Check the existence of the gzipped path explicitly (#704)

* Check the existance of the gzipped path explicitely.

* Fix a typo in the comments.

* Fix a typo.

server/render.js

@@ -2,6 +2,7 @@ import { join } from 'path'
 import { createElement } from 'react'
 import { renderToString, renderToStaticMarkup } from 'react-dom/server'
 import send from 'send'
+import fs from 'mz/fs'
 import accepts from 'accepts'
 import mime from 'mime-types'
 import requireModule from './require'
@@ -148,19 +149,29 @@ export async function serveStaticWithGzip (req, res, path) {
     return serveStatic(req, res, path)
   }
 
-  try {
   const gzipPath = `${path}.gz`
+
+  try {
+    // We need to check the existance of the gzipPath.
+    // Getting `ENOENT` error from the `serveStatic` is inconsistent and
+    // didn't work on all the cases.
+    //
+    // And this won't give us a race condition because we know that
+    // we don't add gzipped files at runtime.
+    await fs.stat(gzipPath)
+  } catch (ex) {
+    if (ex.code === 'ENOENT') {
+      // Seems like there's no gzipped file. Let's serve the uncompressed file.
+      return serveStatic(req, res, path)
+    }
+
+    throw ex
+  }
+
   const contentType = mime.lookup(path) || 'application/octet-stream'
   res.setHeader('Content-Type', contentType)
   res.setHeader('Content-Encoding', 'gzip')
-    await serveStatic(req, res, gzipPath)
+  return serveStatic(req, res, gzipPath)
-  } catch (ex) {
-    if (ex.code === 'ENOENT') {
-      res.removeHeader('Content-Encoding')
-      return serveStatic(req, res, path)
-    }
-    throw ex
-  }
 }
 
 export function serveStatic (req, res, path) {