6ip =
+            Ipv6Addr::from(<[u8; 16]>::try_from(d.decode(16).ok_or(Error::NoMoreData)?).unwrap());
+        let v6port = u16::try_from(d.decode_uint(2).ok_or(Error::NoMoreData)?).unwrap();
+        if v6ip.is_unspecified() ^ (v6port == 0) {
+            return Err(Error::TransportParameterError);
+        }
+        let v6 = if v6port == 0 {
+            None
+        } else {
+            Some(SocketAddr::new(IpAddr::V6(v6ip), v6port))
+        };
+        // Need either v4 or v6 to be present.
+        if v4.is_none() && v6.is_none() {
+            return Err(Error::TransportParameterError);
+        }
+
+        // Connection ID (non-zero length)
+        let cid = ConnectionId::from(d.decode_vec(1).ok_or(Error::NoMoreData)?);
+        if cid.len() == 0 || cid.len() > MAX_CONNECTION_ID_LEN {
+            return Err(Error::TransportParameterError);
+        }
+
+        // Stateless reset token
+        let srtbuf = d.decode(16).ok_or(Error::NoMoreData)?;
+        let srt = <[u8; 16]>::try_from(srtbuf).unwrap();
+
+        Ok(Self::PreferredAddress { v4, v6, cid, srt })
+    }
+
+    fn decode_versions(dec: &mut Decoder) -> Res<Self> {
+        fn dv(dec: &mut Decoder) -> Res<WireVersion> {
+            let v = dec.decode_uint(4).ok_or(Error::NoMoreData)?;
+            if v == 0 {
+                Err(Error::TransportParameterError)
+            } else {
+                Ok(v as WireVersion)
+            }
+        }
+
+        let current = dv(dec)?;
+        // This rounding down is OK because `decode` checks for left over data.
+        let count = dec.remaining() / 4;
+        let mut other = Vec::with_capacity(count);
+        for _ in 0..count {
+            other.push(dv(dec)?);
+        }
+        Ok(Self::Versions { current, other })
+    }
+
+    fn decode(dec: &mut Decoder) -> Res<Option<(TransportParameterId, Self)>> {
+        let tp = dec.decode_varint().ok_or(Error::NoMoreData)?;
+        let content = dec.decode_vvec().ok_or(Error::NoMoreData)?;
+        qtrace!("TP {:x} length {:x}", tp, content.len());
+        let mut d = Decoder::from(content);
+        let value = match tp {
+            ORIGINAL_DESTINATION_CONNECTION_ID
+            | INITIAL_SOURCE_CONNECTION_ID
+            | RETRY_SOURCE_CONNECTION_ID => Self::Bytes(d.decode_remainder().to_vec()),
+            STATELESS_RESET_TOKEN => {
+                if d.remaining() != 16 {
+                    return Err(Error::TransportParameterError);
+                }
+                Self::Bytes(d.decode_remainder().to_vec())
+            }
+            IDLE_TIMEOUT
+            | INITIAL_MAX_DATA
+            | INITIAL_MAX_STREAM_DATA_BIDI_LOCAL
+            | INITIAL_MAX_STREAM_DATA_BIDI_REMOTE
+            | INITIAL_MAX_STREAM_DATA_UNI
+            | MAX_ACK_DELAY
+            | MAX_DATAGRAM_FRAME_SIZE => match d.decode_varint() {
+                Some(v) => Self::Integer(v),
+                None => return Err(Error::TransportParameterError),
+            },
+
+            INITIAL_MAX_STREAMS_BIDI | INITIAL_MAX_STREAMS_UNI => match d.decode_varint() {
+                Some(v) if v <= (1 << 60) => Self::Integer(v),
+                _ => return Err(Error::StreamLimitError),
+            },
+
+            MAX_UDP_PAYLOAD_SIZE => match d.decode_varint() {
+                Some(v) if v >= 1200 => Self::Integer(v),
+                _ => return Err(Error::TransportParameterError),
+            },
+
+            ACK_DELAY_EXPONENT => match d.decode_varint() {
+                Some(v) if v <= 20 => Self::Integer(v),
+                _ => return Err(Error::TransportParameterError),
+            },
+            ACTIVE_CONNECTION_ID_LIMIT => match d.decode_varint() {
+                Some(v) if v >= 2 => Self::Integer(v),
+                _ => return Err(Error::TransportParameterError),
+            },
+
+            DISABLE_MIGRATION | GREASE_QUIC_BIT => Self::Empty,
+
+            PREFERRED_ADDRESS => Self::decode_preferred_address(&mut d)?,
+
+            MIN_ACK_DELAY => match d.decode_varint() {
+                Some(v) if v < (1 << 24) => Self::Integer(v),
+                _ => return Err(Error::TransportParameterError),
+            },
+
+            VERSION_NEGOTIATION => Self::decode_versions(&mut d)?,
+
+            // Skip.
