DNV.Dapr.PubSub 2.1.0-preview.1756358515

DNV.Dapr.PubSub

A comprehensive Dapr Pub/Sub client library that provides simplified APIs for publishing messages to topics with full HttpClient injection support, factory pattern, and bulk publishing capabilities.

Overview

This library provides two main components:

• DNV.Dapr.PubSub.Abstractions: Core abstractions and interfaces
• DNV.Dapr.PubSub: Default implementation with HttpClient injection support

Why This Implementation?

The main purpose of this DaprPubSubClient implementation is to enable HttpClient injection for Pub/Sub operations, which the official Dapr SDK does not natively support. This is crucial for:

• HttpClient Lifecycle Management: Proper disposal and connection pooling through DI container
• Custom HttpClient Configuration: Timeouts, headers, handlers, and other HTTP-specific settings for pub/sub operations
• Testing: Easy mocking and testing with injected HttpClient instances
• Observability: Integration with logging, tracing, and monitoring through HttpClient handlers
• Corporate Policies: Meeting enterprise requirements for HTTP client management and security
• Named Client Support: Multiple pub/sub configurations for different scenarios

Key Features

• Injectable HttpClient: Full control over HttpClient configuration and lifecycle for pub/sub operations
• Named Client Support: Create multiple pub/sub clients with different configurations
• Factory Pattern: IDaprPubSubClientFactory for flexible client creation and management
• Configuration Binding: Support for IConfiguration integration with strongly-typed options
• Default Topic Support: Configure default topics for simplified publishing
• Metadata Support: Attach custom metadata to published messages
• Bulk Publishing: Efficient bulk message publishing with BulkPublishAsync
• Async/Await Support: Full asynchronous operation support throughout
• Exception Handling: Leverages underlying DaprHttpClient exception handling
• URL Encoding: Proper encoding of pub/sub component names and topic names
• Query String Building: Metadata support via query string parameters

Architecture

Core Components

• DaprPubSubClient (Abstract): Base class defining the pub/sub client contract
• DefaultDaprPubSubClient: Concrete implementation using HttpClient for Dapr REST API calls
• IDaprPubSubClientFactory: Factory interface for creating named clients
• DefaultDaprPubSubClientFactory: Default factory implementation
• DaprPubSubOptions: Configuration options for pub/sub clients
• BulkPublishRequestEntry: Model for bulk publishing operations

Installation

# Core abstractions
dotnet add package DNV.Dapr.PubSub.Abstractions

# Full implementation with HttpClient injection
dotnet add package DNV.Dapr.PubSub

Getting Started

Basic Setup with Dependency Injection

Configure named Dapr PubSub clients with HttpClient injection:

using DNV.Dapr.PubSub;
using Microsoft.Extensions.DependencyInjection;

var services = new ServiceCollection();

// Register named Dapr PubSub client
services.AddDaprPubSubClient(
    "orderEvents", 
    o =>
    {
		o.HttpPort = 3501;
        o.PubSubName = "order-pubsub";
        o.TopicName = "order-events";
    }
);

var serviceProvider = services.BuildServiceProvider();
var factory = serviceProvider.GetRequiredService<IDaprPubSubClientFactory>();
var pubsubClient = factory.CreateClient("orderEvents");

Configuration with IConfiguration

// appsettings.json
{
  "PubSubClients": {
    "OrderEvents": {
      "PubSubName": "order-pubsub",
      "TopicName": "order-events"
    },
    "UserNotifications": {
      "PubSubName": "notification-pubsub",
      "TopicName": "user-notifications"
    }
  }
}

// Bind configuration sections
services.AddDaprPubSubClient(
    "OrderEvents",
    configuration.GetSection("PubSubClients:OrderEvents")
);

services.AddDaprPubSubClient(
    "UserNotifications", 
    configuration.GetSection("PubSubClients:UserNotifications")
);

Core API Methods

The DaprPubSubClient abstract class provides four main methods:

