grafana/k6 · error

throttling network: %w

Error message

throttling network: %w

What it means

The CDP command Network.emulateNetworkConditions failed while applying a network profile (latency/download/upload) — i.e. network throttling. ThrottleNetwork short-circuits when the profile is unchanged; the error means the CDP action itself failed on the page session.

Source

Thrown at internal/js/modules/k6/browser/common/network_manager.go:1082

	return nil
}

// ThrottleNetwork changes the network attributes in chrome to simulate slower
// networks e.g. a slow 3G connection.
func (m *NetworkManager) ThrottleNetwork(networkProfile NetworkProfile) error {
	if m.networkProfile == networkProfile {
		return nil
	}
	m.networkProfile = networkProfile

	action := network.EmulateNetworkConditions(
		m.offline,
		m.networkProfile.Latency,
		m.networkProfile.Download,
		m.networkProfile.Upload,
	)
	if err := action.Do(cdp.WithExecutor(m.ctx, m.session)); err != nil {
		return fmt.Errorf("throttling network: %w", err)
	}

	return nil
}

// SetUserAgent overrides the browser user agent string.
func (m *NetworkManager) SetUserAgent(userAgent string) {
	action := emulation.SetUserAgentOverride(userAgent)
	if err := action.Do(cdp.WithExecutor(m.ctx, m.session)); err != nil {
		k6ext.Panicf(m.ctx, "setting user agent: %w", err)
	}
}

// SetCacheEnabled toggles cache on/off.
func (m *NetworkManager) SetCacheEnabled(enabled bool) {
	m.userCacheDisabled = !enabled
	if err := m.updateProtocolCacheDisabled(); err != nil {
		k6ext.Panicf(m.ctx, "%v", err)

View on GitHub (pinned to 93accf6570)

Solutions

1. Apply the network profile at context creation so it is configured once on a live session
2. If throttling per phase, ensure the page is open and idle (not mid-navigation) when it changes
3. Investigate the first failure in DEBUG=k6-browser logs — this message wraps a session-level problem
4. Keep k6 and its bundled chromium in sync; version skew can reject the EmulateNetworkConditions parameters

Example fix

// before
const ctx = browser.newContext();
const page = await ctx.newPage();
await page.close();
await ctx.setNetworkProfile ? null : null; // throttling after teardown

// after
const ctx = browser.newContext({ networkProfile: { latency: 400, download: 500*1024, upload: 500*1024 } });
const page = await ctx.newPage();
await page.goto('https://test.k6.io/');

// Prefer setting the profile once at creation; nothing to guard mid-run
const ctx = browser.newContext({ networkProfile: { latency: 400, download: 512000, upload: 512000 } });

When it happens

Trigger: Creating a browser context with the networkProfile option (e.g. 'Slow 3G' or a custom {latency, download, upload} profile) or calling the throttle API when the page's CDP session is already dead — browser crashed, target destroyed, or context/page closing at that moment.

Common situations: Simulating slow 3G in tests whose pages navigate aggressively (target process swaps during goto while throttling applies); throttling set up late in the iteration; throttling after an earlier crash made every CDP call fail.

Related errors

• emulating network conditions: %w
• attaching new page: %w
• selectHandle.dispose: %w
• attaching worker target ID %v to session ID %v: %w
• disposing element with ID %s: %w

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/290dee407694053c. Report an issue: GitHub.