Скачать или смотреть Resolving the Issue of Angular 7 POST Method Being Called Twice on 400 Bad Request

Discover why your `Angular 7` POST requests are being duplicated on errors and learn effective solutions to fix it!
---
This video is based on the question https://stackoverflow.com/q/75003006/ asked by the user 'GokuSS3' ( https://stackoverflow.com/u/4838175/ ) and on the answer https://stackoverflow.com/a/75004324/ provided by the user 'GokuSS3' ( https://stackoverflow.com/u/4838175/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Angular 7 - Post method called twice on 400 Bad Request

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the Issue: Angular 7 POST Method Called Twice on 400 Bad Request

If you’re working on an Angular 7 application, you may encounter an unexpected behavior with your HTTP POST requests. Specifically, you might find that the login API is being called twice when a 400 Bad Request error occurs. This can lead to confusion, especially when it results in the number of retry attempts getting doubled and locking an account faster than intended. Understanding the root cause and finding a solution is crucial for ensuring a smooth user experience.

The Problem Explained

In this particular case, the application is designed to allow up to 6 retry attempts for a login. However, if a failure occurs (like a 400 Bad Request), the number of attempts gets doubled. What makes this issue puzzling is the observation that there is no explicit code written to call the API twice. After further investigation and debugging, it became clear that the error block in the HttpClient service only triggers after the second API call is made.

Key Observations:

The application’s retry mechanism is being triggered unexpectedly.

One HTTP POST request results in two calls on failure, leading to a premature lockout.

Breaking Down the Solution

Upon troubleshooting, the source of the problem was identified in the application’s error interceptor. Error interceptors are designed to handle HTTP errors globally and can be configured to automatically retry requests under certain conditions. This behavior may not have been intentionally set, which resulted in the duplicated calls.

Step 1: Identifying the Issue with the Interceptor

The error interceptor, which is responsible for catching errors and potentially replaying the request, was inadvertently causing requests to be retried multiple times upon encountering a 400 Bad Request. Here’s how to approach this issue:

Review Your Interceptors: Begin by examining the code within your error interceptor. Look for any logic that automatically retries failed requests.

Check Retry Logic: Ensure that the logic correctly differentiates between retryable and non-retryable status codes. Generally, a 400 Bad Request should not initiate a retry since it indicates a client-side error.

Step 2: Modifying the Interceptor

To resolve this issue, modifications need to be made to the interceptor so that it only retries requests under appropriate circumstances. Below is a simple example of how you might adjust the interceptor:

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

Step 3: Testing and Validating

After making the necessary changes, ensure thorough testing of the login flow under various scenarios, including successful logins, failures, and edge cases to confirm that the behavior is now as expected.

Conclusion

Debugging issues with multiple HTTP calls can be challenging, especially when they stem from a globally applied interceptor. By carefully analyzing your interceptor’s behavior and adjusting the retry logic, you can prevent unintended duplicate requests and safeguard your application’s functionality. In this case, rectifying the interceptor was the key to resolving the issue of the Angular 7 POST method being called twice on 400 Bad Request. Remember, effective error handling can enhance not only user experience but also application performance.

If you have any further questions or need assistance with your Angular application, feel free to reach out!