# Concurrencia y async / await { #concurrency-and-async-await }

Detalles sobre la sintaxis `async def` para *path operation functions* y algunos antecedentes sobre el código asíncrono, la concurrencia y el paralelismo.

## ¿Con prisa? { #in-a-hurry }

<abbr title="too long; didn't read"><strong>TL;DR:</strong></abbr>

Si estás usando paquetes de terceros que te dicen que los llames con `await`, como:

```Python
results = await some_library()
```

                    response = await f(request)
                await response(scope, receive, send)
                # Continues customization
                response_awaited = True
            if not response_awaited:
                raise FastAPIError(
                    "Response not awaited. There's a high chance that the "

@app.websocket("/function-scope")
async def function_scope(websocket: WebSocket, session: SessionFuncDep) -> Any:
    await websocket.accept()
    await websocket.send_json({"is_open": session.open})


@app.websocket("/request-scope")
async def request_scope(websocket: WebSocket, session: SessionRequestDep) -> Any:
    await websocket.accept()
    await websocket.send_json({"is_open": session.open})


@app.websocket("/two-scopes")

app = FastAPI()


@app.get("/")
async def read_main():
    return {"msg": "Hello World"}


@app.websocket("/ws")
async def websocket(websocket: WebSocket):
    await websocket.accept()
    await websocket.send_json({"msg": "Hello WebSocket"})
    await websocket.close()


def test_read_main():
    client = TestClient(app)
    response = client.get("/")
    assert response.status_code == 200

</html>
"""


@app.get("/")
async def get():
    return HTMLResponse(html)


@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()

    stream = io.BytesIO(b"data")
    file = UploadFile(filename="file", file=stream, size=4)
    assert await file.read() == b"data"
    assert file.size == 4
    await file.write(b" and more data!")
    assert await file.read() == b""
    assert file.size == 19
    await file.seek(0)
    assert await file.read() == b"data and more data!"

async def index(websocket: WebSocket, deps: DepList):
    await websocket.accept()
    await websocket.send_text(json.dumps(deps))
    await websocket.close()


@router.websocket("/router", dependencies=[create_dependency("routerindex")])
async def routerindex(websocket: WebSocket, deps: DepList):
    await websocket.accept()
    await websocket.send_text(json.dumps(deps))
    await websocket.close()

async def custom_http_exception_handler(request, exc):
    print(f"OMG! An HTTP error!: {repr(exc)}")
    return await http_exception_handler(request, exc)


@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request, exc):
    print(f"OMG! The client sent invalid data!: {exc}")
    return await request_validation_exception_handler(request, exc)


@app.get("/items/{item_id}")

    ):
        if session is None:
            raise WebSocketException(code=status.WS_1008_POLICY_VIOLATION)
        await websocket.accept()
        while True:
            data = await websocket.receive_text()
            await websocket.send_text(f"Session cookie is: {session}")
            await websocket.send_text(f"Message text was: {data}, for item ID: {item_id}")
    ```
    """

    def __init__(
        self,

from fastapi import Body, FastAPI, Request, Response
from fastapi.routing import APIRoute


class GzipRequest(Request):
    async def body(self) -> bytes:
        if not hasattr(self, "_body"):
            body = await super().body()
            if "gzip" in self.headers.getlist("Content-Encoding"):
                body = gzip.decompress(body)
            self._body = body
        return self._body


class GzipRoute(APIRoute):