From 509ba6753f795c00086ab4a49dd022fe3a22aff0 Mon Sep 17 00:00:00 2001
From: cachescrubber <lars.uffmann@gmail.com>
Date: Thu, 31 Aug 2023 16:55:37 +0200
Subject: [PATCH] Document exec chain behaviour when automatic retries are
 enabled. (#480)

---
 .../http/async/AsyncExecChainHandler.java       | 17 ++++++++++++++++-
 .../client5/http/classic/ExecChainHandler.java  | 16 ++++++++++++++++
 .../impl/async/AsyncHttpRequestRetryExec.java   | 17 +++++++++++++++++
 .../http/impl/classic/HttpRequestRetryExec.java | 17 +++++++++++++++++
 4 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/httpclient5/src/main/java/org/apache/hc/client5/http/async/AsyncExecChainHandler.java b/httpclient5/src/main/java/org/apache/hc/client5/http/async/AsyncExecChainHandler.java
index 3888617fc..5ba3d42cc 100644
--- a/httpclient5/src/main/java/org/apache/hc/client5/http/async/AsyncExecChainHandler.java
+++ b/httpclient5/src/main/java/org/apache/hc/client5/http/async/AsyncExecChainHandler.java
@@ -28,6 +28,9 @@ package org.apache.hc.client5.http.async;
 
 import java.io.IOException;
 
+import org.apache.hc.client5.http.impl.ChainElement;
+import org.apache.hc.client5.http.impl.async.AsyncHttpRequestRetryExec;
+import org.apache.hc.client5.http.impl.async.HttpAsyncClientBuilder;
 import org.apache.hc.core5.annotation.Contract;
 import org.apache.hc.core5.annotation.ThreadingBehavior;
 import org.apache.hc.core5.http.HttpException;
@@ -39,8 +42,20 @@ import org.apache.hc.core5.http.nio.AsyncEntityProducer;
  * chain. Handlers can either be a decorator around another element that implements
  * a cross cutting aspect or a self-contained executor capable of producing a response
  * for the given request.
- *
+ * <p>
+ * For information regarding the handler chain behaviour in case of a request re-execution,
+ * please refer to the {@link AsyncHttpRequestRetryExec} javadoc.
+ * </p>
+ * <p>
+ * Well known request execution handlers could be referred to by name using one of the
+ * {@link ChainElement} enum values.
+ * </p>
  * @since 5.0
+ * @see ChainElement
+ * @see HttpAsyncClientBuilder#addExecInterceptorFirst(String, AsyncExecChainHandler)
+ * @see HttpAsyncClientBuilder#addExecInterceptorBefore(String, String, AsyncExecChainHandler)
+ * @see HttpAsyncClientBuilder#addExecInterceptorAfter(String, String, AsyncExecChainHandler)
+ * @see HttpAsyncClientBuilder#addExecInterceptorLast(String, AsyncExecChainHandler)
  */
 @Contract(threading = ThreadingBehavior.STATELESS)
 public interface AsyncExecChainHandler {
diff --git a/httpclient5/src/main/java/org/apache/hc/client5/http/classic/ExecChainHandler.java b/httpclient5/src/main/java/org/apache/hc/client5/http/classic/ExecChainHandler.java
index 035c1000d..ae5de86bc 100644
--- a/httpclient5/src/main/java/org/apache/hc/client5/http/classic/ExecChainHandler.java
+++ b/httpclient5/src/main/java/org/apache/hc/client5/http/classic/ExecChainHandler.java
@@ -29,6 +29,9 @@ package org.apache.hc.client5.http.classic;
 
 import java.io.IOException;
 
