19. IoT Edge Module を深掘る

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はじめに

今回は前回の続きで、IoT Edge Module を更に深堀り、実用レベルの知識を獲得していきます。

SampleModule を深堀る

前回試した、VS Code での IoT Edge Module 開発ですが、そこで作った SampleModule のコードは、以下の様なものでした。
※ ちょっと長いですが、全てをコピペ

namespace SampleModule
{
    using System;
    using System.IO;
    using System.Runtime.InteropServices;
    using System.Runtime.Loader;
    using System.Security.Cryptography.X509Certificates;
    using System.Text;
    using System.Threading;
    using System.Threading.Tasks;
    using Microsoft.Azure.Devices.Client;
    using Microsoft.Azure.Devices.Client.Transport.Mqtt;

    class Program
    {
        static int counter;

        static void Main(string[] args)
        {
            Init().Wait();

            // Wait until the app unloads or is cancelled
            var cts = new CancellationTokenSource();
            AssemblyLoadContext.Default.Unloading += (ctx) => cts.Cancel();
            Console.CancelKeyPress += (sender, cpe) => cts.Cancel();
            WhenCancelled(cts.Token).Wait();
        }

        /// <summary>
        /// Handles cleanup operations when app is cancelled or unloads
        /// </summary>
        public static Task WhenCancelled(CancellationToken cancellationToken)
        {
            var tcs = new TaskCompletionSource<bool>();
            cancellationToken.Register(s => ((TaskCompletionSource<bool>)s).SetResult(true), tcs);
            return tcs.Task;
        }

        /// <summary>
        /// Initializes the ModuleClient and sets up the callback to receive
        /// messages containing temperature information
        /// </summary>
        static async Task Init()
        {
            MqttTransportSettings mqttSetting = new MqttTransportSettings(TransportType.Mqtt_Tcp_Only);
            ITransportSettings[] settings = { mqttSetting };

            // Open a connection to the Edge runtime
            ModuleClient ioTHubModuleClient = await ModuleClient.CreateFromEnvironmentAsync(settings);
            await ioTHubModuleClient.OpenAsync();
            Console.WriteLine("IoT Hub module client initialized.");

            // Register callback to be called when a message is received by the module
            await ioTHubModuleClient.SetInputMessageHandlerAsync("input1", PipeMessage, ioTHubModuleClient);
        }

        /// <summary>
        /// This method is called whenever the module is sent a message from the EdgeHub. 
        /// It just pipe the messages without any change.
        /// It prints all the incoming messages.
        /// </summary>
        static async Task<MessageResponse> PipeMessage(Message message, object userContext)
        {
            int counterValue = Interlocked.Increment(ref counter);

            var moduleClient = userContext as ModuleClient;
            if (moduleClient == null)
            {
                throw new InvalidOperationException("UserContext doesn't contain " + "expected values");
            }

            byte[] messageBytes = message.GetBytes();
            string messageString = Encoding.UTF8.GetString(messageBytes);
            Console.WriteLine($"Received message: {counterValue}, Body: [{messageString}]");

            if (!string.IsNullOrEmpty(messageString))
            {
                using (var pipeMessage = new Message(messageBytes))
                {
                    foreach (var prop in message.Properties)
                    {
                        pipeMessage.Properties.Add(prop.Key, prop.Value);
                    }
                    await moduleClient.SendEventAsync("output1", pipeMessage);
                
                    Console.WriteLine("Received message sent");
                }
            }
            return MessageResponse.Completed;
        }
    }
}

ご存じの通り、C# のコードなので、最初に起動されるのは、Main method ですね。何をやっているかというと、