feat(server): expose NetworkAutoDetect RTT via a shared handle

The server measures network RTT in its AutoDetectManager, but after run()
takes ownership a backend can no longer call rtt_snapshot(): the
measurement is stranded in the running server. Mirror the existing
display_suppressed handle so the value can be shared out.

Add an Arc<AtomicU32> holding the latest measured RTT in milliseconds
(u32::MAX until the first measurement), a with_autodetect_rtt_handle
builder injector, and an autodetect_rtt_handle() getter. The AutoDetectRsp
handler stores the measured rtt_ms into it. A display backend can then read
a fresh, frame-traffic-independent network RTT for flow control without
polling the server object.

Drop the cfg_attr(egfx) gate on the new() too_many_arguments expect: the
added parameter makes the non-egfx parameter count 8 (was 7), so the lint
now fires in both feature configs and the expect is satisfied
unconditionally.

Author: glamberson

crates/ironrdp-server/src/builder.rs

@@ -1,5 +1,5 @@
 use core::net::SocketAddr;
-use core::sync::atomic::AtomicBool;
+use core::sync::atomic::{AtomicBool, AtomicU32};
 use std::sync::Arc;
 
 use anyhow::Result;
@@ -40,6 +40,7 @@ pub struct BuilderDone {
     #[cfg(feature = "egfx")]
     gfx_factory: Option<Box<dyn GfxServerFactory>>,
     display_suppressed: Option<Arc<AtomicBool>>,
+    autodetect_rtt: Option<Arc<AtomicU32>>,
 }
 
 pub struct RdpServerBuilder<State> {
@@ -138,6 +139,7 @@ impl RdpServerBuilder<WantsDisplay> {
                 #[cfg(feature = "egfx")]
                 gfx_factory: None,
                 display_suppressed: None,
+                autodetect_rtt: None,
             },
         }
     }
@@ -157,6 +159,7 @@ impl RdpServerBuilder<WantsDisplay> {
                 #[cfg(feature = "egfx")]
                 gfx_factory: None,
                 display_suppressed: None,
+                autodetect_rtt: None,
             },
         }
     }
@@ -223,6 +226,17 @@ impl RdpServerBuilder<BuilderDone> {
         self
     }
 
+    /// Inject a shared NetworkAutoDetect RTT handle (milliseconds, `u32::MAX`
+    /// until the first measurement). The server writes the latest measured RTT
+    /// to the same instance the backend reads. When not called, the server
+    /// allocates its own (still readable via
+    /// [`RdpServer::autodetect_rtt_handle`]). The value stays `u32::MAX` unless
+    /// auto-detect is enabled via [`RdpServer::enable_autodetect`].
+    pub fn with_autodetect_rtt_handle(mut self, handle: Arc<AtomicU32>) -> Self {
+        self.state.autodetect_rtt = Some(handle);
+        self
+    }
+
     pub fn build(self) -> RdpServer {
         RdpServer::new(
             RdpServerOptions {
@@ -239,6 +253,7 @@ impl RdpServerBuilder<BuilderDone> {
             #[cfg(feature = "egfx")]
             self.state.gfx_factory,
             self.state.display_suppressed,
+            self.state.autodetect_rtt,
         )
     }
 }

crates/ironrdp-server/src/server.rs

@@ -1,5 +1,5 @@
 use core::net::SocketAddr;
-use core::sync::atomic::{AtomicBool, Ordering};
+use core::sync::atomic::{AtomicBool, AtomicU32, Ordering};
 use core::time::Duration;
 use std::rc::Rc;
 use std::sync::Arc;
@@ -304,6 +304,14 @@ pub struct RdpServer {
     /// and locks up its input dispatch for seconds on refocus while it
     /// chews through the backlog.
     display_suppressed: Arc<AtomicBool>,
+
+    /// Latest NetworkAutoDetect round-trip time in milliseconds, or `u32::MAX`
+    /// until the first measurement (and while auto-detect is disabled). Updated
+    /// on each RTT Measure Response when auto-detect is enabled (see
+    /// [`Self::enable_autodetect`]). Exposed via [`Self::autodetect_rtt_handle`]
+    /// so display backends can read a fresh, frame-traffic-independent network
+    /// RTT for flow control.
+    autodetect_rtt: Arc<AtomicU32>,
 }
 
