Reload a route handler on HMR

[rtritto]

Context

With universal-autorouter, I need to replace a route handler (registered first time on Hono server start) when the related file changes (HMR ~ Hot Module Replacement).

// Register the file to intercept changes
const { default: importedRoute } = viteDevServer.ssrLoadModule(<filepath>, { fixStacktrace: true })
app[<method>](<route>, importedRoute)

// Event for file changes
viteDevServer.watcher.on('change', async (file) => {
  const { default: importedRoute } = await viteDevServer.ssrLoadModule(file, { fixStacktrace: true })
  // Re-register file function in the route
  app[<method>](<route>, importedRoute)
})

After the re-register is called, I get:

Error: Can not add a route since the matcher is already built.
    at SmartRouter.add (file:///C:/Users/<USER>/AppData/Local/Yarn/Berry/cache/hono-npm-4.6.16-e1b105c322-10c0.zip/node_modules/hono/dist/router/smart-router/router.js:12:13)
    at Hono.#addRoute (file:///C:/Users/<USER>/AppData/Local/Yarn/Berry/cache/hono-npm-4.6.16-e1b105c322-10c0.zip/node_modules/hono/dist/hono-base.js:157:17) 
    at file:///C:/Users/<USER>/AppData/Local/Yarn/Berry/cache/hono-npm-4.6.16-e1b105c322-10c0.zip/node_modules/hono/dist/hono-base.js:42:25
    at Array.forEach (<anonymous>)
    at Hono.<computed> [as get] (file:///C:/Users/<USER>/AppData/Local/Yarn/Berry/cache/hono-npm-4.6.16-e1b105c322-10c0.zip/node_modules/hono/dist/hono-base.js:41:14)
    at file:///C:/<PROJECT>/.yarn/unplugged/universal-autorouter-npm-0.2.3-5b1bcaec9b/node_modules/universal-autorouter/dist/index.mjs:62:20

Maybe should I remove the route and then re-register?

[rtritto]

FYI @yusukebe

[rtritto]

I tried with

viteDevServer?.watcher.on('change', async (file) => {
  const { default: importedRoute } = await viteDevServer.ssrLoadModule(file, { fixStacktrace: true })
  app.routes.find((r) => <route> === r.path && <method>.toUpperCase() === r.method).handler = importedRoute
})

but the route handler doesn't change.

[yusukebe]

@rtritto

You can't add a route after app handles a request with app.fetch or app.request(). The code will throw the error but it's expected behavior:

import { Hono } from 'hono'

const app = new Hono()

app.get('/', (c) => c.text('foo'))

await app.request('/')

app.get('/extra', (c) => c.text('foo')) // Error! (expected)

[rtritto]

I'm in the development environment.

Maybe a new feature to serve can be added. Draft:

import { serve } from '@hono/node-server'
import { Hono } from 'hono'

const app = new Hono()

// Code of universal-autorouter
// Register the file to intercept changes
const { default: importedRoute } = viteDevServer.ssrLoadModule(<filepath>, { fixStacktrace: true })
app[<method>](<route>, importedRoute)

// Event for file changes
viteDevServer.watcher.on('change', async (file) => {
  const { default: importedRoute } = await viteDevServer.ssrLoadModule(file, { fixStacktrace: true })
  // Re-register file function in the route
  app[<method>](<route>, importedRoute)
})

serve({
  fetch: app.fetch,
  dev: true  // allow re-register (disable check)
})

[yusukebe]

That is the limitation of Hono routers, not @hono/node-server. So I think you can't.

[rtritto]

Some points that can be achieved one or all to the check in the router:

• add process.env.NODE_ENV === 'production' to condition of the check

• the error is provided only for new routes (check current method and route with the map of routes). Eg:

  import { Hono } from 'hono'
  
  const app = new Hono()
  
  app.get('/', (c) => c.text('foo'))
  
  await app.request('/')
  
  app.get('/', (c) => c.text('foo')) // No Error
  
  app.get('/extra', (c) => c.text('foo')) // Error! (expected)