Versioned API Middleware and Router for FastAPI

Overview

This implementation provides a versioning system for FastAPI routes using the Accept header. It allows clients to request specific versions of an API by including a version number in the Accept header. The middleware will parse this header and route the request to the appropriate API version.

This middleware was found here tiangolo/fastapi#3910 (comment) and is a fantastic example for header version based routing.

Features

• AcceptHeaderVersionMiddleware: Parses the Accept header to extract the API version.
• VersionedAPIRoute: Custom API route that matches the requested version.
• VersionedAPIRouter: Extension of FastAPI's APIRouter to handle versioned routes.

Usage

Middleware: AcceptHeaderVersionMiddleware

This middleware checks for an Accept header in the incoming HTTP or WebSocket request. If the header is present and formatted correctly, it extracts the API version and includes it in the request scope.

Example format for the Accept header: application/vnd.mytestapp.v3+json.

Initialization

from fastapi import FastAPI
from your_module import AcceptHeaderVersionMiddleware, VersionedAPIRouter

app = FastAPI(title="Versioned app")

# Add the middleware
app.add_middleware(
    AcceptHeaderVersionMiddleware, 
    vendor_prefix="mytestapp", 
    latest_version="4"
)

# Include the router
app.include_router(router)

Requesting a Specific Version

Clients can request a specific version of an API endpoint by setting the Accept header:

curl -H "Accept: application/vnd.mytestapp.v3+json" http://localhost:8000/foo

If a specifc version header is not provided it will use the router defined by the middleware's latest version

Handling Unsupported Versions

If a client requests a version that does not exist, the server responds with a 406 Not Acceptable status.