Yaya Express middleware ke aiki?

Question

Accepted Answer

**Middleware** aiki ne ke aiki **a jeri** a lokacin buddin bugi-karashi a Express. Kowannensu yana karɓa `(req, res, next)` kuma zai iya bincika/canja bugi da karashi, gajiya karashi, ko kiran `next()` don kawar da iko ga middleware na gida. Suke yawon zaman gida na yadda ake tsara aikace-aikace Express.

## Sitin da sarari

```js
app.use((req, res, next) => {
  console.log(`${req.method} ${req.url}`); // do something
  next();                                   // ⬅ pass control to the next middleware
});
```

Mahaimmin kaida: **kira `next()`** don ci gida sarari. Manta shi (kuma kada ka aiko da karashi), kuma bugi zai tsaya har abada.

## Jerin aiki

```text
Request → [logger] → [auth] → [body parser] → [route handler] → Response
            next()    next()     next()         res.send()
Each middleware runs in order; any can short-circuit by sending a response.
```

## Sanannun nau'in middleware

```js
// 1. Application-level — runs for all (or path-matched) requests
app.use(express.json());                       // built-in: parse JSON bodies
app.use(cors());                                // third-party

// 2. Custom — e.g. authentication that can SHORT-CIRCUIT
function requireAuth(req, res, next) {
  if (!req.headers.authorization) {
    return res.status(401).json({ error: "Unauthorized" }); // STOP — don't call next()
  }
  req.user = decodeToken(req.headers.authorization);  // attach data for later handlers
  next();                                              // authorized → continue
}

// 3. Route-specific
app.get("/profile", requireAuth, (req, res) => res.json(req.user));
```

Middleware yana iya **tsauri** (aiko da karashi kuma kada ka kira `next()`, misali tsare bugi da ba a yarda ba) ko **ike** bugi (haɗa `req.user` ga gidaje masu azur).

## Middleware na jiyya-gani (sakwanni hudu)

```js
// special signature with 4 params → Express treats it as an error handler
app.use((err, req, res, next) => {
  console.error(err);
  res.status(500).json({ error: "Server error" });
});
// triggered by next(err) or a thrown error; place it LAST
```

Jiyya-gani mai iko da **hudu** sigogi (`err` na farko). Kana isa ta hanyar kiran `next(err)`; ya kamata a yi reshe na ƙarshe.

## Jeri ke matuwa

```text
Middleware runs in the ORDER you register it. Body parser before routes that
read the body; auth before protected routes; error handler last.
```

## Dalilin abin matuwa

Middleware shine tsinkayen tsarin Express (da kuma kamanninsu) — shaida-shaida, ɗagawa, tsaida jiki, CORS, tabbatarwa, da jiyya-gani duk middleware suke.

Sanin jantarwa `(req, res, next)` (musamman cewa dole ne ka kira `next()` ko aiko da karashi), yadda middleware zai iya tsauri ko ike bugi, fuzanta-sakwanni jiyya-gani, da cewa **jeri ke matuwa**, yana da mahimmanci don gina, tsara, da duba aikace-aikace na Express.