Single Message Publishing

// Publish to default topic
Task PublishAsync(object message, IDictionary<string, string>? metadata = null, CancellationToken ct = default)

// Publish to specific topic  
Task PublishAsync(object message, string topicName, IDictionary<string, string>? metadata = null, CancellationToken ct = default)

Bulk Message Publishing

// Bulk publish to default topic
Task BulkPublishAsync(IEnumerable<object> messages, IDictionary<string, string>? metadata = null, CancellationToken ct = default)

// Bulk publish to specific topic
Task BulkPublishAsync(IEnumerable<object> messages, string topicName, IDictionary<string, string>? metadata = null, CancellationToken ct = default)

Usage Examples

Basic Message Publishing

Publish to Default Topic

var orderEvent = new OrderCreatedEvent
{
    OrderId = "ORD-001",
    CustomerId = "CUST-123",
    Amount = 99.99m,
    CreatedAt = DateTime.UtcNow
};

// Publish single message to default topic
await pubsubClient.PublishAsync(orderEvent);

Publish to Specific Topic

// Override default topic
var userEvent = new UserRegisteredEvent
{
    UserId = "USER-456",
    Email = "user@example.com",
    RegistrationDate = DateTime.UtcNow
};

await pubsubClient.PublishAsync(userEvent, "user-events");

Bulk Publishing

Efficiently publish multiple messages in a single operation:

var orderEvents = new OrderCreatedEvent[]
{
    new() { OrderId = "ORD-001", CustomerId = "CUST-123" },
    new() { OrderId = "ORD-002", CustomerId = "CUST-456" },
    new() { OrderId = "ORD-003", CustomerId = "CUST-789" }
};

// Bulk publish to default topic
await pubsubClient.BulkPublishAsync(orderEvents);

// Bulk publish to specific topic
await pubsubClient.BulkPublishAsync(orderEvents, "order-events");

Publishing with Metadata

Add custom metadata to messages:

var metadata = new Dictionary<string, string>
{
    ["source"] = "order-service",
    ["version"] = "1.0",
    ["correlation-id"] = Guid.NewGuid().ToString(),
    ["trace-id"] = Activity.Current?.Id ?? "unknown"
};

var orderEvent = new OrderUpdatedEvent
{
    OrderId = "ORD-001",
    Status = "Shipped",
    UpdatedAt = DateTime.UtcNow
};

await pubsubClient.PublishAsync(orderEvent, metadata);

Multiple Named Clients

Configure and use multiple pub/sub clients for different business domains:

// Configure multiple clients
services.AddDaprPubSubClient("orders", options =>
{
    options.PubSubName = "order-pubsub";
    options.TopicName = "order-events";
});

services.AddDaprPubSubClient("notifications", options =>
{
    options.PubSubName = "notification-pubsub";
    options.TopicName = "email-notifications";
});

// Use in application
public class OrderService
{
    private readonly DaprPubSubClient _orderClient;
    private readonly DaprPubSubClient _notificationClient;

    public OrderService(IDaprPubSubClientFactory factory)
    {
        _orderClient = factory.CreateClient("orders");
        _notificationClient = factory.CreateClient("notifications");
    }

    public async Task ProcessOrderAsync(Order order)
    {
        // Publish order event
        await _orderClient.PublishAsync(new OrderCreatedEvent { OrderId = order.Id });
        
        // Publish notification
        await _notificationClient.PublishAsync(new EmailNotification 
        { 
            To = order.CustomerEmail, 
            Subject = "Order Confirmation" 
        });
    }
}

Advanced Configuration

HttpClient Customization

The key benefit of this implementation is full HttpClient control:

services.AddDaprPubSubClient("monitored", options =>
{
    options.PubSubName = "events";
    options.TopicName = "system-events";
});

// Configure the underlying HttpClient
services.ConfigureHttpClientDefaults(builder =>
{
    builder.AddStandardResilienceHandler(); // Polly integration
    builder.ConfigureHttpClient(client =>
    {
        client.Timeout = TimeSpan.FromSeconds(60);
        client.DefaultRequestHeaders.Add("X-Publisher", "MyService");
    });
});

