Introduce ClientHello::get_extension

boring/src/ssl/mod.rs

@@ -1591,6 +1591,26 @@ pub struct CipherBits {
 #[repr(transparent)]
 pub struct ClientHello(ffi::SSL_CLIENT_HELLO);
 
+impl ClientHello {
+    /// Returns the data of a given extension, if present.
+    ///
+    /// This corresponds to [`SSL_early_callback_ctx_extension_get`].
+    ///
+    /// [`SSL_early_callback_ctx_extension_get`]: https://commondatastorage.googleapis.com/chromium-boringssl-docs/ssl.h.html#SSL_early_callback_ctx_extension_get
+    pub fn get_extension(&self, ext_type: u16) -> Option<&[u8]> {
+        unsafe {
+            let mut ptr = ptr::null();
+            let mut len = 0;
+            let result =
+                ffi::SSL_early_callback_ctx_extension_get(&self.0, ext_type, &mut ptr, &mut len);
+            if result == 0 {
+                return None;
+            }
+            Some(slice::from_raw_parts(ptr, len))
+        }
+    }
+}
+
 /// Information about a cipher.
 pub struct SslCipher(*mut ffi::SSL_CIPHER);
 

boring/src/ssl/test/mod.rs

@@ -505,6 +505,53 @@ fn test_select_cert_error() {
     client.connect_err();
 }
 
+#[test]
+fn test_select_cert_unknown_extension() {
+    let mut server = Server::builder();
+    let unknown_extension = std::sync::Arc::new(std::sync::Mutex::new(None));
+
+    server.ctx().set_select_certificate_callback({
+        let unknown = unknown_extension.clone();
+        move |client_hello| {
+            *unknown.lock().unwrap() = client_hello.get_extension(1337).map(ToOwned::to_owned);
+            Ok(())
+        }
+    });
+
+    let server = server.build();
+    let client = server.client();
+
+    client.connect();
+    assert_eq!(unknown_extension.lock().unwrap().as_deref(), None);
+}
+
+#[test]
+fn test_select_cert_alpn_extension() {
+    let mut server = Server::builder();
+    let alpn_extension = std::sync::Arc::new(std::sync::Mutex::new(None));
+    server.ctx().set_select_certificate_callback({
+        let alpn = alpn_extension.clone();
+        move |client_hello| {
+            *alpn.lock().unwrap() = Some(
+                client_hello
+                    .get_extension(ffi::TLSEXT_TYPE_application_layer_protocol_negotiation as u16)
+                    .unwrap()
+                    .to_owned(),
+            );
+            Ok(())
+        }
+    });
+    let server = server.build();
+
+    let mut client = server.client();
+    client.ctx().set_alpn_protos(b"\x06http/2").unwrap();
+    client.connect();
+    assert_eq!(
+        alpn_extension.lock().unwrap().as_deref(),
+        Some(&b"\x00\x07\x06http/2"[..]),
+    );
+}
+
 #[test]
 #[should_panic(expected = "blammo")]
 fn write_panic() {