Allow returning GetSessionPendingError from get session callbacks

boring/src/ssl/callbacks.rs

@@ -1,9 +1,9 @@
 #![forbid(unsafe_op_in_unsafe_fn)]
 
 use super::{
-    AlpnError, ClientHello, PrivateKeyMethod, PrivateKeyMethodError, SelectCertError, SniError,
-    Ssl, SslAlert, SslContext, SslContextRef, SslRef, SslSession, SslSessionRef,
-    SslSignatureAlgorithm, SESSION_CTX_INDEX,
+    AlpnError, ClientHello, GetSessionPendingError, PrivateKeyMethod, PrivateKeyMethodError,
+    SelectCertError, SniError, Ssl, SslAlert, SslContext, SslContextRef, SslRef, SslSession,
+    SslSessionRef, SslSignatureAlgorithm, SESSION_CTX_INDEX,
 };
 use crate::error::ErrorStack;
 use crate::ffi;
@@ -13,7 +13,6 @@ use foreign_types::ForeignTypeRef;
 use libc::c_char;
 use libc::{c_int, c_uchar, c_uint, c_void};
 use std::ffi::CStr;
-use std::mem;
 use std::ptr;
 use std::slice;
 use std::str;
@@ -323,7 +322,10 @@ pub(super) unsafe extern "C" fn raw_get_session<F>(
     copy: *mut c_int,
 ) -> *mut ffi::SSL_SESSION
 where
-    F: Fn(&mut SslRef, &[u8]) -> Option<SslSession> + 'static + Sync + Send,
+    F: Fn(&mut SslRef, &[u8]) -> Result<Option<SslSession>, GetSessionPendingError>
+        + 'static
+        + Sync
+        + Send,
 {
     // SAFETY: boring provides valid inputs.
     let ssl = unsafe { SslRef::from_ptr_mut(ssl) };
@@ -342,13 +344,15 @@ where
     let callback = unsafe { &*(callback as *const F) };
 
     match callback(ssl, data) {
-        Some(session) => {
-            let p = session.as_ptr();
-            mem::forget(session);
+        Ok(Some(session)) => {
+            let p = session.into_ptr();
+
             *copy = 0;
+
             p
         }
-        None => ptr::null_mut(),
+        Ok(None) => ptr::null_mut(),
+        Err(GetSessionPendingError) => unsafe { ffi::SSL_magic_pending_session_ptr() },
     }
 }
 

boring/src/ssl/mod.rs

@@ -1599,12 +1599,15 @@ impl SslContextBuilder {
     ///
     /// # Safety
     ///
-    /// The returned `SslSession` must not be associated with a different `SslContext`.
+    /// The returned [`SslSession`] must not be associated with a different [`SslContext`].
     ///
     /// [`SSL_CTX_sess_set_get_cb`]: https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_set_new_cb.html
     pub unsafe fn set_get_session_callback<F>(&mut self, callback: F)
     where
-        F: Fn(&mut SslRef, &[u8]) -> Option<SslSession> + 'static + Sync + Send,
+        F: Fn(&mut SslRef, &[u8]) -> Result<Option<SslSession>, GetSessionPendingError>
+            + 'static
+            + Sync
+            + Send,
     {
         self.set_ex_data(SslContext::cached_ex_index::<F>(), callback);
         ffi::SSL_CTX_sess_set_get_cb(self.as_ptr(), Some(callbacks::raw_get_session::<F>));
@@ -1978,6 +1981,13 @@ impl SslContextRef {
     }
 }
 
+/// Error returned by the callback to get a session when operation
+/// could not complete and should be retried later.
+///
+/// See [`SslContextBuilder::set_get_session_callback`].
+#[derive(Debug)]
+pub struct GetSessionPendingError;
+
 #[cfg(not(any(feature = "fips", feature = "fips-link-precompiled")))]
 type ProtosLen = usize;
 #[cfg(any(feature = "fips", feature = "fips-link-precompiled"))]

boring/src/ssl/test/session.rs

@@ -1,10 +1,11 @@
+use std::io::Write;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::OnceLock;
 
 use crate::ssl::test::server::Server;
 use crate::ssl::{
-    Ssl, SslContext, SslContextBuilder, SslMethod, SslOptions, SslSession, SslSessionCacheMode,
-    SslVersion,
+    ErrorCode, GetSessionPendingError, HandshakeError, Ssl, SslContext, SslContextBuilder,
+    SslMethod, SslOptions, SslSession, SslSessionCacheMode, SslVersion,
 };
 
 #[test]
@@ -53,7 +54,7 @@ fn new_get_session_callback() {
     unsafe {
         server.ctx().set_get_session_callback(|_, id| {
             let Some(der) = SERVER_SESSION_DER.get() else {
-                return None;
+                return Ok(None);
             };
 
             let session = SslSession::from_der(der).unwrap();
@@ -62,7 +63,7 @@ fn new_get_session_callback() {
 
             assert_eq!(id, session.id());
 
-            Some(session)
+            Ok(Some(session))
         });
     }
     server.ctx().set_session_id_context(b"foo").unwrap();
@@ -100,6 +101,54 @@ fn new_get_session_callback() {
     assert!(FOUND_SESSION.load(Ordering::SeqCst));
 }
 
+#[test]
+fn new_get_session_callback_pending() {
+    static CALLED_SERVER_CALLBACK: AtomicBool = AtomicBool::new(false);
+
+    let mut server = Server::builder();
+
+    server
+        .ctx()
+        .set_max_proto_version(Some(SslVersion::TLS1_2))
+        .unwrap();
+    server.ctx().set_options(SslOptions::NO_TICKET);
+    server
+        .ctx()
+        .set_session_cache_mode(SslSessionCacheMode::SERVER | SslSessionCacheMode::NO_INTERNAL);
+    unsafe {
+        server.ctx().set_get_session_callback(|_, _| {
+            if !CALLED_SERVER_CALLBACK.swap(true, Ordering::SeqCst) {
+                return Err(GetSessionPendingError);
+            }
+
+            Ok(None)
+        });
+    }
+    server.ctx().set_session_id_context(b"foo").unwrap();
+    server.err_cb(|error| {
+        let HandshakeError::WouldBlock(mid_handshake) = error else {
+            panic!("should be WouldBlock");
+        };
+
+        assert!(mid_handshake.error().would_block());
+        assert_eq!(mid_handshake.error().code(), ErrorCode::PENDING_SESSION);
+
+        let mut socket = mid_handshake.handshake().unwrap();
+
+        socket.write_all(&[0]).unwrap();
+    });
+
+    let server = server.build();
+
+    let mut client = server.client();
+
+    client
+        .ctx()
+        .set_session_cache_mode(SslSessionCacheMode::CLIENT);
+
+    client.connect();
+}
+
 #[test]
 fn new_session_callback_swapped_ctx() {
     static CALLED_BACK: AtomicBool = AtomicBool::new(false);