Custom HttpClient Handlers

Add middleware-style handlers for cross-cutting concerns:

public class PublishingMetricsHandler : DelegatingHandler
{
    private readonly IMetrics _metrics;

    public PublishingMetricsHandler(IMetrics metrics)
    {
        _metrics = metrics;
    }

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        using var timer = _metrics.Measure.Timer.Time("pubsub.publish.duration");
        
        try
        {
            var response = await base.SendAsync(request, cancellationToken);
            _metrics.Measure.Counter.Increment("pubsub.publish.success");
            return response;
        }
        catch
        {
            _metrics.Measure.Counter.Increment("pubsub.publish.error");
            throw;
        }
    }
}

// Register the handler
services.AddHttpClient("monitored")
    .AddHttpMessageHandler<PublishingMetricsHandler>();

Cancellation Token Support

All methods support cancellation tokens for proper async operation control:

var cts = new CancellationTokenSource(TimeSpan.FromSeconds(10));

try
{
    await pubsubClient.PublishAsync(
        criticalEvent,
        "important-events", 
        metadata: null,
        ct: cts.Token
    );
}
catch (OperationCanceledException)
{
    Console.WriteLine("Publish operation was cancelled due to timeout");
}

Configuration Model

DaprPubSubOptions

public class DaprPubSubOptions : DaprHttpClientOptions
{
    /// <summary>
    /// Name of the Dapr pub/sub component (required).
    /// Must match the component name in your Dapr configuration.
    /// </summary>
    public string? PubSubName { get; set; }

    /// <summary>
    /// Default topic name for publishing (optional).
    /// Can be overridden in individual publish calls.
    /// </summary>
    public string? TopicName { get; set; }
}

Configuration Examples

Environment-based configuration:

{
  "PubSubClients": {
    "Orders": {
      "PubSubName": "redis-pubsub",
      "TopicName": "order-events"
    }
  }
}

Multiple environments:

{
  "Development": {
    "PubSubClients": {
      "Orders": {
        "PubSubName": "memory-pubsub",
        "TopicName": "dev-order-events"
      }
    }
  },
  "Production": {
    "PubSubClients": {
      "Orders": {
        "PubSubName": "azure-servicebus",
        "TopicName": "prod-order-events"
      }
    }
  }
}

Testing

Unit Testing with Mock HttpClient

[Test]
public async Task PublishAsync_WithValidMessage_PublishesSuccessfully()
{
    // Arrange
    var mockHandler = new MockHttpMessageHandler();
    mockHandler
        .When("POST", "http://localhost:3500/v1.0/publish/test-pubsub/test-topic")
        .Respond(HttpStatusCode.NoContent);

    var httpClient = new HttpClient(mockHandler)
    {
        BaseAddress = new Uri("http://localhost:3500")
    };

    var options = new DaprPubSubOptions
    {
        PubSubName = "test-pubsub",
        TopicName = "test-topic"
    };

    var client = new DefaultDaprPubSubClient(httpClient, options);
    var testEvent = new { Message = "Test Event", Timestamp = DateTime.UtcNow };

    // Act
    await client.PublishAsync(testEvent);

    // Assert
    mockHandler.VerifyNoOutstandingExpectation();
}

Troubleshooting

Common Issues

1. "PubSub component not found"

   • Verify PubSubName matches your Dapr component configuration
   • Check Dapr sidecar logs for component loading errors

2. "Topic not found"

   • Some pub/sub backends require manual topic creation
   • Check if your pub/sub component supports auto-topic creation

3. Message size limits

   • Redis: ~512MB default
   • Azure Service Bus: 1MB (Standard), 100MB (Premium)
   • Consider message compression for large payloads

4. Serialization issues

   • Ensure your event models are JSON serializable
   • Check for circular references in object graphs

5. Network timeouts

   • Increase HttpClient timeout for large messages
   • Implement retry policies for transient failures