Dapr - Publish/Subscibe - Using Web APIs

Ashwin Gatadi — Thu, 02 Nov 2023 19:10:39 +0000

Pre-requisites

Install Dapr CLI
.NET 6 SDK installed.
Docker Desktop

Create a Web API Publish Service

Create a ASP.Net Core Web API project with .Net 6.0 framework version. Say name of the project as publisher
Add nuget package Dapr.AspNetCore (I have used version 1.12.0)
Add a directory say dapr-components into your project. Add file pubsub.yaml into the folder, which should look as below

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: myapp-pubsub
spec:
  type: pubsub.redis
  version: v1
  metadata:
    - name: redisHost
      value: localhost:6379
    - name: redisPassword
      value: ""
scopes:
  - publisher
  - subscriber

Add below line of code into your program.cs

builder.Services.AddDaprClient();

Your program.cs should look as below

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddDaprClient();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();
app.Run();

Add a WebAPI controller, say it as PublishController.cs. The code looks as below

using Dapr.Client;
using Microsoft.AspNetCore.Mvc;
using System;

namespace Publisher.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class PublishController : ControllerBase
    {
        private readonly DaprClient daprClient;
        private readonly ILogger<PublishController> logger;

        public PublishController(DaprClient daprClient, ILogger<PublishController> logger) 
        { 
            this.daprClient = daprClient;
            this.logger = logger;
        }

        [HttpPost]
        public async Task Post([FromBody] string value)
        {
            await daprClient.PublishEventAsync("myapp-pubsub", "test-dapr-topic", $"{DateTime.Now} - {value}");
            logger.LogInformation($"Published data at {DateTime.Now} - {value}");
        }
    }
}

Create a Web API Subscribe Service

Create a ASP.Net Core Web API project with .Net 6.0 framework version. Say name of the project as subscriber
Add nuget package Dapr.AspNetCore (I have used version 1.12.0)
Add a directory say dapr-components into your project. Add file pubsub.yaml into the folder, which should look as below

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: myapp-pubsub
spec:
  type: pubsub.redis
  version: v1
  metadata:
    - name: redisHost
      value: localhost:6379
    - name: redisPassword
      value: ""
scopes:
  - publisher
  - subscriber

Add below two lines of code into your program.cs

/* The call to UseCloudEvents adds CloudEvents middleware into to the 
 * ASP.NET Core middleware pipeline. 
 * This middleware will unwrap requests that use the CloudEvents structured 
 * format, so the receiving method can read the event payload directly. */
app.UseCloudEvents();

/* The call to MapSubscribeHandler in the endpoint routing configuration 
 * will add a Dapr subscribe endpoint to the application.
 * 
 * This endpoint will respond to requests on /dapr/subscribe.
 * When this endpoint is called, it will automatically find all WebAPI
 * action methods decorated with the Topic attribute and instruct
 * Dapr to create subscriptions for them. */
app.MapSubscribeHandler();

your program.cs should look as follows

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();
app.UseAuthorization();
app.UseCloudEvents();
app.MapSubscribeHandler();
app.MapControllers();
app.Run();

Add a WebAPI controller, say it as SubscriberController.cs. The code looks as below

using Dapr;
using Microsoft.AspNetCore.Mvc;

namespace Subscriber.Controllers
{
    [ApiController]
    [Route("api/[controller]")]
    public class SubscriberController : ControllerBase
    {
        ILogger<SubscriberController> logger;

        public SubscriberController(ILogger<SubscriberController> logger)
        {
            this.logger = logger;
        }

        [Topic("myapp-pubsub", "test-dapr-topic")]
        [HttpPost("subscriber")]
        public IActionResult Post([FromBody] string value)
        {
            logger.LogInformation(value);
            return Ok(value);
        }
    }
}

Testing our web api's publish subscribe

Open docker desktop
Use below command to run publisher

dapr run --app-id publisher --app-port <port used in launch settings for https> --app-protocol https --dapr-http-port 3608 --resources-path dapr-components -- dotnet run

Use below command to run subscriber

dapr run --app-id subscriber --app-port <port used in launch settings for https> --app-protocol https --dapr-http-port 3610 --resources-path dapr-components -- dotnet run

Test using postman. Hit publisher endpoint. You can see in the logs that publisher published message and subscriber received message

Source code

dapr-publisher
dapr-subscriber

DEV Community: Ashwin Gatadi

Dapr - Publish/Subscibe - Using Web APIs