hono

name	hono
description	Use when writing, editing, or reviewing anything in core/ that touches HTTP — routing, middleware, request/response handling, SSE streaming, error handling, auth mounting, or route tests. Keywords: Hono, new Hono, app.get/post, c.json, c.req.valid, MiddlewareHandler, ContextVariableMap, streamSSE, bodyLimit, app.onError, app.request, hono/node-server, better-auth handler.

Hono in RSC (core/)

Hono ^4.x is core's entire HTTP layer. core/ is never browser-facing (CLAUDE.md invariant): the web app is the only client, and it talks to core over plain fetch. Everything here runs on @hono/node-server under Node's native type-stripping — no build step, no bundler.

The whole app is assembled in one place: core/src/api/app.ts (createApp), with middleware factories in core/src/api/auth.ts. Read those two files before adding a route — match them, don't invent a parallel style.

House style — what THIS repo does (and deliberately does NOT)

Concern	RSC does	Do NOT reach for
Errors	return c.json({ error: '…' }, status); domain errors bubble to app.onError (DomainError → 400)	HTTPException / throw in handlers
Validation	hand-rolled guards (isString, isValidFeedUrl, readJsonBody)	@hono/zod-validator, adding zod
Typed context	global declare module 'hono' { interface ContextVariableMap … }	per-instance new Hono<{ Variables }>() generics
Middleware	factory fns returning MiddlewareHandler (sessionAuth, requireAdmin…)	inline app.use closures for auth
Web↔core	plain fetch + the /api/auth proxy	Hono RPC / hc client / AppType export
Tests	app.request(path, init) against createApp(...)	testClient, running a real server

These are deliberate (YAGNI + no-new-deps). Don't "modernize" a route to zValidator/HTTPException/RPC without an explicit ask — it breaks the pattern and widens the dep surface.

Patterns as they appear here

Route + guard + hand validation (app.ts):

app.post('/posts', authed, async (c) => {          // authed = sessionAuth(...) factory
  const body = await readJsonBody(c)               // try/catch c.req.json() → null
  if (!body) return c.json({ error: 'body invalid' }, 400)
  if (!isString(body.content, 1, N)) return c.json({ error: 'content invalid' }, 400)
  const me = c.get('coreUser')                     // typed via ContextVariableMap
  return c.json({ post: await service.create(me, ...) }, 201)
})

Typed context variables — augment once, globally (api/auth.ts top):

declare module 'hono' {
  interface ContextVariableMap { coreUser: User; sessionIsAnonymous: boolean; isAdmin: boolean }
}

Then c.set('coreUser', …) in middleware and c.get('coreUser') in handlers are typed everywhere with no per-route generics.

Middleware factory returning MiddlewareHandler (api/auth.ts):

export function requireAdmin(): MiddlewareHandler {
  return async (c, next) => {
    if (!c.get('isAdmin')) return c.json({ error: 'admin only' }, 403)
    return next()   // NOTE: `return next()` — adminOrToken composes middleware
  }                 //       manually and needs the returned Response to propagate
}

Compose them positionally: app.post('/x', authed, requireAdmin(), handler).

Central error handler (app.ts) — the only place internal errors are shaped:

app.onError((err, c) => {
  if (err instanceof DomainError) return c.json({ error: err.message }, 400)
  console.error(err); return c.json({ error: 'internal error' }, 500)
})

Body limits on public/federation POSTs (hono/body-limit):

app.post('/hub', bodyLimit({ maxSize: MAX_FORM_BYTES, onError: rejectOversized }), handler)

SSE — the live timeline (hono/streaming, app.ts:/timeline/stream):

return streamSSE(c, async (stream) => {
  const off = bus.onNewPost((e) => stream.writeSSE({ event: 'post', data: JSON.stringify(e) }))
  stream.onAbort(off)                     // cleanup on client drop — required
  while (!stream.aborted) { await stream.writeSSE({ event: 'ping', data: '' }); await stream.sleep(15000) }
})

Mounting better-auth — core delegates the whole /api/auth/* surface to the better-auth handler with the raw request (app.ts):

app.on(['GET', 'POST'], '/api/auth/*', (c) => deps.auth.handler(c.req.raw))

(Some POSTs are mail-gated first — see the MAIL_GATED set.) See the better-auth side in core/src/auth.ts; use the better-auth MCP (search_docs/get_doc) for its API, per CLAUDE.md.

Testing — Web-standard, no server (core/test/*.test.ts):

const app = createApp({ service, bus, token: 'secret', auth, users: repo, feeds })
const res = await app.request('/posts', { method: 'POST', headers: auth, body: JSON.stringify({ content: 'x' }) })
expect(res.status).toBe(201)

Type-stripping means vitest passes on type errors — always also run tsc --noEmit (see testing-gotchas in memory).

Going deeper

Don't write Hono APIs from memory (CLAUDE.md rule). For anything not shown above:

• better-auth MCP for auth-handler details.
• context7 MCP (resolve-library-id → query-docs) for current Hono docs.
• Full offline copy: https://hono.dev/llms-full.txt (index: llms.txt, condensed: llms-small.txt).
• Installed source: core/node_modules/hono/.