azure-eventgrid-dotnet

# Azure.Messaging.EventGrid (.NET)

Client library for publishing events to Azure Event Grid topics, domains, and namespaces.

## Installation

```bash
# For topics and domains (push delivery)
dotnet add package Azure.Messaging.EventGrid

# For namespaces (pull delivery)
dotnet add package Azure.Messaging.EventGrid.Namespaces

# For CloudNative CloudEvents interop
dotnet add package Microsoft.Azure.Messaging.EventGrid.CloudNativeCloudEvents
```

**Current Version**: 4.28.0 (stable)

## Environment Variables

```bash
# Topic/Domain endpoint
EVENT_GRID_TOPIC_ENDPOINT=https://<topic-name>.<region>.eventgrid.azure.net/api/events
EVENT_GRID_TOPIC_KEY=<access-key>

# Namespace endpoint (for pull delivery)
EVENT_GRID_NAMESPACE_ENDPOINT=https://<namespace>.<region>.eventgrid.azure.net
EVENT_GRID_TOPIC_NAME=<topic-name>
EVENT_GRID_SUBSCRIPTION_NAME=<subscription-name>
```

## Client Hierarchy

```
Push Delivery (Topics/Domains)
└── EventGridPublisherClient
    ├── SendEventAsync(EventGridEvent)
    ├── SendEventsAsync(IEnumerable<EventGridEvent>)
    ├── SendEventAsync(CloudEvent)
    └── SendEventsAsync(IEnumerable<CloudEvent>)

Pull Delivery (Namespaces)
├── EventGridSenderClient
│   └── SendAsync(CloudEvent)
└── EventGridReceiverClient
    ├── ReceiveAsync()
    ├── AcknowledgeAsync()
    ├── ReleaseAsync()
    └── RejectAsync()
```

## Authentication

### API Key Authentication

```csharp
using Azure;
using Azure.Messaging.EventGrid;

EventGridPublisherClient client = new(
    new Uri("https://mytopic.eastus-1.eventgrid.azure.net/api/events"),
    new AzureKeyCredential("<access-key>"));
```

### Microsoft Entra ID (Recommended)

```csharp
using Azure.Identity;
using Azure.Messaging.EventGrid;

EventGridPublisherClient client = new(
    new Uri("https://mytopic.eastus-1.eventgrid.azure.net/api/events"),
    new DefaultAzureCredential());
```

### SAS Token Authentication

```csharp
string sasToken = EventGridPublisherClient.BuildSharedAccessSignature(
    new Uri(topicEndpoint),
    DateTimeOffset.UtcNow.AddHours(1),
    new AzureKeyCredential(topicKey));

var sasCredential = new AzureSasCredential(sasToken);
EventGridPublisherClient client = new(
    new Uri(topicEndpoint),
    sasCredential);
```

## Publishing Events

### EventGridEvent Schema

```csharp
EventGridPublisherClient client = new(
    new Uri(topicEndpoint),
    new AzureKeyCredential(topicKey));

// Single event
EventGridEvent egEvent = new(
    subject: "orders/12345",
    eventType: "Order.Created",
    dataVersion: "1.0",
    data: new { OrderId = "12345", Amount = 99.99 });

await client.SendEventAsync(egEvent);

// Batch of events
List<EventGridEvent> events = new()
{
    new EventGridEvent(
        subject: "orders/12345",
        eventType: "Order.Created",
        dataVersion: "1.0",
        data: new OrderData { OrderId = "12345", Amount = 99.99 }),
    new EventGridEvent(
        subject: "orders/12346",
        eventType: "Order.Created",
        dataVersion: "1.0",
        data: new OrderData { OrderId = "12346", Amount = 149.99 })
};

await client.SendEventsAsync(events);
```

### CloudEvent Schema

```csharp
CloudEvent cloudEvent = new(
    source: "/orders/system",
    type: "Order.Created",
    data: new { OrderId = "12345", Amount = 99.99 });

cloudEvent.Subject = "orders/12345";
cloudEvent.Id = Guid.NewGuid().ToString();
cloudEvent.Time = DateTimeOffset.UtcNow;

await client.SendEventAsync(cloudEvent);

// Batch of CloudEvents
List<CloudEvent> cloudEvents = new()
{
    new CloudEvent("/orders", "Order.Created", new { OrderId = "1" }),
    new CloudEvent("/orders", "Order.Updated", new { OrderId = "2" })
};

await client.SendEventsAsync(cloudEvents);
```

