Demystify IoTHub SDKs

demystify-iohub.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <RootNamespace>demistify_iothub</RootNamespace>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="MQTTnet" Version="3.1.2" />
  </ItemGroup>

</Project>

MqttNetExtensions.cs

using MQTTnet.Client.Options;
using System.Text;

namespace demistify_iothub
{
    public static class MqttNetExtensions
    {
        public static MqttClientOptionsBuilder WithAzureIoTHubCredentialsSas(this MqttClientOptionsBuilder builder, string hostName, string deviceId, string sasKey, string modelId = "", int sasMinutes = 60)
        {
            (string username, string password) = SasAuth.GenerateHubSasCredentials(hostName, deviceId, sasKey, modelId, sasMinutes);
            builder
                .WithTcpServer(hostName, 8883)
                .WithTls()
                .WithClientId(deviceId)
                .WithCredentials(username, password);
            return builder;
        }
    }
}

Program.cs

using demistify_iothub;
using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Client.Options;
using System.Text;
using System.Text.Json;
using System.Web;

// Connect

IMqttClient mqttClient = new MqttFactory().CreateMqttClient();
var connAck = await mqttClient.ConnectAsync(new MqttClientOptionsBuilder()
    .WithAzureIoTHubCredentialsSas(
        hostName: "rido-freetier.azure-devices.net",
        deviceId: "myDevice",
        sasKey: "MDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDA="
    )
    .Build());

Console.WriteLine($"connAck resaon: {connAck.ResultCode} IsConnected: {mqttClient.IsConnected}");

// Telemetry

var pubAck = await mqttClient.PublishAsync(
        $"devices/{mqttClient.Options.ClientId}/messages/events/",
        JsonSerializer.Serialize(new { Environment.WorkingSet }) );
Console.WriteLine($"Telemetry sent with pubAck: {pubAck.ReasonCode}" );


await mqttClient.SubscribeAsync("$iothub/methods/POST/#");
await mqttClient.SubscribeAsync("$iothub/twin/res/#");
await mqttClient.SubscribeAsync("$iothub/twin/PATCH/properties/desired/#");

mqttClient.UseApplicationMessageReceivedHandler(async m =>
{
    var topic = m.ApplicationMessage.Topic;
    var segments = topic.Split('/');
    // Command
    if (topic.StartsWith("$iothub/methods/POST/"))
    {
        var qs = HttpUtility.ParseQueryString(segments[^1]);
        _ = int.TryParse(qs["$rid"], out int rid);
        var cmdName = segments[3];
        var cmdPayload = Encoding.UTF8.GetString(m.ApplicationMessage.Payload);

        Console.WriteLine($"Executing command {cmdName} with rid {rid} and payload {cmdPayload}");
        await mqttClient.PublishAsync($"$iothub/methods/res/200/?$rid={rid}", cmdPayload);
    }

    //GetTwin reponse
    if (topic.StartsWith("$iothub/twin/res/200"))
    {
        var qs = HttpUtility.ParseQueryString(segments[^1]);
        _ = int.TryParse(qs["$rid"], out int rid);
        var twin = Encoding.UTF8.GetString(m.ApplicationMessage.Payload);
        Console.WriteLine(twin);
    }

    // UpdateTwin response
    if (topic.StartsWith("$iothub/twin/res/204"))
    {
        var qs = HttpUtility.ParseQueryString(segments[^1]);
        var twinVersion = Convert.ToInt32(qs["$version"]);
        System.Console.WriteLine(twinVersion);
    }

    if (topic.StartsWith("$iothub/twin/PATCH/properties/desired"))
    {
        string msg = Encoding.UTF8.GetString(m.ApplicationMessage.Payload);
        System.Console.WriteLine(msg);
    }
});

await mqttClient.PublishAsync($"$iothub/twin/GET/?$rid=1");
await mqttClient.PublishAsync(
    "$iothub/twin/PATCH/properties/reported/?$rid=2",
    JsonSerializer.Serialize(new { myProperty = "myValue" }));
Console.ReadLine();

SasAuth.cs

using System.Text;

namespace demistify_iothub
{
    public class SasAuth
    {
        private const string apiversion_2020_09_30 = "2020-09-30";
        public static string GetUserName(string hostName, string deviceId, string modelId = "") =>
            $"{hostName}/{deviceId}/?api-version={apiversion_2020_09_30}&model-id={modelId}";

        private static string Sign(string requestString, string key)
        {
            using (var algorithm = new System.Security.Cryptography.HMACSHA256(Convert.FromBase64String(key)))
            {
                return Convert.ToBase64String(algorithm.ComputeHash(Encoding.UTF8.GetBytes(requestString)));
            }
        }

        public static string CreateSasToken(string resource, string sasKey, int minutes)
        {
            var expiry = DateTimeOffset.UtcNow.AddMinutes(minutes).ToUnixTimeSeconds().ToString();
            var sig = System.Net.WebUtility.UrlEncode(Sign($"{resource}\n{expiry}", sasKey));
            return $"SharedAccessSignature sr={resource}&sig={sig}&se={expiry}";
        }

        public static (string username, string password) GenerateHubSasCredentials(string hostName, string deviceId, string sasKey, string modelId, int minutes = 60) =>
            (GetUserName(hostName, deviceId, modelId), CreateSasToken($"{hostName}/devices/{deviceId}", sasKey, minutes));
    }
}

companion code for post https://blog.rido.dev/mqtt/2022/04/04/demystify-iothub-sdk