DaprPublishSubscribeClient usage

Essential tips and advice for using DaprPublishSubscribeClient

Lifetime management

A DaprPublishSubscribeClient is a version of the Dapr client that is dedicated to interacting with the Dapr Messaging API. It can be registered alongside a DaprClient and other Dapr clients without issue.

It maintains access to networking resources in the form of TCP sockets used to communicate with the Dapr sidecar and implements IAsyncDisposable to support the eager cleanup of resources.

For best performance, create a single long-lived instance of DaprPublishSubscribeClient and provide access to that shared instance throughout your application. DaprPublishSubscribeClient instances are thread-safe and intended to be shared.

This can be aided by utilizing the dependency injection functionality. The registration method supports registration using as a singleton, a scoped instance or as transient (meaning it’s recreated every time it’s injected), but also enables registration to utilize values from an IConfiguration or other injected service in a way that’s impractical when creating the client from scratch in each of your classes.

Avoid creating a DaprPublishSubscribeClient for each operation and disposing it when the operation is complete. It’s intended that the DaprPublishSubscribeClient should only be disposed when you no longer wish to receive events on the subscription as disposing it will cancel the ongoing receipt of new events.

Configuring DaprPublishSubscribeClient via the DaprPublishSubscribeClientBuilder

A DaprPublishSubscribeClient can be configured by invoking methods on the DaprPublishSubscribeClientBuilder class before calling .Build() to create the client itself. The settings for each DaprPublishSubscribeClient are separate and cannot be changed after calling .Build().

var daprPubsubClient = new DaprPublishSubscribeClientBuilder()
    .UseDaprApiToken("abc123") // Specify the API token used to authenticate to other Dapr sidecars
    .Build();

The DaprPublishSubscribeClientBuilder contains settings for:

  • The HTTP endpoint of the Dapr sidecar
  • The gRPC endpoint of the Dapr sidecar
  • The JsonSerializerOptions object used to configure JSON serialization
  • The GrpcChannelOptions object used to configure gRPC
  • The API token used to authenticate requests to the sidecar
  • The factory method used to create the HttpClient instance used by the SDK
  • The timeout used for the HttpClient instance when making requests to the sidecar

The SDK will read the following environment variables to configure the default values:

  • DAPR_HTTP_ENDPOINT: used to find the HTTP endpoint of the Dapr sidecar, example: https://dapr-api.mycompany.com
  • DAPR_GRPC_ENDPOINT: used to find the gRPC endpoint of the Dapr sidecar, example: https://dapr-grpc-api.mycompany.com
  • DAPR_HTTP_PORT: if DAPR_HTTP_ENDPOINT is not set, this is used to find the HTTP local endpoint of the Dapr sidecar
  • DAPR_GRPC_PORT: if DAPR_GRPC_ENDPOINT is not set, this is used to find the gRPC local endpoint of the Dapr sidecar
  • DAPR_API_TOKEN: used to set the API token

Configuring gRPC channel options

Dapr’s use of CancellationToken for cancellation relies on the configuration of the gRPC channel options. If you need to configure these options yourself, make sure to enable the ThrowOperationCanceledOnCancellation setting.

var daprPubsubClient = new DaprPublishSubscribeClientBuilder()
    .UseGrpcChannelOptions(new GrpcChannelOptions { ... ThrowOperationCanceledOnCancellation = true })
    .Build();

Using cancellation with DaprPublishSubscribeClient

The APIs on DaprPublishSubscribeClient perform asynchronous operations and accept an optional CancellationToken parameter. This follows a standard .NET practice for cancellable operations. Note that when cancellation occurs, there is no guarantee that the remote endpoint stops processing the request, only that the client has stopped waiting for completion.

When an operation is cancelled, it will throw an OperationCancelledException.

Configuring DaprPublishSubscribeClient via dependency injection

Using the built-in extension methods for registering the DaprPublishSubscribeClient in a dependency injection container can provide the benefit of registering the long-lived service a single time, centralize complex configuration and improve performance by ensuring similarly long-lived resources are re-purposed when possible (e.g. HttpClient instances).

There are three overloads available to give the developer the greatest flexibility in configuring the client for their scenario. Each of these will register the IHttpClientFactory on your behalf if not already registered, and configure the DaprPublishSubscribeClientBuilder to use it when creating the HttpClient instance in order to re-use the same instance as much as possible and avoid socket exhaustion and other issues.

In the first approach, there’s no configuration done by the developer and the DaprPublishSubscribeClient is configured with the default settings.

var builder = WebApplication.CreateBuilder(args);

builder.Services.DaprPublishSubscribeClient(); //Registers the `DaprPublishSubscribeClient` to be injected as needed
var app = builder.Build();

Sometimes the developer will need to configure the created client using the various configuration options detailed above. This is done through an overload that passes in the DaprJobsClientBuiler and exposes methods for configuring the necessary options.

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddDaprJobsClient((_, daprPubSubClientBuilder) => {
   //Set the API token
   daprPubSubClientBuilder.UseDaprApiToken("abc123");
   //Specify a non-standard HTTP endpoint
   daprPubSubClientBuilder.UseHttpEndpoint("http://dapr.my-company.com");
});

var app = builder.Build();

Finally, it’s possible that the developer may need to retrieve information from another service in order to populate these configuration values. That value may be provided from a DaprClient instance, a vendor-specific SDK or some local service, but as long as it’s also registered in DI, it can be injected into this configuration operation via the last overload:

var builder = WebApplication.CreateBuilder(args);

//Register a fictional service that retrieves secrets from somewhere
builder.Services.AddSingleton<SecretService>();

builder.Services.AddDaprPublishSubscribeClient((serviceProvider, daprPubSubClientBuilder) => {
    //Retrieve an instance of the `SecretService` from the service provider
    var secretService = serviceProvider.GetRequiredService<SecretService>();
    var daprApiToken = secretService.GetSecret("DaprApiToken").Value;

    //Configure the `DaprPublishSubscribeClientBuilder`
    daprPubSubClientBuilder.UseDaprApiToken(daprApiToken);
});

var app = builder.Build();