Fix node detection omfg (nodejs#2341)

* fix node detection

* remove comment

* change name

* fix regex for windows paths

lib/fetch/index.js

@@ -1344,7 +1344,7 @@ async function httpNetworkOrCacheFetch (
   //    user agents should append `User-Agent`/default `User-Agent` value to
   //    httpRequest’s header list.
   if (!httpRequest.headersList.contains('user-agent')) {
-    httpRequest.headersList.append('user-agent', __filename.endsWith('index.js') ? 'undici' : 'node')
+    httpRequest.headersList.append('user-agent', typeof esbuildDetection === 'undefined' ? 'undici' : 'node')
   }
 
   //    15. If httpRequest’s cache mode is "default" and httpRequest’s header

package.json

@@ -70,7 +70,7 @@
     "docs"
   ],
   "scripts": {
-    "build:node": "npx esbuild@0.14.38 index-fetch.js --bundle --platform=node --outfile=undici-fetch.js",
+    "build:node": "node scripts/esbuild-build.mjs",
     "prebuild:wasm": "node build/wasm.js --prebuild",
     "build:wasm": "node build/wasm.js --docker",
     "lint": "standard | snazzy",
@@ -109,6 +109,7 @@
     "delay": "^5.0.0",
     "dns-packet": "^5.4.0",
     "docsify-cli": "^4.4.3",
+    "esbuild": "^0.19.4",
     "form-data": "^4.0.0",
     "formdata-node": "^4.3.1",
     "https-pem": "^3.0.0",

scripts/esbuild-build.mjs

@@ -0,0 +1,24 @@
+import * as esbuild from 'esbuild'
+import fs from 'node:fs'
+
+const bundle = {
+  name: 'bundle',
+  setup (build) {
+    build.onLoad({ filter: /lib(\/|\\)fetch(\/|\\)index.js/ }, async (args) => {
+      const text = await fs.promises.readFile(args.path, 'utf8')
+
+      return {
+        contents: `var esbuildDetection = 1;${text}`,
+        loader: 'js'
+      }
+    })
+  }
+}
+
+await esbuild.build({
+  entryPoints: ['index-fetch.js'],
+  bundle: true,
+  outfile: 'undici-fetch.js',
+  plugins: [bundle],
+  platform: 'node'
+})