Replace auto-read with proper flow-control in HTTP pipeline (#127259)

Re-applying #126441 with the extra `FlowControlHandler` needed to ensure
one-chunk-per-read semantics - see #127111 for related tests.

Author: DaveCTurner

docs/changelog/127259.yaml

@@ -0,0 +1,5 @@
+pr: 127259
+summary: Replace auto-read with proper flow-control in HTTP pipeline
+area: Network
+type: enhancement
+issues: []

modules/transport-netty4/src/internalClusterTest/java/org/elasticsearch/http/netty4/Netty4IncrementalRequestHandlingIT.java

@@ -205,7 +205,6 @@ public void testClientConnectionCloseMidStream() throws Exception {
 
             // await stream handler is ready and request full content
             var handler = clientContext.awaitRestChannelAccepted(opaqueId);
-            assertBusy(() -> assertNotEquals(0, handler.stream.bufSize()));
 
             assertFalse(handler.isClosed());
 
@@ -215,7 +214,6 @@ public void testClientConnectionCloseMidStream() throws Exception {
             assertEquals(requestTransmittedLength, handler.readUntilClose());
 
             assertTrue(handler.isClosed());
-            assertEquals(0, handler.stream.bufSize());
         }
     }
 
@@ -232,7 +230,6 @@ public void testServerCloseConnectionMidStream() throws Exception {
 
             // await stream handler is ready and request full content
             var handler = clientContext.awaitRestChannelAccepted(opaqueId);
-            assertBusy(() -> assertNotEquals(0, handler.stream.bufSize()));
             assertFalse(handler.isClosed());
 
             // terminate connection on server and wait resources are released
@@ -241,7 +238,6 @@ public void testServerCloseConnectionMidStream() throws Exception {
             handler.channel.request().getHttpChannel().close();
             assertThat(safeGet(exceptionFuture), instanceOf(ClosedChannelException.class));
             assertTrue(handler.isClosed());
-            assertBusy(() -> assertEquals(0, handler.stream.bufSize()));
         }
     }
 
@@ -257,7 +253,6 @@ public void testServerExceptionMidStream() throws Exception {
 
             // await stream handler is ready and request full content
             var handler = clientContext.awaitRestChannelAccepted(opaqueId);
-            assertBusy(() -> assertNotEquals(0, handler.stream.bufSize()));
             assertFalse(handler.isClosed());
 
             // terminate connection on server and wait resources are released
@@ -269,7 +264,6 @@ public void testServerExceptionMidStream() throws Exception {
             final var exception = asInstanceOf(RuntimeException.class, safeGet(exceptionFuture));
             assertEquals(ServerRequestHandler.SIMULATED_EXCEPTION_MESSAGE, exception.getMessage());
             safeAwait(handler.closedLatch);
-            assertBusy(() -> assertEquals(0, handler.stream.bufSize()));
         }
     }
 
@@ -310,7 +304,7 @@ public void testClientBackpressure() throws Exception {
                 });
                 handler.readBytes(partSize);
             }
-            assertTrue(handler.stream.hasLast());
+            assertTrue(handler.receivedLastChunk);
         }
     }
 

