How to Return a Stream from ASP.NET Core Web API and Read it in Angular

Learn how to effectively stream data from an ASP.NET Core Web API to your Angular application using EventSource and Axios. Enhance user experience with real-time updates in your UI.
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Stream Data from ASP.NET Core Web API to Angular

In modern web applications, providing real-time updates has become a necessity, especially when performing long-running processes. This guide will guide you through the process of returning a stream from an ASP.NET Core Web API and reading that stream on the Angular side, allowing your UI to display updates in real-time.

The Problem

You have an API that facilitates backend processing and sends a response as a series of text lines. The challenge lies in:

Returning a stream of data to the client as it is generated, rather than waiting for the entire process to complete.

Updating the UI in Angular to reflect the ongoing results as they arrive.

Here’s an overview of the initial implementation:

[[See Video to Reveal this Text or Code Snippet]]

In this setup, you want the output to be streamed to the UI, so your users can see updates instantly.

The Solution

The solution involves a two-part process, covering both the ASP.NET Core API and the Angular application.

1. Modifying the ASP.NET Core Controller

Firstly, you will need to adjust your ASP.NET Core controller to use asynchronous streaming. You can do this by returning an IAsyncEnumerable<string> or a ContentResult with the media type text/event-stream.

Here's an example implementation:

[[See Video to Reveal this Text or Code Snippet]]

Key Points:

IAsyncEnumerable: This allows for asynchronous iteration over a collection.

Streaming Format: Each result sent should be formatted as data: <value>\n\n to comply with the EventSource specification.

2. Setting Up Angular to Receive the Stream

On the Angular side, you will use the EventSource API to establish a connection to the streaming endpoint. This allows your application to listen for incoming messages.

Here’s a basic implementation of an Angular service to handle the stream:

[[See Video to Reveal this Text or Code Snippet]]

Integrating the Service in Your Component

To use this service in your component, simply inject it and subscribe to the stream.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

With these implementations, you can successfully stream data from your ASP.NET Core Web API to your Angular application, ensuring a reactive and engaging user experience. Users will receive real-time updates as the backend processing continues, making your application feel more dynamic and responsive.

Feel free to adapt the example code to fit your specific application requirements and don’t hesitate to explore further to enhance your implementations!