Pipeline: Subscriber

The subscribers pipeline is a series of middleware components that process a GraphQL subscriber. Each middleware component in the pipeline has the opportunity to inspect, modify, or short-circuit the subscriber and response. The pipeline is defined using the SubscriberPipelineBuilder class.

Defining the Subscribers Pipeline

The subscribers pipeline is defined using the SubscriberPipelineBuilder class. The SubscriberPipelineBuilder class provides methods for adding middleware components to the pipeline. The following example shows how to define a simple subscribers pipeline:

var builder = new SubscriberPipelineBuilder();

builder.Use(next => async context =>
{
    // Middleware component 1
    Console.WriteLine("Before Middleware 1");
    await next(context);
    Console.WriteLine("After Middleware 1");
});

builder.Use(next => async context =>
{
    // Middleware component 2
    Console.WriteLine("Before Middleware 2");
    await next(context);
    Console.WriteLine("After Middleware 2");
});

var subscribersPipeline = builder.Build();

In this example, the subscribers pipeline consists of two middleware components. Each middleware component writes a message to the console before and after calling the next middleware component in the pipeline.

Using the Subscribers Pipeline

The subscribers pipeline is used to process a GraphQL subscriber. The following example shows how to use the subscribers pipeline to process a GraphQL subscriber:

var schema = new Schema();
var executor = new Executor(schema);

var request = new GraphQLRequest
{
    Query = new ExecutableDocument
    {
        Definitions = new List<IDefinition>
        {
            new OperationDefinition
            {
                Operation = OperationType.Subscription,
                SelectionSet = new SelectionSet
                {
                    Selections = new List<ISelection>
                    {
                        new FieldSelection
                        {
                            Name = new Name("messageAdded")
                        }
                    }
                }
            }
        }
    }
};

var queryContext = executor.BuildQueryContextAsync(request);
await subscribersPipeline(queryContext);

await foreach (var result in queryContext.Response)
{
    Console.WriteLine(result.Data);
}

In this example, the subscribers pipeline is used to process a GraphQL subscriber. The subscribersPipeline delegate is called with the queryContext object, which contains the GraphQL request and other context information. The queryContext.Response property contains the response stream, which is an IAsyncEnumerable<ExecutionResult>.

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