Kepiye carane middleware bisa gumana ing FastAPI?

Question

Accepted Answer

**Middleware** ing FastAPI iku kode sing dijalanake kanggo **saben request lan response** — mbungkus endpoint-mu kanggo nangani masalah lintas-potong kayata logging, timing, CORS, lan nambah header. FastAPI nggunakake sistem middleware Starlette (basis ASGI).

## Nulis middleware khusus

```python
import time

@app.middleware("http")
async def add_timing(request: Request, call_next):
    start = time.time()
    response = await call_next(request)        # call the endpoint (and any inner middleware)
    response.headers["X-Process-Time"] = str(time.time() - start)   # modify the response
    return response
```

Pola: kode sadurungé `await call_next(request)` dijalanake ing jalan **mlebu** (sadurungé endpoint), `call_next` narakake endpoint, lan kode sawise dijalanake ing jalan **metu** (ngowahi response). Iki mbungkus saben request — kene, nambah header timing kanggo kabeh response.

## Alur request/response

```text
Request  → MW1 → MW2 → endpoint
Response ← MW1 ← MW2 ← endpoint
Middleware wraps the endpoint; runs in order on the way in, reverse on the way out.
```

## Middleware built-in / umum

```python
from fastapi.middleware.cors import CORSMiddleware
from fastapi.middleware.gzip import GZipMiddleware

app.add_middleware(CORSMiddleware, allow_origins=["https://app.example.com"], ...)  # CORS
app.add_middleware(GZipMiddleware, minimum_size=1000)                               # compression
```

Middleware umume ditambahake via `add_middleware` — CORS (terake request lintas-asal), GZip (kompres response), lan trusted-host checks minangka built-in sing khas.

## Kagunaan middleware sing umum

```text
✓ Logging / request timing / metrics
✓ CORS (cross-origin request handling)
✓ Adding security or custom headers
✓ Response compression (GZip)
✓ Request ID / correlation ID injection
```

## Middleware vs dependensi

```text
Middleware   → runs for ALL requests; works at the raw request/response level (headers,
               timing, the whole response). Best for truly global concerns.
Dependencies → per-endpoint (or grouped) logic with access to parsed params, DI, and
               typed values. Best for auth, validation, shared parameters.
→ Use middleware for global cross-cutting concerns; dependencies for endpoint logic.
```

## Mengapa iku penting

Middleware iku mekanisme sing tepat kanggo **kasusu global lan lintas-potong** ing FastAPI — logika sing kudu diterapake ing saben request lan response, kayata logging, timing request, CORS, kompresi, lan custom header.

Pangerten iku penting kanggo nstruktur aplikasi kanthi bener: middleware mbungkus kabeh endpoint (mlaku sadurungé lan sawise, kanthi kemampuan kanggo ngowahi request lan response), ndadeke iku ideal kanggo kelakuan tingkat-app sing bakal aneh lan gampang salah upaya ing saben endpoint.

Kaandel bédane antara **middleware** (global, tingkat request/response mentah) lan **dependensi** (per-endpoint, kanthi akses menyang nilai sing gawan/dingetik lan DI — luwih apik kanggo auth lan validasi) minangka kunci kanggo milih alat sing tepat.

Kabutuhan umum kayata CORS lan kompresi ditangani dening middleware built-in, dene middleware khusus nutupi logging lan instrumentasi — ndadeke pengetahuan praktis lan kerep digunakake kanggo mbangun API sing terstruktur kanthi bener lan bisa diamati.