Add FFI for encrypted-dns-proxy for iOS

ios/MullvadRustRuntime/include/mullvad_rust_runtime.h

@@ -5,17 +5,55 @@
 #include <stdint.h>
 #include <stdlib.h>
 
-typedef struct EphemeralPeerCancelToken {
-  void *context;
-} EphemeralPeerCancelToken;
+typedef struct EncryptedDnsProxyState EncryptedDnsProxyState;
 
 typedef struct ProxyHandle {
   void *context;
   uint16_t port;
 } ProxyHandle;
 
+typedef struct EphemeralPeerCancelToken {
+  void *context;
+} EphemeralPeerCancelToken;
+
 extern const uint16_t CONFIG_SERVICE_PORT;
 
+/**
+ * Initializes a valid pointer to an instance of `EncryptedDnsProxyState`.
+ */
+struct EncryptedDnsProxyState *encrypted_dns_proxy_init(void);
+
+/**
+ * This must be called only once to deallocate `EncryptedDnsProxyState`.
+ *
+ * # Safety
+ * `ptr` must be a valid, exclusive pointer to `EncryptedDnsProxyState`, initialized
+ * by `encrypted_dns_proxy_init`. This function is not thread safe, and should only be called
+ * once.
+ */
+void encrypted_dns_proxy_free(struct EncryptedDnsProxyState *ptr);
+
+/**
+ * # Safety
+ * encrypted_dns_proxy must be a valid, exclusive pointer to `EncryptedDnsProxyState`, initialized
+ * by `encrypted_dns_proxy_init`. This function is not thread safe.
+ * `proxy_handle` must be pointing to a valid memory region for the size of a `ProxyHandle`. This
+ * function is not thread safe, but it can be called repeatedly. Each successful invocation should
+ * clean up the resulting proxy via `[encrypted_dns_proxy_stop]`.
+ *
+ * `proxy_handle` will only contain valid values if the return value is zero. It is still valid to
+ * deallocate the memory.
+ */
+int32_t encrypted_dns_proxy_start(struct EncryptedDnsProxyState *encrypted_dns_proxy,
+                                  struct ProxyHandle *proxy_handle);
+
+/**
+ * # Safety
+ * `proxy_config` must be a valid pointer to a `ProxyHandle` as initialized by
+ * [`encrypted_dns_proxy_start`]. It should only ever be called once.
+ */
+int32_t encrypted_dns_proxy_stop(struct ProxyHandle *proxy_config);
+
 /**
  * Called by the Swift side to signal that the ephemeral peer exchange should be cancelled.
  * After this call, the cancel token is no longer valid.

mullvad-encrypted-dns-proxy/src/config/mod.rs

@@ -39,8 +39,11 @@ impl std::error::Error for Error {}
 /// order. E.g. an IPv6 address such as `7f7f:2323::`  would have a proxy type value of `0x2323`.
 #[derive(PartialEq, Debug)]
 enum ProxyType {
+    /// Plain proxy type
     Plain,
+    /// XorV1 - deprecated
     XorV1,
+    /// XorV2
     XorV2,
 }
 

mullvad-encrypted-dns-proxy/src/config_resolver.rs

@@ -4,28 +4,39 @@ use crate::config;
 use core::fmt;
 use hickory_resolver::{config::*, error::ResolveError, TokioAsyncResolver};
 use rustls::ClientConfig;
-use std::{net::IpAddr, sync::Arc};
+use std::{net::IpAddr, sync::Arc, time::Duration};
+use tokio::time::error::Elapsed;
 
 /// The port to connect to the DoH resolvers over.
 const RESOLVER_PORT: u16 = 443;
+const DEFAULT_TIMEOUT: Duration = std::time::Duration::from_secs(10);
 
 pub struct Nameserver {
     pub name: String,
     pub addr: Vec<IpAddr>,
 }
 
 #[derive(Debug)]
-pub struct ResolutionError(ResolveError);
+pub enum Error {
+    ResolutionError(ResolveError),
+    Timeout(Elapsed),
+}
 