modules/transport-netty4/src/main/java/org/elasticsearch/http/netty4/MissingReadDetector.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package org.elasticsearch.http.netty4;
+
+import io.netty.channel.ChannelDuplexHandler;
+import io.netty.channel.ChannelHandlerContext;
+import io.netty.util.concurrent.ScheduledFuture;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.elasticsearch.common.time.TimeProvider;
+import org.elasticsearch.common.util.concurrent.FutureUtils;
+
+import java.util.concurrent.TimeUnit;
+
+/**
+ * When channel auto-read is disabled handlers are responsible to read from channel.
+ * But it's hard to detect when read is missing. This helper class print warnings
+ * when no reads where detected in given time interval. Normally, in tests, 10 seconds is enough
+ * to avoid test hang for too long, but can be increased if needed.
+ */
+class MissingReadDetector extends ChannelDuplexHandler {
+
+    private static final Logger logger = LogManager.getLogger(MissingReadDetector.class);
+
+    private final long interval;
+    private final TimeProvider timer;
+    private boolean pendingRead;
+    private long lastRead;
+    private ScheduledFuture<?> checker;
+
+    MissingReadDetector(TimeProvider timer, long missingReadIntervalMillis) {
+        this.interval = missingReadIntervalMillis;
+        this.timer = timer;
+    }
+
+    @Override
+    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
+        checker = ctx.channel().eventLoop().scheduleAtFixedRate(() -> {
+            if (pendingRead == false) {
+                long now = timer.absoluteTimeInMillis();
+                if (now >= lastRead + interval) {
+                    logger.warn("chan-id={} haven't read from channel for [{}ms]", ctx.channel().id(), (now - lastRead));
+                }
+            }
+        }, interval, interval, TimeUnit.MILLISECONDS);
+        super.handlerAdded(ctx);
+    }
+
+    @Override
+    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
+        if (checker != null) {
+            FutureUtils.cancel(checker);
+        }
+        super.handlerRemoved(ctx);
+    }
+
+    @Override
+    public void read(ChannelHandlerContext ctx) throws Exception {
+        pendingRead = true;
+        ctx.read();
+    }
+
+    @Override
+    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
+        assert ctx.channel().config().isAutoRead() == false : "auto-read must be always disabled";
+        pendingRead = false;
+        lastRead = timer.absoluteTimeInMillis();
+        ctx.fireChannelRead(msg);
+    }
+}

modules/transport-netty4/src/main/java/org/elasticsearch/http/netty4/Netty4HttpAggregator.java

@@ -15,6 +15,7 @@
 import io.netty.handler.codec.http.HttpObjectAggregator;
 import io.netty.handler.codec.http.HttpRequest;
 import io.netty.handler.codec.http.HttpRequestDecoder;
+import io.netty.handler.codec.http.LastHttpContent;
 
 import org.elasticsearch.http.HttpPreRequest;
 import org.elasticsearch.http.netty4.internal.HttpHeadersAuthenticatorUtils;
@@ -48,6 +49,9 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
         }
         if (aggregating || msg instanceof FullHttpRequest) {
             super.channelRead(ctx, msg);
+            if (msg instanceof LastHttpContent == false) {
+                ctx.read(); // HttpObjectAggregator is tricky with auto-read off, it might not call read again, calling on its behalf
+            }
         } else {
             streamContentSizeHandler.channelRead(ctx, msg);
         }

modules/transport-netty4/src/main/java/org/elasticsearch/http/netty4/Netty4HttpContentSizeHandler.java

@@ -123,6 +123,7 @@ private void handleRequest(ChannelHandlerContext ctx, HttpRequest request) {
                 isContinueExpected = true;
             } else {
                 ctx.writeAndFlush(EXPECTATION_FAILED_CLOSE.retainedDuplicate()).addListener(ChannelFutureListener.CLOSE);
+                ctx.read();
                 return;
             }
         }
@@ -136,6 +137,7 @@ private void handleRequest(ChannelHandlerContext ctx, HttpRequest request) {
                 decoder.reset();
             }
             ctx.writeAndFlush(TOO_LARGE.retainedDuplicate()).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
+            ctx.read();
         } else {
             ignoreContent = false;
             currentContentLength = 0;
@@ -150,11 +152,13 @@ private void handleRequest(ChannelHandlerContext ctx, HttpRequest request) {
     private void handleContent(ChannelHandlerContext ctx, HttpContent msg) {
         if (ignoreContent) {
             msg.release();
+            ctx.read();
         } else {
             currentContentLength += msg.content().readableBytes();
             if (currentContentLength > maxContentLength) {
                 msg.release();
                 ctx.writeAndFlush(TOO_LARGE_CLOSE.retainedDuplicate()).addListener(ChannelFutureListener.CLOSE);
+                ctx.read();
             } else {
                 ctx.fireChannelRead(msg);
             }