Rewrite parts of the Encrypted DNS proxy parsing and handling

mullvad-encrypted-dns-proxy/examples/forwarder.rs

@@ -1,31 +1,37 @@
 use std::env::args;
 
-use mullvad_encrypted_dns_proxy::{config::Obfuscator, config_resolver, forwarder};
+use mullvad_encrypted_dns_proxy::{config_resolver, forwarder};
 use tokio::net::TcpListener;
 
 /// This can be tested out by using curl:
 /// `curl https://api.mullvad.net:$port/api/v1/relays --resolve api.mullvad.net:$port:$addr`
 ///  where $addr and $port are the listening address of the proxy (bind_addr).
 #[tokio::main]
 async fn main() {
-    let mut configs =
+    let bind_addr = args().nth(1).unwrap_or("127.0.0.1:0".to_string());
+
+    let configs =
         config_resolver::resolve_configs(config_resolver::default_resolvers(), "frakta.eu")
             .await
             .expect("Failed to resolve configs");
 
-    let bind_addr = args().nth(1).unwrap_or("127.0.0.1:0".to_string());
-    let obfuscator = configs.xor.pop().expect("No XOR config");
-    println!("Obfuscator in use - {:?}", obfuscator);
-    let obfuscator: Box<dyn Obfuscator> = Box::new(obfuscator);
+    let proxy_config = configs
+        .into_iter()
+        .find(|c| c.obfuscation.is_some())
+        .expect("No XOR config");
+    println!("Proxy config in use: {:?}", proxy_config);
+
     let listener = TcpListener::bind(bind_addr)
         .await
         .expect("Failed to bind listener socket");
+
     let listen_addr = listener
         .local_addr()
         .expect("failed to obtain listen address");
     println!("Listening on {listen_addr}");
+
     while let Ok((client_conn, _client_addr)) = listener.accept().await {
-        let connected = crate::forwarder::Forwarder::connect(obfuscator.clone())
+        let connected = crate::forwarder::Forwarder::connect(&proxy_config)
             .await
             .expect("failed to connect to obfuscator");
         let _ = connected.forward(client_conn).await;

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

@@ -1,129 +1,117 @@
 //! Parse and use various proxy configurations as they are retrieved via AAAA records, hopefully
 //! served by DoH resolvers.
-use std::{
-    io::Cursor,
-    net::{Ipv6Addr, SocketAddrV4},
-};
 
-use byteorder::{LittleEndian, ReadBytesExt};
+use core::fmt;
+use std::net::{Ipv6Addr, SocketAddrV4};
 
 mod plain;
 mod xor;
-pub use plain::Plain;
-pub use xor::Xor;
 
-/// An error that happens when parsing IPv6 addresses into proxy configurations.
-#[derive(Debug)]
+pub use xor::XorKey;
+
+#[derive(Debug, Eq, PartialEq)]
 pub enum Error {
-    /// IP address representing a Xor proxy was not valid
-    InvalidXor(xor::Error),
-    /// IP address representing the plain proxy was not valid
-    InvalidPlain(plain::Error),
-    /// IP addresses did not contain any valid proxy configuration
-    NoProxies,
+    /// The proxy type field has a value this library is not compatible with
+    UnknownProxyType(u16),
+    /// The XorV1 proxy type is deprecated and not supported
+    XorV1Unsupported,
+    /// The port is not valid
+    InvalidPort(u16),
+    /// The key to use for XOR obfuscation was empty (all zeros)
+    EmptyXorKey,
 }
 
-/// If a given IPv6 address does not contain a valid value for the proxy version, this error type
-/// will contain the unrecognized value.
-#[derive(Debug)]
-pub struct ErrorUnknownType(u16);
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::UnknownProxyType(t) => write!(f, "Unknown type of proxy: {t:#x}"),
+            Self::XorV1Unsupported => write!(f, "XorV1 proxy types are not supported"),
+            Self::InvalidPort(port) => write!(f, "Port {port} is not valid for remote endpoint"),
+            Self::EmptyXorKey => write!(f, "The key material for XOR obfuscation is empty"),
+        }
+    }
+}
+
+impl std::error::Error for Error {}
 
 /// Type of a proxy configuration. Derived from the 2nd hextet of an IPv6 address in network byte
 /// order. E.g. an IPv6 address such as `7f7f:2323::`  would have a proxy type value of `0x2323`.
 #[derive(PartialEq, Debug)]
-#[repr(u16)]
 enum ProxyType {
-    Plain = 0x01,
-    XorV1 = 0x02,
-    XorV2 = 0x03,
+    Plain,
+    XorV1,
+    XorV2,
 }
 
-impl TryFrom<Ipv6Addr> for ProxyType {
-    type Error = ErrorUnknownType;
-
-    /// A proxy type is represented by the second hexlet in an IPv6 address, and it is to be
-    /// interpreted as little endian. All other data is disregarded.
-    fn try_from(value: Ipv6Addr) -> Result<Self, Self::Error> {
-        let mut data = Cursor::new(value.octets());
-        // skip the first 2 bytes since it's just padding to make the IP look more like a legit
-        // IPv6 address.
-
-        data.set_position(2);
-        match data
-            .read_u16::<LittleEndian>()
-            .expect("IPv6 must have at least 16 bytes")
-        {
+impl TryFrom<[u8; 2]> for ProxyType {
+    type Error = Error;
+
+    fn try_from(bytes: [u8; 2]) -> Result<Self, Self::Error> {
+        match u16::from_le_bytes(bytes) {
             0x01 => Ok(Self::Plain),
             0x02 => Ok(Self::XorV1),
             0x03 => Ok(Self::XorV2),
-            unknown => Err(ErrorUnknownType(unknown)),
+            unknown => Err(Error::UnknownProxyType(unknown)),
         }
     }
 }
 
