seankearney/sdk-csharp

CSharp SDK for CloudEvents

Status

This SDK current supports the following versions of CloudEvents:

• v1.0

sdk-csharp

.NET Standard 2.0 (C#) SDK for CloudEvents

The CloudNative.CloudEvents package provides utility methods and classes for creating, encoding, decoding, sending, and receiving CNCF CloudEvents.

A few gotchas highlighted for the impatient who don't usually read docs

1. The CloudEvent class is not meant to be used with object serializers like JSON.NET and does not have a default constructor to underline this. If you need to serialize or deserialize a CloudEvent directly, always use an ICloudEventFormatter like the JsonEventFormatter.
2. The transport integration is provided in the form of extensions and the objective of those extensions is to map the CloudEvent to and from the respective protocol message, like an HTTP request or response object, but the application is otherwise fully in control of the client. Therefore, the extensions do not add security headers or credentials or any other headers or properties that may be required to interact with a particular product or service. Adding this information is up to the application.

CloudEvent

The CloudEvent class reflects the event envelope defined by the CNCF CloudEvents 1.0 specification. It supports version 1.0 of CloudEvents by default. It can also handle the pre-release versions 0.1, 0.2, and 0.3 of the CloudEvents specification.

The strongly typed API reflects the 1.0 standard.

If required for compatibility with code that leans on one of the prerelease specifications, you can override the specification version explicitly: new CloudEvent(CloudEventsSpecVersion.V0_1). The SpecVersion property also allows the version to be switched, meaning you can receive a 0.1 event, switch the version number, and forward it as a 1.0 event, with all required mappings done for you.

1.0	Property name	CLR type
id	CloudEvent.Id	System.String
type	CloudEvent.Type	System.String
specversion	CloudEvent.SpecVersion	System.String
time	CloudEvent.Time	System.DateTime
source	CloudEvent.Source	System.Uri
subject	CloudEvent.Subject	System.String
dataschema	CloudEvent.DataSchema	System.Uri
datacontenttype	CloudEvent.ContentType	System.Net.Mime.ContentType
data	CloudEvent.Data	System.Object

The CloudEvent.Data property is object typed, and may hold any valid serializable CLR type. The following types have special handling:

• System.String: In binary content mode, strings are copied into the transport message payload body using UTF-8 encoding.
• System.Byte[]: In binary content mode, byte array content is copied into the message paylaod body without further transformation.
• System.Stream: In binary content mode, stream content is copied into the message paylaod body without further transformation.

Any other data type is transformed using the given event formatter for the operation or the JSON formatter by default before being added to the transport payload body.

All extension attributes can be reached via the CloudEvent.GetAttributes() method, which returns the internal attribute collection. The internal collection performs all required validations.

Extensions

CloudEvent extensions are represented by implementations of the ICloudEventExtension interface. The SDK includes strongly-typed implementations for all offical CloudEvents extensions:

• DistributedTracingExtension for distributed tracing
• SampledRateExtension for sampled rate
• SequenceExtension for sequence

Extension classes provide type-safe access to the extension attributes as well as implement the required validations and type mappings. An extension object is always created as an independent entity and is then attached to a CloudEvent instance. Once attached, the extension object's attributes are merged into the CloudEvent instance.

This snippet shows how to create a CloudEvent with an extension:

 var cloudEvent = new CloudEvent(
    "com.github.pull.create",
    new Uri("https://github.com/cloudevents/spec/pull/123"),
    new DistributedTracingExtension()
    {
        TraceParent = "value",
        TraceState = "value"
    })
{
    ContentType = new ContentType("application/json"),
    Data = "[]"
};

The extension can later be accessed via the Extension<T>() method:

 var s = cloudEvent.Extension<DistributedTracingExtension>().TraceParent

All APIs where a CloudEvent is constructed from an incoming event (or request or response) allow for extension instances to be added via their respective methods, and the extensions are invoked in the mapping process (for instance, to extract information from headers that deviate from the CloudEvents default mapping).

For example, the server-side mapping for HttpRequestMessage allows adding extensions like this:

public async Task<HttpResponseMessage> Run( HttpRequestMessage req, ILogger log)
{
    var cloudEvent = req.ToCloudEvent(new DistributedTracingExtension());
}

Transport Bindings

This SDK helps with mapping CloudEvents to and from messages or transport frames of popular .NET clients in such a way as to be agnostic of your application's choices of how you want to send an event (be it via HTTP PUT or POST) or how you want to handle settlement of transfers in AMQP or MQTT. The transport binding classes and extensions therefore don't wrap the send and receive operations; you still use the native API of the respective library.

HTTP - System.Net.Http.HttpClient

The .NET HttpClient uses the HttpContent abstraction to wrap payloads for sending requests that carry entity bodies.

