fix: Only restart after port is free

lib/_inspect.js

@@ -22,6 +22,7 @@
 'use strict';
 const { spawn } = require('child_process');
 const { EventEmitter } = require('events');
+const net = require('net');
 const util = require('util');
 
 const runAsStandalone = typeof __dirname !== 'undefined';
@@ -90,6 +91,43 @@ function createAgentProxy(domain, client) {
   });
 }
 
+function portIsFree(host, port, timeout = 2000) {
+  const retryDelay = 150;
+  let didTimeOut = false;
+
+  return new Promise((resolve, reject) => {
+    setTimeout(() => {
+      didTimeOut = true;
+      reject(new Error(
+        `Timeout (${timeout}) waiting for ${host}:${port} to be free`));
+    }, timeout);
+
+    function pingPort() {
+      const socket = net.connect(port, host);
+      let didRetry = false;
+      function retry() {
+        if (!didRetry && !didTimeOut) {
+          didRetry = true;
+          setTimeout(pingPort, retryDelay);
+        }
+      }
+
+      socket.on('error', (error) => {
+        if (error.code === 'ECONNREFUSED') {
+          resolve();
+        } else {
+          retry();
+        }
+      });
+      socket.on('connect', () => {
+        socket.destroy();
+        retry();
+      });
+    }
+    pingPort();
+  });
+}
+
 class NodeInspector {
   constructor(options, stdin, stdout) {
     this.options = options;
@@ -169,7 +207,14 @@ class NodeInspector {
 
   run() {
     this.killChild();
-    return this._runScript().then((child) => {
+    const { host, port } = this.options;
+
+    const runOncePortIsFree = () => {
+      return portIsFree(host, port)
+        .then(() => this._runScript());
+    };
+
+    return runOncePortIsFree().then((child) => {
       this.child = child;
 
       let connectionAttempts = 0;
@@ -194,7 +239,6 @@ class NodeInspector {
           });
       };
 
-      const { host, port } = this.options;
       this.print(`connecting to ${host}:${port} ..`, true);
       return attemptConnect();
     });