+import org.apache.hc.client5.http.impl.ChainElement;
+import org.apache.hc.client5.http.impl.classic.HttpClientBuilder;
+import org.apache.hc.client5.http.impl.classic.HttpRequestRetryExec;
 import org.apache.hc.core5.annotation.Contract;
 import org.apache.hc.core5.annotation.ThreadingBehavior;
 import org.apache.hc.core5.http.ClassicHttpRequest;
@@ -46,8 +49,21 @@ import org.apache.hc.core5.http.HttpException;
  * by calling {@link ClassicHttpResponse#close()} methods in case of an I/O, protocol or
  * runtime exception, or in case the response is not propagated to the caller.
  * </p>
+ * <p>
+ * For information regarding the handler chain behaviour in case of a request re-execution,
+ * please refer to the {@link HttpRequestRetryExec} javadoc.
+ * </p>
+ *<p>
+ * Well known request execution handlers could be referred to by name using one of the
+ * {@link ChainElement} enum values.
+ *</p>
  *
  * @since 4.3
+ * @see ChainElement
+ * @see HttpClientBuilder#addExecInterceptorFirst(String, ExecChainHandler)
+ * @see HttpClientBuilder#addExecInterceptorBefore(String, String, ExecChainHandler)
+ * @see HttpClientBuilder#addExecInterceptorAfter(String, String, ExecChainHandler)
+ * @see HttpClientBuilder#addExecInterceptorLast(String, ExecChainHandler)
  */
 @Contract(threading = ThreadingBehavior.STATELESS)
 public interface ExecChainHandler {
diff --git a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/AsyncHttpRequestRetryExec.java b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/AsyncHttpRequestRetryExec.java
index 9fc7c3296..a1c338777 100644
--- a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/AsyncHttpRequestRetryExec.java
+++ b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/AsyncHttpRequestRetryExec.java
@@ -33,6 +33,7 @@ import org.apache.hc.client5.http.HttpRoute;
 import org.apache.hc.client5.http.async.AsyncExecCallback;
 import org.apache.hc.client5.http.async.AsyncExecChain;
 import org.apache.hc.client5.http.async.AsyncExecChainHandler;
+import org.apache.hc.client5.http.impl.ChainElement;
 import org.apache.hc.client5.http.protocol.HttpClientContext;
 import org.apache.hc.core5.annotation.Contract;
 import org.apache.hc.core5.annotation.Internal;
@@ -61,6 +62,22 @@ import org.slf4j.LoggerFactory;
  * endpoint is delegated to the next executor in the request execution
  * chain.
  * </p>
+ * <p>
+ * If this handler is active, pay particular attention to the placement
+ * of other handlers within the handler chain relative to the retry handler.
+ * Use {@link ChainElement#RETRY} as name when referring to this handler.
+ * </p>
+ * <p>
+ * If a custom handler is placed <b>before</b> the retry handler, the handler will
+ * see the initial request and the final outcome after the last retry. Elapsed time
+ * will account for any delays imposed by the retry handler.
+ * </p>
+ *
+ * <p>
+ * A custom handler which is placed <b>after</b> the retry handler will be invoked for
+ * each individual retry. Elapsed time will measure each individual http request,
+ * without the delay imposed by the retry handler.
+ * </p>
  *
  * @since 5.0
  */
diff --git a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpRequestRetryExec.java b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpRequestRetryExec.java
index 75e75d19f..fbd464c94 100644
--- a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpRequestRetryExec.java
+++ b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpRequestRetryExec.java
@@ -35,6 +35,7 @@ import org.apache.hc.client5.http.classic.ExecChain;
 import org.apache.hc.client5.http.classic.ExecChain.Scope;
 import org.apache.hc.client5.http.classic.ExecChainHandler;
 import org.apache.hc.client5.http.config.RequestConfig;
+import org.apache.hc.client5.http.impl.ChainElement;
 import org.apache.hc.client5.http.protocol.HttpClientContext;
 import org.apache.hc.core5.annotation.Contract;
 import org.apache.hc.core5.annotation.Internal;
@@ -61,6 +62,22 @@ import org.slf4j.LoggerFactory;
  * endpoint is delegated to the next executor in the request execution
  * chain.
  * </p>
+ * <p>
+ * If this handler is active, pay particular attention to the placement
+ * of other handlers within the handler chain relative to the retry handler.
+ * Use {@link ChainElement#RETRY} as name when referring to this handler.
+ * </p>
+ * <p>
+ * If a custom handler is placed <b>before</b> the retry handler, the handler will
+ * see the initial request and the final outcome after the last retry. Elapsed time
+ * will account for any delays imposed by the retry handler.
+ * </p>
+ *
+ * <p>
+ * A custom handler which is placed <b>after</b> the retry handler will be invoked for
+ * each individual retry. Elapsed time will measure each individual http request,
+ * without the delay imposed by the retry handler.
+ * </p>
  *
  * @since 5.0
  */