Think of Middleware like a Security Guard or a Receptionist at the entrance of a building (your App).

Entry: Every visitor (Request) has to stop at the desk first. The receptionist notes the time they arrived.

Pass-through: The receptionist lets them go up to the specific office they need (The Endpoint).

Exit: When the visitor comes back down to leave, they pass the receptionist again. The receptionist notes the time they left and calculates how long the visit took.

The Flow of Your Code
Here is exactly what happens when a user hits your API (e.g., GET /home):

1. The Setup (Global Scope)
Before any request comes in, Python reads the file.

It sets up a logger (a tool to write messages).

It creates a FileHandler to write those messages to logging.txt.

2. The Request Arrives
A user sends a request. The FastAPI app receives it. Because you added app.add_middleware(RequestLoggingMiddleware), the request does not go straight to your function. It goes to your RequestLoggingMiddleware class first.

3. The dispatch Method (The Core)
This is the heart of the middleware. The dispatch function is triggered.

Step A: Start the Clock start_time = time.time() You take a snapshot of the current time.

Step B: Pass the Baton (call_next) response = await call_next(request) This line is crucial. It tells FastAPI: "Okay, I'm done with my pre-checks. Go run the actual function for this route (e.g., login, get_users, etc.) and bring me back the result."

Step C: The Return Trip Once the actual route finishes, the code resumes exactly where it left off (after call_next). duration = (time.time() - start_time) * 1000 You check the time again to see how many milliseconds passed.

Step D: Log It logger.info(...) You write a line into your log file saying: "Hey, the request to /home took 150ms and returned a 200 OK status."




For incoming requests: C → B → A → Route
For outgoing responses: A → B → C → Client

It's like a stack - last in, first out!

Think of it like security checkpoints:

You add checkpoint A, B, C
Visitor goes through C first (newest), then B, then A
On the way out: A, then B, then C

# 1. Middleware order is wrong
app.add_middleware(CORSMiddleware, ...)    # Added first
app.add_middleware(RequestLoggingMiddleware)  # Added last
# But they run in REVERSE order! Logging runs before CORS!

# 2. CORS is too permissive
allow_origins= ['*']  # ❌ Anyone from anywhere can access!

# 3. No rate limiting
# Missing: app.add_middleware(RateLimitingMiddleware)