var rpcClient = new RPCClient();

Console.WriteLine(" [x] Requesting fib(30)");
var response = rpcClient.Call("30");
Console.WriteLine(" [.] Got '{0}'", response);

rpcClient.Close();

var corrId = Guid.NewGuid().ToString();
var props = channel.CreateBasicProperties();
props.ReplyTo = replyQueueName;
props.CorrelationId = corrId;

var messageBytes = Encoding.UTF8.GetBytes(message);
channel.BasicPublish(exchange: "",
                     routingKey: "rpc_queue",
                     basicProperties: props,
                     body: messageBytes);

// ... then code to read a response message from the callback_queue ...

private static int fib(int n)
  {
    if (n == 0 || n == 1) return n;
    return fib(n - 1) + fib(n - 2);
  }

 1  using System;
 2 using RabbitMQ.Client;
 3 using RabbitMQ.Client.Events;
 4 using System.Text;
 5 
 6 class RPCServer
 7 {
 8     public static void Main()
 9     {
10         var factory = new ConnectionFactory() { HostName = "localhost" };
11         using (var connection = factory.CreateConnection())
12         using (var channel = connection.CreateModel())
13         {
14             channel.QueueDeclare(queue: "rpc_queue", durable: false,
15               exclusive: false, autoDelete: false, arguments: null);
16             channel.BasicQos(0, 1, false);
17             var consumer = new EventingBasicConsumer(channel);
18             channel.BasicConsume(queue: "rpc_queue",
19               noAck: false, consumer: consumer);
20             Console.WriteLine(" [x] Awaiting RPC requests");
21 
22             consumer.Received += (model, ea) =>
23             {
24                 string response = null;
25 
26                 var body = ea.Body;
27                 var props = ea.BasicProperties;
28                 var replyProps = channel.CreateBasicProperties();
29                 replyProps.CorrelationId = props.CorrelationId;
30 
31                 try
32                 {
33                     var message = Encoding.UTF8.GetString(body);
34                     int n = int.Parse(message);
35                     Console.WriteLine(" [.] fib({0})", message);
36                     response = fib(n).ToString();
37                 }
38                 catch (Exception e)
39                 {
40                     Console.WriteLine(" [.] " + e.Message);
41                     response = "";
42                 }
43                 finally
44                 {
45                     var responseBytes = Encoding.UTF8.GetBytes(response);
46                     channel.BasicPublish(exchange: "", routingKey: props.ReplyTo,
47                       basicProperties: replyProps, body: responseBytes);
48                     channel.BasicAck(deliveryTag: ea.DeliveryTag,
49                       multiple: false);
50                 }
51             };
52 
53             Console.WriteLine(" Press [enter] to exit.");
54             Console.ReadLine();
55         }
56     }
57 
58     ///
59 
60     /// Assumes only valid positive integer input.
61     /// Don't expect this one to work for big numbers, and it's
62     /// probably the slowest recursive implementation possible.
63     ///
64 
65     private static int fib(int n)
66     {
67         if (n == 0 || n == 1)
68         {
69             return n;
70         }
71 
72         return fib(n - 1) + fib(n - 2);
73     }
74 }

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 using RabbitMQ.Client;
 7 using RabbitMQ.Client.Events;
 8 
 9 class RPCClient
10 {
11     private IConnection connection;
12     private IModel channel;
13     private string replyQueueName;
14     private QueueingBasicConsumer consumer;
15 
16     public RPCClient()
17     {
18         var factory = new ConnectionFactory() { HostName = "localhost" };
19         connection = factory.CreateConnection();
20         channel = connection.CreateModel();
21         replyQueueName = channel.QueueDeclare().QueueName;
22         consumer = new QueueingBasicConsumer(channel);
23         channel.BasicConsume(queue: replyQueueName,
24                              noAck: true,
25                              consumer: consumer);
26     }
27 
28     public string Call(string message)
29     {
30         var corrId = Guid.NewGuid().ToString();
31         var props = channel.CreateBasicProperties();
32         props.ReplyTo = replyQueueName;
33         props.CorrelationId = corrId;
34 
35         var messageBytes = Encoding.UTF8.GetBytes(message);
36         channel.BasicPublish(exchange: "",
37                              routingKey: "rpc_queue",
38                              basicProperties: props,
39                              body: messageBytes);
40 
41         while(true)
42         {
43             var ea = (BasicDeliverEventArgs)consumer.Queue.Dequeue();
44             if(ea.BasicProperties.CorrelationId == corrId)
45             {
46                 return Encoding.UTF8.GetString(ea.Body);
47             }
48         }
49     }
50 
51     public void Close()
52     {
53         connection.Close();
54     }
55 }
56 
57 class RPC
58 {
59     public static void Main()
60     {
61         var rpcClient = new RPCClient();
62 
63         Console.WriteLine(" [x] Requesting fib(30)");
64         var response = rpcClient.Call("30");
65         Console.WriteLine(" [.] Got '{0}'", response);
66 
67         rpcClient.Close();
68     }
69 }

var rpcClient = new RPCClient();

Console.WriteLine(" [x] Requesting fib(30)");
var response = rpcClient.Call("30");
Console.WriteLine(" [.] Got '{0}'", response);

rpcClient.Close();

cd RPCServer
dotnet run
# => [x] Awaiting RPC requests

cd RPCClient
dotnet run
# => [x] Requesting fib(30)