Browser Rendering Architecture

Kroki-rs implements a native Rust browser engine strategy to eliminate the dependency on Node.js and external Puppeteer/Playwright CLI wrappers.

Native Browser Strategy¶

We use the headless_chrome crate to communicate directly with Chromium via the DevTools Protocol (CDP).

• Performance: Zero-latency evaluation via pre-warmed tabs.

• Security: Strict process isolation and memory limits.

• Simplicity: No Node.js or npm required in the runtime environment.

The Browser Manager¶

The BrowserManager orchestrates the lifecycle of the Chromium instance:

1. Tab Pooling: A pool of pre-warmed tabs is maintained to handle bursts of diagram requests.

2. Harness Evaluation: Diagrams are rendered using a specialized browser-harness.js that loads the required JS libraries (Mermaid, BPMN, etc.) from local resources.

3. Adaptive Recycling: Tabs are gracefully recycled after a fixed number of requests to prevent memory accumulation.

Font Management¶

Consistent font rendering is achieved by:

• Packaging core fonts (Inter, Roboto) in the Docker image.

• Mounting system font directories into the container.

• Configuring fontconfig to prioritize these paths.

Supported Engines¶

• Mermaid: Reference

• BPMN: Reference

• Vega / Vega-Lite: Reference