Nats By Example Request Reply

src/Samples/Miscellany/Miscellany.cs

@@ -10,7 +10,7 @@ class Miscellany
         public static void Main(string[] args)
         {
             // Set the args manually to run the code you want.
-            // args = new[] { "KvIntro" };
+            args = new[] { "RequestReply" };
 
             if (args.Length == 1)
             {
@@ -24,6 +24,10 @@ public static void Main(string[] args)
                         NatsByExample.PubSub.PubSubMain();
                         return;
 
+                    case "RequestReply":
+                        NatsByExample.RequestReply.RequestReplyMain();
+                        return;
+
                     case "KvIntro":
                         NatsByExample.KvIntro.KvIntroMain();
                         return;
@@ -35,6 +39,7 @@ public static void Main(string[] args)
                 + "\nAvailable programs:"
                 + "\n   CrossClientValidation" 
                 + "\n   PubSub"
+                + "\n   RequestReply"
                 + "\n   KvIntro"
             );
         }

src/Samples/Miscellany/NatsByExample/PubSub.cs

@@ -32,8 +32,8 @@ public static void PubSubMain()
             opts.Url = natsUrl;
 
             // Creates a connection to nats server at the `natsUrl`
-            // An `IConnection` is `IDisposable` so it can be use
-            // within `using` statement. 
+            // An `IConnection` is `IDisposable` so it can be used
+            // within a `using` statement. 
             ConnectionFactory cf = new ConnectionFactory();
             IConnection c = cf.CreateConnection(opts);
 

src/Samples/Miscellany/NatsByExample/RequestReply.cs

@@ -0,0 +1,112 @@
+// Copyright 2022 The NATS Authors
+// 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.
+
+using System;
+using System.Text;
+using System.Threading.Tasks;
+using NATS.Client;
+
+namespace NATSExamples.NatsByExample
+{
+    abstract class RequestReply
+    {
+        public static void RequestReplyMain()
+        {
+            string natsUrl = Environment.GetEnvironmentVariable("NATS_URL");
+            if (natsUrl == null)
+            {
+                natsUrl = "nats://127.0.0.1:4222";
+            }
+
+            // Create a new connection factory to create a connection.
+            Options opts = ConnectionFactory.GetDefaultOptions();
+            opts.Url = natsUrl;
+
+            // Creates a connection to nats server at the `natsUrl`
+            // An `IConnection` is `IDisposable` so it can be used
+            // within a `using` statement. 
+            ConnectionFactory cf = new ConnectionFactory();
+            IConnection c = cf.CreateConnection(opts);
+
+            // ### Reply
+            // Create a message event handler and then subscribe to the target
+            // subject which leverages a wildcard `greet.*`.
+            // When a user makes a "request", the client populates
+            // the reply-to field and then listens (subscribes) to that
+            // as a subject.
+            // The replier simply publishes a message to that reply-to.
+            EventHandler<MsgHandlerEventArgs> handler = (sender, args) =>
+            {
+                string name = args.Message.Subject.Substring(6);
+                string response = $"hello {name}";
+                c.Publish(args.Message.Reply, Encoding.UTF8.GetBytes(response));
+            };
+            IAsyncSubscription sub = c.SubscribeAsync("greet.*", handler);
+
+            // ### Request
+            // Make a request and wait a most 1 second for a response.
+            try
+            {
+                Msg m0 = c.Request("greet.bob", null, 1000);
+                Console.WriteLine("Response received: " + Encoding.UTF8.GetString(m0.Data));
+            }
+            catch (NATSTimeoutException)
+            {
+                Console.WriteLine($"NATSTimeoutException: The request did not complete in time.");
+            }
+
+            // A request can also be made asynchronously
+            Task<Msg> task1 = c.RequestAsync("greet.pam", null);
+            task1.Wait(1000);
+            Msg m1 = task1.Result;
+            Console.WriteLine("Response received: " + Encoding.UTF8.GetString(m1.Data));
+
+            // Once we unsubscribe there will be no subscriptions to reply.
+            sub.Unsubscribe();
+
+            // If there are no-responders to a synchronous request
+            // we get a `NATSNoRespondersException`.
+            try
+            {
+                c.Request("greet.fred", null, 1000);
+            }
+            catch (NATSNoRespondersException)
+            {
+                Console.WriteLine($"NATSNoRespondersException: There were no responders listening for the subject.");
+            }
+            catch (NATSTimeoutException)
+            {
+                Console.WriteLine($"NATSTimeoutException: The request did not complete in time.");
+            }
+
+            // If there are no-responders to an asynchronous request
+            // we get a `NATSNoRespondersException` wrapped inside the `AggregateException`
+            try
+            {
+                Task<Msg> task2 = c.RequestAsync("greet.sue", null);
+                task2.Wait(1000);
+            }
+            catch (AggregateException ae)
+            {
+                if (ae.InnerExceptions[0] is NATSNoRespondersException)
+                {
+                    Console.WriteLine($"NATSNoRespondersException: There were no responders listening for the subject.");
+                }
+                else
+                {
+                    Console.WriteLine($"Some exception: " + ae.Message);
+                }
+            }
+        }
+    }
+}