Allows the webserver's write buffer size to be set to 0 (#9313)

* Allows the webserver's write buffer size to be set to 0 (or less). The underlying output stream shall not be wrapped into a buffered output stream one unless this value is greater than 0.

* Improves Javadoc and renames same variables for better code readability.

webserver/tests/webserver/src/test/java/io/helidon/webserver/tests/OutputStreamBufferSizeTest.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2024 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.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.helidon.webserver.tests;
+
+import io.helidon.webclient.http1.Http1Client;
+import io.helidon.webserver.WebServerConfig;
+import io.helidon.webserver.testing.junit5.ServerTest;
+import io.helidon.webserver.testing.junit5.SetUpServer;
+
+@ServerTest
+class OutputStreamBufferSizeTest extends OutputStreamTest {
+
+    OutputStreamBufferSizeTest(Http1Client client) {
+        super(client);
+    }
+
+    @SetUpServer
+    static void setup(WebServerConfig.Builder builder) {
+        builder.writeBufferSize(0);         // should accept buffer size of 0
+    }
+}

webserver/tests/webserver/src/test/java/io/helidon/webserver/tests/OutputStreamTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, 2023 Oracle and/or its affiliates.
+ * Copyright (c) 2022, 2024 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.
@@ -59,7 +59,7 @@ void verifyAutoFlush() {
         }
     }
 
-    private static class Service {
+    protected static class Service {
 
         public static void outputStream(ServerRequest req, ServerResponse res) throws IOException {
             InputStream in = new ByteArrayInputStream("Hello World".getBytes(StandardCharsets.UTF_8));

webserver/webserver/src/main/java/io/helidon/webserver/ListenerConfigBlueprint.java

@@ -175,7 +175,8 @@ interface ListenerConfigBlueprint {
 
     /**
      * Initial buffer size in bytes of {@link java.io.BufferedOutputStream} created internally to
-     * write data to a socket connection. Default is {@code 4096}.
+     * write data to a socket connection. Default is {@code 4096}. Set buffer size to a value
+     * less than one to turn off buffering.
      *
      * @return initial buffer size used for writing
      */

webserver/webserver/src/main/java/io/helidon/webserver/http1/Http1ServerResponse.java

@@ -753,55 +753,59 @@ private void writeContent(BufferData buffer) throws IOException {
      * A special stream that provides buffering for a delegate and special handling
      * of close logic. Note that due to some locking issues in the JDK, this class
      * must use delegation with {@link BufferedOutputStream} instead of subclassing.
+     *
+     * <p>If the buffer size is less or equal to zero, it will not wrap the
+     * {@link io.helidon.webserver.http1.Http1ServerResponse.BlockingOutputStream}
+     * with a {@link java.io.BufferedOutputStream}.
      */
     static class ClosingBufferedOutputStream extends OutputStream {
 
-        private final BlockingOutputStream delegate;
-        private final BufferedOutputStream bufferedDelegate;
+        private final BlockingOutputStream closingDelegate;
+        private final OutputStream delegate;
 
         ClosingBufferedOutputStream(BlockingOutputStream out, int size) {
-            this.delegate = out;
-            this.bufferedDelegate = new BufferedOutputStream(out, size);
+            this.closingDelegate = out;
+            this.delegate = size <= 0 ? out : new BufferedOutputStream(out, size);
         }
 
         @Override
         public void write(int b) throws IOException {
-            bufferedDelegate.write(b);
+            delegate.write(b);
         }
 
         @Override
         public void write(byte[] b) throws IOException {
-            bufferedDelegate.write(b);
+            delegate.write(b);
         }
 
         @Override
         public void write(byte[] b, int off, int len) throws IOException {
-            bufferedDelegate.write(b, off, len);
+            delegate.write(b, off, len);
         }
 
         @Override
         public void flush() throws IOException {
-            bufferedDelegate.flush();
+            delegate.flush();
         }
 
         @Override
         public void close() {
-            delegate.closing();     // inform of imminent call to close for last flush
+            closingDelegate.closing();     // inform of imminent call to close for last flush
             try {
-                bufferedDelegate.close();
+                delegate.close();
             } catch (IOException e) {
                 throw new ServerConnectionException("Failed to close server output stream", e);
             }
         }
 
         long totalBytesWritten() {
-            return delegate.totalBytesWritten();
+            return closingDelegate.totalBytesWritten();
         }
 
         void commit() {
             try {
                 flush();
-                delegate.commit();
+                closingDelegate.commit();
             } catch (IOException e) {
                 throw new ServerConnectionException("Failed to flush server output stream", e);
             }