fix: restore express prototypes so injecting doesn't break http requests (#333)

Signed-off-by: Niall Molloy <niall.molloy@engineering.digital.dwp.gov.uk>

Author: gunjam

index.js

@@ -74,8 +74,21 @@ function doInject (dispatchFunc, options, callback) {
 
   // Express.js detection
   if (dispatchFunc.request && dispatchFunc.request.app === dispatchFunc) {
-    Object.setPrototypeOf(Object.getPrototypeOf(dispatchFunc.request), RequestConstructor.prototype)
-    Object.setPrototypeOf(Object.getPrototypeOf(dispatchFunc.response), Response.prototype)
+    const reqProto = Object.getPrototypeOf(dispatchFunc.request)
+    const resProto = Object.getPrototypeOf(dispatchFunc.response)
+    const reqExpressProto = Object.getPrototypeOf(reqProto)
+    const resExpressProto = Object.getPrototypeOf(resProto)
+    Object.setPrototypeOf(reqProto, RequestConstructor.prototype)
+    Object.setPrototypeOf(resProto, Response.prototype)
+
+    // Restore original express prototypes after dispatch is called
+    const distpach = dispatchFunc
+    dispatchFunc = function (req, res) {
+      const result = distpach.call(this, req, res)
+      Object.setPrototypeOf(reqProto, reqExpressProto)
+      Object.setPrototypeOf(resProto, resExpressProto)
+      return result
+    }
   }
 
   if (typeof callback === 'function') {

test/index.test.js

@@ -2129,6 +2129,36 @@ test("passes payload when using express' send", (t, done) => {
   })
 })
 
+test('can both inject and make HTTP requests with express', (t, done) => {
+  t.plan(5)
+
+  const app = express()
+
+  app.get('/hello', (_req, res) => {
+    res.send('some text')
+  })
+
+  const server = app.listen()
+  t.after(() => server.close())
+
+  inject(app, { method: 'GET', url: 'http://example.com:8080/hello' }, (err, res) => {
+    t.assert.ifError(err)
+    t.assert.strictEqual(res.headers['content-length'], '9')
+    t.assert.strictEqual(res.payload, 'some text')
+
+    fetch(`http://localhost:${server.address().port}/hello`)
+      .then((res) => {
+        t.assert.strictEqual(res.headers.get('content-length'), '9')
+        return res.text()
+      })
+      .then(body => {
+        t.assert.strictEqual(body, 'some text')
+        done()
+      })
+      .catch((err) => done(err))
+  })
+})
+
 test('request that is destroyed errors', (t, done) => {
   t.plan(2)
   const dispatch = function (req, res) {