fix: replace detect-port with native net-based port detection for Alpine compatibility

The `detect-port` package shells out to `ps -p` to check process ownership
of ports, which fails on Alpine Linux / BusyBox where `ps` does not support
the `-p` flag. Replace it with a pure Node.js implementation using
`net.createServer()` that works on all platforms without spawning subprocesses.

Fixes #33847

Author: Your Name

code/core/package.json

@@ -276,7 +276,6 @@
     "@testing-library/dom": "^10.4.1",
     "@testing-library/react": "^14.0.0",
     "@types/cross-spawn": "^6.0.6",
-    "@types/detect-port": "^1.3.0",
     "@types/diff": "^5.0.9",
     "@types/ejs": "^3.1.1",
     "@types/js-yaml": "^4.0.5",
@@ -305,7 +304,6 @@
     "deep-object-diff": "^1.1.0",
     "dequal": "^2.0.2",
     "detect-indent": "^7.0.1",
-    "detect-port": "^1.6.1",
     "diff": "^8.0.2",
     "downshift": "^9.0.4",
     "ejs": "^3.1.10",

code/core/src/core-server/utils/server-address.test.ts

@@ -1,6 +1,6 @@
-import { describe, expect, it, vi } from 'vitest';
+import net from 'node:net';
 
-import detectPort from 'detect-port';
+import { describe, expect, it, vi } from 'vitest';
 
 import { getServerAddresses, getServerChannelUrl, getServerPort } from './server-address';
 
@@ -11,7 +11,7 @@ vi.mock('node:os', () => ({
     signals: {},
   },
 }));
-vi.mock('detect-port');
+vi.mock('node:net');
 vi.mock('storybook/internal/node-logger');
 
 describe('getServerAddresses', () => {
@@ -60,7 +60,17 @@ describe('getServerPort', () => {
   it('should resolve with a free port', async () => {
     const expectedFreePort = 4000;
 
-    vi.mocked(detectPort).mockResolvedValue(expectedFreePort);
+    const mockServer = {
+      unref: vi.fn(),
+      on: vi.fn(),
+      listen: vi.fn((_port: number, cb: () => void) => {
+        cb();
+        return mockServer;
+      }),
+      address: vi.fn(() => ({ port: expectedFreePort })),
+      close: vi.fn((cb: () => void) => cb()),
+    };
+    vi.mocked(net.createServer).mockReturnValue(mockServer as unknown as net.Server);
 
     const result = await getServerPort(port);
 

code/core/src/core-server/utils/server-address.ts

@@ -1,9 +1,8 @@
+import net from 'node:net';
 import os from 'node:os';
 
 import { logger } from 'storybook/internal/node-logger';
 
-import detectFreePort from 'detect-port';
-
 export function getServerAddresses(
   port: number,
   host: string | undefined,
@@ -31,6 +30,37 @@ interface PortOptions {
   exactPort?: boolean;
 }
 
+/**
+ * Checks if a given port is available by attempting to bind a TCP server to it.
+ * Returns the port if available, or rejects with an error if it is in use.
+ * This avoids shelling out to `ps` (which fails on Alpine/BusyBox environments).
+ */
+function checkPort(port: number): Promise<number> {
+  return new Promise((resolve, reject) => {
+    const server = net.createServer();
+    server.unref();
+    server.on('error', reject);
+    server.listen(port, () => {
+      const { port: assignedPort } = server.address() as net.AddressInfo;
+      server.close(() => resolve(assignedPort));
+    });
+  });
+}
+
+/**
+ * Finds a free port starting from the given port number.
+ * Falls back to an OS-assigned port (port 0) when the requested port is unavailable.
+ */
+export function detectFreePort(port?: number): Promise<number> {
+  return checkPort(port || 0).catch((err) => {
+    if (err.code === 'EADDRINUSE') {
+      // Let the OS assign a free port
+      return checkPort(0);
+    }
+    return Promise.reject(err);
+  });
+}
+
 export const getServerPort = (port?: number, { exactPort }: PortOptions = {}) =>
   detectFreePort(port)
     .then((freePort) => {