Custom inbox prefix

src/NATS.Client/Conn.cs

@@ -3224,9 +3224,11 @@ public Task<Msg> RequestAsync(string subject, byte[] data, int offset, int count
         /// <returns>A unique inbox string.</returns>
         public string NewInbox()
         {
+            var prefix = opts.CustomInboxPrefix ?? IC.inboxPrefix;
+
             if (!opts.UseOldRequestStyle)
             {
-                return IC.inboxPrefix + Guid.NewGuid().ToString("N");
+                return prefix + Guid.NewGuid().ToString("N");
             }
             else
             {
@@ -3237,7 +3239,7 @@ public string NewInbox()
 
                 r.NextBytes(buf);
 
-                return IC.inboxPrefix + BitConverter.ToString(buf).Replace("-","");
+                return prefix + BitConverter.ToString(buf).Replace("-","");
             }
         }
 

src/NATS.Client/Options.cs

@@ -189,6 +189,8 @@ public void SetJWTEventHandlers(EventHandler<UserJWTEventArgs> JWTEventHandler,
         internal string token;
         internal string nkey;
 
+        internal string customInboxPrefix;
+
         // Options can only be publicly created through 
         // ConnectionFactory.GetDefaultOptions();
         internal Options() { }
@@ -222,6 +224,7 @@ internal Options(Options o)
             verbose = o.verbose;
             subscriberDeliveryTaskCount = o.subscriberDeliveryTaskCount;
             subscriptionBatchSize = o.subscriptionBatchSize;
+            customInboxPrefix = o.customInboxPrefix;
 
             if (o.url != null)
             {
@@ -463,6 +466,21 @@ public string Token
             set { token = value; }
         }
 
+        /// <summary>
+        /// Gets or sets a custom inbox prefix.
+        /// </summary>
+        public string CustomInboxPrefix
+        {
+            get => customInboxPrefix;
+            set
+            {
+                if (value != null && !Subscription.IsValidPrefix(value))
+                    throw new ArgumentException("Prefix would result in an invalid subject.");
+
+                customInboxPrefix = value;
+            }
+        }
+
         /// <summary>
         /// Adds an X.509 certifcate from a file for use with a secure connection.
         /// </summary>

src/NATS.Client/Subscription.cs

@@ -698,6 +698,19 @@ public static bool IsValidSubject(string subject)
             return true;
         }
 
+        /// <summary>
+        /// Checks if a prefix is valid.
+        /// </summary>
+        /// <param name="prefix"></param>
+        /// <returns></returns>
+        public static bool IsValidPrefix(string prefix)
+        {
+            if (ContainsInvalidChars(prefix))
+                return false;
+
+            return !prefix.StartsWith(".") && prefix.EndsWith(".");
+        }
+
         /// <summary>
         /// Checks if the queue group name is valid.
         /// </summary>

src/Tests/IntegrationTests/TestSubscriptions.cs

@@ -1055,6 +1055,43 @@ public void TestRespond()
             }
         }
 
+        [Fact]
+        public void TestRespondWithCustomInbox()
+        {
+            var opts = Context.GetTestOptionsWithDefaultTimeout(Context.Server1.Port);
+            opts.CustomInboxPrefix = "_TEST.";
+
+            using (NATSServer.CreateFastAndVerify(Context.Server1.Port))
+            {
+                using (var cn = Context.ConnectionFactory.CreateConnection(opts))
+                using (var requestSub = cn.SubscribeSync("foo"))
+                {
+                    var replyTo = cn.NewInbox();
+                    Assert.StartsWith("_TEST.", replyTo);
+
+                    using (var responderSub = cn.SubscribeSync(replyTo))
+                    {
+                        cn.Publish("foo", replyTo, SamplePayload.Random());
+
+                        var request = requestSub.NextMessage(1000);
+                        Assert.NotNull(request);
+                        Assert.Equal(replyTo, request.Reply);
+
+                        var reply = SamplePayload.Random();
+                        request.Respond(reply);
+
+                        var response = responderSub.NextMessage(1000);
+                        Assert.NotNull(response);
+                        Assert.Equal(replyTo, response.Subject);
+                        Assert.Equal(reply, response.Data);
+
+                        requestSub.Unsubscribe();
+                        responderSub.Unsubscribe();
+                    }
+                }
+            }
+        }
+
         [Fact]
         public void TestRespondWithAutoUnsubscribe()
         {

src/Tests/UnitTests/TestOptions.cs

@@ -12,6 +12,7 @@
 // limitations under the License.
 
 using System;
+using System.Reflection.Emit;
 using NATS.Client;
 using Xunit;
 
@@ -38,5 +39,31 @@ public void TestBadOptionSubscriptionBatchSize()
 
             Assert.ThrowsAny<ArgumentException>(() => opts.SubscriptionBatchSize = 0);
         }
+
+        [Theory]
+        [InlineData("")]
+        [InlineData("\r")]
+        [InlineData("\n")]
+        [InlineData("\t")]
+        [InlineData("Test")]
+        [InlineData(".Test.")]
+        public void TestBadCustomPrefix(string customPrefix)
+        {
+            var opts = GetDefaultOptions();
+
+            Assert.ThrowsAny<ArgumentException>(() => opts.CustomInboxPrefix = customPrefix);
+        }
+
+        [Theory]
+        [InlineData("Test.")]
+        [InlineData("Test.SubTest.")]
+        [InlineData("_Test.")]
+        [InlineData("_Test.SubTest.")]
+        public void TestOkCustomPrefix(string customPrefix)
+        {
+            var opts = GetDefaultOptions();
+
+            opts.CustomInboxPrefix = customPrefix;
+        }
     }
 }