SSE Chaos

Server-Sent Events use EventSource, not fetch, so streaming UI needs a separate chaos surface. Chaos Maker wraps globalThis.EventSource and intercepts inbound MessageEvents before app listeners see them.

Config shape

await injectChaos(page, {
  seed: 42,
  sse: {
    drops: [{ urlPattern: '/events', probability: 0.1 }],
    delays: [{ urlPattern: '/events', delayMs: 500, probability: 1 }],
    corruptions: [{ urlPattern: '/events', strategy: 'truncate', probability: 0.05 }],
    closes: [{ urlPattern: '/events', afterMs: 2000, probability: 0.02 }],
  },
});

All SSE rules support urlPattern, probability, and request counting with onNth, everyNth, or afterN. Drop, delay, and corruption rules also support eventType.

Event types

sse: {
  drops: [
    { urlPattern: '/events', eventType: 'token', probability: 0.2 },
    { urlPattern: '/events', eventType: '*', probability: 0.05 },
  ],
}

eventType: 'message' targets unnamed default events. A named value targets event: frames with that name. eventType: '*' applies to every data event and automatically attaches when the app subscribes to new named events.

Events

Chaos Maker emits:

Event	Meaning
sse:drop	An inbound SSE event was skipped.
sse:delay	An inbound event was scheduled for later delivery.
sse:corrupt	event.data was rewritten.
sse:close	The EventSource was closed by chaos.

Each SSE event includes detail.url. Drop, delay, and corruption events include detail.eventType, and corruption events also include detail.strategy. Close events include detail.reason instead of detail.eventType.

Targeting with matchers

Every SSE rule accepts the cross-transport matcher surface: urlPattern, hostname, queryParams, and the matcher: 'name' reference into a registered NamedMatcher. Mix and match exactly like network rules, with the same matcher_inline_conflict validation guarantee covering both the matcher-plus-inline conflict and the no-targeting case.

await injectChaos(page, {
  sse: {
    drops: [
      {
        urlPattern: '/feed',
        queryParams: { topic: 'alerts' },
        probability: 1,
      },
    ],
  },
});

await injectChaos(page, {
  matchers: {
    realtimeApi: { hostname: /realtime/ },
  },
  sse: {
    drops: [
      { matcher: 'realtimeApi', probability: 0.2 },
    ],
  },
});

See Advanced matchers for the full field semantics and debug attribution.

Preset

import { presets } from '@chaos-maker/core';

await injectChaos(page, {
  ...presets.unreliableEventStream,
  seed: 42,
});

unreliableEventStream combines low-probability drops, a 200 ms delay, and occasional closes.