### Publishing to Event Grid Domain

```csharp
// Events must specify the Topic property for domain routing
List<EventGridEvent> events = new()
{
    new EventGridEvent(
        subject: "orders/12345",
        eventType: "Order.Created",
        dataVersion: "1.0",
        data: new { OrderId = "12345" })
    {
        Topic = "orders-topic"  // Domain topic name
    },
    new EventGridEvent(
        subject: "inventory/item-1",
        eventType: "Inventory.Updated",
        dataVersion: "1.0",
        data: new { ItemId = "item-1" })
    {
        Topic = "inventory-topic"
    }
};

await client.SendEventsAsync(events);
```

### Custom Serialization

```csharp
using System.Text.Json;

var serializerOptions = new JsonSerializerOptions
{
    PropertyNamingPolicy = JsonNamingPolicy.CamelCase
};

var customSerializer = new JsonObjectSerializer(serializerOptions);

EventGridEvent egEvent = new(
    subject: "orders/12345",
    eventType: "Order.Created",
    dataVersion: "1.0",
    data: customSerializer.Serialize(new OrderData { OrderId = "12345" }));

await client.SendEventAsync(egEvent);
```

## Pull Delivery (Namespaces)

### Send Events to Namespace Topic

```csharp
using Azure;
using Azure.Messaging;
using Azure.Messaging.EventGrid.Namespaces;

var senderClient = new EventGridSenderClient(
    new Uri(namespaceEndpoint),
    topicName,
    new AzureKeyCredential(topicKey));

// Send single event
CloudEvent cloudEvent = new("employee_source", "Employee.Created", 
    new { Name = "John", Age = 30 });
await senderClient.SendAsync(cloudEvent);

// Send batch
await senderClient.SendAsync(new[]
{
    new CloudEvent("source", "type", new { Name = "Alice" }),
    new CloudEvent("source", "type", new { Name = "Bob" })
});
```

### Receive and Process Events

```csharp
var receiverClient = new EventGridReceiverClient(
    new Uri(namespaceEndpoint),
    topicName,
    subscriptionName,
    new AzureKeyCredential(topicKey));

// Receive events
ReceiveResult result = await receiverClient.ReceiveAsync(maxEvents: 10);

List<string> lockTokensToAck = new();
List<string> lockTokensToRelease = new();

foreach (ReceiveDetails detail in result.Details)
{
    CloudEvent cloudEvent = detail.Event;
    string lockToken = detail.BrokerProperties.LockToken;
    
    try
    {
        // Process the event
        Console.WriteLine($"Event: {cloudEvent.Type}, Data: {cloudEvent.Data}");
        lockTokensToAck.Add(lockToken);
    }
    catch (Exception)
    {
        // Release for retry
        lockTokensToRelease.Add(lockToken);
    }
}

// Acknowledge successfully processed events
if (lockTokensToAck.Any())
{
    await receiverClient.AcknowledgeAsync(lockTokensToAck);
}

// Release events for retry
if (lockTokensToRelease.Any())
{
    await receiverClient.ReleaseAsync(lockTokensToRelease);
}
```

### Reject Events (Dead Letter)

```csharp
// Reject events that cannot be processed
await receiverClient.RejectAsync(new[] { lockToken });
```

## Consuming Events (Azure Functions)

### EventGridEvent Trigger

```csharp
using Azure.Messaging.EventGrid;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.EventGrid;

public static class EventGridFunction
{
    [FunctionName("ProcessEventGridEvent")]
    public static void Run(
        [EventGridTrigger] EventGridEvent eventGridEvent,
        ILogger log)
    {
        log.LogInformation($"Event Type: {eventGridEvent.EventType}");
        log.LogInformation($"Subject: {eventGridEvent.Subject}");
        log.LogInformation($"Data: {eventGridEvent.Data}");
    }
}
```

### CloudEvent Trigger

```csharp
using Azure.Messaging;
using Microsoft.Azure.Functions.Worker;

public class CloudEventFunction
{
    [Function("ProcessCloudEvent")]
    public void Run(
        [EventGridTrigger] CloudEvent cloudEvent,
        FunctionContext context)
    {
        var logger = context.GetLogger("ProcessCloudEvent");
        logger.LogInformation($"Event Type: {cloudEvent.Type}");
        logger.LogInformation($"Source: {cloudEvent.Source}");
        logger.LogInformation($"Data: {cloudEvent.Data}");
    }
}
```

## Parsing Events

### Parse EventGridEvent

```csharp
// From JSON string
string json = "..."; // Event Grid webhook payload
EventGridEvent[] events = EventGridEvent.ParseMany(BinaryData.FromString(json));

foreach (EventGridEvent egEvent in events)
{
    if (egEvent.TryGetSystemEventData(out object systemEvent))
    {
        // Handle system event
        switch (systemEvent)
        {
            case StorageBlobCreatedEventData blobCreated:
                Console.WriteLine($"Blob created: {blobCreated.Url}");
                break;
        }
    }
    else
    {
        // Handle custom event
        var customData = egEvent.Data.ToObjectFromJson<MyCustomData>();
    }
}
```

