From 65a962d4591d52e43d95ae3902adb7c86b1b453b Mon Sep 17 00:00:00 2001
From: Santiago Pericas-Geertsen <santiago.pericasgeertsen@oracle.com>
Date: Mon, 30 Jan 2023 09:44:24 -0500
Subject: [PATCH] Switch default back-pressure strategy to AUTO_FLUSH from
 LINEAR. (#5983)

Signed-off-by: Santiago Pericasgeertsen <santiago.pericasgeertsen@oracle.com>
---
 .../reactive/webserver/ServerConfiguration.java   |  4 ++--
 .../reactive/webserver/SocketConfiguration.java   | 11 ++++++-----
 .../webserver/WaterMarkedBackpressureIT.java      | 15 ++++++++++++++-
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/reactive/webserver/webserver/src/main/java/io/helidon/reactive/webserver/ServerConfiguration.java b/reactive/webserver/webserver/src/main/java/io/helidon/reactive/webserver/ServerConfiguration.java
index e5d031ffd4b..5bfb00e3a85 100644
--- a/reactive/webserver/webserver/src/main/java/io/helidon/reactive/webserver/ServerConfiguration.java
+++ b/reactive/webserver/webserver/src/main/java/io/helidon/reactive/webserver/ServerConfiguration.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2022 Oracle and/or its affiliates.
+ * Copyright (c) 2017, 2023 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -543,7 +543,7 @@ public Builder backpressureBufferSize(long size) {
          * <li>PREFETCH - After first data chunk arrives, probable number of chunks needed to fill the buffer up to watermark is calculated and requested.</li>
          * <li>NONE - No backpressure is applied, Long.MAX_VALUE(unbounded) is requested from upstream.</li>
          * </ul>
-         * @param backpressureStrategy One of NONE, PREFETCH or LINEAR, default is LINEAR
+         * @param backpressureStrategy One of NONE, PREFETCH, LINEAR or AUTO_FLUSH, default is AUTO_FLUSH
          * @return an updated builder
          */
         @Override
diff --git a/reactive/webserver/webserver/src/main/java/io/helidon/reactive/webserver/SocketConfiguration.java b/reactive/webserver/webserver/src/main/java/io/helidon/reactive/webserver/SocketConfiguration.java
index ff552e5699f..c8b6b84380c 100644
--- a/reactive/webserver/webserver/src/main/java/io/helidon/reactive/webserver/SocketConfiguration.java
+++ b/reactive/webserver/webserver/src/main/java/io/helidon/reactive/webserver/SocketConfiguration.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2022 Oracle and/or its affiliates.
+ * Copyright (c) 2017, 2023 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -177,11 +177,12 @@ default long backpressureBufferSize() {
 
     /**
      * Strategy for applying backpressure to the reactive stream of response data.
+     * Switched default to {@link BackpressureStrategy#AUTO_FLUSH} since 3.1.1.
      *
      * @return strategy identifier for applying backpressure
      */
     default BackpressureStrategy backpressureStrategy() {
-        return BackpressureStrategy.LINEAR;
+        return BackpressureStrategy.AUTO_FLUSH;
     }
 
     /**
@@ -404,10 +405,10 @@ default B tls(Supplier<WebServerTls> tlsConfig) {
          * <li>PREFETCH - After first data chunk arrives, probable number of chunks needed to fill the buffer up to watermark is calculated and requested.</li>
          * <li>NONE - No backpressure is applied, Long.MAX_VALUE(unbounded) is requested from upstream.</li>
          * </ul>
-         * @param backpressureStrategy One of NONE, PREFETCH or LINEAR, default is LINEAR
+         * @param backpressureStrategy One of NONE, PREFETCH, LINEAR or AUTO_FLUSH, default is AUTO_FLUSH
          * @return this builder
          */
-        @ConfiguredOption("LINEAR")
+        @ConfiguredOption("AUTO_FLUSH")
         B backpressureStrategy(BackpressureStrategy backpressureStrategy);
 
         /**
@@ -500,7 +501,7 @@ final class Builder implements SocketConfigurationBuilder<Builder>, io.helidon.c
         private int initialBufferSize = 128;
         private boolean enableCompression = false;
         private long maxPayloadSize = -1;
-        private BackpressureStrategy backpressureStrategy = BackpressureStrategy.LINEAR;
+        private BackpressureStrategy backpressureStrategy = BackpressureStrategy.AUTO_FLUSH;
         private int maxUpgradeContentLength = 64 * 1024;
         private long maxBufferSize = 5 * 1024 * 1024;
 
diff --git a/reactive/webserver/webserver/src/test/java/io/helidon/reactive/webserver/WaterMarkedBackpressureIT.java b/reactive/webserver/webserver/src/test/java/io/helidon/reactive/webserver/WaterMarkedBackpressureIT.java
index 8c7c0869748..bec5b050746 100644
--- a/reactive/webserver/webserver/src/test/java/io/helidon/reactive/webserver/WaterMarkedBackpressureIT.java
+++ b/reactive/webserver/webserver/src/test/java/io/helidon/reactive/webserver/WaterMarkedBackpressureIT.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022 Oracle and/or its affiliates.
+ * Copyright (c) 2022, 2023 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -58,6 +58,19 @@ void tearDown() {
         executorService.shutdown();
     }
 
+    /**
+     * Verifies default back-pressure strategy is {@link BackpressureStrategy#AUTO_FLUSH}
+     * on all sockets.
+     */
+    @Test
+    void defaultStrategy() {
+        WebServer webServer = WebServer.builder().build();
+        webServer.configuration()
+                .sockets()
+                .values()
+                .forEach(sc -> assertThat(sc.backpressureStrategy(), is(AUTO_FLUSH)));
+    }
+
     @Test
     void linear() {
         AtomicLong receivedSize = new AtomicLong(0);