Consider the status of IPv6

mullvad-daemon/src/tunnel.rs

@@ -8,10 +8,7 @@ use std::{
 
 use tokio::sync::Mutex;
 
-#[cfg(not(target_os = "android"))]
-use mullvad_relay_selector::{GetRelay, RelaySelector, WireguardConfig};
-#[cfg(target_os = "android")]
-use mullvad_relay_selector::{GetRelay, RelaySelector, WireguardConfig};
+use mullvad_relay_selector::{GetRelay, RelaySelector, RuntimeParameters, WireguardConfig};
 use mullvad_types::{
     endpoint::MullvadWireguardEndpoint, location::GeoIpLocation, relay_list::Relay,
     settings::TunnelOptions,
@@ -143,11 +140,15 @@ impl ParametersGenerator {
 }
 
 impl InnerParametersGenerator {
-    async fn generate(&mut self, retry_attempt: u32) -> Result<TunnelParameters, Error> {
+    async fn generate(
+        &mut self,
+        retry_attempt: u32,
+        ipv6: bool,
+    ) -> Result<TunnelParameters, Error> {
         let data = self.device().await?;
         let selected_relay = self
             .relay_selector
-            .get_relay(retry_attempt as usize)
+            .get_relay_with_runtime_params(retry_attempt as usize, RuntimeParameters { ipv6 })
             .map_err(|err| match err {
                 mullvad_relay_selector::Error::NoBridge => Error::NoBridgeAvailable,
                 _ => Error::NoRelayAvailable,
@@ -277,12 +278,13 @@ impl TunnelParametersGenerator for ParametersGenerator {
     fn generate(
         &mut self,
         retry_attempt: u32,
+        ipv6: bool,
     ) -> Pin<Box<dyn Future<Output = Result<TunnelParameters, ParameterGenerationError>>>> {
         let generator = self.0.clone();
         Box::pin(async move {
             let mut inner = generator.lock().await;
             inner
-                .generate(retry_attempt)
+                .generate(retry_attempt, ipv6)
                 .await
                 .map_err(|error| match error {
                     Error::NoBridgeAvailable => ParameterGenerationError::NoMatchingBridgeRelay,

mullvad-relay-selector/src/lib.rs

@@ -10,6 +10,6 @@ mod relay_selector;
 pub use error::Error;
 pub use relay_selector::detailer;
 pub use relay_selector::{
-    query, GetRelay, RelaySelector, SelectedBridge, SelectedObfuscator, SelectorConfig,
-    WireguardConfig, RETRY_ORDER,
+    query, GetRelay, RelaySelector, RuntimeParameters, SelectedBridge, SelectedObfuscator,
+    SelectorConfig, WireguardConfig, RETRY_ORDER,
 };

mullvad-relay-selector/src/relay_selector/mod.rs

@@ -107,6 +107,41 @@ pub struct SelectorConfig {
     pub bridge_settings: BridgeSettings,
 }
 
+/// Values which affect the choice of relay but are only known at runtime.
+#[derive(Clone, Debug)]
+pub struct RuntimeParameters {
+    /// Whether IPv6 is available
+    pub ipv6: bool,
+}
+
+impl RuntimeParameters {
+    /// Return whether a given [query][`RelayQuery`] is valid given the current runtime parameters
+    pub fn compatible(&self, query: &RelayQuery) -> bool {
+        if !self.ipv6 {
+            let must_use_ipv6 = matches!(
+                query.wireguard_constraints.ip_version,
+                Constraint::Only(talpid_types::net::IpVersion::V6)
+            );
+            if must_use_ipv6 {
+                log::trace!(
+                    "{query:?} is incompatible with {self:?} due to IPv6 not being available"
+                );
+                return false;
+            }
+        }
+        true
+    }
+}
+
+// Note: It is probably not a good idea to rely on derived default values to be correct for our use
+// case.
+#[allow(clippy::derivable_impls)]
+impl Default for RuntimeParameters {
+    fn default() -> Self {
+        RuntimeParameters { ipv6: false }
+    }
+}
+
 /// This enum exists to separate the two types of [`SelectorConfig`] that exists.
 ///
 /// The first one is a "regular" config, where [`SelectorConfig::relay_settings`] is [`RelaySettings::Normal`].
@@ -429,7 +464,19 @@ impl RelaySelector {
     ///
     /// [`RETRY_ORDER`]: crate::RETRY_ORDER
     pub fn get_relay(&self, retry_attempt: usize) -> Result<GetRelay, Error> {
-        self.get_relay_with_order(&RETRY_ORDER, retry_attempt)
+        self.get_relay_with_custom_params(retry_attempt, &RETRY_ORDER, RuntimeParameters::default())
+    }
+
+    /// Returns a random relay and relay endpoint matching the current constraints corresponding to
+    /// `retry_attempt` in [`RETRY_ORDER`] while considering [runtime_params][`RuntimeParameters`].
+    ///
+    /// [`RETRY_ORDER`]: crate::RETRY_ORDER
+    pub fn get_relay_with_runtime_params(
+        &self,
+        retry_attempt: usize,
+        runtime_params: RuntimeParameters,
+    ) -> Result<GetRelay, Error> {
+        self.get_relay_with_custom_params(retry_attempt, &RETRY_ORDER, runtime_params)
     }
 
