Support custom server name resolution (#269)

Co-authored-by: Daniel McCarney <daniel@binaryparadox.net>

src/connector.rs

@@ -24,7 +24,7 @@ pub struct HttpsConnector<T> {
     force_https: bool,
     http: T,
     tls_config: Arc<rustls::ClientConfig>,
-    override_server_name: Option<String>,
+    server_name_resolver: Arc<dyn ResolveServerName + Sync + Send>,
 }
 
 impl<T> HttpsConnector<T> {
@@ -90,24 +90,10 @@ where
         };
 
         let cfg = self.tls_config.clone();
-        let mut hostname = match self.override_server_name.as_deref() {
-            Some(h) => h,
-            None => dst.host().unwrap_or_default(),
-        };
-
-        // Remove square brackets around IPv6 address.
-        if let Some(trimmed) = hostname
-            .strip_prefix('[')
-            .and_then(|h| h.strip_suffix(']'))
-        {
-            hostname = trimmed;
-        }
-
-        let hostname = match ServerName::try_from(hostname) {
-            Ok(dns_name) => dns_name.to_owned(),
-            Err(_) => {
-                let err = io::Error::new(io::ErrorKind::Other, "invalid dnsname");
-                return Box::pin(async move { Err(Box::new(err).into()) });
+        let hostname = match self.server_name_resolver.resolve(&dst) {
+            Ok(hostname) => hostname,
+            Err(e) => {
+                return Box::pin(async move { Err(e) });
             }
         };
 
@@ -135,7 +121,7 @@ where
             force_https: false,
             http,
             tls_config: cfg.into(),
-            override_server_name: None,
+            server_name_resolver: Arc::new(DefaultServerNameResolver::default()),
         }
     }
 }
@@ -147,3 +133,69 @@ impl<T> fmt::Debug for HttpsConnector<T> {
             .finish()
     }
 }
+
+/// The default server name resolver, which uses the hostname in the URI.
+#[derive(Default)]
+pub struct DefaultServerNameResolver(());
+
+impl ResolveServerName for DefaultServerNameResolver {
+    fn resolve(
+        &self,
+        uri: &Uri,
+    ) -> Result<ServerName<'static>, Box<dyn std::error::Error + Sync + Send>> {
+        let mut hostname = uri.host().unwrap_or_default();
+
+        // Remove square brackets around IPv6 address.
+        if let Some(trimmed) = hostname
+            .strip_prefix('[')
+            .and_then(|h| h.strip_suffix(']'))
+        {
+            hostname = trimmed;
+        }
+
+        ServerName::try_from(hostname.to_string()).map_err(|e| Box::new(e) as _)
+    }
+}
+
+/// A server name resolver which always returns the same fixed name.
+pub struct FixedServerNameResolver {
+    name: ServerName<'static>,
+}
+
+impl FixedServerNameResolver {
+    /// Creates a new resolver returning the specified name.
+    pub fn new(name: ServerName<'static>) -> Self {
+        Self { name }
+    }
+}
+
+impl ResolveServerName for FixedServerNameResolver {
+    fn resolve(
+        &self,
+        _: &Uri,
+    ) -> Result<ServerName<'static>, Box<dyn std::error::Error + Sync + Send>> {
+        Ok(self.name.clone())
+    }
+}
+
+impl<F, E> ResolveServerName for F
+where
+    F: Fn(&Uri) -> Result<ServerName<'static>, E>,
+    E: Into<Box<dyn std::error::Error + Sync + Send>>,
+{
+    fn resolve(
+        &self,
+        uri: &Uri,
+    ) -> Result<ServerName<'static>, Box<dyn std::error::Error + Sync + Send>> {
+        self(uri).map_err(Into::into)
+    }
+}
+
+/// A trait implemented by types that can resolve a [`ServerName`] for a request.
+pub trait ResolveServerName {
+    /// Maps a [`Uri`] into a [`ServerName`].
+    fn resolve(
+        &self,
+        uri: &Uri,
+    ) -> Result<ServerName<'static>, Box<dyn std::error::Error + Sync + Send>>;
+}

src/connector/builder.rs

@@ -1,11 +1,14 @@
+use std::sync::Arc;
+
 use hyper_util::client::legacy::connect::HttpConnector;
 #[cfg(any(feature = "rustls-native-certs", feature = "webpki-roots"))]
 use rustls::crypto::CryptoProvider;
 use rustls::ClientConfig;
 
