[kernel-1116] browser debug: add cdp monitor

[archandatta]

Tests

• run the chromium-headful image
• run curl -v -X POST http://localhost:444/events/start to start the event capture stream
• look through the docker container logs for /var/logs/ and there should files created for console.log, network.log etc.

I did some browsing and started a yt video and got these logs from it:

• network.log was the largest - open to thoughts on filtering some of it to reduce the size

  • Static assets (by MIME type):
  • Images: image/svg+xml (111), image/gif (45), image/jpeg (17), image/png
    (14), image/avif (14), image/x-icon (12), image/webp (1)
  • JavaScript: text/javascript (69), application/x-javascript (25),
    application/javascript (4)
  • CSS: text/css (34)
  • Fonts: font/woff2 (15)
  • Media: audio/mpeg (4), application/vnd.yt-ump (7)

  Other skipped:

  • text/html (23) — these are likely iframe/subframe HTML documents where
    the body fetch returned empty or the resource type was filtered

  What we ARE capturing bodies for (30 responses):

  • application/json (21) — API responses, the most useful data
  • text/plain (3)
  • text/html (2) — top-level page HTML
  • application/json+protobuf (2)
  • application/manifest+json (1)

  ┌─────────────────┬───────┬─────────────────────────────────────────────┐
  │    Log File     │ Lines │                 Event Types                 │
  ├─────────────────┼───────┼─────────────────────────────────────────────┤
  │ console.log     │ 2     │ console_log (2)                             │
  ├─────────────────┼───────┼─────────────────────────────────────────────┤
  │                 │       │ network_request (483), network_response     │
  │ network.log     │ 921   │ (417), network_loading_failed (18),         │
  │                 │       │ network_idle (3)                            │
  ├─────────────────┼───────┼─────────────────────────────────────────────┤
  │                 │       │ layout_shift (28), navigation (13),         │
  │ page.log        │ 55    │ dom_content_loaded (5), page_load (5),      │
  │                 │       │ layout_settled (3), navigation_settled (1)  │
  ├─────────────────┼───────┼─────────────────────────────────────────────┤
  │ interaction.log │ 9     │ interaction_click (7), interaction_key (1), │
  │                 │       │  scroll_settled (1)                         │
  ├─────────────────┼───────┼─────────────────────────────────────────────┤
  │ system.log      │ 4     │ screenshot (4)                              │
  └─────────────────┴───────┴─────────────────────────────────────────────┘

  ┌─────────────────┬──────┐
  │      File       │ Size │
  ├─────────────────┼──────┤
  │ console.log     │ 19K  │
  ├─────────────────┼──────┤
  │ interaction.log │ 4.5K │
  ├─────────────────┼──────┤
  │ network.log     │ 2.3M │
  ├─────────────────┼──────┤
  │ page.log        │ 40K  │
  ├─────────────────┼──────┤
  │ system.log      │ 658K │
  └─────────────────┴──────┘

---

Note

Medium Risk
Adds a substantial new CDP WebSocket monitor (network/body capture, injected JS, timers, reconnect/backoff) and adjusts global events.CategoryFor parsing, which could affect event categorization across the pipeline.

Overview
Introduces a full cdpmonitor implementation that connects to Chrome DevTools via WebSocket, auto-attaches to page targets (including pre-existing ones), enables key CDP domains, and injects interaction.js to emit click/key/scroll events via a runtime binding.

Adds event handlers that publish normalized events for console output/exceptions, navigation/DOM/page load, network requests/responses (optionally fetching and truncating textual bodies while skipping binary types), and layout shifts; plus computed meta-events (network_idle, layout_settled, navigation_settled) driven by debounced timers.

Implements lifecycle management with safe Start/Stop, in-flight command unblocking, and upstream-restart reconnection with backoff and monitor_disconnected/monitor_reconnected events, and adds rate-limited screenshot capture via ffmpeg with downscaling to stay under size thresholds. Updates events.CategoryFor to derive categories from underscore-delimited event types (and treats layout_* as page events).

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Redirect requests double-increment netPending, blocking network_idle

High Severity

handleNetworkRequest unconditionally calls m.computed.onRequest() (incrementing netPending) for every Network.requestWillBeSent event. In CDP, HTTP redirects reuse the same requestId and fire additional requestWillBeSent events (with a redirectResponse field), but only a single loadingFinished fires per chain. The pendingRequests map correctly overwrites the entry, but netPending gets incremented again without a corresponding decrement. This permanently inflates netPending, preventing network_idle and navigation_settled from ever firing on pages with any HTTP redirects.

Additional Locations (1)

• server/lib/cdpmonitor/computed.go#L83-L91

 

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