fix: use available ephemeral ports for app service on production

lib/electron/main.mjs

@@ -1,9 +1,37 @@
 import path from 'node:path'
+import net from 'node:net'
 import { pathToFileURL } from 'node:url'
 import { BrowserWindow, app } from 'electron'
 
 process.env.ROOT = path.join(process.resourcesPath)
 
+async function findAvailablePort(startPort, endPort) {
+  for (let port = startPort; port <= endPort; port++) {
+    const isPortAvailable = await isPortFree(port)
+    if (isPortAvailable) return port
+  }
+  throw new Error('No available ports in the specified range.')
+}
+function isPortFree(port) {
+  return new Promise((resolve) => {
+    const server = net.createServer()
+    server.once('error', (err) => {
+      if (err.code === 'EADDRINUSE') resolve(false)
+      else throw err
+    })
+    server.once('listening', () => {
+      server.close()
+      resolve(true)
+    })
+    server.listen(port, '127.0.0.1')
+  })
+}
+
+// Ports in the range 49152 to 65535 are often referred to as "private" or "ephemeral" ports -
+// and are less likely to be used by other applications.
+const startPort = 49152
+const endPort = 65535
+
 function createWindow() {
   const win = new BrowserWindow({
     width: 800,
@@ -13,15 +41,25 @@ function createWindow() {
     },
     autoHideMenuBar: true,
   })
-  win.loadURL('http://localhost:3000')
+  win.loadURL(`http://127.0.0.1:${process.env.PORT || 3000}`)
 }
 
 app.whenReady()
   .then(async () => {
-    const modulePath = path.join(process.env.ROOT, '.output/server/index.mjs')
-    const moduleUrl = pathToFileURL(modulePath).href
-    const { default: startServer } = await import(moduleUrl)
-    if (typeof startServer === 'function') startServer()
+    try {
+      console.info('finding available port for app service')
+      const port = await findAvailablePort(startPort, endPort)
+      process.env.PORT = port
+      console.info(`starting app service on port ${port}`)
+
+      const modulePath = path.join(process.env.ROOT, '.output/server/index.mjs')
+      const moduleUrl = pathToFileURL(modulePath).href
+      const { default: startServer } = await import(moduleUrl)
+      if (typeof startServer === 'function') startServer()
+    }
+    catch (error) {
+      throw new Error('failed to start app service')
+    }
   })
   .then(createWindow)