Bug: User Info Returns 200 Instead Of 404 On Not Found

Dec 3, 2025 by Alex Johnson 55 views

Bug: Internal user/info Returns 200 Instead of Expected 404

Introduction

In this article, we will delve into a peculiar bug encountered within the BerriAI litellm project. The issue revolves around the /user/info endpoint, which unexpectedly returns a 200 OK status code instead of the anticipated 404 Not Found when attempting to retrieve information for a non-existent user. This behavior deviates from standard RESTful API conventions and can lead to confusion and potential errors in applications relying on this endpoint. We will explore the details of the bug, the steps to reproduce it, the workaround implemented, and the implications for developers and the overall system.

The core of the problem lies in the incorrect HTTP status code returned when a user is not found. According to established web standards, a 404 status code should be returned to indicate that the requested resource (in this case, user information) does not exist. However, the endpoint in question erroneously returns a 200 OK, suggesting that the request was successful even when no user data is available. This discrepancy can lead to misinterpretations by client applications, potentially resulting in incorrect data processing or unexpected behavior.

The implications of this bug are significant. Developers relying on the /user/info endpoint to verify user existence may be misled by the incorrect status code. This can lead to scenarios where applications attempt to access or manipulate user data that does not exist, resulting in errors or inconsistencies. Furthermore, the lack of a clear 404 signal makes it harder to implement proper error handling and debugging mechanisms, as applications may not be able to reliably distinguish between successful requests and cases where a user is genuinely not found. Addressing this issue is crucial for maintaining the integrity and reliability of the system.

What Happened?

The bug was identified when a curl command was used to query the /user/info endpoint with a user_id that did not correspond to an existing user. The command executed was:

$ curl -H "Authorization: Bearer sk-asdf" 'http://localhost:4000/user/info?user_id=not_created_user'

Instead of the expected 404 Not Found, the endpoint returned a 200 OK status code along with the following JSON response:

{"user_id":"not_created_user","user_info":{"spend":0},"keys":[],"teams":[]}

This response indicates that the server processed the request successfully, but the user information is essentially empty, with spend set to 0, and empty arrays for keys and teams. The crucial point here is that the 200 OK status code contradicts the fact that the user was not found, leading to a discrepancy between the expected and actual behavior.

This unexpected behavior can be attributed to a few potential underlying causes. One possibility is that the endpoint's logic does not properly check for the existence of the user before constructing the response. Instead, it might be creating a default or empty user object and returning it with a 200 OK, regardless of whether the user actually exists in the system. Another possibility is that there is an error in the status code handling logic, where the 404 condition is not being correctly triggered when a user is not found. It is also conceivable that there is a misconfiguration in the server or framework that is causing the default 200 OK to be returned even in error scenarios. Identifying the precise root cause will require a deeper investigation into the endpoint's implementation and the surrounding codebase.

Expected Behavior

The expected behavior for the /user/info endpoint, when queried with a non-existent user_id, is to return a 404 Not Found status code. This is in line with standard RESTful API design principles, where a 404 status code indicates that the requested resource could not be found on the server. Returning a 404 allows client applications to accurately determine that the user does not exist and handle the situation accordingly, such as displaying an error message or taking alternative actions.

To further clarify the importance of this expectation, consider the alternative. If the endpoint consistently returns a 200 OK, even when a user is not found, client applications have no reliable way to distinguish between a successful retrieval of user data and a case where the user simply does not exist. This ambiguity can lead to several problems. For instance, an application might mistakenly assume that a user exists based on the 200 OK status and attempt to perform operations on that user's data, resulting in errors or unexpected behavior. Similarly, it becomes difficult to implement proper error handling and retry mechanisms, as the application cannot accurately determine whether a request failed due to a non-existent user or some other issue.

The 404 Not Found status code serves as a clear and unambiguous signal to the client that the requested resource is not available. This allows the client to take appropriate action, such as displaying an error message to the user, logging the error for debugging purposes, or attempting to retrieve the resource from a different source. Adhering to this standard practice is crucial for building robust and reliable applications that interact with APIs.

Workaround

As a temporary workaround, the user implemented a check for the user_id inside the user_info struct. The observation was that the user_info struct does not seem to be populated for invalid users. This means that even though the endpoint returns a 200 OK, the absence of data within the user_info struct can be used as an indicator that the user was not found.

