Once Campfire in Rust: one binary, the Rails app's data, 19–44× faster

Once Campfire in Rust is a complete port of a Rails-based chat app into a single Rust executable that preserves the original frontend (CSS, Stimulus, Turbo and vendored JS) and reads the Rails app’s SQLite database and storage layout. The port reproduces Rails behavior byte-for-byte where required using a set of crates that map to Rails subsystems - rails_compat (cookies, signed IDs), kit (Rack/Action Dispatch on Axum), db (Active Record-like rusqlite), richtext (Action Text pipeline), storage (Active Storage with libvips/ffmpeg), cable (Action Cable protocol), assets, views and routes - while documenting deliberate divergences. Parity is proven with a Playwright harness that runs Rails and Rust side-by-side on identical seed data and frozen clocks, comparing 225 screen states across Chromium/Firefox/WebKit (server HTML, live DOM, accessibility tree, subresources, Action Cable frames and pixel-perfect screenshots). Early checks compared 5,018 cells and later gates pass 873/874 checked cells.

Benchmarks show dramatic improvements in throughput, latency, real-time scaling, startup and memory. Typical page routes moved from hundreds of req/s to tens of thousands (room page 212→20,213 req/s, 95×; messages 411→23,092 req/s, 56×), p50 room latency 10.4 ms→0.19 ms (54×) and p99 461 ms→5.2 ms (88×). Action Cable deliveries scale from ~9-12k/sec to hundreds of thousands (10,000 clients: 9,485→656,183 deliveries/sec, 69×) and connecting/subscribing 10,000 clients fell from 29.2 s to 1.6 s. Cold start dropped 2,607 ms→143 ms (18×), idle memory 355 MB→15 MB (24×), and image/unpacked size 933 MB→169 MB (5.5×). The Rust port replaces Ruby/Puma/Redis/Resque/Thruster while keeping the UI identical and documents known differences.