### Parse CloudEvent

```csharp
CloudEvent[] cloudEvents = CloudEvent.ParseMany(BinaryData.FromString(json));

foreach (CloudEvent cloudEvent in cloudEvents)
{
    var data = cloudEvent.Data.ToObjectFromJson<MyEventData>();
    Console.WriteLine($"Type: {cloudEvent.Type}, Data: {data}");
}
```

## System Events

```csharp
// Common system event types
using Azure.Messaging.EventGrid.SystemEvents;

// Storage events
StorageBlobCreatedEventData blobCreated;
StorageBlobDeletedEventData blobDeleted;

// Resource events
ResourceWriteSuccessEventData resourceCreated;
ResourceDeleteSuccessEventData resourceDeleted;

// App Service events
WebAppUpdatedEventData webAppUpdated;

// Container Registry events
ContainerRegistryImagePushedEventData imagePushed;

// IoT Hub events
IotHubDeviceCreatedEventData deviceCreated;
```

## Key Types Reference

| Type | Purpose |
|------|---------|
| `EventGridPublisherClient` | Publish to topics/domains |
| `EventGridSenderClient` | Send to namespace topics |
| `EventGridReceiverClient` | Receive from namespace subscriptions |
| `EventGridEvent` | Event Grid native schema |
| `CloudEvent` | CloudEvents 1.0 schema |
| `ReceiveResult` | Pull delivery response |
| `ReceiveDetails` | Event with broker properties |
| `BrokerProperties` | Lock token, delivery count |

## Event Schemas Comparison

| Feature | EventGridEvent | CloudEvent |
|---------|----------------|------------|
| Standard | Azure-specific | CNCF standard |
| Required fields | subject, eventType, dataVersion, data | source, type |
| Extensibility | Limited | Extension attributes |
| Interoperability | Azure only | Cross-platform |

## Best Practices

1. **Use CloudEvents** — Prefer CloudEvents for new implementations (industry standard)
2. **Batch events** — Send multiple events in one call for efficiency
3. **Use Entra ID** — Prefer managed identity over access keys
4. **Idempotent handlers** — Events may be delivered more than once
5. **Set event TTL** — Configure time-to-live for namespace events
6. **Handle partial failures** — Acknowledge/release events individually
7. **Use dead-letter** — Configure dead-letter for failed events
8. **Validate schemas** — Validate event data before processing

## Error Handling

```csharp
using Azure;

try
{
    await client.SendEventAsync(cloudEvent);
}
catch (RequestFailedException ex) when (ex.Status == 401)
{
    Console.WriteLine("Authentication failed - check credentials");
}
catch (RequestFailedException ex) when (ex.Status == 403)
{
    Console.WriteLine("Authorization failed - check RBAC permissions");
}
catch (RequestFailedException ex) when (ex.Status == 413)
{
    Console.WriteLine("Payload too large - max 1MB per event, 1MB total batch");
}
catch (RequestFailedException ex)
{
    Console.WriteLine($"Event Grid error: {ex.Status} - {ex.Message}");
}
```

## Failover Pattern

```csharp
try
{
    var primaryClient = new EventGridPublisherClient(primaryUri, primaryKey);
    await primaryClient.SendEventsAsync(events);
}
catch (RequestFailedException)
{
    // Failover to secondary region
    var secondaryClient = new EventGridPublisherClient(secondaryUri, secondaryKey);
    await secondaryClient.SendEventsAsync(events);
}
```

## Related SDKs

| SDK | Purpose | Install |
|-----|---------|---------|
| `Azure.Messaging.EventGrid` | Topics/Domains (this SDK) | `dotnet add package Azure.Messaging.EventGrid` |
| `Azure.Messaging.EventGrid.Namespaces` | Pull delivery | `dotnet add package Azure.Messaging.EventGrid.Namespaces` |
| `Azure.Identity` | Authentication | `dotnet add package Azure.Identity` |
| `Microsoft.Azure.WebJobs.Extensions.EventGrid` | Azure Functions trigger | `dotnet add package Microsoft.Azure.WebJobs.Extensions.EventGrid` |

## Reference Links

| Resource | URL |
|----------|-----|
| NuGet Package | https://www.nuget.org/packages/Azure.Messaging.EventGrid |
| API Reference | https://learn.microsoft.com/dotnet/api/azure.messaging.eventgrid |
| Quickstart | https://learn.microsoft.com/azure/event-grid/custom-event-quickstart |
| Pull Delivery | https://learn.microsoft.com/azure/event-grid/pull-delivery-overview |
| GitHub Source | https://github.com/Azure/azure-sdk-for-net/tree/main/sdk/eventgrid/Azure.Messaging.EventGrid |