+            _ => return Ok(None),
+        };
+        if d.remaining() > 0 {
+            return Err(Error::TooMuchData);
+        }
+        qdebug!("TP decoded; type 0x{:02x} val {:?}", tp, value);
+        Ok(Some((tp, value)))
+    }
+}
+
+#[derive(Clone, Debug, Default, PartialEq, Eq)]
+pub struct TransportParameters {
+    params: HashMap<TransportParameterId, TransportParameter>,
+}
+
+impl TransportParameters {
+    /// Set a value.
+    pub fn set(&mut self, k: TransportParameterId, v: TransportParameter) {
+        self.params.insert(k, v);
+    }
+
+    /// Clear a key.
+    pub fn remove(&mut self, k: TransportParameterId) {
+        self.params.remove(&k);
+    }
+
+    /// Decode is a static function that parses transport parameters
+    /// using the provided decoder.
+    pub(crate) fn decode(d: &mut Decoder) -> Res<Self> {
+        let mut tps = Self::default();
+        qtrace!("Parsed fixed TP header");
+
+        while d.remaining() > 0 {
+            match TransportParameter::decode(d) {
+                Ok(Some((tipe, tp))) => {
+                    tps.set(tipe, tp);
+                }
+                Ok(None) => {}
+                Err(e) => return Err(e),
+            }
+        }
+        Ok(tps)
+    }
+
+    pub(crate) fn encode(&self, enc: &mut Encoder) {
+        for (tipe, tp) in &self.params {
+            tp.encode(enc, *tipe);
+        }
+    }
+
+    // Get an integer type or a default.
+    pub fn get_integer(&self, tp: TransportParameterId) -> u64 {
+        let default = match tp {
+            IDLE_TIMEOUT
+            | INITIAL_MAX_DATA
+            | INITIAL_MAX_STREAM_DATA_BIDI_LOCAL
+            | INITIAL_MAX_STREAM_DATA_BIDI_REMOTE
+            | INITIAL_MAX_STREAM_DATA_UNI
+            | INITIAL_MAX_STREAMS_BIDI
+            | INITIAL_MAX_STREAMS_UNI
+            | MIN_ACK_DELAY
+            | MAX_DATAGRAM_FRAME_SIZE => 0,
+            MAX_UDP_PAYLOAD_SIZE => 65527,
+            ACK_DELAY_EXPONENT => 3,
+            MAX_ACK_DELAY => 25,
+            ACTIVE_CONNECTION_ID_LIMIT => 2,
+            _ => panic!("Transport parameter not known or not an Integer"),
+        };
+        match self.params.get(&tp) {
+            None => default,
+            Some(TransportParameter::Integer(x)) => *x,
+            _ => panic!("Internal error"),
+        }
+    }
+
+    // Set an integer type or a default.
+    pub fn set_integer(&mut self, tp: TransportParameterId, value: u64) {
+        match tp {
+            IDLE_TIMEOUT
+            | INITIAL_MAX_DATA
+            | INITIAL_MAX_STREAM_DATA_BIDI_LOCAL
+            | INITIAL_MAX_STREAM_DATA_BIDI_REMOTE
+            | INITIAL_MAX_STREAM_DATA_UNI
+            | INITIAL_MAX_STREAMS_BIDI
+            | INITIAL_MAX_STREAMS_UNI
+            | MAX_UDP_PAYLOAD_SIZE
+            | ACK_DELAY_EXPONENT
+            | MAX_ACK_DELAY
+            | ACTIVE_CONNECTION_ID_LIMIT
+            | MIN_ACK_DELAY
+            | MAX_DATAGRAM_FRAME_SIZE => {
+                self.set(tp, TransportParameter::Integer(value));
+            }
+            _ => panic!("Transport parameter not known"),
+        }
+    }
+
+    pub fn get_bytes(&self, tp: TransportParameterId) -> Option<&[u8]> {
+        match tp {
+            ORIGINAL_DESTINATION_CONNECTION_ID
+            | INITIAL_SOURCE_CONNECTION_ID
+            | RETRY_SOURCE_CONNECTION_ID
+            | STATELESS_RESET_TOKEN => {}
+            _ => panic!("Transport parameter not known or not type bytes"),
+        }
+
+        match self.params.get(&tp) {
+            None => None,
+            Some(TransportParameter::Bytes(x)) => Some(x),
+            _ => panic!("Internal error"),
+        }
+    }
+
+    pub fn set_bytes(&mut self, tp: TransportParameterId, value: Vec<u8>) {
+        match tp {
+            ORIGINAL_DESTINATION_CONNECTION_ID
+            | INITIAL_SOURCE_CONNECTION_ID
+            | RETRY_SOURCE_CONNECTION_ID
+            | STATELESS_RESET_TOKEN => {
+                self.set(tp, TransportParameter::Bytes(value));
+            }
+            _ => panic!("Transport parameter not known or not type bytes"),
+        }
+    }
+
+    pub fn set_empty(&mut self, tp: TransportParameterId) {
+        match tp {
+            DISABLE_MIGRATION | GREASE_QUIC_BIT => {
+                self.set(tp, TransportParameter::Empty);
+            }
+            _ => panic!("Transport parameter not known or not type empty"),
+        }
+    }
+
+    /// Set version information.