 #[derive(Debug)]
@@ -338,15 +346,9 @@ enum RunState {
 }
 
 impl RdpServer {
-    // The lint only fires with the `egfx` feature on (8 args including
-    // `gfx_factory`); without it the parameter count is 7 and the lint
-    // is satisfied. `cfg_attr` keeps `#[expect]` strict in both modes.
-    #[cfg_attr(
-        feature = "egfx",
-        expect(
-            clippy::too_many_arguments,
-            reason = "called via the builder; positional parameters are an internal detail"
-        )
+    #[expect(
+        clippy::too_many_arguments,
+        reason = "called via the builder; positional parameters are an internal detail"
     )]
     pub fn new(
         opts: RdpServerOptions,
@@ -357,6 +359,7 @@ impl RdpServer {
         connection_handler: Option<Box<dyn ConnectionHandler>>,
         #[cfg(feature = "egfx")] mut gfx_factory: Option<Box<dyn GfxServerFactory>>,
         display_suppressed: Option<Arc<AtomicBool>>,
+        autodetect_rtt: Option<Arc<AtomicU32>>,
     ) -> Self {
         let (ev_sender, ev_receiver) = ServerEvent::create_channel();
         if let Some(cliprdr) = cliprdr_factory.as_mut() {
@@ -388,6 +391,7 @@ impl RdpServer {
             autodetect: None,
             connection_handler,
             display_suppressed: display_suppressed.unwrap_or_else(|| Arc::new(AtomicBool::new(false))),
+            autodetect_rtt: autodetect_rtt.unwrap_or_else(|| Arc::new(AtomicU32::new(u32::MAX))),
         }
     }
 
@@ -432,6 +436,16 @@ impl RdpServer {
         Arc::clone(&self.display_suppressed)
     }
 
+    /// Returns a handle to the latest NetworkAutoDetect RTT in milliseconds
+    /// (`u32::MAX` until the first measurement, and while auto-detect is
+    /// disabled). The server updates it on each RTT Measure Response; backends
+    /// clone the handle to read a fresh network RTT for flow control. Inject a
+    /// shared instance at construction with
+    /// [`RdpServerBuilder::with_autodetect_rtt_handle`](crate::RdpServerBuilder::with_autodetect_rtt_handle).
+    pub fn autodetect_rtt_handle(&self) -> Arc<AtomicU32> {
+        Arc::clone(&self.autodetect_rtt)
+    }
+
     /// Returns the shared ECHO server handle for runtime probe requests and RTT measurements.
     pub fn echo_handle(&self) -> &EchoServerHandle {
         &self.echo_handle
@@ -1218,6 +1232,7 @@ impl RdpServer {
                 rdp::headers::ShareDataPdu::AutoDetectRsp(response) => {
                     if let Some(ref mut ad) = self.autodetect {
                         if let Some(rtt_ms) = ad.handle_response(&response) {
+                            self.autodetect_rtt.store(rtt_ms, Ordering::Relaxed);
                             debug!(rtt_ms, seq = response.sequence_number(), "RTT measured");
                         } else {
                             trace!(seq = response.sequence_number(), "Unmatched auto-detect response");

crates/ironrdp-testsuite-core/tests/server/autodetect.rs

@@ -77,6 +77,44 @@ fn sequence_number_wraps_at_u16_max() {
     assert_eq!(req2.sequence_number(), 0, "should wrap around");
 }
 
+#[test]
+fn autodetect_rtt_handle_defaults_to_sentinel() {
+    use core::net::{Ipv4Addr, SocketAddr};
+    use core::sync::atomic::Ordering;
+
+    use ironrdp_server::RdpServer;
+
+    let server = RdpServer::builder()
+        .with_addr(SocketAddr::from((Ipv4Addr::LOCALHOST, 0)))
+        .with_no_security()
+        .with_no_input()
+        .with_no_display()
+        .build();
+
+    assert_eq!(server.autodetect_rtt_handle().load(Ordering::Relaxed), u32::MAX);
+}
+
+#[test]
+fn with_autodetect_rtt_handle_round_trips_the_same_arc() {
+    use core::net::{Ipv4Addr, SocketAddr};
+    use core::sync::atomic::{AtomicU32, Ordering};
+    use std::sync::Arc;
+
+    use ironrdp_server::RdpServer;
+
+    let handle = Arc::new(AtomicU32::new(42));
+    let server = RdpServer::builder()
+        .with_addr(SocketAddr::from((Ipv4Addr::LOCALHOST, 0)))
+        .with_no_security()
+        .with_no_input()
+        .with_no_display()
+        .with_autodetect_rtt_handle(Arc::clone(&handle))
+        .build();
+
+    assert!(Arc::ptr_eq(&handle, &server.autodetect_rtt_handle()));
+    assert_eq!(server.autodetect_rtt_handle().load(Ordering::Relaxed), 42);
+}
+
 #[test]
 fn stale_probe_expiry() {
     let mut mgr = AutoDetectManager::new();