From a384ee2edbebd37aee5c2c62b35046b9cdfb7d7f Mon Sep 17 00:00:00 2001
From: Benjamin Saunders <ben.e.saunders@gmail.com>
Date: Sun, 10 Oct 2021 13:18:30 -0700
Subject: [PATCH] Erase crypto::Session::HandshakeData

---
 quinn-proto/src/crypto.rs        |  7 ++-----
 quinn-proto/src/crypto/rustls.rs |  9 ++++-----
 quinn-proto/src/tests/mod.rs     |  2 ++
 quinn/examples/server.rs         |  1 +
 quinn/src/connection.rs          | 13 ++++++++++---
 5 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/quinn-proto/src/crypto.rs b/quinn-proto/src/crypto.rs
index 09702e063..e8b7c04df 100644
--- a/quinn-proto/src/crypto.rs
+++ b/quinn-proto/src/crypto.rs
@@ -8,7 +8,7 @@
 //! Note that usage of any protocol (version) other than TLS 1.3 does not conform to any
 //! published versions of the specification, and will not be supported in QUIC v1.
 
-use std::str;
+use std::{any::Any, str};
 
 use bytes::BytesMut;
 
@@ -29,9 +29,6 @@ pub(crate) mod types;
 
 /// A cryptographic session (commonly TLS)
 pub trait Session: Send + Sized {
-    /// Parameters determined when the handshake begins, e.g. server name and/or application
-    /// protocol
-    type HandshakeData;
     /// Cryptographic identity of the peer
     type Identity: Sized;
     /// Type used to hold configuration for client sessions
@@ -53,7 +50,7 @@ pub trait Session: Send + Sized {
     /// Get data negotiated during the handshake, if available
     ///
     /// Returns `None` until the connection emits `HandshakeDataReady`.
-    fn handshake_data(&self) -> Option<Self::HandshakeData>;
+    fn handshake_data(&self) -> Option<Box<dyn Any>>;
 
     /// Get the peer's identity, if available
     fn peer_identity(&self) -> Option<Self::Identity>;
diff --git a/quinn-proto/src/crypto/rustls.rs b/quinn-proto/src/crypto/rustls.rs
index b2040f3ff..724ba42e4 100644
--- a/quinn-proto/src/crypto/rustls.rs
+++ b/quinn-proto/src/crypto/rustls.rs
@@ -1,4 +1,4 @@
-use std::{convert::TryInto, io, str, sync::Arc};
+use std::{any::Any, convert::TryInto, io, str, sync::Arc};
 
 use bytes::BytesMut;
 use ring::{aead, hkdf, hmac};
@@ -36,7 +36,6 @@ impl TlsSession {
 }
 
 impl crypto::Session for TlsSession {
-    type HandshakeData = HandshakeData;
     type Identity = CertificateChain;
     type ClientConfig = Arc<rustls::ClientConfig>;
     type HmacKey = hmac::Key;
@@ -59,17 +58,17 @@ impl crypto::Session for TlsSession {
         }
     }
 
-    fn handshake_data(&self) -> Option<HandshakeData> {
+    fn handshake_data(&self) -> Option<Box<dyn Any>> {
         if !self.got_handshake_data {
             return None;
         }
-        Some(HandshakeData {
+        Some(Box::new(HandshakeData {
             protocol: self.inner.alpn_protocol().map(|x| x.into()),
             server_name: match self.inner {
                 Connection::Client(_) => None,
                 Connection::Server(ref session) => session.sni_hostname().map(|x| x.into()),
             },
-        })
+        }))
     }
 
     fn peer_identity(&self) -> Option<CertificateChain> {
diff --git a/quinn-proto/src/tests/mod.rs b/quinn-proto/src/tests/mod.rs
index 166ae9f09..01a686d38 100644
--- a/quinn-proto/src/tests/mod.rs
+++ b/quinn-proto/src/tests/mod.rs
@@ -561,6 +561,8 @@ fn alpn_success() {
         .client_conn_mut(client_ch)
         .crypto_session()
         .handshake_data()
+        .unwrap()
+        .downcast::<crate::crypto::rustls::HandshakeData>()
         .unwrap();
     assert_eq!(hd.protocol.unwrap(), &b"bar"[..]);
 }
diff --git a/quinn/examples/server.rs b/quinn/examples/server.rs
index a0a179ae8..a9f0bee1b 100644
--- a/quinn/examples/server.rs
+++ b/quinn/examples/server.rs
@@ -156,6 +156,7 @@ async fn handle_connection(root: Arc<Path>, conn: quinn::Connecting) -> Result<(
         protocol = %connection
             .handshake_data()
             .unwrap()
+            .downcast::<quinn::crypto::rustls::HandshakeData>().unwrap()
             .protocol
             .map_or_else(|| "<none>".into(), |x| String::from_utf8_lossy(&x).into_owned())
     );
diff --git a/quinn/src/connection.rs b/quinn/src/connection.rs
index 8b1825e94..187e123a7 100644
--- a/quinn/src/connection.rs
+++ b/quinn/src/connection.rs
@@ -1,4 +1,5 @@
 use std::{
+    any::Any,
     fmt,
     future::Future,
     mem,
@@ -111,7 +112,12 @@ where
     }
 
     /// Parameters negotiated during the handshake
-    pub async fn handshake_data(&mut self) -> Result<S::HandshakeData, ConnectionError> {
+    ///
+    /// The dynamic type returned is determined by the configured
+    /// [`Session`](proto::crypto::Session). For the default `rustls` session, the return value can
+    /// be [`downcast`](Box::downcast) to a
+    /// [`crypto::rustls::HandshakeData`](crate::crypto::rustls::HandshakeData).
+    pub async fn handshake_data(&mut self) -> Result<Box<dyn Any>, ConnectionError> {
         // Taking &mut self allows us to use a single oneshot channel rather than dealing with
         // potentially many tasks waiting on the same event. It's a bit of a hack, but keeps things
         // simple.
@@ -459,10 +465,11 @@ where
     /// Parameters negotiated during the handshake
     ///
     /// Guaranteed to return `Some` on fully established connections or after
-    /// [`Connecting::handshake_data()`] succeeds.
+    /// [`Connecting::handshake_data()`] succeeds. See that method's documentations for details on
+    /// the returned value.
     ///
     /// [`Connection::handshake_data()`]: crate::generic::Connecting::handshake_data
-    pub fn handshake_data(&self) -> Option<S::HandshakeData> {
+    pub fn handshake_data(&self) -> Option<Box<dyn Any>> {
         self.0
             .lock("handshake_data")
             .inner