fix: cy.intercept delay works correctly with 204 No Content

packages/driver/cypress/integration/commands/net_stubbing_spec.ts

@@ -1682,6 +1682,30 @@ describe('network stubbing', { retries: 2 }, function () {
       .then(() => testDelay()).wait('@get')
     })
 
+    // https://github.com/cypress-io/cypress/issues/15188
+    it('delay works correctly with 204 No Content', (done) => {
+      cy.on('fail', (err) => {
+        expect(err.message).to.include('No response ever occurred')
+
+        done()
+      })
+
+      cy.intercept('POST', '/post-only', {
+        statusCode: 204, // delay is not respected
+        delay: 5000,
+      }).as('create')
+
+      cy.window().then((win) => {
+        win.eval(
+          `fetch("/post-only", {
+            method: 'POST', // *GET, POST, PUT, DELETE, etc.
+          });`,
+        )
+      })
+
+      cy.wait('@create', { timeout: 500 })
+    })
+
     // @see https://github.com/cypress-io/cypress/issues/15901
     it('can intercept utf-8 request bodies without crashing', function () {
       cy.intercept('POST', 'http://localhost:5000/api/sample')

packages/net-stubbing/lib/server/driver-events.ts

@@ -73,7 +73,7 @@ async function sendStaticResponse (state: NetStubbingState, getFixture: GetFixtu
 
   await setResponseFromFixture(getFixture, options.staticResponse)
 
-  _sendStaticResponse(request, options.staticResponse)
+  await _sendStaticResponse(request, options.staticResponse)
 }
 
 export function _restoreMatcherOptionsTypes (options: AnnotatedRouteMatcherOptions) {

packages/net-stubbing/lib/server/intercepted-request.ts

@@ -194,7 +194,7 @@ export class InterceptedRequest {
           }
 
           if (immediateStaticResponse) {
-            sendStaticResponse(this, immediateStaticResponse)
+            await sendStaticResponse(this, immediateStaticResponse)
 
             return data
           }

packages/net-stubbing/lib/server/middleware/response.ts

@@ -79,7 +79,7 @@ export const InterceptResponse: ResponseMiddleware = async function () {
 
   mergeChanges(request.res as any, modifiedRes)
 
-  const bodyStream = getBodyStream(modifiedRes.body, _.pick(modifiedRes, ['throttleKbps', 'delay']) as any)
+  const bodyStream = await getBodyStream(modifiedRes.body, _.pick(modifiedRes, ['throttleKbps', 'delay']) as any)
 
   return request.continueResponse!(bodyStream)
 }

packages/net-stubbing/lib/server/util.ts

@@ -153,7 +153,7 @@ export async function setResponseFromFixture (getFixtureFn: GetFixtureFn, static
  * @param backendRequest BackendRequest object.
  * @param staticResponse BackendStaticResponse object.
  */
-export function sendStaticResponse (backendRequest: Pick<InterceptedRequest, 'res' | 'onError' | 'onResponse'>, staticResponse: BackendStaticResponse) {
+export async function sendStaticResponse (backendRequest: Pick<InterceptedRequest, 'res' | 'onError' | 'onResponse'>, staticResponse: BackendStaticResponse) {
   const { onError, onResponse } = backendRequest
 
   if (staticResponse.forceNetworkError) {
@@ -173,12 +173,12 @@ export function sendStaticResponse (backendRequest: Pick<InterceptedRequest, 're
     body,
   })
 
-  const bodyStream = getBodyStream(body, _.pick(staticResponse, 'throttleKbps', 'delay'))
+  const bodyStream = await getBodyStream(body, _.pick(staticResponse, 'throttleKbps', 'delay'))
 
   onResponse!(incomingRes, bodyStream)
 }
 
-export function getBodyStream (body: Buffer | string | Readable | undefined, options: { delay?: number, throttleKbps?: number }): Readable {
+export async function getBodyStream (body: Buffer | string | Readable | undefined, options: { delay?: number, throttleKbps?: number }): Promise<Readable> {
   const { delay, throttleKbps } = options
   const pt = new PassThrough()
 
@@ -203,11 +203,19 @@ export function getBodyStream (body: Buffer | string | Readable | undefined, opt
     return writable.end()
   }
 
-  delay ? setTimeout(sendBody, delay) : sendBody()
+  delay ? await wait(sendBody, delay) : sendBody()
 
   return pt
 }
 
+function wait (fn, ms) {
+  return new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(fn())
+    }, ms)
+  })
+}
+
 export function mergeDeletedHeaders (before: CyHttpMessages.BaseMessage, after: CyHttpMessages.BaseMessage) {
   for (const k in before.headers) {
     // a header was deleted from `after` but was present in `before`, delete it in `before` too