Rewriting a .NET Blazor app in Go without losing parity

"Rewrite it in Go" is a satisfying sentence. It is also, in this case, mostly a lie — and noticing that early is what made the rewrite tractable.

Blazor Server is the UI

The original NFTMixer is a C#/.NET 6 Blazor Server app. Its .razor files are not templates — Blazor Server is a stateful framework that renders on the server and pushes DOM diffs to the browser over a websocket. Go has no equivalent. So while the generation engine, compositing, database access, S3, and wallet auth all port to Go cleanly, roughly 70% of the work was frontend, rebuilt from scratch in Next.js. Budgeting for that up front is the difference between a plan and a surprise.

Parity means behaviour, not files

Full parity does not mean porting every file. Several things were deliberately left behind because they were dead or dangerous:

an unauthenticated full-database-dump endpoint,
unfinished IPFS publishing that never actually uploaded,
entire generations of superseded components that were referenced but unreachable.

Porting those would have been faithfully reproducing debt.

Fixing the things that were simply broken

The most interesting part of a rewrite is the bugs you refuse to carry over. The original's "authentication" believed whatever wallet the browser claimed — no signature, anywhere:

Old flow:  browser says "I am 0xADMIN…"  →  server believes it.
New flow:  server issues nonce  →  wallet signs  →  server RECOVERS the address
           from the signature (go-ethereum).  Same effort, actually secure.

Alongside real SIWE, ownership is now derived from the session rather than a URL parameter, and sessions expire via a Mongo TTL index instead of living forever in an in-memory map.

Deliberate parity breaks

A rewrite is also a chance to be correct where the original was wrong: metadata now follows the OpenSea standard instead of a flat dictionary, and every layer is resized to the output dimensions so non-uniform art composites without misalignment. Those are intentional divergences — parity with the intent, not the mistake.