Cannot find context with specified id

[inancgumus]

Reported by Tom on Oct, 30th:

• I was getting nil pointer exceptions here and somewhere here as a result of frame being nil. Moving the if blocks inside the preceding if frame != nil block got me past these. Not sure what the implications are beyond that though, but I guess having a nil frame is expected if there's already code checking for that condition?! 😅
• Currently seeing a ERRO[0026] unable to evaluate expression: Cannot find context with specified id (-32000). Not sure why - I think this was working before I pulled the latest xk6-browser.
• Also seeing a panic: send on closed channel but I think that might be happening as a result of earlier errors (like the above), i.e. during shutdown.

Example stack trace

panic: send on closed channel

goroutine 46 [running]:
go.k6.io/k6/stats.PushIfNotDone(...)
        go.k6.io/[email protected]/stats/stats.go:433
github.com/grafana/xk6-browser/common.(*NetworkManager).emitResponseReceived(0xc0010c0280, 0xc0006085b0)
        github.com/grafana/[email protected]/common/network_manager.go:131 +0x87a
github.com/grafana/xk6-browser/common.(*NetworkManager).onResponseReceived(0xc0010c0280, 0xc0005de8c0)
        github.com/grafana/[email protected]/common/network_manager.go:356 +0xc5
github.com/grafana/xk6-browser/common.(*NetworkManager).handleEvents(0xc0010c0280, 0xc00057a5a0)
        github.com/grafana/[email protected]/common/network_manager.go:245 +0x1cf
github.com/grafana/xk6-browser/common.(*NetworkManager).initEvents.func1()
        github.com/grafana/[email protected]/common/network_manager.go:220 +0x37
created by github.com/grafana/xk6-browser/common.(*NetworkManager).initEvents
        github.com/grafana/[email protected]/common/network_manager.go:219 +0x125

Here's the JS code I'm running, with the failure happening in clickBrowseDesigns (which is odd as it is very similar to the preceding clickBusinessCards).

Script

import { sleep, group } from 'k6';
import launcher from 'k6/x/browser';

import { randomIntBetween } from 'https://jslib.k6.io/k6-utils/1.1.0/index.js';

export const options = {};

let browser, context, page;

const pauseMin = 1;
const pauseMax = 1;

export default function() {
  initialize();
  
  navigateToHomepage();
  clickBusinessCards();
  clickBrowseDesigns();
  clickDesign('Standard (3.5" x 2")');
}

function initialize() {
  browser = launcher.launch('chromium', {
    args: [],
    debug: false,
    devtools: false,
    env: {},
    executablePath: null,
    headless: false,
    ignoreDefaultArgs: [],
    proxy: {},
    slowMo: '500ms',
    timeout: '30s',
  });

  context = browser.newContext({
    ignoreHTTPSErrors: true
  });

  page = context.newPage();
}

function navigateToHomepage() {
  group("Navigate to Homepage", () => {
    page.goto('https://vistaprint.ca', { waitUntil: 'domcontentloaded' });
  });

  sleep(randomIntBetween(pauseMin, pauseMax));
}

function clickBusinessCards() {
  const elem = page.$("//span[text()='Business Cards']");

  console.log(JSON.stringify(elem));

  group("Click Business Cards", () => {
    elem.click();
    
    // Wait for next page to load
    page.waitForLoadState('networkidle');
  });

  sleep(randomIntBetween(pauseMin, pauseMax));
}

function clickBrowseDesigns() {
  const elem = page.$("//a[text()='Browse designs']");

  console.log(JSON.stringify(elem));

  group("Click Browse Designs", () => {
    elem.click();
    
    page.waitForLoadState('networkidle');
  });

  sleep(randomIntBetween(pauseMin, pauseMax));
}

function clickDesign(designName) {
  // fetch all of the design options
  const designOptions = page.$("li.design-tile");
  console.log(JSON.stringify(designOptions));
  console.log(`Found ${designOptions.length} design options.`);

  console.log(`Selecting "${designName}"...`);

  JSON.stringify(designOptions);
}

---

This PR fixes the nil pointer issues.

[inancgumus]

I tried this script with the initial commit (git reset --hard a59352f) but the result is similar:

invalid memory address or nil pointer

It's weird that Tom was not getting an error before. 🤷

[inancgumus]

I tried to fix some issues but not the panic: send on closed channel.

--> #50

@imiric Do you have any idea why k6 closes the Samples channel? Any idea when an extension can receive send on closed channel for state.Samples? I guess it happens if m.ctx is done.

xk6-browser/common/network_manager.go

Lines 130 to 132 in 5d95a9e

	sampleTags := k6stats.IntoSampleTags(&tags)
	k6stats.PushIfNotDone(m.ctx, state.Samples, k6stats.ConnectedSamples{
	Samples: []k6stats.Sample{

[imiric]

@inancgumus Can you reproduce the panic?

I haven't looked into this yet, but my hunch would be that there's a race condition between the extension code and the Engine shutdown, which closes the Samples channel after the globalCtx is done:
https://github.com/grafana/k6/blob/b8164eed5413732e94f0f334b9a873146bd0f58b/core/engine.go#L315-L323

So this might be a general problem all extensions would have. I'll take a deeper look later today.

We might want to have a separate issue for that, if #50 fixes the nil pointer panics.

[inancgumus]

@inancgumus Can you reproduce the panic?

Yep, I can. Can you try it on your machine? I checked the context propagation path and it seems fine. Yeah, there may be another issue.

[imiric]

@tom-miseur I'm not able to reproduce the last two issues (Cannot find context with specified id and the panic) on the latest main (9ceafb3) with your script, and AFAIK neither can Inanc. Can you try doing the same and letting us know if the issue persists? I'm not able to reproduce it on older commits either... 😕 Was the issue persistent or did it happen intermittently?

I'm making some context changes and updating the extension to the new ModulesV2 variant, which could improve things, but it's difficult to know without being able to reproduce this.

[inancgumus]

We fixed the nil pointer and session context errors, but this issue persists. When I run the script, k6 throws a Cannot find context with specified id error.

After element clicks, pages do change on the opened browser. However, the page object in the script never changes. For example, after an element click, it still prints the previous page's title when I print the page title in the script.

I'm suspicious that click actions do not change page objects. Should they?

@robingustafsson Do you have an idea why the page objects never change?

[imiric]

@inancgumus Can you post Tom's script or a minimal version of it here that reproduces the Cannot find context with specified id issue?

[inancgumus]

@imiric It's the same script :(

[imiric]

I wasn't able to reproduce either the panic or that issue with the script from the description on Linux. It happens consistently for you on current main?

[inancgumus]

Yep, it happens all the time, maybe we should add a test for this.

[inancgumus]

On hold because: #125 (comment)