fix: allow using vite as a proxy for another vite server

packages/vite/src/node/server/middlewares/proxy.ts

@@ -4,7 +4,6 @@ import httpProxy from 'http-proxy'
 import type { Connect } from 'dep-types/connect'
 import type { HttpProxy } from 'dep-types/http-proxy'
 import colors from 'picocolors'
-import { HMR_HEADER } from '../ws'
 import { createDebugger } from '../../utils'
 import type { CommonServerOptions, ResolvedConfig } from '../..'
 
@@ -103,10 +102,9 @@ export function proxyMiddleware(
         if (doesProxyContextMatchUrl(context, url)) {
           const [proxy, opts] = proxies[context]
           if (
-            (opts.ws ||
-              opts.target?.toString().startsWith('ws:') ||
-              opts.target?.toString().startsWith('wss:')) &&
-            req.headers['sec-websocket-protocol'] !== HMR_HEADER
+            opts.ws ||
+            opts.target?.toString().startsWith('ws:') ||
+            opts.target?.toString().startsWith('wss:')
           ) {
             if (opts.rewrite) {
               req.url = opts.rewrite(url)

packages/vite/src/node/server/ws.ts

@@ -1,3 +1,4 @@
+import path from 'node:path'
 import type { Server } from 'node:http'
 import { STATUS_CODES, createServer as createHttpServer } from 'node:http'
 import type { ServerOptions as HttpsServerOptions } from 'node:https'
@@ -101,9 +102,17 @@ export function createWebSocketServer(
   const host = (hmr && hmr.host) || undefined
 
   if (wsServer) {
+    let hmrBase = config.base
+    const hmrPath = hmr ? hmr.path : undefined
+    if (hmrPath) {
+      hmrBase = path.posix.join(hmrBase, hmrPath)
+    }
     wss = new WebSocketServerRaw({ noServer: true })
     wsServer.on('upgrade', (req, socket, head) => {
-      if (req.headers['sec-websocket-protocol'] === HMR_HEADER) {
+      if (
+        req.headers['sec-websocket-protocol'] === HMR_HEADER &&
+        req.url === hmrBase
+      ) {
         wss.handleUpgrade(req, socket as Socket, head, (ws) => {
           wss.emit('connection', ws, req)
         })

playground/proxy-hmr/__tests__/proxy-hmr.spec.ts

@@ -0,0 +1,15 @@
+import { test } from 'vitest'
+import { editFile, page, untilUpdated, viteTestUrl } from '~utils'
+
+test('proxy-hmr', async () => {
+  await page.goto(viteTestUrl)
+  const otherAppTextLocator = page.frameLocator('iframe').locator('.content')
+  await untilUpdated(() => otherAppTextLocator.textContent(), 'other app')
+  editFile('other-app/index.html', (code) =>
+    code.replace('app', 'modified app'),
+  )
+  await untilUpdated(
+    () => otherAppTextLocator.textContent(),
+    'other modified app',
+  )
+})

playground/proxy-hmr/__tests__/serve.ts

@@ -0,0 +1,27 @@
+// this is automatically detected by playground/vitestSetup.ts and will replace
+// the default e2e test serve behavior
+
+import path from 'node:path'
+import { rootDir, setViteUrl } from '~utils'
+
+export async function serve(): Promise<{ close(): Promise<void> }> {
+  const vite = await import('vite')
+  const rootServer = await vite.createServer({
+    root: rootDir,
+    logLevel: 'silent',
+  })
+  const otherServer = await vite.createServer({
+    root: path.join(rootDir, 'other-app'),
+    logLevel: 'silent',
+  })
+
+  await Promise.all([rootServer.listen(), otherServer.listen()])
+  const viteUrl = rootServer.resolvedUrls.local[0]
+  setViteUrl(viteUrl)
+
+  return {
+    async close() {
+      await Promise.all([rootServer.close(), otherServer.close()])
+    },
+  }
+}

playground/proxy-hmr/index.html

@@ -0,0 +1,2 @@
+root app<br />
+<iframe src="/anotherApp" style="border: 0"></iframe>

playground/proxy-hmr/other-app/index.html

@@ -0,0 +1 @@
+<span class="content">other app</span>

playground/proxy-hmr/other-app/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "@vitejs/test-other-app",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vite build",
+    "preview": "vite preview"
+  }
+}

playground/proxy-hmr/other-app/vite.config.js

@@ -0,0 +1,9 @@
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  base: '/anotherApp',
+  server: {
+    port: 9607,
+    strictPort: true,
+  },
+})

playground/proxy-hmr/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "@vitejs/test-proxy-hmr",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vite build",
+    "preview": "vite preview"
+  }
+}

playground/proxy-hmr/vite.config.js

@@ -0,0 +1,13 @@
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  server: {
+    port: 9606,
+    proxy: {
+      '/anotherApp': {
+        target: 'http://localhost:9607',
+        ws: true,
+      },
+    },
+  },
+})

playground/test-utils.ts

@@ -30,6 +30,8 @@ export const ports = {
   'ssr-noexternal': 9603,
   'ssr-pug': 9604,
   'ssr-webworker': 9605,
+  'proxy-hmr': 9606, // not imported but used in `proxy-hmr/vite.config.js`
+  'proxy-hmr/other-app': 9607, // not imported but used in `proxy-hmr/other-app/vite.config.js`
   'css/postcss-caching': 5005,
   'css/postcss-plugins-different-dir': 5006,
   'css/dynamic-import': 5007,