doxa-maps/internal/backend-dev-plugin.mjs

/**
 * internal/backend-dev-plugin.mjs — `bun run dev` starts the local plugin backends.
 *
 * WHY: some plugins ship to DESKTOP with a local backend (rudder-voice → backend/bin/rudder-engine,
 * run as a Tauri sidecar). In the Plugin Studio the same backend must be running, or the plugin can't
 * be tested in the browser. This plugin starts each built backend with the dev server, forwards its
 * /api/<name>/ routes, and stops it when the dev server stops. A backend that isn't built is skipped
 * with a hint: plugins without a backend never notice this file.
 *
 * ★ ONE BACKEND PER `bun run dev`, SURVIVING VITE RESTARTS. Vite restarts itself whenever vite.config.js
 * or anything it imports changes, and re-runs configureServer. Stopping the backend on every restart and
 * starting a new one at once raced the old process for its port: the new one died with "address already
 * in use" and Rudder showed "engine offline" until `bun run dev` was restarted by hand (measured
 * 2026-09-27, twice in one session). Each backend now lives in a process-wide registry (globalThis — the
 * config module itself is re-imported on a restart): a restart REUSES the running backend, it is stopped
 * only when the dev process exits, and it is restarted (up to 5 times) if it crashes.
 *
 * DEV ONLY (`apply: 'serve'`). A production build never starts or bundles a backend.
 */
import { spawn } from 'node:child_process'
import { existsSync } from 'node:fs'
import { resolve } from 'node:path'

// name → how to run it. `route` is proxied to `port` on 127.0.0.1.
export const DEV_BACKENDS = [
  {
    name: 'rudder-engine',
    bin: 'backend/bin/rudder-engine',
    build: 'cd backend/rudder-engine && go build -o ../bin/rudder-engine .',
    route: '/api/rudder',
    port: Number(process.env.RUDDER_PORT || 5193),
    env: { RUDDER_PORT: String(process.env.RUDDER_PORT || 5193), RUDDER_NEMO_PORT: String(process.env.RUDDER_NEMO_PORT || 5194) },
  },
]

// The proxy table for vite's `server.proxy`. SSE (`/events`) streams through unbuffered.
export function devBackendProxy() {
  return Object.fromEntries(DEV_BACKENDS.map((b) => [b.route, { target: `http://127.0.0.1:${b.port}`, changeOrigin: false }]))
}

const REG = (globalThis.__dxDevBackends ||= { procs: new Map(), exitHooked: false, stopping: false })
const isAlive = (name) => { const e = REG.procs.get(name); return !!e && e.child.exitCode === null && e.child.signalCode === null }

function stopAll() {
  REG.stopping = true
  for (const { child } of REG.procs.values()) { try { child.kill('SIGTERM') } catch {} }
}

function start(root, b, logger, restarts = 0) {
  const tag = `[${b.name}]`
  const child = spawn(resolve(root, b.bin), [], { cwd: root, env: { ...process.env, ...b.env }, stdio: ['ignore', 'pipe', 'pipe'] })
  const entry = { child, restarts, logger }
  REG.procs.set(b.name, entry)
  const out = (d) => String(d).trim().split('\n').forEach((l) => l && entry.logger.info(`${tag} ${l}`))
  child.stdout.on('data', out)
  child.stderr.on('data', out)
  child.on('exit', (code) => {
    if (REG.procs.get(b.name) !== entry) return
    REG.procs.delete(b.name)
    if (REG.stopping) return
    entry.logger.warn(`${tag} exited (${code})`)
    // Crashed on its own: restart it, after its port has had a moment to free up.
    if (entry.restarts < 5) {
      setTimeout(() => {
        if (REG.stopping || REG.procs.has(b.name)) return
        entry.logger.warn(`${tag} restarting (${entry.restarts + 1}/5)`)
        start(root, b, entry.logger, entry.restarts + 1)
      }, 2000)
    }
  })
  logger.info(`${tag} started → ${b.route} on 127.0.0.1:${b.port}`)
}

export function backendDevPlugin(root) {
  return {
    name: 'dx-backend-dev',
    apply: 'serve',
    configureServer(server) {
      // ENGINE NOT RUNNING, QUIETLY (dx-shepherd, R500): with no backend process the proxy answered
      // 500 ECONNREFUSED, which every page showed as console errors. While a backend is down its routes get
      // well-formed answers instead: /events streams ONE status event saying the engine is offline (the
      // plugin renders its own "engine not running" state from it), anything else returns an empty JSON
      // list. Registered here, so it runs before vite's proxy.
      for (const b of DEV_BACKENDS) {
        server.middlewares.use(b.route, (req, res, next) => {
          if (isAlive(b.name)) return next()
          if ((req.url || '').startsWith('/events')) {
            res.writeHead(200, { 'Content-Type': 'text/event-stream', 'Cache-Control': 'no-cache', Connection: 'keep-alive' })
            res.write(`data: ${JSON.stringify({ type: 'status', status: { engine: 'offline', error: 'The desktop engine is not running.' } })}\n\n`)
            return   // held open, so the EventSource does not reconnect in a loop
          }
          res.writeHead(200, { 'Content-Type': 'application/json' })
          res.end('[]')
        })
      }
      const logger = server.config.logger
      if (!REG.exitHooked) {
        REG.exitHooked = true
        process.once('exit', stopAll)
        process.once('SIGINT', () => { stopAll(); process.exit(0) })
        process.once('SIGTERM', () => { stopAll(); process.exit(0) })
      }
      for (const b of DEV_BACKENDS) {
        if (isAlive(b.name)) {
          REG.procs.get(b.name).logger = logger   // log through the restarted server
          logger.info(`[${b.name}] still running → ${b.route} (kept across the dev-server restart)`)
          continue
        }
        if (!existsSync(resolve(root, b.bin))) {
          logger.warn(`[backend] ${b.name} not built — its plugin will show "engine offline". Build: ${b.build}`)
          continue
        }
        start(root, b, logger)
      }
    },
  }
}