This SDK provides a [CloudEventContent] class derived from HttpContent that can be created from a CloudEvent instance, the desired ContentMode, and an event formatter.

var cloudEvent = new CloudEvent("com.example.myevent", new Uri("urn:example-com:mysource"))
{
    ContentType = new ContentType(MediaTypeNames.Application.Json),
    Data = JsonConvert.SerializeObject("hey there!")
};

var content = new CloudEventContent( cloudEvent,
                                     ContentMode.Structured,
                                     new JsonEventFormatter());

var httpClient = new HttpClient();
var result = (await httpClient.PostAsync(this.Url, content));

For responses, HttpClient puts all custom headers onto the HttpResponseMessage rather than on the carried HttpContent instance. Therefore, if an event is retrieved with HttpClient (for instance, from a queue-like structure) the CloudEvent is created from the response message object rather than the content object using the ToCloudEvent() extension method on HttpResponseMessage:

var httpClient = new HttpClient();
// delete and receive message from top of the queue
var result = await httpClient.DeleteAsync(new Uri("https://example.com/queue/messages/top"));
if (HttpStatusCode.OK == result.StatusCode) {
   var receivedCloudEvent = await result.ToCloudEvent();
}

HTTP - System.Net.HttpWebRequest

If your application uses the HttpWebRequest client, you can copy a CloudEvent into the request payload in structured or binary mode:

HttpWebRequest httpWebRequest = WebRequest.CreateHttp("https://example.com/target");
httpWebRequest.Method = "POST";
await httpWebRequest.CopyFromAsync(cloudEvent, ContentMode.Structured, new JsonEventFormatter());

Bear in mind that the Method property must be set to an HTTP method that allows an entity body to be sent, otherwise the copy operation will fail.

HTTP - System.Net.HttpListener (HttpRequestMessage)

On the server-side, you can extract a CloudEvent from the server-side HttpRequestMessage with the ToCloudEventAsync() extension. If your code handles HttpRequestContext, you will use the Request property:

var cloudEvent = await context.Request.ToCloudEventAsync();

If you use a functions framework that lets you handle HttpResponseMessage and return HttpResponseMessage, you will call the extension on the request object directly:

public async Task<HttpResponseMessage> Run( HttpRequestMessage req, ILogger log)
{
    var cloudEvent = await req.ToCloudEventAsync();
}

The extension implementation will read the ContentType header of the incoming request and automatically select the correct built-in event format decoder. Your code can always pass an overriding format decoder instance as the first argument if needed.

If your HTTP handler needs to return a CloudEvent, you copy the CloudEvent into the response with the CopyFromAsync() extension method:

var cloudEvent = new CloudEvent("com.example.myevent", new Uri("urn:example-com:mysource"))
{
    ContentType = new ContentType(MediaTypeNames.Application.Json),
    Data = JsonConvert.SerializeObject("hey there!")
};

await context.Response.CopyFromAsync(cloudEvent,
                                     ContentMode.Structured,
                                     new JsonEventFormatter());
context.Response.StatusCode = (int)HttpStatusCode.OK;

HTTP - Microsoft.AspNetCore.Http.HttpRequest

On the server-side, you can extract a CloudEvent from the server-side HttpRequest with the ReadCloudEventAsync() extension.

var cloudEvent = await HttpContext.Request.ReadCloudEventAsync();

HTTP - ASP.NET Core MVC

If you would like to deserialize CloudEvents in actions directly, you can register the CloudEventJsonInputFormatter in the MVC options:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc(opts =>
    {
        opts.InputFormatters.Insert(0, new CloudEventJsonInputFormatter());
    });
}

This formatter will only intercept parameters where CloudEvent is the expected type.

You can then receive CloudEvent objects in controller actions:

[HttpPost("resource")]
public IActionResult ReceiveCloudEvent([FromBody] CloudEvent cloudEvent)
{
    return Ok();
}

AMQP

The SDK provides extensions for the AMQPNetLite package.

For AMQP support, you must reference the CloudNative.CloudEvents.Amqp assembly and reference the namespace in your code with using CloudNative.CloudEvents.Amqp.

The AmqpCloudEventMessage extends the AMQPNetLite.Message class. The constructor allows creating a new AMQP message that holds a CloudEvent in either structured or binary content mode.

var cloudEvent = new CloudEvent("com.example.myevent", new Uri("urn:example-com:mysource"))
{
    ContentType = new ContentType(MediaTypeNames.Application.Json),
    Data = JsonConvert.SerializeObject("hey there!")
};

var message = new AmqpCloudEventMessage( cloudEvent,
                                         ContentMode.Structured,
                                         new JsonEventFormatter());

For mapping a received Message to a CloudEvent, you can use the ToCloudEvent() method:

   var receivedCloudEvent = await message.ToCloudEvent();

MQTT

The SDK provides extensions for the MQTTnet package. For MQTT support, you must reference the CloudNative.CloudEvents.Mqtt assembly and reference the namespace in your code with using CloudNative.CloudEvents.Mqtt.

The MqttCloudEventMessage extends the MqttApplicationMessage class. The constructor allows creating a new MQTT message that holds a CloudEvent in structured content mode.

var cloudEvent = new CloudEvent("com.example.myevent", new Uri("urn:example-com:mysource"))
{
    ContentType = new ContentType(MediaTypeNames.Application.Json),
    Data = JsonConvert.SerializeObject("hey there!")
};

var message = new MqttCloudEventMessage( cloudEvent,
                                         new JsonEventFormatter());

For mapping a received MqttApplicationMessage to a CloudEvent, you can use the ToCloudEvent() method:

   var receivedCloudEvent = await message.ToCloudEvent();

Community

• There are bi-weekly calls immediately following the Serverless/CloudEvents call at 9am PT (US Pacific). Which means they will typically start at 10am PT, but if the other call ends early then the SDK call will start early as well. See the CloudEvents meeting minutes to determine which week will have the call.
• Slack: #cloudeventssdk channel under CNCF's Slack workspace.
• Contact for additional information: Clemens Vasters (@Clemens Vasters on slack).