-impl fmt::Display for ResolutionError {
+impl fmt::Display for Error {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        self.0.fmt(f)
+        match self {
+            Error::ResolutionError(err) => err.fmt(f),
+            Error::Timeout(err) => err.fmt(f),
+        }
     }
 }
 
-impl std::error::Error for ResolutionError {
+impl std::error::Error for Error {
     fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-        self.0.source()
+        match self {
+            Self::ResolutionError(ref err) => Some(err),
+            Self::Timeout(ref err) => Some(err),
+        }
     }
 }
 
@@ -50,13 +61,17 @@ pub fn default_resolvers() -> Vec<Nameserver> {
     ]
 }
 
+pub async fn resolve_default_config() -> Result<Vec<config::ProxyConfig>, Error> {
+    resolve_configs(&default_resolvers(), "frakta.eu").await
+}
+
 /// Look up the `domain` towards the given `resolvers`, and try to deserialize all the returned
 /// AAAA records into [`ProxyConfig`](config::ProxyConfig)s.
 pub async fn resolve_configs(
     resolvers: &[Nameserver],
     domain: &str,
-) -> Result<Vec<config::ProxyConfig>, ResolutionError> {
-    let mut resolver_config = ResolverConfig::new();
+) -> Result<Vec<config::ProxyConfig>, Error> {
+    let mut nameservers = ResolverConfig::new();
     for resolver in resolvers.iter() {
         let ns_config_group = NameServerConfigGroup::from_ips_https(
             &resolver.addr,
@@ -66,25 +81,28 @@ pub async fn resolve_configs(
         )
         .into_inner();
         for ns_config in ns_config_group {
-            resolver_config.add_name_server(ns_config);
+            nameservers.add_name_server(ns_config);
         }
     }
 
-    resolver_config.set_tls_client_config(Arc::new(client_config_tls12()));
+    nameservers.set_tls_client_config(Arc::new(client_config_tls12()));
+    let mut resolver_config: ResolverOpts = Default::default();
 
-    resolve_config_with_resolverconfig(resolver_config, Default::default(), domain).await
+    resolver_config.timeout = Duration::from_secs(5);
+    resolve_config_with_resolverconfig(nameservers, resolver_config, domain, DEFAULT_TIMEOUT).await
 }
 
 pub async fn resolve_config_with_resolverconfig(
     resolver_config: ResolverConfig,
     options: ResolverOpts,
     domain: &str,
-) -> Result<Vec<config::ProxyConfig>, ResolutionError> {
+    timeout: Duration,
+) -> Result<Vec<config::ProxyConfig>, Error> {
     let resolver = TokioAsyncResolver::tokio(resolver_config, options);
-    let lookup = resolver
-        .ipv6_lookup(domain)
+    let lookup = tokio::time::timeout(timeout, resolver.ipv6_lookup(domain))
         .await
-        .map_err(ResolutionError)?;
+        .map_err(Error::Timeout)?
+        .map_err(Error::ResolutionError)?;
 
     let addrs = lookup.into_iter().map(|aaaa_record| aaaa_record.0);
 