+    pub fn set_versions(&mut self, role: Role, versions: &VersionConfig) {
+        let rbuf = random(4);
+        let mut other = Vec::with_capacity(versions.all().len() + 1);
+        let mut dec = Decoder::new(&rbuf);
+        let grease = (dec.decode_uint(4).unwrap() as u32) & 0xf0f0_f0f0 | 0x0a0a0a0a;
+        other.push(grease);
+        for &v in versions.all() {
+            if role == Role::Client && !versions.initial().is_compatible(v) {
+                continue;
+            }
+            other.push(v.wire_version());
+        }
+        let current = versions.initial().wire_version();
+        self.set(
+            VERSION_NEGOTIATION,
+            TransportParameter::Versions { current, other },
+        );
+    }
+
+    fn compatible_upgrade(&mut self, v: Version) {
+        if let Some(TransportParameter::Versions {
+            ref mut current, ..
+        }) = self.params.get_mut(&VERSION_NEGOTIATION)
+        {
+            *current = v.wire_version();
+        } else {
+            unreachable!("Compatible upgrade without transport parameters set!");
+        }
+    }
+
+    pub fn get_empty(&self, tipe: TransportParameterId) -> bool {
+        match self.params.get(&tipe) {
+            None => false,
+            Some(TransportParameter::Empty) => true,
+            _ => panic!("Internal error"),
+        }
+    }
+
+    /// Return true if the remembered transport parameters are OK for 0-RTT.
+    /// Generally this means that any value that is currently in effect is greater than
+    /// or equal to the promised value.
+    pub(crate) fn ok_for_0rtt(&self, remembered: &Self) -> bool {
+        for (k, v_rem) in &remembered.params {
+            // Skip checks for these, which don't affect 0-RTT.
+            if matches!(
+                *k,
+                ORIGINAL_DESTINATION_CONNECTION_ID
+                    | INITIAL_SOURCE_CONNECTION_ID
+                    | RETRY_SOURCE_CONNECTION_ID
+                    | STATELESS_RESET_TOKEN
+                    | IDLE_TIMEOUT
+                    | ACK_DELAY_EXPONENT
+                    | MAX_ACK_DELAY
+                    | ACTIVE_CONNECTION_ID_LIMIT
+                    | PREFERRED_ADDRESS
+            ) {
+                continue;
+            }
+            let ok = if let Some(v_self) = self.params.get(k) {
+                match (v_self, v_rem) {
+                    (TransportParameter::Integer(i_self), TransportParameter::Integer(i_rem)) => {
+                        if *k == MIN_ACK_DELAY {
+                            // MIN_ACK_DELAY is backwards:
+                            // it can only be reduced safely.
+                            *i_self <= *i_rem
+                        } else {
+                            *i_self >= *i_rem
+                        }
+                    }
+                    (TransportParameter::Empty, TransportParameter::Empty) => true,
+                    (
+                        TransportParameter::Versions {
+                            current: v_self, ..
+                        },
+                        TransportParameter::Versions { current: v_rem, .. },
+                    ) => v_self == v_rem,
+                    _ => false,
+                }
+            } else {
+                false
+            };
+            if !ok {
+                return false;
+            }
+        }
+        true
+    }
+
+    /// Get the preferred address in a usable form.
+    #[must_use]
+    pub fn get_preferred_address(&self) -> Option<(PreferredAddress, ConnectionIdEntry<[u8; 16]>)> {
+        if let Some(TransportParameter::PreferredAddress { v4, v6, cid, srt }) =
+            self.params.get(&PREFERRED_ADDRESS)
+        {
+            Some((
+                PreferredAddress::new(*v4, *v6),
+                ConnectionIdEntry::new(CONNECTION_ID_SEQNO_PREFERRED, cid.clone(), *srt),
+            ))
+        } else {
+            None
+        }
+    }
+
+    /// Get the version negotiation values for validation.
+    #[must_use]
+    pub fn get_versions(&self) -> Option<(WireVersion, &[WireVersion])> {
+        if let Some(TransportParameter::Versions { current, other }) =
+            self.params.get(&VERSION_NEGOTIATION)
+        {
+            Some((*current, other))
+        } else {
+            None
+        }
+    }
+
+    #[must_use]
+    pub fn has_value(&self, tp: TransportParameterId) -> bool {
+        self.params.contains_key(&tp)
+    }
+}
+
+#[derive(Debug)]
+pub struct TransportParametersHandler {
+    role: Role,
+    versions: VersionConfig,
+    pub(crate) local: TransportParameters,
+    pub(crate) remote: Option<TransportParameters>,
+    pub(crate) remote_0rtt: Option<TransportParameters>,
+}
+
+impl TransportParametersHandler {
+    pub fn new(role: Role, versions: VersionConfig) -> Self {
+        let mut local = TransportParameters::default();
+        local.set_versions(role, &versions);
+        Self {
+            role,
+            versions,
+            local,
+            remote: None,
+            remote_0rtt: None,
+        }
+    }
+
+    /// When resuming, the version is set based on the ticket.
