find available port (#86)

lib/cmd-fns/dev/find-available-port.ts

@@ -0,0 +1,30 @@
+import net from 'net'
+
+const MAX_PORT = 65535 // Maximum valid port number
+
+export const findAvailablePort = async (startPort: number): Promise<number> => {
+  let port = startPort
+
+  while (port <= MAX_PORT) {
+    if (!(await isPortInUse(port))) {
+      return port
+    }
+    port++
+  }
+
+  throw new Error(`Unable to find an available port in range ${startPort}-${MAX_PORT}`)
+}
+
+const isPortInUse = (port: number): Promise<boolean> => {
+  return new Promise((resolve) => {
+    const server = net.createServer()
+    server.once('error', () => {
+      resolve(true)
+    })
+    server.once('listening', () => {
+      server.close()
+      resolve(false)
+    })
+    server.listen(port)
+  })
+}

lib/cmd-fns/dev/index.ts

@@ -18,6 +18,7 @@ import { startFsWatcher } from "./start-fs-watcher"
 import { uploadExamplesFromDirectory } from "./upload-examples-from-directory"
 import posthog from "lib/posthog"
 import crypto from 'crypto'
+import { findAvailablePort } from "./find-available-port"
 
 export const devCmd = async (ctx: AppContext, args: any) => {
   const params = z
@@ -26,9 +27,12 @@ export const devCmd = async (ctx: AppContext, args: any) => {
     })
     .parse(args)
 
-  const { port } = params
+  let { port } = params
   const { cwd } = ctx
 
+  // Find an available port
+  port = await findAvailablePort(port)
+
   const projectHash = crypto.createHash('md5').update(cwd).digest('hex')
 
   posthog.capture({