from fastapi.testclient import TestClient

from docs_src.advanced_middleware.tutorial001 import app


def test_middleware():
    client = TestClient(app, base_url="https://testserver")
    response = client.get("/")
    assert response.status_code == 200, response.text

    client = TestClient(app)
    response = client.get("/", follow_redirects=False)
    assert response.status_code == 307, response.text

!!! note "Технические детали"
    Вы также можете использовать `from starlette.middleware.cors import CORSMiddleware`.

from sqlalchemy.orm import Session

from . import crud, models, schemas
from .database import SessionLocal, engine

models.Base.metadata.create_all(bind=engine)

app = FastAPI()


@app.middleware("http")
async def db_session_middleware(request: Request, call_next):
    response = Response("Internal server error", status_code=500)
    try:
        request.state.db = SessionLocal()
        response = await call_next(request)

    assert data["context_a"] == "started a"
    assert data["bg"] == "not set"
    middleware_state = json.loads(response.headers["x-state"])
    assert middleware_state["context_b"] == "finished b with a: started a"
    assert middleware_state["context_a"] == "finished a"
    assert middleware_state["bg"] == "not set"
    assert state["context_b"] == "finished b with a: started a"

### Dependencies with `yield` or middleware

Adding a **middleware** here is similar to what a dependency with `yield` does, with some differences:

* It requires more code and is a bit more complex.
* The middleware has to be an `async` function.

from sqlalchemy.orm import Session

from . import crud, models, schemas
from .database import SessionLocal, engine

models.Base.metadata.create_all(bind=engine)

app = FastAPI()


@app.middleware("http")
async def db_session_middleware(request: Request, call_next):
    response = Response("Internal server error", status_code=500)
    try:
        request.state.db = SessionLocal()
        response = await call_next(request)

            - get
            - put
            - post
            - delete
            - options
            - head
            - patch
            - trace
            - on_event
            - middleware

!!! note "기술적 세부 사항"
    `from starlette.middleware.cors import CORSMiddleware` 역시 사용할 수 있습니다.

		// Wrap the actual handler with the appropriate tracing middleware.
		var tracedHandler http.HandlerFunc
		if handlerFlags.has(traceHdrsS3HFlag) {
			tracedHandler = httpTraceHdrs(f)
		} else {
			tracedHandler = httpTraceAll(f)
		}

		// Skip wrapping with the gzip middleware if specified.
		var gzippedHandler http.HandlerFunc = tracedHandler
		if !handlerFlags.has(noGZS3HFlag) {

# Custom Request and APIRoute class

In some cases, you may want to override the logic used by the `Request` and `APIRoute` classes.

In particular, this may be a good alternative to logic in a middleware.

For example, if you want to read or manipulate the request body before it is processed by your application.

!!! danger
    This is an "advanced" feature.

    If you are just starting with **FastAPI** you might want to skip this section.