Hono

Wiring

import { Hono } from "hono";
import { versionless, versionlessRewrites } from "@versionless/adapter-hono";
import { v } from "./versionless";

const app = new Hono();
app.use("*", versionless(v));       // before your routes
app.get("/users/:id", handler);     // handlers speak the current shape
app.post("/users", handler);

versionlessRewrites(v, app);        // after routes — alias routes for `rewrite:` changes

How it works

• Route detection. Inside an app.use("*") middleware, c.req.routePath is the middleware's own pattern (/*), not the handler's — so the adapter reads c.req.matchedRoutes and takes the last non-wildcard pattern. When none exists (404, or only catch-alls matched), core falls back to matching the raw path against the set of changed routes.
• Request up. The JSON body is parsed, upped, and written back by replacing c.req.raw with a new Request — the same pattern Hono's own bodyLimit middleware uses. The body cache is cleared so the handler's c.req.json() sees the transformed body, not a stale cached one.
• Response down. After next(), c.res is replaced with a new Response carrying the downed body (status and headers preserved, content-length recomputed). Status ≥ 400 goes through error.down chains.
• Malformed JSON despite a JSON content-type is left untouched, so your handler surfaces its own parse error instead of versionless masking it.

Only application/json bodies under 1MB are transformed; everything else passes through. Rewrite-matched requests skip body work entirely — the inner re-dispatched request runs its own exchange.

Rewrites

Hono routes before middleware can intervene on unrouted paths, so — like Elysia — rewrites need alias routes. versionlessRewrites(v, app) registers one per rewrite:

• Old-pinned client → re-dispatched through app.fetch to the rewritten target (method swapped if the rewrite changes it).
• Current client → c.notFound().

Call it after all changes are registered and all routes are wired.

Sunsets, errors, serverless

• Sunset headers go on every response for scheduled versions; past the cutoff the middleware returns 410 with the structured body itself.
• Invalid version strings return 400 { "error": "invalid_api_version", "message": ... }.
• On Workers/Edge under VERCEL, the telemetry flush is handed to c.executionCtx.waitUntil; elsewhere it settles as fire-and-forget.