fix: allow controlling hmr bind host (#13692)

trick to make it easier to control where the hmr server binds. usefuly when running medusa dev through proxies, docker containers, etc.

packages/admin/admin-bundler/src/utils/config.ts

@@ -17,6 +17,7 @@ export async function getViteConfig(
     ? parseInt(process.env.HMR_PORT)
     : await getPort.default()
   const hmrOptions = getHmrConfig(hmrPort)
+  const allowedHosts = getAllowedHosts()
 
   const root = path.resolve(process.cwd(), ".medusa/client")
 
@@ -54,6 +55,7 @@ export async function getViteConfig(
         allow: [searchForWorkspaceRoot(process.cwd())],
       },
       hmr: hmrOptions,
+      ...(allowedHosts && { allowedHosts }),
     },
     plugins: [
       writeStaticFiles({
@@ -72,7 +74,9 @@ export async function getViteConfig(
   }
 
   // Inject plugin environment variables with vite define
-  const pluginEnv: Record<string, string | undefined> = { BACKEND_URL: backendUrl }
+  const pluginEnv: Record<string, string | undefined> = {
+    BACKEND_URL: backendUrl,
+  }
   for (const [key, value] of Object.entries(process.env)) {
     if (key.startsWith("PLUGIN_")) {
       pluginEnv[key.replace(/^PLUGIN_/, "")] = value
@@ -80,12 +84,41 @@ export async function getViteConfig(
   }
   baseConfig.define!["process.env"] = JSON.stringify(pluginEnv)
 
+  let finalConfig = baseConfig
   if (options.vite) {
     const customConfig = options.vite(baseConfig)
-    return mergeConfig(baseConfig, customConfig)
+    finalConfig = mergeConfig(baseConfig, customConfig)
   }
 
-  return baseConfig
+  // Handle HMR_BIND_HOST after merge to detect conflicts
+  if (process.env.HMR_BIND_HOST) {
+    if (finalConfig.server?.hmr && typeof finalConfig.server.hmr === "object" && finalConfig.server.hmr.server) {
+      console.warn(
+        "HMR_BIND_HOST is set but a custom hmr.server is already configured. HMR_BIND_HOST will be ignored."
+      )
+    } else {
+      const { createServer } = require("http")
+      const hmrServer = createServer()
+      hmrServer.listen(hmrPort, process.env.HMR_BIND_HOST)
+      if (!finalConfig.server) {
+        finalConfig.server = {}
+      }
+      if (!finalConfig.server.hmr || typeof finalConfig.server.hmr !== "object") {
+        finalConfig.server.hmr = {}
+      }
+      finalConfig.server.hmr.server = hmrServer
+    }
+  }
+
+  return finalConfig
+}
+
+function getAllowedHosts(): string[] | undefined {
+  const hosts = process.env.__MEDUSA_ADMIN_ADDITIONAL_ALLOWED_HOSTS
+  if (!hosts) {
+    return undefined
+  }
+  return hosts.split(",").map((host) => host.trim())
 }
 
 function getHmrConfig(hmrPort: number): HmrOptions | boolean {