mullvad-ios/src/encrypted_dns_proxy.rs

@@ -0,0 +1,221 @@
+use crate::ProxyHandle;
+
+use mullvad_encrypted_dns_proxy::{config::ProxyConfig, config_resolver, Forwarder};
+use std::{
+    collections::HashSet,
+    io, mem,
+    net::{Ipv4Addr, SocketAddr},
+    ptr,
+};
+use tokio::{net::TcpListener, task::JoinHandle};
+
+pub struct EncryptedDnsProxyState {
+    /// Note that we rely on the randomness of the ordering of the items in the hashset to pick a
+    /// random configurations every time.
+    configurations: HashSet<ProxyConfig>,
+    tried_configurations: HashSet<ProxyConfig>,
+}
+
+#[derive(Debug)]
+pub enum Error {
+    /// Failed to initialize tokio runtime.
+    TokioRuntime,
+    /// Failed to bind a local listening socket, the one that will be forwarded through the proxy.
+    BindLocalSocket(io::Error),
+    /// Failed to get local listening address of the local listening socket.
+    GetBindAddr(io::Error),
+    /// Failed to initialize forwarder.
+    Forwarder(io::Error),
+    /// Failed to fetch a proxy configuration over DNS.
+    FetchConfig(config_resolver::Error),
+    /// Failed to initialize with a valid configuration.
+    NoConfigs,
+}
+
+impl From<Error> for i32 {
+    fn from(err: Error) -> Self {
+        match err {
+            Error::TokioRuntime => -1,
+            Error::BindLocalSocket(_) => -2,
+            Error::GetBindAddr(_) => -3,
+            Error::Forwarder(_) => -4,
+            Error::FetchConfig(_) => -5,
+            Error::NoConfigs => -6,
+        }
+    }
+}
+
+impl EncryptedDnsProxyState {
+    async fn start(&mut self) -> Result<ProxyHandle, Error> {
+        self.fetch_configs().await?;
+        let proxy_configuration = self.next_configuration().ok_or(Error::NoConfigs)?;
+
+        let local_socket = Self::bind_local_addr()
+            .await
+            .map_err(Error::BindLocalSocket)?;
+        let bind_addr = local_socket.local_addr().map_err(Error::GetBindAddr)?;
+        let forwarder = Forwarder::connect(&proxy_configuration)
+            .await
+            .map_err(Error::Forwarder)?;
+        let join_handle = Box::new(tokio::spawn(async move {
+            if let Ok((client_conn, _)) = local_socket.accept().await {
+                let _ = forwarder.forward(client_conn).await;
+            }
+        }));
+
+        Ok(ProxyHandle {
+            context: Box::into_raw(join_handle).cast(),
+            port: bind_addr.port(),
+        })
+    }
+
+    async fn bind_local_addr() -> io::Result<TcpListener> {
+        let bind_addr = SocketAddr::new(Ipv4Addr::UNSPECIFIED.into(), 0);
+        TcpListener::bind(bind_addr).await
+    }
+
+    /// Select a config.
+    /// Always select an obfuscated configuration, if there are any left untried. If no obfuscated
+    /// configurations exist, try plain configurations. The order is randomized due to the hash set
+    /// storing the configurations in a random order.
+    fn next_configuration(&mut self) -> Option<ProxyConfig> {
+        if self.should_reset() {
+            self.reset();
+        }
+        // TODO: currently, the randomized order of proxy config retrieval depends on the random
+        // iteration order of a given HashSet instance. Since for now, there will be only 2
+        // different configurations, it barely matters. In the future, we should use `rand`
+        // instead, so that the behavior is explicit and clear.
+
+        // First, try getting an obfuscated configuration, if there exist any.
+        let config = if let Some(obfuscated_config) = self
+            .configurations
+            .difference(&self.tried_configurations)
+            .find(|config| config.obfuscation.is_some())
+            .cloned()
+        {
+            obfuscated_config
+        } else {
+            // If no obfuscated configurations exist, try the next untried configuration.
+            self.configurations
+                .difference(&self.tried_configurations)
+                .next()
+                .cloned()?
+        };
+
+        self.tried_configurations.insert(config.clone());
+        Some(config)
+    }
+
+    /// Fetch a config, but error out only when no existing configuration was there.