-use super::HttpsConnector;
+use super::{DefaultServerNameResolver, HttpsConnector, ResolveServerName};
 #[cfg(any(feature = "rustls-native-certs", feature = "webpki-roots"))]
 use crate::config::ConfigBuilderExt;
+use pki_types::ServerName;
 
 /// A builder for an [`HttpsConnector`]
 ///
@@ -153,7 +156,7 @@ impl ConnectorBuilder<WantsSchemes> {
         ConnectorBuilder(WantsProtocols1 {
             tls_config: self.0.tls_config,
             https_only: true,
-            override_server_name: None,
+            server_name_resolver: None,
         })
     }
 
@@ -165,7 +168,7 @@ impl ConnectorBuilder<WantsSchemes> {
         ConnectorBuilder(WantsProtocols1 {
             tls_config: self.0.tls_config,
             https_only: false,
-            override_server_name: None,
+            server_name_resolver: None,
         })
     }
 }
@@ -177,7 +180,7 @@ impl ConnectorBuilder<WantsSchemes> {
 pub struct WantsProtocols1 {
     tls_config: ClientConfig,
     https_only: bool,
-    override_server_name: Option<String>,
+    server_name_resolver: Option<Arc<dyn ResolveServerName + Sync + Send>>,
 }
 
 impl WantsProtocols1 {
@@ -186,7 +189,9 @@ impl WantsProtocols1 {
             force_https: self.https_only,
             http: conn,
             tls_config: std::sync::Arc::new(self.tls_config),
-            override_server_name: self.override_server_name,
+            server_name_resolver: self
+                .server_name_resolver
+                .unwrap_or_else(|| Arc::new(DefaultServerNameResolver::default())),
         }
     }
 
@@ -237,6 +242,22 @@ impl ConnectorBuilder<WantsProtocols1> {
         })
     }
 
+    /// Override server name for the TLS stack
+    ///
+    /// By default, for each connection hyper-rustls will extract host portion
+    /// of the destination URL and verify that server certificate contains
+    /// this value.
+    ///
+    /// If this method is called, hyper-rustls will instead use this resolver
+    /// to compute the value used to verify the server certificate.
+    pub fn with_server_name_resolver(
+        mut self,
+        resolver: impl ResolveServerName + 'static + Sync + Send,
+    ) -> Self {
+        self.0.server_name_resolver = Some(Arc::new(resolver));
+        self
+    }
+
     /// Override server name for the TLS stack
     ///
     /// By default, for each connection hyper-rustls will extract host portion
@@ -246,9 +267,22 @@ impl ConnectorBuilder<WantsProtocols1> {
     /// If this method is called, hyper-rustls will instead verify that server
     /// certificate contains `override_server_name`. Domain name included in
     /// the URL will not affect certificate validation.
-    pub fn with_server_name(mut self, override_server_name: String) -> Self {
-        self.0.override_server_name = Some(override_server_name);
-        self
+    #[deprecated(
+        since = "0.27.1",
+        note = "use Self::with_server_name_resolver with FixedServerNameResolver instead"
+    )]
+    pub fn with_server_name(self, mut override_server_name: String) -> Self {
+        // remove square brackets around IPv6 address.
+        if let Some(trimmed) = override_server_name
+            .strip_prefix('[')
+            .and_then(|s| s.strip_suffix(']'))
+        {
+            override_server_name = trimmed.to_string();
+        }
+
+        self.with_server_name_resolver(move |_: &_| {
+            ServerName::try_from(override_server_name.clone())
+        })
     }
 }
 

src/lib.rs

@@ -55,7 +55,9 @@ mod log {
 
 pub use crate::config::ConfigBuilderExt;
 pub use crate::connector::builder::ConnectorBuilder as HttpsConnectorBuilder;
-pub use crate::connector::HttpsConnector;
+pub use crate::connector::{
+    DefaultServerNameResolver, FixedServerNameResolver, HttpsConnector, ResolveServerName,
+};
 pub use crate::stream::MaybeHttpsStream;
 
 /// The various states of the [`HttpsConnectorBuilder`]