Скачать или смотреть Resolving Blazor HTTP Requests to WebApi: Tackling CORS Issues

An in-depth guide on how to resolve HTTP request failures from Blazor to WebApi due to CORS issues, enabling seamless integration and API communication.
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This video is based on the question https://stackoverflow.com/q/63356245/ asked by the user 'mz1378' ( https://stackoverflow.com/u/737453/ ) and on the answer https://stackoverflow.com/a/63382578/ provided by the user 'mz1378' ( https://stackoverflow.com/u/737453/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving Blazor HTTP Requests to WebApi: Tackling CORS Issues

In developing web applications with Blazor and WebApi, you might encounter a perplexing issue: your Blazor client does not seem to send HTTP requests to your WebApi project even when they are properly set up. This can be quite frustrating, especially when everything appears to be in order. In this guide, we will dissect the problem of Blazor failing to communicate with WebApi and provide a clear solution to ensure smooth API integration.

Understanding the Problem

You've created a robust solution that includes a Blazor WebAssembly project, class libraries, and a WebApi project. Each component is set to run on different ports due to the restrictions of the development environment. However, even though you can access your API endpoints directly through tools like Postman, your Blazor application fails to send requests to these endpoints.

This situation often arises from a common security feature in web applications called Cross-Origin Resource Sharing (CORS). CORS is a protocol that allows secure cross-origin requests and data sharing between web pages and servers.

Scenario Breakdown

In your setup:

Your WebApi runs successfully at http://localhost:36855/.

Your Blazor application is configured correctly but cannot connect to the WebApi.

You have implemented the HTTP client to handle requests.

Key Snippet

You have a method handling login submissions in Blazor, as shown below:

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

Diagnosing the Issue

Upon investigation (using the browser's developer tools), you discovered that CORS was the root of the problem. Without proper CORS configuration, browsers block requests sent from one origin (your Blazor app) to another (your WebApi), leading to failures in HTTP calls.

Solution: Enabling CORS in WebApi

To resolve your issue and enable your Blazor application to successfully communicate with your WebApi, follow these steps to configure CORS.

Step 1: Open Your WebApi Project

Locate the Startup.cs file in your WebApi project, where you can define middleware and services for your application.

Step 2: Add CORS Services

In the ConfigureServices method, add the CORS services. Add the following line:

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

Step 3: Configure CORS Policy

Next, in the Configure method, set up the CORS policy to allow requests:

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

This setup allows any origin to access your WebApi calls, which is essential for development purposes. However, keep in mind that in a production environment, you should restrict the origins to only those you trust.

Step 4: Restart Your WebApi Project

Once you’ve made these changes, ensure to rebuild and restart your WebApi project for the modifications to take effect.

Conclusion

By enabling CORS in your WebApi configuration, you've effectively resolved the communication barrier between your Blazor application and the API project. This solution not only fixes the immediate problem of request failures but also enhances your understanding of API security practices.

As you continue to develop your Blazor applications, always pay attention to CORS settings, as they can often be the source of connectivity issues between different components of your app. If you encounter other challenges, don't hesitate to dive into browser developer tools - they can provide valuable insights into what might be going wrong.

With this solution implemented, you can confidently build powerful and interactive applications using Blazor and WebApi. Happy coding!