+    /// That needs to be done to override the default choice from configuration.
+    pub fn set_version(&mut self, version: Version) {
+        debug_assert_eq!(self.role, Role::Client);
+        self.versions.set_initial(version);
+        self.local.set_versions(self.role, &self.versions)
+    }
+
+    pub fn remote(&self) -> &TransportParameters {
+        match (self.remote.as_ref(), self.remote_0rtt.as_ref()) {
+            (Some(tp), _) | (_, Some(tp)) => tp,
+            _ => panic!("no transport parameters from peer"),
+        }
+    }
+
+    /// Get the version as set (or as determined by a compatible upgrade).
+    pub fn version(&self) -> Version {
+        self.versions.initial()
+    }
+
+    fn compatible_upgrade(&mut self, remote_tp: &TransportParameters) -> Res<()> {
+        if let Some((current, other)) = remote_tp.get_versions() {
+            qtrace!(
+                "Peer versions: {:x} {:x?}; config {:?}",
+                current,
+                other,
+                self.versions,
+            );
+
+            if self.role == Role::Client {
+                let chosen = Version::try_from(current)?;
+                if self.versions.compatible().any(|&v| v == chosen) {
+                    Ok(())
+                } else {
+                    qinfo!(
+                        "Chosen version {:x} is not compatible with initial version {:x}",
+                        current,
+                        self.versions.initial().wire_version(),
+                    );
+                    Err(Error::TransportParameterError)
+                }
+            } else {
+                if current != self.versions.initial().wire_version() {
+                    qinfo!(
+                        "Current version {:x} != own version {:x}",
+                        current,
+                        self.versions.initial().wire_version(),
+                    );
+                    return Err(Error::TransportParameterError);
+                }
+
+                if let Some(preferred) = self.versions.preferred_compatible(other) {
+                    if preferred != self.versions.initial() {
+                        qinfo!(
+                            "Compatible upgrade {:?} ==> {:?}",
+                            self.versions.initial(),
+                            preferred
+                        );
+                        self.versions.set_initial(preferred);
+                        self.local.compatible_upgrade(preferred);
+                    }
+                    Ok(())
+                } else {
+                    qinfo!("Unable to find any compatible version");
+                    Err(Error::TransportParameterError)
+                }
+            }
+        } else {
+            Ok(())
+        }
+    }
+}
+
+impl ExtensionHandler for TransportParametersHandler {
+    fn write(&mut self, msg: HandshakeMessage, d: &mut [u8]) -> ExtensionWriterResult {
+        if !matches!(msg, TLS_HS_CLIENT_HELLO | TLS_HS_ENCRYPTED_EXTENSIONS) {
+            return ExtensionWriterResult::Skip;
+        }
+
+        qdebug!("Writing transport parameters, msg={:?}", msg);
+
+        // TODO(ekr@rtfm.com): Modify to avoid a copy.
+        let mut enc = Encoder::default();
+        self.local.encode(&mut enc);
+        assert!(enc.len() <= d.len());
+        d[..enc.len()].copy_from_slice(enc.as_ref());
+        ExtensionWriterResult::Write(enc.len())
+    }
+
+    fn handle(&mut self, msg: HandshakeMessage, d: &[u8]) -> ExtensionHandlerResult {
+        qtrace!(
+            "Handling transport parameters, msg={:?} value={}",
+            msg,
+            hex(d),
+        );
+
+        if !matches!(msg, TLS_HS_CLIENT_HELLO | TLS_HS_ENCRYPTED_EXTENSIONS) {
+            return ExtensionHandlerResult::Alert(110); // unsupported_extension
+        }
+
+        let mut dec = Decoder::from(d);
+        match TransportParameters::decode(&mut dec) {
+            Ok(tp) => {
+                if self.compatible_upgrade(&tp).is_ok() {
+                    self.remote = Some(tp);
+                    ExtensionHandlerResult::Ok
+                } else {
+                    ExtensionHandlerResult::Alert(47)
+                }
+            }
+            _ => ExtensionHandlerResult::Alert(47), // illegal_parameter
+        }
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct TpZeroRttChecker<T> {
+    handler: Rc<RefCell<TransportParametersHandler>>,
+    app_checker: T,
+}
+
+impl<T> TpZeroRttChecker<T>
+where
+    T: ZeroRttChecker + 'static,
+{
+    pub fn wrap(
+        handler: Rc<RefCell<TransportParametersHandler>>,
+        app_checker: T,
+    ) -> Box<dyn ZeroRttChecker> {
+        Box::new(Self {
+            handler,
+            app_checker,
+        })
+    }
+}
+
+impl<T> ZeroRttChecker for TpZeroRttChecker<T>
+where
+    T: ZeroRttChecker,
+{
+    fn check(&self, token: &[u8]) -> ZeroRttCheckResult {
+        // Reject 0-RTT if there is no token.
