fix(errors): add res param to onError hook and guard against internal throw (#102)

* fix(errors): add res param to onError hook and guard against internal throw

- onError(err, req, res): response object now available for observability
- Wrap onError call in try/catch — hook failure must not suppress original error
- Type definition updated: onError?: (error: Error, request: Request, response: Response) => void

Closes #101

* fix(types): use Node http.IncomingMessage/ServerResponse for onError params

restana.Request/Response are generic types requiring Protocol<P> — incompatible
with the Hooks interface which is not parameterized. Node's native types are the
correct base types (restana extends them) and require no type arguments.

* fix(onError): use Function type, await async hooks, add 4 tests

- Type: use Function for onError (consistent with all other hooks in Hooks interface)
- Async: await onError call so async hooks that reject are caught by try/catch
- Tests: 4 new tests covering sync, async, throwing, and no-error paths
- All 4 new tests pass (54 total, 1 pre-existing failure unchanged)

* docs: add onError hook to lifecycle hooks documentation

* fix(test): update on-request-error assertion for restana v5.2.0

restana v5.2.0 sanitizes error messages — returns 'Internal Server Error'
instead of the thrown message. The test contract is '500 is returned',
not the specific error string.

---------

Co-authored-by: molty3000 <molty@21no.de>

Author: molty3000

docs/README.md

@@ -201,6 +201,11 @@ module.exports.handler = serverless(service)
       onResponse (req, res, stream) {
         // do some post-processing here
         // ...
+      },
+      onError (err, req, res) {
+        // called when the request pipeline throws (e.g., onRequest error, proxy failure)
+        // hook failures are silently caught — the original error still propagates to the client
+        // can be sync or async
       }
 
       // if proxyType= 'http', other options allowed https://www.npmjs.com/package/fast-proxy-lite#opts

index.d.ts

@@ -59,6 +59,7 @@ declare namespace fastgateway {
     onRequest?: Function
     rewriteHeaders?: Function
     onResponse?: Function
+    onError?: Function
     rewriteRequestHeaders?: Function
     request?: {
       timeout?: number

index.js

@@ -173,6 +173,15 @@ const handler = (route, proxy, proxyHandler) => async (req, res, next) => {
       proxyHandler(req, res, req.url, proxy, proxyOpts)
     }
   } catch (err) {
+    const { onError } = hooks
+    if (typeof onError === 'function') {
+      try {
+        await onError(err, req, res)
+      } catch (_) {
+        // onError hook failure must not suppress the original error
+      }
+    }
+
     return next(err)
   }
 }