Document Context#isRequesterAlive(Message)

Author: acogoluegnes

src/docs/asciidoc/usage.adoc

@@ -242,6 +242,18 @@ The prefix is different for each `Requester` instance and the suffix is incremen
 * it sets the _request_ https://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#type-properties[`message-id` property] to the generated correlation ID.
 * it extracts the correlation ID from the _reply_ https://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#type-properties[`correlation-id` property] to correlate a reply with the appropriate request.
 
+If the responder will perform expensive work, it can proactively check whether the requester is still present with the `Context#isRequesterAlive(Message)` method:
+
+.Checking the requester
+[source,java,indent=0]
+--------
+include::{test-examples}/RequestResponseApi.java[tag=is-requester-alive]
+--------
+<1> Check if the requester is still connected
+
+The requester can check the requester at any time - when a request comes in or even during a long processing - and react accordingly by stopping the processing.
+Note each call to `Context#isRequesterAlive(Message)` implies a request to the broker.
+
 Let's see how to customize some of the request/response support mechanics.
 Imagine the request `message-id` property is a critical piece of information and we do not want to use it as the correlation ID.
 The request can use the `correlation-id` property and the responder just has to extract the correlation ID from this property (instead of the `message-id` property by default).

src/test/java/com/rabbitmq/client/amqp/docs/RequestResponseApi.java

@@ -19,9 +19,9 @@ void withDefaults() throws Exception {
     Responder responder = connection.responderBuilder() // <1>
         .requestQueue("request-queue") // <2>
         .handler((ctx, req) -> { // <3>
-          String in = new String(req.body(), UTF_8);
-          String out = "*** " + in + " ***";
-          return ctx.message(out.getBytes(UTF_8)); // <4>
+            String in = new String(req.body(), UTF_8);
+            String out = "*** " + in + " ***";
+            return ctx.message(out.getBytes(UTF_8)); // <4>
         }).build();
     // end::responder-creation[]
 
@@ -39,7 +39,24 @@ void withDefaults() throws Exception {
     // end::requester-request[]
   }
 
-  void withCustomSettings() {
+  void isRequesterAlive() {
+    Connection connection = null;
+    // tag::is-requester-alive[]
+    Responder responder = connection.responderBuilder()
+        .requestQueue("request-queue")
+        .handler((ctx, req) -> {
+            if (ctx.isRequesterAlive(req)) { // <1>
+              String in = new String(req.body(), UTF_8);
+              String out = "*** " + in + " ***";
+              return ctx.message(out.getBytes(UTF_8));
+            } else {
+              return null;
+            }
+        }).build();
+    // end::is-requester-alive[]
+  }
+
+    void withCustomSettings() {
     Connection connection = null;
     // tag::custom-requester-creation[]
     String replyToQueue = connection.management().queue()
@@ -61,9 +78,9 @@ void withCustomSettings() {
         .correlationIdExtractor(Message::correlationId) // <1>
         .requestQueue("request-queue")
         .handler((ctx, req) -> {
-          String in = new String(req.body(), UTF_8);
-          String out = "*** " + in + " ***";
-          return ctx.message(out.getBytes(UTF_8));
+            String in = new String(req.body(), UTF_8);
+            String out = "*** " + in + " ***";
+            return ctx.message(out.getBytes(UTF_8));
         }).build();
     // end::custom-responder-creation[]
   }