MessageSender.cs

// <copyright file="MessageSender.cs" company="OpenTelemetry Authors">
// Copyright The OpenTelemetry 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.
// </copyright>

using System.Diagnostics;
using System.Text;
using Microsoft.Extensions.Logging;
using OpenTelemetry;
using OpenTelemetry.Context.Propagation;
using RabbitMQ.Client;

namespace Utils.Messaging
{
    public class MessageSender : IDisposable
    {
        private static readonly ActivitySource ActivitySource = new(nameof(MessageSender));
        private static readonly TextMapPropagator Propagator = Propagators.DefaultTextMapPropagator;

        private readonly ILogger<MessageSender> logger;
        private readonly IConnection connection;
        private readonly IModel channel;

        public MessageSender(ILogger<MessageSender> logger)
        {
            this.logger = logger;
            this.connection = RabbitMqHelper.CreateConnection();
            this.channel = RabbitMqHelper.CreateModelAndDeclareTestQueue(this.connection);
        }

        public void Dispose()
        {
            this.channel.Dispose();
            this.connection.Dispose();
        }

        public string SendMessage()
        {
            try
            {
                // Start an activity with a name following the semantic convention of the OpenTelemetry messaging specification.
                // https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/semantic_conventions/messaging.md#span-name
                var activityName = $"{RabbitMqHelper.TestQueueName} send";

                using var activity = ActivitySource.StartActivity(activityName, ActivityKind.Producer);
                var props = this.channel.CreateBasicProperties();

                // Depending on Sampling (and whether a listener is registered or not), the
                // activity above may not be created.
                // If it is created, then propagate its context.
                // If it is not created, the propagate the Current context,
                // if any.
                ActivityContext contextToInject = default;
                if (activity != null)
                {
                    contextToInject = activity.Context;
                }
                else if (Activity.Current != null)
                {
                    contextToInject = Activity.Current.Context;
                }

                // Inject the ActivityContext into the message headers to propagate trace context to the receiving service.
                Propagator.Inject(new PropagationContext(contextToInject, Baggage.Current), props, this.InjectTraceContextIntoBasicProperties);

                // The OpenTelemetry messaging specification defines a number of attributes. These attributes are added here.
                RabbitMqHelper.AddMessagingTags(activity);
                var body = $"Published message: DateTime.Now = {DateTime.Now}.";

                this.channel.BasicPublish(
                    exchange: RabbitMqHelper.DefaultExchangeName,
                    routingKey: RabbitMqHelper.TestQueueName,
                    basicProperties: props,
                    body: Encoding.UTF8.GetBytes(body));

                this.logger.LogInformation($"Message sent: [{body}]");

                return body;
            }
            catch (Exception ex)
            {
                this.logger.LogError(ex, "Message publishing failed.");
                throw;
            }
        }

        private void InjectTraceContextIntoBasicProperties(IBasicProperties props, string key, string value)
        {
            try
            {
                if (props.Headers == null)
                {
                    props.Headers = new Dictionary<string, object>();
                }

                props.Headers[key] = value;
            }
            catch (Exception ex)
            {
                this.logger.LogError(ex, "Failed to inject trace context.");
            }
        }
    }
}