From 6cd25848b0872dcaa007e55418c4c6c7acea62a0 Mon Sep 17 00:00:00 2001
From: Sergei Minaev <sergey@questdb.com>
Date: Thu, 10 Sep 2026 13:17:37 +0100
Subject: [PATCH] test(qwp): close TestWebSocketServer connections gracefully
 so scripted drops deliver their acks

ClientHandler.close() closed the socket outright. With the peer's trailing
frames still unread, that close is a TCP RST, and the Nagle-held second ack
write (STATUS_DURABLE_ACK) of the last acked batch was purged with it. The
drainer then saw a reset with no ack progress, and
BackgroundDrainerMidDrainCapabilityGapTest#testDeliveringBetweenTwoGapWindowsGrantsAFreshSettleBudget
failed on the JDK 8 CI job (java-questdb-client #91, run 34368418967).

Now: TCP_NODELAY on accepted sockets, shutdownOutput() before close() so the
written frames are followed by FIN, a bounded drain of unread input when the
close runs on the read thread (the scripted-drop path), and no self-join of
the read thread -- that join(5000) inside the synchronized handler callback
serialized every scripted drop at 5 s.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017S9gyXv4MwoDHEohA9At5d
---
 .../qwp/websocket/TestWebSocketServer.java    | 28 ++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/core/src/test/java/io/questdb/client/test/cutlass/qwp/websocket/TestWebSocketServer.java b/core/src/test/java/io/questdb/client/test/cutlass/qwp/websocket/TestWebSocketServer.java
index 908e3bd5..87576a24 100644
--- a/core/src/test/java/io/questdb/client/test/cutlass/qwp/websocket/TestWebSocketServer.java
+++ b/core/src/test/java/io/questdb/client/test/cutlass/qwp/websocket/TestWebSocketServer.java
@@ -398,6 +398,7 @@ public void start() throws IOException {
             while (running.get()) {
                 try {
                     Socket clientSocket = serverSocket.accept();
+                    clientSocket.setTcpNoDelay(true);
                     ClientHandler clientHandler = new ClientHandler(clientSocket);
                     clients.add(clientHandler);
                     clientHandler.start();
@@ -445,12 +446,22 @@ public class ClientHandler implements Closeable {
         @Override
         public void close() {
             running.set(false);
+            try {
+                // FIN after the frames already written, never an RST: closing with unread input
+                // resets the connection and purges anything still queued for the peer.
+                socket.shutdownOutput();
+                if (readThread == Thread.currentThread()) {
+                    drainInput();
+                }
+            } catch (IOException e) {
+                // ignore
+            }
             try {
                 socket.close();
             } catch (IOException e) {
                 // ignore
             }
-            if (readThread != null) {
+            if (readThread != null && readThread != Thread.currentThread()) {
                 try {
                     readThread.join(5000);
                 } catch (InterruptedException e) {
@@ -459,6 +470,21 @@ public void close() {
             }
         }
 
+        private void drainInput() throws IOException {
+            socket.setSoTimeout(20);
+            byte[] scratch = new byte[8192];
+            long deadlineNanos = System.nanoTime() + 200_000_000L;
+            while (System.nanoTime() < deadlineNanos) {
+                try {
+                    if (in.read(scratch) < 0) {
+                        return;
+                    }
+                } catch (SocketTimeoutException e) {
+                    return;
+                }
+            }
+        }
+
         public synchronized void sendBinary(byte[] data) throws IOException {
             writeFrame(WebSocketOpcode.BINARY, data, data.length);
         }