Eliminate unnecessary file read

server/middleware/findFile.js

@@ -64,21 +64,10 @@ function findFile(req, res, next) {
   } else {
     // No filename in the URL. Try to figure out which file they want by
     // checking package.json's "unpkg", "browser", and "main" fields.
-    fs.readFile(path.join(req.packageDir, 'package.json'), 'utf8', function (error, data) {
-      if (error) {
-        console.error(error)
-        return res.status(500).send(`Cannot read ${req.packageSpec}/package.json`)
-      }
-
-      let packageConfig
-      try {
-        packageConfig = JSON.parse(data)
-      } catch (error) {
-        return res.status(500).send(`Cannot parse ${req.packageSpec}/package.json: ${error.message}`)
-      }
-
     let mainFilename
-      const queryMain = query && query.main
+
+    const packageConfig = req.packageConfig
+    const queryMain = req.query.main
 
     if (queryMain) {
       if (!(queryMain in packageConfig))
@@ -111,7 +100,6 @@ function findFile(req, res, next) {
         next()
       }
     })
-    })
   }
 }