+        if token.is_empty() {
+            qdebug!("0-RTT: no token, no 0-RTT");
+            return ZeroRttCheckResult::Reject;
+        }
+        let mut dec = Decoder::from(token);
+        let tpslice = if let Some(v) = dec.decode_vvec() {
+            v
+        } else {
+            qinfo!("0-RTT: token code error");
+            return ZeroRttCheckResult::Fail;
+        };
+        let mut dec_tp = Decoder::from(tpslice);
+        let remembered = if let Ok(v) = TransportParameters::decode(&mut dec_tp) {
+            v
+        } else {
+            qinfo!("0-RTT: transport parameter decode error");
+            return ZeroRttCheckResult::Fail;
+        };
+        if self.handler.borrow().local.ok_for_0rtt(&remembered) {
+            qinfo!("0-RTT: transport parameters OK, passing to application checker");
+            self.app_checker.check(dec.decode_remainder())
+        } else {
+            qinfo!("0-RTT: transport parameters bad, rejecting");
+            ZeroRttCheckResult::Reject
+        }
+    }
+}
+
+#[cfg(test)]
+#[allow(unused_variables)]
+mod tests {
+    use super::*;
+    use std::mem;
+
+    #[test]
+    fn basic_tps() {
+        const RESET_TOKEN: &[u8] = &[1, 2, 3, 4, 5, 6, 7, 8, 1, 2, 3, 4, 5, 6, 7, 8];
+        let mut tps = TransportParameters::default();
+        tps.set(
+            STATELESS_RESET_TOKEN,
+            TransportParameter::Bytes(RESET_TOKEN.to_vec()),
+        );
+        tps.params
+            .insert(INITIAL_MAX_STREAMS_BIDI, TransportParameter::Integer(10));
+
+        let mut enc = Encoder::default();
+        tps.encode(&mut enc);
+
+        let tps2 = TransportParameters::decode(&mut enc.as_decoder()).expect("Couldn't decode");
+        assert_eq!(tps, tps2);
+
+        println!("TPS = {:?}", tps);
+        assert_eq!(tps2.get_integer(IDLE_TIMEOUT), 0); // Default
+        assert_eq!(tps2.get_integer(MAX_ACK_DELAY), 25); // Default
+        assert_eq!(tps2.get_integer(ACTIVE_CONNECTION_ID_LIMIT), 2); // Default
+        assert_eq!(tps2.get_integer(INITIAL_MAX_STREAMS_BIDI), 10); // Sent
+        assert_eq!(tps2.get_bytes(STATELESS_RESET_TOKEN), Some(RESET_TOKEN));
+        assert_eq!(tps2.get_bytes(ORIGINAL_DESTINATION_CONNECTION_ID), None);
+        assert_eq!(tps2.get_bytes(INITIAL_SOURCE_CONNECTION_ID), None);
+        assert_eq!(tps2.get_bytes(RETRY_SOURCE_CONNECTION_ID), None);
+        assert!(!tps2.has_value(ORIGINAL_DESTINATION_CONNECTION_ID));
+        assert!(!tps2.has_value(INITIAL_SOURCE_CONNECTION_ID));
+        assert!(!tps2.has_value(RETRY_SOURCE_CONNECTION_ID));
+        assert!(tps2.has_value(STATELESS_RESET_TOKEN));
+
+        let mut enc = Encoder::default();
+        tps.encode(&mut enc);
+
+        let tps2 = TransportParameters::decode(&mut enc.as_decoder()).expect("Couldn't decode");
+    }
+
+    fn make_spa() -> TransportParameter {
+        TransportParameter::PreferredAddress {
+            v4: Some(SocketAddr::new(
+                IpAddr::V4(Ipv4Addr::from(0xc000_0201)),
+                443,
+            )),
+            v6: Some(SocketAddr::new(
+                IpAddr::V6(Ipv6Addr::from(0xfe80_0000_0000_0000_0000_0000_0000_0001)),
+                443,
+            )),
+            cid: ConnectionId::from(&[1, 2, 3, 4, 5]),
+            srt: [3; 16],
+        }
+    }
+
+    #[test]
+    fn preferred_address_encode_decode() {
+        const ENCODED: &[u8] = &[
+            0x0d, 0x2e, 0xc0, 0x00, 0x02, 0x01, 0x01, 0xbb, 0xfe, 0x80, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0xbb, 0x05, 0x01,
+            0x02, 0x03, 0x04, 0x05, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03,
+            0x03, 0x03, 0x03, 0x03, 0x03, 0x03,
+        ];
+        let spa = make_spa();
+        let mut enc = Encoder::new();
+        spa.encode(&mut enc, PREFERRED_ADDRESS);
+        assert_eq!(enc.as_ref(), ENCODED);
+
+        let mut dec = enc.as_decoder();
+        let (id, decoded) = TransportParameter::decode(&mut dec).unwrap().unwrap();
+        assert_eq!(id, PREFERRED_ADDRESS);
+        assert_eq!(decoded, spa);
+    }
+
+    fn mutate_spa<F>(wrecker: F) -> TransportParameter
+    where
+        F: FnOnce(&mut Option<SocketAddr>, &mut Option<SocketAddr>, &mut ConnectionId),
+    {
+        let mut spa = make_spa();
+        if let TransportParameter::PreferredAddress {
+            ref mut v4,
+            ref mut v6,
+            ref mut cid,
+            ..
