Cypress.automation('remote:debugger:protocol') command started failing in Cypress 7.3.0

Current behavior

Starting in 7.3.0, the test code below (mostly copied from https://www.cypress.io/blog/2020/11/12/testing-application-in-offline-network-mode/) throws this error:

CypressError: `cy.then()` timed out after waiting `4000ms`.

Your callback function returned a promise that never resolved.

The callback function was:

() => Cypress.automation('remote:debugger:protocol', {
      command: 'Network.emulateNetworkConditions',
      params: {
        offline: true,
        latency: -1,
        downloadThroughput: -1,
        uploadThroughput: -1
      }
    })
    at https://www.cypress.io/__cypress/runner/cypress_runner.js:136167:24
From previous event:
    at Context.thenFn (https://www.cypress.io/__cypress/runner/cypress_runner.js:136166:13)
    at Context.then (https://www.cypress.io/__cypress/runner/cypress_runner.js:136597:21)
    at Context.<anonymous> (https://www.cypress.io/__cypress/runner/cypress_runner.js:151455:21)
From Your Spec Code:
    at Context.eval (https://www.cypress.io/__cypress/tests?p=cypress/integration/spec.js:133:9)

Desired behavior

The test should run without error.

Test code to reproduce

Set the baseUrl configuration key (e.g. "https://www.cypress.io") and run the following spec. I can reproduce without setting the baseUrl but it’s a little more complicated and I think this is better as a MWE.

describe('page', () => {
  it('tries to go offline', () => {
    cy.log('**go offline**')
    .then(() =>
      Cypress.automation('remote:debugger:protocol', { command: 'Network.enable' })
    )
      .then(() => 
        Cypress.automation('remote:debugger:protocol', {
          command: 'Network.emulateNetworkConditions',
          params: {
            offline: true,
            latency: -1,
            downloadThroughput: -1,
            uploadThroughput: -1
          }
        })
      );
    cy.visit('/');
  });
});

Cypress Version

7.3.0

Other

I encountered this when attempting to update to the latest version of Cypress, but traced it back to 7.3.0. Version 7.2.0 runs without error.

It looks like at least a couple other people have encountered this based on the comments on that blog post. I found that modifying the callback in the second then to not return anything did allow my tests to get further, only to hang indefinitely at random places in my test file so, as I suspected, that isn’t a real solution.

[weilu]

Can we please get this working? None of the workarounds above works anymore. I hate to be stuck with version 6.9 because of this

[szhong-becls]

According to my investigation, this issue may be injected by this commit in socketio/engine.io-client repo. It supports a listen to the "offline" event feature in version 5.0.0 (2021-03-10).

The problemic code is as follows:

+ if (this.hostname !== "localhost") {
+   this.offlineEventListener = () => {
+     this.onClose("transport close");
+   };
+   addEventListener("offline", this.offlineEventListener, false);
+ }

The socket is closed after sending CDP command: { "command": "Network.emulateNetworkConditions", "parameters": { "offline": true } }. Then the command response is never received and Cypress.automation('remote:debugger:protocol', { ... }) is timeout.