This workaround, while functional, is not ideal. It introduces additional complexity into the client application, as it needs to inspect the response body to determine the actual outcome of the request. This deviates from the standard practice of relying on HTTP status codes for indicating success or failure. Furthermore, the workaround is fragile, as it depends on the specific structure of the response body. If the response format changes in the future, the workaround might break, leading to unexpected behavior.

To illustrate the limitations of this approach, consider a scenario where the API is updated to include default values for the user_info struct, even for non-existent users. In such a case, the workaround would no longer be effective, as the presence of data in the user_info struct would no longer be a reliable indicator of user existence. This highlights the importance of addressing the underlying issue of the incorrect status code, rather than relying on temporary workarounds.

While this workaround provides a temporary solution, it is strongly recommended that the underlying bug be fixed to ensure proper API behavior and prevent potential issues in the future.

Additional Information

Are you a ML Ops Team? Yes
What LiteLLM version are you on? 1.80.7-nightly
Discussion category: BerriAI, litellm

This information provides context about the environment in which the bug was encountered. The fact that the user is part of an ML Ops team suggests that this issue is relevant to production systems and workflows. The LiteLLM version (1.80.7-nightly) indicates that the bug is present in a relatively recent version of the software, potentially affecting other users who are running the same version. The discussion category (BerriAI, litellm) helps to categorize the issue and direct it to the appropriate developers or maintainers.

It is important to consider this additional information when addressing the bug. Understanding the context in which the bug was encountered can help to prioritize the fix and ensure that it is effective in real-world scenarios. For instance, if the bug is prevalent in production environments, it might warrant a higher priority fix compared to a bug that only occurs in development or testing environments. Similarly, knowing the specific LiteLLM version can help to narrow down the search for the root cause and identify any recent changes that might have introduced the bug.

Relevant Log Output

Unfortunately, no relevant log output was provided in the initial report. Log output can be invaluable for debugging and troubleshooting issues, as it often contains detailed information about the system's state and the sequence of events leading up to an error. In this case, log output from the server-side processing of the /user/info request could have provided insights into why the incorrect status code was being returned. For example, the logs might have revealed whether the user lookup failed, whether an exception was thrown, or whether there were any errors in the status code handling logic.

In the absence of log output, it becomes more challenging to pinpoint the root cause of the bug. Developers need to rely on other debugging techniques, such as code inspection, unit testing, and integration testing, to understand the behavior of the system. If the issue persists, it is highly recommended to enable logging and capture the relevant log output when the bug is reproduced. This will provide valuable information for diagnosing the problem and developing an effective fix.

To enhance future bug reports, users should be encouraged to include relevant log output whenever possible. This can significantly expedite the debugging process and reduce the time it takes to resolve issues.

Conclusion

The bug where the /user/info endpoint returns a 200 OK status code instead of the expected 404 when a user is not found is a significant issue that needs to be addressed. The incorrect status code can lead to misinterpretations by client applications, potentially resulting in errors or unexpected behavior. While a workaround has been implemented to check for the user_id inside the user_info struct, this is not an ideal solution and the underlying bug should be fixed.

The lack of a proper 404 response hinders the ability of applications to reliably determine the existence of a user. This can lead to problems in various scenarios, such as user authentication, data retrieval, and error handling. The incorrect status code also makes it harder to implement proper debugging mechanisms, as applications may not be able to accurately distinguish between successful requests and cases where a user is genuinely not found.

To resolve this issue, developers should investigate the endpoint's logic and identify the reason why the incorrect status code is being returned. Potential causes include errors in the user lookup process, issues with status code handling, or misconfigurations in the server or framework. Once the root cause is identified, a fix should be implemented to ensure that the endpoint returns a 404 Not Found status code when a user is not found.

In addition to fixing the bug, it is also important to improve the logging and error reporting mechanisms in the system. This will make it easier to diagnose and resolve similar issues in the future. Users should be encouraged to include relevant log output in their bug reports, as this can significantly expedite the debugging process.

By addressing this bug and implementing best practices for error handling and logging, the BerriAI litellm project can improve the reliability and robustness of its API, providing a better experience for developers and users alike.

For more information on HTTP status codes and RESTful API design, visit the Mozilla Developer Network (MDN).