fix: InterceptedRequestRouter.handleWrite arity issue

lib/intercepted_request_router.js

@@ -143,7 +143,8 @@ class InterceptedRequestRouter {
 
   // from docs: When write function is called with empty string or buffer, it does nothing and waits for more input.
   // However, actually implementation checks the state of finished and aborted before checking if the first arg is empty.
-  handleWrite(buffer, encoding, callback) {
+  handleWrite(...args) {
+    let [buffer, encoding] = args || []
     debug('request write')
     const { req } = this
 
@@ -171,6 +172,9 @@ class InterceptedRequestRouter {
     }
     this.requestBodyBuffers.push(buffer)
 
+    // writable.write encoding is param is optional
+    // so if callback is present it's the last argument
+    const callback = args ? args[args.length - 1] : undefined
     // can't use instanceof Function because some test runners
     // run tests in vm.runInNewContext where Function is not same
     // as that in the current context

tests/test_request_overrider.js

@@ -89,6 +89,40 @@ describe('Request Overrider', () => {
     })
   })
 
+  it('write callback called when encoding is not supplied', done => {
+    const scope = nock('http://example.test')
+      .filteringRequestBody(/mia/, 'nostra')
+      .post('/', 'mamma nostra')
+      .reply()
+
+    const reqWriteCallback = sinon.spy()
+
+    const req = http.request(
+      {
+        host: 'example.test',
+        method: 'POST',
+        path: '/',
+        port: 80,
+      },
+      res => {
+        expect(reqWriteCallback).to.have.been.calledOnce()
+        expect(res.statusCode).to.equal(200)
+        res.on('end', () => {
+          scope.done()
+          done()
+        })
+        // Streams start in 'paused' mode and must be started.
+        // See https://nodejs.org/api/stream.html#stream_class_stream_readable
+        res.resume()
+      }
+    )
+
+    req.write('mamma mia', () => {
+      reqWriteCallback()
+      req.end()
+    })
+  })
+
   it('write callback is not called if the provided chunk is undefined', done => {
     const scope = nock('http://example.test').post('/').reply()