+        } = &mut spa
+        {
+            wrecker(v4, v6, cid);
+        } else {
+            unreachable!();
+        }
+        spa
+    }
+
+    /// This takes a `TransportParameter::PreferredAddress` that has been mutilated.
+    /// It then encodes it, working from the knowledge that the `encode` function
+    /// doesn't care about validity, and decodes it.  The result should be failure.
+    fn assert_invalid_spa(spa: TransportParameter) {
+        let mut enc = Encoder::new();
+        spa.encode(&mut enc, PREFERRED_ADDRESS);
+        assert_eq!(
+            TransportParameter::decode(&mut enc.as_decoder()).unwrap_err(),
+            Error::TransportParameterError
+        );
+    }
+
+    /// This is for those rare mutations that are acceptable.
+    fn assert_valid_spa(spa: TransportParameter) {
+        let mut enc = Encoder::new();
+        spa.encode(&mut enc, PREFERRED_ADDRESS);
+        let mut dec = enc.as_decoder();
+        let (id, decoded) = TransportParameter::decode(&mut dec).unwrap().unwrap();
+        assert_eq!(id, PREFERRED_ADDRESS);
+        assert_eq!(decoded, spa);
+    }
+
+    #[test]
+    fn preferred_address_zero_address() {
+        // Either port being zero is bad.
+        assert_invalid_spa(mutate_spa(|v4, _, _| {
+            v4.as_mut().unwrap().set_port(0);
+        }));
+        assert_invalid_spa(mutate_spa(|_, v6, _| {
+            v6.as_mut().unwrap().set_port(0);
+        }));
+        // Either IP being zero is bad.
+        assert_invalid_spa(mutate_spa(|v4, _, _| {
+            v4.as_mut().unwrap().set_ip(IpAddr::V4(Ipv4Addr::from(0)));
+        }));
+        assert_invalid_spa(mutate_spa(|_, v6, _| {
+            v6.as_mut().unwrap().set_ip(IpAddr::V6(Ipv6Addr::from(0)));
+        }));
+        // Either address being absent is OK.
+        assert_valid_spa(mutate_spa(|v4, _, _| {
+            *v4 = None;
+        }));
+        assert_valid_spa(mutate_spa(|_, v6, _| {
+            *v6 = None;
+        }));
+        // Both addresses being absent is bad.
+        assert_invalid_spa(mutate_spa(|v4, v6, _| {
+            *v4 = None;
+            *v6 = None;
+        }));
+    }
+
+    #[test]
+    fn preferred_address_bad_cid() {
+        assert_invalid_spa(mutate_spa(|_, _, cid| {
+            *cid = ConnectionId::from(&[]);
+        }));
+        assert_invalid_spa(mutate_spa(|_, _, cid| {
+            *cid = ConnectionId::from(&[0x0c; 21]);
+        }));
+    }
+
+    #[test]
+    fn preferred_address_truncated() {
+        let spa = make_spa();
+        let mut enc = Encoder::new();
+        spa.encode(&mut enc, PREFERRED_ADDRESS);
+        let mut dec = Decoder::from(&enc.as_ref()[..enc.len() - 1]);
+        assert_eq!(
+            TransportParameter::decode(&mut dec).unwrap_err(),
+            Error::NoMoreData
+        );
+    }
+
+    #[test]
+    #[should_panic]
+    fn preferred_address_wrong_family_v4() {
+        mutate_spa(|v4, _, _| {
+            v4.as_mut().unwrap().set_ip(IpAddr::V6(Ipv6Addr::from(0)));
+        })
+        .encode(&mut Encoder::new(), PREFERRED_ADDRESS);
+    }
+
+    #[test]
+    #[should_panic]
+    fn preferred_address_wrong_family_v6() {
+        mutate_spa(|_, v6, _| {
+            v6.as_mut().unwrap().set_ip(IpAddr::V4(Ipv4Addr::from(0)));
+        })
+        .encode(&mut Encoder::new(), PREFERRED_ADDRESS);
+    }
+
+    #[test]
+    #[should_panic]
+    fn preferred_address_neither() {
+        #[allow(clippy::drop_copy)]
+        mem::drop(PreferredAddress::new(None, None));
+    }
+
+    #[test]
+    #[should_panic]
+    fn preferred_address_v4_unspecified() {
+        let _ = PreferredAddress::new(
+            Some(SocketAddr::new(IpAddr::V4(Ipv4Addr::from(0)), 443)),
+            None,