-/// Contains valid proxy configurations as derived from a set of IPv6 addresses.
-pub struct AvailableProxies {
-    /// Plain proxies just forward traffic without any obfuscation.
-    pub plain: Vec<Plain>,
-    /// Xor proxies xor a pre-shared key with all the traffic.
-    pub xor: Vec<Xor>,
+pub trait Obfuscator: Send {
+    /// Applies obfuscation to a given buffer of bytes. Changes the data in place.
+    fn obfuscate(&mut self, buffer: &mut [u8]);
 }
 
-impl TryFrom<Vec<Ipv6Addr>> for AvailableProxies {
-    type Error = Error;
+#[derive(Debug, Eq, PartialEq)]
+pub struct ProxyConfig {
+    pub addr: SocketAddrV4,
+    pub obfuscation: Option<ObfuscationConfig>,
+}
 
-    fn try_from(ips: Vec<Ipv6Addr>) -> Result<Self, Self::Error> {
-        let mut proxies = AvailableProxies {
-            plain: vec![],
-            xor: vec![],
-        };
-
-        for ip in ips {
-            match ProxyType::try_from(ip) {
-                Ok(ProxyType::Plain) => {
-                    proxies
-                        .plain
-                        .push(Plain::try_from(ip).map_err(Error::InvalidPlain)?);
-                }
-                Ok(ProxyType::XorV2) => {
-                    proxies
-                        .xor
-                        .push(Xor::try_from(ip).map_err(Error::InvalidXor)?);
-                }
-
-                // V1 types are ignored and so are errors
-                Ok(ProxyType::XorV1) => continue,
-
-                Err(ErrorUnknownType(unknown_proxy_type)) => {
-                    log::error!("Unknown proxy type {unknown_proxy_type}");
-                }
-            }
-        }
-        if proxies.plain.is_empty() && proxies.xor.is_empty() {
-            return Err(Error::NoProxies);
-        }
+#[derive(Debug, Eq, PartialEq)]
+pub enum ObfuscationConfig {
+    XorV2(xor::XorKey),
+}
 
-        Ok(proxies)
+impl ObfuscationConfig {
+    /// Instantiate an obfuscator from the given obfuscation config.
+    pub fn create_obfuscator(&self) -> Box<dyn Obfuscator> {
+        match self {
+            Self::XorV2(key) => Box::new(xor::XorObfuscator::new(*key)),
+        }
     }
 }
 
-/// A trait that can be used by a forwarder to forward traffic.
-pub trait Obfuscator: Send {
-    /// Provides the endpoint for the proxy. This address must be connected and all traffic to it
-    /// should first be obfuscated with `Obfuscator::obfuscate`.
-    fn addr(&self) -> SocketAddrV4;
-    /// Applies obfuscation to a given buffer of bytes.
-    fn obfuscate(&mut self, buffer: &mut [u8]);
-    /// Constructs a new obfuscator of the same type and configuration, with it's internal state
-    /// reset.
-    fn clone(&self) -> Box<dyn Obfuscator>;
+impl TryFrom<Ipv6Addr> for ProxyConfig {
+    type Error = Error;
+
+    fn try_from(ip: Ipv6Addr) -> Result<Self, Self::Error> {
+        let data = ip.octets();
+
+        let proxy_type_bytes = <[u8; 2]>::try_from(&data[2..4]).unwrap();
+        let proxy_config_payload = <[u8; 12]>::try_from(&data[4..16]).unwrap();
+
+        let proxy_type = ProxyType::try_from(proxy_type_bytes)?;
+
+        match proxy_type {
+            ProxyType::Plain => plain::parse_plain(proxy_config_payload),
+            ProxyType::XorV1 => Err(Error::XorV1Unsupported),
+            ProxyType::XorV2 => xor::parse_xor(proxy_config_payload),
+        }
+    }
 }
 
-#[test]
-fn wrong_proxy_type() {
-    let addr: Ipv6Addr = "ffff:2345::".parse().unwrap();
-    match ProxyType::try_from(addr) {
-        Err(ErrorUnknownType(0x4523)) => (),
-        anything_else => panic!("Expected unknown type 0x33, got {anything_else:x?}"),
+#[cfg(test)]
+mod tests {
+    use std::net::Ipv6Addr;
+
+    use super::{Error, ProxyConfig};
+
+    #[test]
+    fn wrong_proxy_type() {
+        let addr: Ipv6Addr = "ffff:2345::".parse().unwrap();
+        match ProxyConfig::try_from(addr) {
+            Err(Error::UnknownProxyType(0x4523)) => (),
+            anything_else => panic!("Unexpected proxy config parse result: {anything_else:?}"),
+        }
     }
 }