Je, middleware inafanyaje kazi katika FastAPI?

Question

Accepted Answer

**Middleware** katika FastAPI ni msimbo unaoendeshwa kwa **kila ombi na jibu** — ukifunika endpoints zako ili kushughulikia masuala mtambuka kama uwekaji kumbukumbu (logging), upimaji muda (timing), CORS, na kuongeza headers. FastAPI hutumia mfumo wa middleware wa Starlette (umejengwa kwa ASGI).

## Kuandika middleware maalum

```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
```

Mfumo: msimbo kabla ya `await call_next(request)` huendeshwa wakati wa **kuingia** (kabla ya endpoint), `call_next` huita endpoint, na msimbo baada yake huendeshwa wakati wa **kutoka** (ukirekebisha jibu). Hii hufunika kila ombi — hapa, ikiongeza header ya muda kwa majibu yote.

## Mtiririko wa ombi/jibu

```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 iliyojengwa ndani / ya kawaida

```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 kawaida huongezwa kupitia `add_middleware` — CORS (kuruhusu maombi ya asili tofauti), GZip (kubana majibu), na ukaguzi wa trusted-host ni vya kawaida vilivyojengwa ndani.

## Matumizi ya kawaida ya middleware

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

## Middleware dhidi ya dependencies

```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.
```

## Kwa nini ni muhimu

Middleware ni utaratibu sahihi kwa **masuala mtambuka ya kimataifa** katika FastAPI — mantiki inayopaswa kutumika kwa kila ombi na jibu, kama logging, upimaji muda wa ombi, CORS, ubanaji (compression), na headers maalum.

Kuelewa ni muhimu kwa kupanga programu kwa usahihi: middleware hufunika endpoints zote (ikiendeshwa kabla na baada, ikiwa na uwezo wa kurekebisha ombi na jibu vyote), jambo linaloifanya bora kwa tabia ya programu nzima ambayo ingekuwa ya kuchosha na yenye makosa kuirudia kwenye kila endpoint.

Kujua tofauti kati ya **middleware** (kimataifa, kiwango cha ombi/jibu ghafi) na **dependencies** (kwa kila endpoint, na ufikiaji wa thamani zilizopangwa/zenye aina na DI — bora kwa uthibitishaji na uthibitisho) ni ufunguo wa kuchagua zana sahihi.

Mahitaji ya kawaida kama CORS na ubanaji hushughulikiwa na middleware iliyojengwa ndani, wakati middleware maalum hushughulikia logging na uchunguzi (instrumentation) — jambo linalofanya haya kuwa maarifa ya vitendo, yanayotumika mara kwa mara ya kujenga API zilizopangwa vizuri na zinazoonekana (observable).