Implement SMB Oplocks Phase 3+5

Phase 3: NotificationQueue
- Add notification_tx to Connection struct
- Modify writer.rs to use tokio::select! for response + notification
- Add write_to_bytes() to OplockBreakNotification
- Support server→client async messages

Phase 5: WRITE Handler oplock break
- Get path/share_access before write
- Trigger OplockManager.break_oplock()
- Send OPLOCK_BREAK_NOTIFICATION to affected clients
- Encode and send via notification channel

All 229 tests pass.

vendor/smb-server/src/conn/mod.rs

@@ -24,12 +24,18 @@ pub async fn connection_loop(stream: TcpStream, server: Arc<ServerState>) -> io:
         server.config.max_write_size,
     ));
     let conn_id = server.active_connections.register(&conn).await;
-    let (tx, rx) = mpsc::channel::<writer::FramePayload>(writer::WRITER_CHANNEL);
+    
+    // Phase 3: Two channels - responses and notifications
+    let (response_tx, response_rx) = mpsc::channel::<writer::FramePayload>(writer::WRITER_CHANNEL);
+    let (notification_tx, notification_rx) = mpsc::channel::<writer::FramePayload>(writer::NOTIFICATION_CHANNEL);
+    
+    // Store notification sender in Connection for oplock breaks
+    conn.notification_tx.write().await.replace(notification_tx);
 
-    let writer_handle = tokio::spawn(writer::writer_task(write_half, rx));
+    let writer_handle = tokio::spawn(writer::writer_task(write_half, response_rx, notification_rx));
 
     info!("connection accepted");
-    let reader_result = reader::reader_task(read_half, server.clone(), conn.clone(), tx).await;
+    let reader_result = reader::reader_task(read_half, server.clone(), conn.clone(), response_tx).await;
     debug!(?reader_result, "reader exited");
     // Wait for writer to drain.
     let _ = writer_handle.await;

vendor/smb-server/src/conn/state.rs

@@ -8,7 +8,7 @@ use std::sync::{Arc, Mutex};
 use crate::proto::auth::ntlm::{Identity, NtlmServer};
 use crate::proto::crypto::{PreauthIntegrity, SigningAlgo};
 use crate::proto::messages::{Dialect, FileId};
-use tokio::sync::RwLock;
+use tokio::sync::{mpsc, RwLock};
 use uuid::Uuid;
 
 use crate::backend::Handle;
@@ -16,6 +16,9 @@ use crate::builder::Access;
 use crate::path::SmbPath;
 use crate::server::ShareBindings;
 
+/// Phase 3: Notification sender type for server→client async messages.
+pub type NotificationSender = mpsc::Sender<Vec<u8>>;
+
 /// In-flight NTLM acceptor + a `is_raw_ntlmssp` flag (true = raw, false =
 /// SPNEGO-wrapped). The handler hands the second-round response back in the
 /// same form the client opened with.
@@ -54,6 +57,9 @@ pub struct Connection {
 
     /// Monotonic SessionId allocator.
     next_session_id: AtomicU64,
+    
+    /// Phase 3: Notification sender for server→client async messages (oplock breaks).
+    pub notification_tx: RwLock<Option<NotificationSender>>,
 }
 
 impl Connection {
@@ -70,6 +76,7 @@ impl Connection {
             pending_auths: RwLock::new(HashMap::new()),
             session_preauth: RwLock::new(HashMap::new()),
             next_session_id: AtomicU64::new(1),
+            notification_tx: RwLock::new(None),
         }
     }
 

vendor/smb-server/src/conn/writer.rs

@@ -1,5 +1,7 @@
 //! Per-connection writer task: serializes responses, applies signing, and
 //! frames the bytes onto the wire.
+//!
+//! Phase 3: Added notification channel for server→client async messages.
 
 use crate::proto::framing::encode_frame;
 use tokio::io::{AsyncWriteExt, WriteHalf};
@@ -15,18 +17,45 @@ pub type FramePayload = Vec<u8>;
 /// the dispatcher.
 pub const WRITER_CHANNEL: usize = 64;
 
-pub async fn writer_task(mut writer: WriteHalf<TcpStream>, mut rx: mpsc::Receiver<FramePayload>) {
-    while let Some(payload) = rx.recv().await {
-        let mut out = Vec::with_capacity(payload.len() + 4);
-        encode_frame(&payload, &mut out);
-        if let Err(e) = writer.write_all(&out).await {
-            error!(error = %e, "writer task: socket write failed");
-            return;
+/// Notification channel size (Phase 3).
+pub const NOTIFICATION_CHANNEL: usize = 32;
+
+/// Phase 3: Writer task that handles both responses and notifications.
+pub async fn writer_task(
+    mut writer: WriteHalf<TcpStream>,
+    mut response_rx: mpsc::Receiver<FramePayload>,
+    mut notification_rx: mpsc::Receiver<FramePayload>,
+) {
+    loop {
+        tokio::select! {
+            // Priority: responses first
+            Some(payload) = response_rx.recv() => {
+                if let Err(e) = write_frame(&mut writer, &payload).await {
+                    error!(error = %e, "writer task: response write failed");
+                    return;
+                }
+                debug!(len = payload.len(), "wrote response frame");
+            }
+            // Then notifications (oplock breaks, etc.)
+            Some(payload) = notification_rx.recv() => {
+                if let Err(e) = write_frame(&mut writer, &payload).await {
+                    error!(error = %e, "writer task: notification write failed");
+                    return;
+                }
+                debug!(len = payload.len(), "wrote notification frame");
+            }
+            else => break,
         }
-        debug!(len = out.len(), "wrote frame");
     }
-    // Channel closed — flush and bail.
+    // Channels closed — flush and bail.
     if let Err(e) = writer.shutdown().await {
         debug!(error = %e, "writer shutdown error (best-effort)");
     }
 }
+
+/// Helper: write a framed payload to the wire.
+async fn write_frame(writer: &mut WriteHalf<TcpStream>, payload: &[u8]) -> std::io::Result<()> {
+    let mut out = Vec::with_capacity(payload.len() + 4);
+    encode_frame(payload, &mut out);
+    writer.write_all(&out).await
+}