     /// Peek at which [`TunnelType`] that would be returned for a certain connection attempt for a given
@@ -445,9 +492,10 @@ impl RelaySelector {
             SpecializedSelectorConfig::Custom(_) => None,
             SpecializedSelectorConfig::Normal(config) => Some(
                 Self::pick_and_merge_query(
+                    connection_attempt,
                     &RETRY_ORDER,
+                    RuntimeParameters::default(),
                     RelayQuery::from(config),
-                    connection_attempt,
                 )
                 .tunnel_protocol
                 .unwrap_or(TunnelType::Wireguard),
@@ -456,11 +504,12 @@ impl RelaySelector {
     }
 
     /// Returns a random relay and relay endpoint matching the current constraints defined by
-    /// `retry_order` corresponsing to `retry_attempt`.
-    pub fn get_relay_with_order(
+    /// `retry_order` corresponding to `retry_attempt`.
+    pub fn get_relay_with_custom_params(
         &self,
-        retry_order: &[RelayQuery],
         retry_attempt: usize,
+        retry_order: &[RelayQuery],
+        runtime_params: RuntimeParameters,
     ) -> Result<GetRelay, Error> {
         let config_guard = self.config.lock().unwrap();
         let config = SpecializedSelectorConfig::from(&*config_guard);
@@ -475,8 +524,12 @@ impl RelaySelector {
                 let parsed_relays = &self.parsed_relays.lock().unwrap();
                 // Merge user preferences with the relay selector's default preferences.
                 let user_preferences = RelayQuery::from(normal_config.clone());
-                let query =
-                    Self::pick_and_merge_query(retry_order, user_preferences, retry_attempt);
+                let query = Self::pick_and_merge_query(
+                    retry_attempt,
+                    retry_order,
+                    runtime_params,
+                    user_preferences,
+                );
                 Self::get_relay_inner(&query, parsed_relays, &normal_config)
             }
         }
@@ -488,15 +541,23 @@ impl RelaySelector {
     /// This algorithm will loop back to the start of `retry_order` if `retry_attempt < retry_order.len()`.
     /// If `user_preferences` is not compatible with any of the pre-defined queries in `retry_order`, `user_preferences`
     /// is returned.
+    ///
+    /// Runtime parameters may affect which of the default queries that are considered. For example,
+    /// queries which rely on IPv6 will not be considered if working IPv6 is not available at runtime.
     fn pick_and_merge_query(
+        retry_attempt: usize,
         retry_order: &[RelayQuery],
+        runtime_params: RuntimeParameters,
         user_preferences: RelayQuery,
-        retry_attempt: usize,
     ) -> RelayQuery {
+        log::trace!("Merging user preferences {user_preferences:?} with default retry strategy");
         retry_order
             .iter()
+            // Remove candidate queries based on runtime parameters before trying to merge user
+            // settings
+            .filter(|query| runtime_params.compatible(query))
             .cycle()
-            .filter_map(|constraint| constraint.clone().intersection(user_preferences.clone()))
+            .filter_map(|query| query.clone().intersection(user_preferences.clone()))
             .nth(retry_attempt)
             .unwrap_or(user_preferences)
     }

mullvad-relay-selector/tests/relay_selector.rs

@@ -12,7 +12,8 @@ use talpid_types::net::{
 
 use mullvad_relay_selector::{
     query::{builder::RelayQueryBuilder, BridgeQuery, OpenVpnRelayQuery},
-    Error, GetRelay, RelaySelector, SelectorConfig, WireguardConfig, RETRY_ORDER,
+    Error, GetRelay, RelaySelector, RuntimeParameters, SelectorConfig, WireguardConfig,
+    RETRY_ORDER,
 };
 use mullvad_types::{
     constraints::Constraint,
@@ -876,7 +877,7 @@ fn test_openvpn_auto_bridge() {
         .take(100 * retry_order.len())
     {
         let relay = relay_selector
-            .get_relay_with_order(&retry_order, retry_attempt)
+            .get_relay_with_custom_params(retry_attempt, &retry_order, RuntimeParameters::default())
             .unwrap();
         match relay {
             GetRelay::OpenVpn { bridge, .. } => {

talpid-core/src/tunnel_state_machine/connecting_state.rs

@@ -69,7 +69,7 @@ impl ConnectingState {
         match shared_values.runtime.block_on(
             shared_values
                 .tunnel_parameters_generator
-                .generate(retry_attempt),
+                .generate(retry_attempt, shared_values.connectivity.has_ipv6()),
         ) {
             Err(err) => {
                 ErrorState::enter(shared_values, ErrorStateCause::TunnelParameterError(err))

talpid-core/src/tunnel_state_machine/mod.rs

@@ -417,6 +417,7 @@ pub trait TunnelParametersGenerator: Send + 'static {
     fn generate(
         &mut self,
         retry_attempt: u32,
+        ipv6: bool,
     ) -> Pin<Box<dyn Future<Output = Result<TunnelParameters, ParameterGenerationError>>>>;
 }
 

talpid-types/src/net/mod.rs

@@ -555,6 +555,16 @@ impl Connectivity {
         )
     }
 
+    /// Whether IPv6 connectivity seems to be available on the host.
+    ///
+    /// If IPv6 status is unknown, `false` is returned.
+    pub fn has_ipv6(&self) -> bool {
+        match self {
+            Connectivity::Status { ipv6, .. } => *ipv6,
+            _ => false,
+        }
+    }
+
     /// If the host does not have configured IPv6 routes, we have no way of
     /// reaching the internet so we consider ourselves offline.
     #[cfg(target_os = "android")]