+    async fn fetch_configs(&mut self) -> Result<(), Error> {
+        match mullvad_encrypted_dns_proxy::config_resolver::resolve_default_config().await {
+            Ok(new_configs) => {
+                self.configurations = HashSet::from_iter(new_configs.into_iter());
+            }
+            Err(err) => {
+                log::error!("Failed to fetch a new proxy configuration: {err:?}");
+                if self.is_empty() {
+                    return Err(Error::FetchConfig(err));
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn is_empty(&self) -> bool {
+        self.configurations.is_empty()
+    }
+
+    /// Checks if the `tried_configurations` set should be reset.
+    /// It should only be reset if the difference between `configurations` and
+    /// `tried_configurations` is an empty set - in this case all available configurations have
+    /// been tried.
+    fn should_reset(&self) -> bool {
+        self.configurations
+            .difference(&self.tried_configurations)
+            .count()
+            == 0
+    }
+
+    /// Clears the `tried_configurations` set.
+    fn reset(&mut self) {
+        self.tried_configurations.clear();
+    }
+}
+
+/// Initializes a valid pointer to an instance of `EncryptedDnsProxyState`.
+#[no_mangle]
+pub unsafe extern "C" fn encrypted_dns_proxy_init() -> *mut EncryptedDnsProxyState {
+    let state = Box::new(EncryptedDnsProxyState {
+        configurations: Default::default(),
+        tried_configurations: Default::default(),
+    });
+    Box::into_raw(state)
+}
+
+/// This must be called only once to deallocate `EncryptedDnsProxyState`.
+///
+/// # Safety
+/// `ptr` must be a valid, exclusive pointer to `EncryptedDnsProxyState`, initialized
+/// by `encrypted_dns_proxy_init`. This function is not thread safe, and should only be called
+/// once.
+#[no_mangle]
+pub unsafe extern "C" fn encrypted_dns_proxy_free(ptr: *mut EncryptedDnsProxyState) {
+    let _ = unsafe { Box::from_raw(ptr) };
+}
+
+/// # Safety
+/// encrypted_dns_proxy must be a valid, exclusive pointer to `EncryptedDnsProxyState`, initialized
+/// by `encrypted_dns_proxy_init`. This function is not thread safe.
+/// `proxy_handle` must be pointing to a valid memory region for the size of a `ProxyHandle`. This
+/// function is not thread safe, but it can be called repeatedly. Each successful invocation should
+/// clean up the resulting proxy via `[encrypted_dns_proxy_stop]`.
+///
+/// `proxy_handle` will only contain valid values if the return value is zero. It is still valid to
+/// deallocate the memory.
+#[no_mangle]
+pub unsafe extern "C" fn encrypted_dns_proxy_start(
+    encrypted_dns_proxy: *mut EncryptedDnsProxyState,
+    proxy_handle: *mut ProxyHandle,
+) -> i32 {
+    let handle = match crate::mullvad_ios_runtime() {
+        Ok(handle) => handle,
+        Err(err) => {
+            log::error!("Cannot instantiate a tokio runtime: {}", err);
+            return Error::TokioRuntime.into();
+        }
+    };
+
+    let mut encrypted_dns_proxy = unsafe { Box::from_raw(encrypted_dns_proxy) };
+    let proxy_result = handle.block_on(encrypted_dns_proxy.start());
+    mem::forget(encrypted_dns_proxy);
+
+    match proxy_result {
+        Ok(handle) => unsafe { ptr::write(proxy_handle, handle) },
+        Err(err) => {
+            let empty_handle = ProxyHandle {
+                context: ptr::null_mut(),
+                port: 0,
+            };
+            unsafe { ptr::write(proxy_handle, empty_handle) }
+            log::error!("Failed to create a proxy connection: {err:?}");
+            return err.into();
+        }
+    }
+
+    0
+}
+
+/// # Safety
+/// `proxy_config` must be a valid pointer to a `ProxyHandle` as initialized by
+/// [`encrypted_dns_proxy_start`]. It should only ever be called once.
+#[no_mangle]
+pub unsafe extern "C" fn encrypted_dns_proxy_stop(proxy_config: *mut ProxyHandle) -> i32 {
+    let ptr = unsafe { (*proxy_config).context };
+    if !ptr.is_null() {
+        let handle: Box<JoinHandle<()>> = unsafe { Box::from_raw(ptr.cast()) };
+        handle.abort();
+    }
+    0i32
+}

mullvad-ios/src/ephemeral_peer_proxy/mod.rs

@@ -1,3 +1,4 @@
+#![cfg(target_os = "ios")]
 pub mod ios_runtime;
 pub mod ios_tcp_connection;