use simplest solution

Author: cwaldren-ld

libs/server-sent-events/src/client.cpp

@@ -44,6 +44,10 @@ auto const kDefaultInitialReconnectDelay = std::chrono::seconds(1);
 // Maximum duration between backoff attempts.
 auto const kDefaultMaxBackoffDelay = std::chrono::seconds(30);
 
+// Maximum time to spend gracefully terminating the SSL session before
+// closing the TCP socket.
+auto const kGracefulShutdownTimeout = std::chrono::seconds(1);
+
 static boost::optional<net::ssl::context&> ToOptRef(
     std::optional<net::ssl::context>& maybe_val) {
     if (maybe_val) {
@@ -340,8 +344,28 @@ class FoxyClient : public Client,
         shutting_down_ = true;
         // If any backoff is taking place, cancel that as well.
         backoff_timer_.cancel();
-        
-        boost::system::error_code ec = {};
+
+        // Cancels the outstanding read.
+        if (session_->stream.is_ssl()) {
+            session_->stream.ssl().next_layer().cancel();
+        } else {
+            session_->stream.plain().cancel();
+        }
+
+        // Ideally we would call session_->async_shutdown() here to gracefully
+        // terminate the SSL session. For unknown reasons, this call appears to
+        // hang indefinitely and never complete until the SDK client is
+        // destroyed.
+        //
+        // A workaround is to set a timeout on the operation, say 1 second. This
+        // gives the opportunity to shutdown gracefully and then if that fails,
+        // we could close the socket directly. But that also doesn't seem to
+        // work: even with the timeout, the operation still doesn't complete.
+        //
+        // So the most robust solution appears to be closing the socket
+        // directly. This is not ideal because it doesn't send a close_notify to
+        // the server.
+        boost::system::error_code ec;
         session_->stream.plain().shutdown(
             boost::asio::ip::tcp::socket::shutdown_both, ec);
         session_->stream.plain().close(ec);