Middleware in fastAPI

According to official documentation, FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.6+ based on standard Python type hints.

The key features are:

Fast: Very high performance, on par with NodeJS and Go (thanks to Starlette and Pydantic). One of the fastest Python frameworks available.

Fast to code: Increase the speed to develop features by about 200% to 300%. *

Fewer bugs: Reduce about 40% of human (developer) induced errors. *

Intuitive: Great editor support. Completion everywhere. Less time debugging.

Easy: Designed to be easy to use and learn. Less time reading docs.

Short: Minimize code duplication. Multiple features from each parameter declaration. Fewer bugs.

Robust: Get production-ready code. With automatic interactive documentation.

Standards-based: Based on (and fully compatible with) the open standards for APIs: OpenAPI (previously known as Swagger) and JSON Schema.

Middleware.

A "middleware" is a function that works with every request before it is processed by any specific path operation. And also with every response before returning it.

It takes each request that comes to your application.

It can then do something to that request or run any needed code.

Then it passes the request to be processed by the rest of the application (by some path operation).

It then takes the response generated by the application (by some path operation).

It can do something to that response or run any needed code. Then it returns the response.

Create a middleware

To create a middleware you use the decorator @app.middleware("http") on top of a function.

The middleware function receives:

The request.

A function call_next that will receive the request as a parameter.

This function will pass the request to the corresponding path operation.
Then it returns the response generated by the corresponding path operation.

You can then modify further the response before returning it.

@app.middleware("http")
     async def log_requests(request: Request, call_next):
     idem = ''.join(random.choices(string.ascii_uppercase + string.digits, k=6))
     logger.info(f"rid={idem} start request path={request.url.path}")
     start_time = time.time()

     response = await call_next(request)

     process_time = (time.time() - start_time) * 1000
     formatted_process_time = '{0:.2f}'.format(process_time)
     logger.info(f"rid={idem} completed_in={formatted_process_time}ms status_code={response.status_code}")

     return response`

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Middleware in fastAPI

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