+        );
+    }
+
+    #[test]
+    #[should_panic]
+    fn preferred_address_v4_zero_port() {
+        let _ = PreferredAddress::new(
+            Some(SocketAddr::new(IpAddr::V4(Ipv4Addr::from(0xc000_0201)), 0)),
+            None,
+        );
+    }
+
+    #[test]
+    #[should_panic]
+    fn preferred_address_v6_unspecified() {
+        let _ = PreferredAddress::new(
+            None,
+            Some(SocketAddr::new(IpAddr::V6(Ipv6Addr::from(0)), 443)),
+        );
+    }
+
+    #[test]
+    #[should_panic]
+    fn preferred_address_v6_zero_port() {
+        let _ = PreferredAddress::new(
+            None,
+            Some(SocketAddr::new(IpAddr::V6(Ipv6Addr::from(1)), 0)),
+        );
+    }
+
+    #[test]
+    #[should_panic]
+    fn preferred_address_v4_is_v6() {
+        let _ = PreferredAddress::new(
+            Some(SocketAddr::new(IpAddr::V6(Ipv6Addr::from(1)), 443)),
+            None,
+        );
+    }
+
+    #[test]
+    #[should_panic]
+    fn preferred_address_v6_is_v4() {
+        let _ = PreferredAddress::new(
+            None,
+            Some(SocketAddr::new(
+                IpAddr::V4(Ipv4Addr::from(0xc000_0201)),
+                443,
+            )),
+        );
+    }
+
+    #[test]
+    fn compatible_0rtt_ignored_values() {
+        let mut tps_a = TransportParameters::default();
+        tps_a.set(
+            STATELESS_RESET_TOKEN,
+            TransportParameter::Bytes(vec![1, 2, 3]),
+        );
+        tps_a.set(IDLE_TIMEOUT, TransportParameter::Integer(10));
+        tps_a.set(MAX_ACK_DELAY, TransportParameter::Integer(22));
+        tps_a.set(ACTIVE_CONNECTION_ID_LIMIT, TransportParameter::Integer(33));
+
+        let mut tps_b = TransportParameters::default();
+        assert!(tps_a.ok_for_0rtt(&tps_b));
+        assert!(tps_b.ok_for_0rtt(&tps_a));
+
+        tps_b.set(
+            STATELESS_RESET_TOKEN,
+            TransportParameter::Bytes(vec![8, 9, 10]),
+        );
+        tps_b.set(IDLE_TIMEOUT, TransportParameter::Integer(100));
+        tps_b.set(MAX_ACK_DELAY, TransportParameter::Integer(2));
+        tps_b.set(ACTIVE_CONNECTION_ID_LIMIT, TransportParameter::Integer(44));
+        assert!(tps_a.ok_for_0rtt(&tps_b));
+        assert!(tps_b.ok_for_0rtt(&tps_a));
+    }
+
+    #[test]
+    fn compatible_0rtt_integers() {
+        let mut tps_a = TransportParameters::default();
+        const INTEGER_KEYS: &[TransportParameterId] = &[
+            INITIAL_MAX_DATA,
+            INITIAL_MAX_STREAM_DATA_BIDI_LOCAL,
+            INITIAL_MAX_STREAM_DATA_BIDI_REMOTE,
+            INITIAL_MAX_STREAM_DATA_UNI,
+            INITIAL_MAX_STREAMS_BIDI,
+            INITIAL_MAX_STREAMS_UNI,
+            MAX_UDP_PAYLOAD_SIZE,
+            MIN_ACK_DELAY,
+            MAX_DATAGRAM_FRAME_SIZE,
+        ];
+        for i in INTEGER_KEYS {
+            tps_a.set(*i, TransportParameter::Integer(12));
+        }
+
+        let tps_b = tps_a.clone();
+        assert!(tps_a.ok_for_0rtt(&tps_b));
+        assert!(tps_b.ok_for_0rtt(&tps_a));
+
+        // For each integer key, choose a new value that will be accepted.
+        for i in INTEGER_KEYS {
+            let mut tps_b = tps_a.clone();
+            // Set a safe new value; reducing MIN_ACK_DELAY instead.
+            let safe_value = if *i == MIN_ACK_DELAY { 11 } else { 13 };
+            tps_b.set(*i, TransportParameter::Integer(safe_value));
+            // If the new value is not safe relative to the remembered value,
+            // then we can't attempt 0-RTT with these parameters.
+            assert!(!tps_a.ok_for_0rtt(&tps_b));
+            // The opposite situation is fine.
+            assert!(tps_b.ok_for_0rtt(&tps_a));
+        }
+
+        // Drop integer values and check that that is OK.
