refactor: tighten up cloudflare detection (brianc#3170)

* refactor: tighten up cloudflare detection

The previous approach to detecting whether to use Cloudflare's sockets was to check for missing polyfills.
But as we improve the polyfills that Wrangler can provide these checks are no longer valid.

Now we just try to use the Cloudflare API first and fallback to Node.js if those are not available.

* fixup! refactor: tighten up cloudflare detection

Author: petebacondarwin

packages/pg/lib/stream.js

@@ -1,28 +1,81 @@
+const { getStream, getSecureStream } = getStreamFuncs()
+
+module.exports = {
+  /**
+   * Get a socket stream compatible with the current runtime environment.
+   * @returns {Duplex}
+   */
+  getStream,
+  /**
+   * Get a TLS secured socket, compatible with the current environment,
+   * using the socket and other settings given in `options`.
+   * @returns {Duplex}
+   */
+  getSecureStream,
+}
+
 /**
- * Get a socket stream compatible with the current runtime environment.
- * @returns {Duplex}
+ * The stream functions that work in Node.js
  */
-module.exports.getStream = function getStream(ssl) {
-  const net = require('net')
-  if (typeof net.Socket === 'function') {
+function getNodejsStreamFuncs() {
+  function getStream(ssl) {
+    const net = require('net')
     return new net.Socket()
-  } else {
-    const { CloudflareSocket } = require('pg-cloudflare')
-    return new CloudflareSocket(ssl)
+  }
+
+  function getSecureStream(options) {
+    var tls = require('tls')
+    return tls.connect(options)
+  }
+  return {
+    getStream,
+    getSecureStream,
   }
 }
 
 /**
- * Get a TLS secured socket, compatible with the current environment,
- * using the socket and other settings given in `options`.
- * @returns {Duplex}
+ * The stream functions that work in Cloudflare Workers
  */
-module.exports.getSecureStream = function getSecureStream(options) {
-  var tls = require('tls')
-  if (tls.connect) {
-    return tls.connect(options)
-  } else {
+function getCloudflareStreamFuncs() {
+  function getStream(ssl) {
+    const { CloudflareSocket } = require('pg-cloudflare')
+    return new CloudflareSocket(ssl)
+  }
+
+  function getSecureStream(options) {
     options.socket.startTls(options)
     return options.socket
   }
+  return {
+    getStream,
+    getSecureStream,
+  }
+}
+
+/**
+ * Are we running in a Cloudflare Worker?
+ *
+ * @returns true if the code is currently running inside a Cloudflare Worker.
+ */
+function isCloudflareRuntime() {
+  // Since 2022-03-21 the `global_navigator` compatibility flag is on for Cloudflare Workers
+  // which means that `navigator.userAgent` will be defined.
+  if (typeof navigator === 'object' && navigator !== null && typeof navigator.userAgent === 'string') {
+    return navigator.userAgent === 'Cloudflare-Workers'
+  }
+  // In case `navigator` or `navigator.userAgent` is not defined then try a more sneaky approach
+  if (typeof Response === 'function') {
+    const resp = new Response(null, { cf: { thing: true } })
+    if (typeof resp.cf === 'object' && resp.cf !== null && resp.cf.thing) {
+      return true
+    }
+  }
+  return false
+}
+
+function getStreamFuncs() {
+  if (isCloudflareRuntime()) {
+    return getCloudflareStreamFuncs()
+  }
+  return getNodejsStreamFuncs()
 }