FastAPI: Why Do I Get Unsupported Upgrade Request with DELETE Request?

Are you frustrated with the “Unsupported upgrade request” error when making a DELETE request with FastAPI? You’re not alone! In this article, we’ll dive into the reasons behind this error and provide you with clear solutions to overcome it.

What is the “Unsupported upgrade request” error?

This error occurs when your client (e.g., a web browser or a curl request) sends an Upgrade header in a DELETE request, which is not supported by FastAPI. But before we dive into the fix, let’s understand why this error happens in the first place.

The Upgrade header: A brief explanation

The Upgrade header is used to specify additional communication protocols that the client can handle. For example, when a client sends a request with the Upgrade header set to “websocket”, it indicates that the client can switch to the WebSocket protocol if the server supports it. In the case of DELETE requests, the Upgrade header is not necessary, and that’s where the problem begins.

Why does FastAPI reject the Upgrade header with DELETE requests?

FastAPI rejects the Upgrade header with DELETE requests because it’s not a part of the HTTP/1.1 specification. According to the spec, the Upgrade header should only be used with the Upgrade method (which is not a standard method in HTTP/1.1). By rejecting the Upgrade header, FastAPI ensures that it adheres to the HTTP/1.1 specification and prevents potential security vulnerabilities.

Solutions to the “Unsupported upgrade request” error

Now that we understand the reason behind the error, let’s explore the solutions:

Solution 1: Remove the Upgrade header from the client

The simplest solution is to remove the Upgrade header from the client request. This can be done by:

• Checking the client-side code to ensure that the Upgrade header is not being sent.
• Using a client library that allows you to customize the request headers.
• Configuring the client to use a different protocol or connection.

Here’s an example of how to remove the Upgrade header using Python’s requests library:

import requests

headers = {'Upgrade': None}
response = requests.delete('https://example.com/resource', headers=headers)

Solution 2: Use a proxy server

If removing the Upgrade header is not feasible, you can use a proxy server to strip the Upgrade header from the request. This approach is useful when you have no control over the client-side code or when the client is a third-party library.

Here’s an example of how to use NGINX as a proxy server to remove the Upgrade header:

http {
    ...
    server {
        listen 80;
        location / {
            proxy_pass http://fastapi_app;
            proxy_set_header Upgrade '';
        }
    }
}

Solution 3: Use a custom FastAPI middleware

Another solution is to create a custom FastAPI middleware that strips the Upgrade header from the request. This approach requires modifying your FastAPI application code.

Here’s an example of a custom FastAPI middleware that removes the Upgrade header:

from fastapi import FastAPI, Request

app = FastAPI()

class StripUpgradeHeader:
    def __init__(self, app):
        self.app = app

    async def __call__(self, request: Request):
        if 'Upgrade' in request.headers:
            del request.headers['Upgrade']
        return await self.app(request)

app.middleware('http')(StripUpgradeHeader)

Best practices to avoid the “Unsupported upgrade request” error

To avoid this error in the future, follow these best practices:

1. Verify client-side code: Ensure that your client-side code does not send unnecessary headers, including the Upgrade header.
2. Test with different clients: Test your API with different clients and libraries to ensure that none of them send the Upgrade header with DELETE requests.
3. Use a proxy server: Consider using a proxy server to filter out unnecessary headers from client requests.
4. Implement robust error handling: Implement robust error handling in your FastAPI application to catch and handle unexpected errors.

Conclusion

In this article, we explored the reasons behind the “Unsupported upgrade request” error with FastAPI and DELETE requests. We also provided three solutions to overcome this error, including removing the Upgrade header from the client, using a proxy server, and creating a custom FastAPI middleware. By following the best practices outlined in this article, you can ensure that your FastAPI application is robust and error-free.

Solution	Description
Remove Upgrade header from client	Modify client-side code to remove the Upgrade header from the request.
Use a proxy server	Configure a proxy server to remove the Upgrade header from the request.
Use a custom FastAPI middleware	Create a custom FastAPI middleware to remove the Upgrade header from the request.

By understanding the underlying causes of the “Unsupported upgrade request” error and implementing the solutions outlined in this article, you’ll be well on your way to building a robust and error-free FastAPI application.

Frequently Asked Question

Are you stuck with FastAPI and DELETE requests?