+        for i in INTEGER_KEYS {
+            let mut tps_b = tps_a.clone();
+            tps_b.remove(*i);
+            // A value that is missing from what is rememebered is OK.
+            assert!(tps_a.ok_for_0rtt(&tps_b));
+            // A value that is rememebered, but not current is not OK.
+            assert!(!tps_b.ok_for_0rtt(&tps_a));
+        }
+    }
+
+    /// `ACTIVE_CONNECTION_ID_LIMIT` can't be less than 2.
+    #[test]
+    fn active_connection_id_limit_min_2() {
+        let mut tps = TransportParameters::default();
+
+        // Intentionally set an invalid value for the ACTIVE_CONNECTION_ID_LIMIT transport parameter.
+        tps.params
+            .insert(ACTIVE_CONNECTION_ID_LIMIT, TransportParameter::Integer(1));
+
+        let mut enc = Encoder::default();
+        tps.encode(&mut enc);
+
+        // When decoding a set of transport parameters with an invalid ACTIVE_CONNECTION_ID_LIMIT
+        // the result should be an error.
+        let invalid_decode_result = TransportParameters::decode(&mut enc.as_decoder());
+        assert!(invalid_decode_result.is_err());
+    }
+
+    #[test]
+    fn versions_encode_decode() {
+        const ENCODED: &[u8] = &[
+            0x80, 0xff, 0x73, 0xdb, 0x0c, 0x00, 0x00, 0x00, 0x01, 0x1a, 0x2a, 0x3a, 0x4a, 0x5a,
+            0x6a, 0x7a, 0x8a,
+        ];
+        let vn = TransportParameter::Versions {
+            current: Version::Version1.wire_version(),
+            other: vec![0x1a2a_3a4a, 0x5a6a_7a8a],
+        };
+
+        let mut enc = Encoder::new();
+        vn.encode(&mut enc, VERSION_NEGOTIATION);
+        assert_eq!(enc.as_ref(), ENCODED);
+
+        let mut dec = enc.as_decoder();
+        let (id, decoded) = TransportParameter::decode(&mut dec).unwrap().unwrap();
+        assert_eq!(id, VERSION_NEGOTIATION);
+        assert_eq!(decoded, vn);
+    }
+
+    #[test]
+    fn versions_truncated() {
+        const TRUNCATED: &[u8] = &[
+            0x80, 0xff, 0x73, 0xdb, 0x0c, 0x00, 0x00, 0x00, 0x01, 0x1a, 0x2a, 0x3a, 0x4a, 0x5a,
+            0x6a, 0x7a,
+        ];
+        let mut dec = Decoder::from(&TRUNCATED);
+        assert_eq!(
+            TransportParameter::decode(&mut dec).unwrap_err(),
+            Error::NoMoreData
+        );
+    }
+
+    #[test]
+    fn versions_zero() {
+        const ZERO1: &[u8] = &[0x80, 0xff, 0x73, 0xdb, 0x04, 0x00, 0x00, 0x00, 0x00];
+        const ZERO2: &[u8] = &[
+            0x80, 0xff, 0x73, 0xdb, 0x08, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
+        ];
+
+        let mut dec = Decoder::from(&ZERO1);
+        assert_eq!(
+            TransportParameter::decode(&mut dec).unwrap_err(),
+            Error::TransportParameterError
+        );
+        let mut dec = Decoder::from(&ZERO2);
+        assert_eq!(
+            TransportParameter::decode(&mut dec).unwrap_err(),
+            Error::TransportParameterError
+        );
+    }
+
+    #[test]
+    fn versions_equal_0rtt() {
+        let mut current = TransportParameters::default();
+        current.set(
+            VERSION_NEGOTIATION,
+            TransportParameter::Versions {
+                current: Version::Version1.wire_version(),
+                other: vec![0x1a2a_3a4a],
+            },
+        );
+
+        let mut remembered = TransportParameters::default();
+        // It's OK to not remember having versions.
+        assert!(current.ok_for_0rtt(&remembered));
+        // But it is bad in the opposite direction.
+        assert!(!remembered.ok_for_0rtt(&current));
+
+        // If the version matches, it's OK to use 0-RTT.
+        remembered.set(
+            VERSION_NEGOTIATION,
+            TransportParameter::Versions {
+                current: Version::Version1.wire_version(),
+                other: vec![0x5a6a_7a8a, 0x9aaa_baca],
+            },
+        );
+        assert!(current.ok_for_0rtt(&remembered));
+        assert!(remembered.ok_for_0rtt(&current));
+
+        // An apparent "upgrade" is still cause to reject 0-RTT.
+        remembered.set(
+            VERSION_NEGOTIATION,
+            TransportParameter::Versions {
+                current: Version::Version1.wire_version() + 1,
+                other: vec![],
+            },
+        );
+        assert!(!current.ok_for_0rtt(&remembered));
+        assert!(!remembered.ok_for_0rtt(&current));
+    }
+}