Windows: Do our file filtration with case-insensitive checks

app/protocol_filter.js

@@ -25,27 +25,35 @@ function _createFileHandler({ userDataPath, installPath, isWindows }) {
   return (request, callback) => {
     // normalize() is primarily useful here for switching / to \ on windows
     const target = path.normalize(_urlToPath(request.url, { isWindows }));
+    // here we attempt to follow symlinks to the ultimate final path, reflective of what
+    //   we do in main.js on userDataPath and installPath
     const realPath = fs.existsSync(target) ? fs.realpathSync(target) : target;
+    // finally we do case-insensitive checks on windows
+    const properCasing = isWindows ? realPath.toLowerCase() : realPath;
 
-    if (!path.isAbsolute(realPath)) {
+    if (!path.isAbsolute(properCasing)) {
       console.log(
-        `Warning: denying request to non-absolute path '${realPath}'`
+        `Warning: denying request to non-absolute path '${properCasing}'`
       );
       return callback();
     }
 
     if (
-      !realPath.startsWith(userDataPath) &&
-      !realPath.startsWith(installPath)
+      !properCasing.startsWith(
+        isWindows ? userDataPath.toLowerCase() : userDataPath
+      ) &&
+      !properCasing.startsWith(
+        isWindows ? installPath.toLowerCase() : installPath
+      )
     ) {
       console.log(
-        `Warning: denying request to path '${realPath}' (userDataPath: '${userDataPath}', installPath: '${installPath}')`
+        `Warning: denying request to path '${properCasing}' (userDataPath: '${userDataPath}', installPath: '${installPath}')`
       );
       return callback();
     }
 
     return callback({
-      path: realPath,
+      path: properCasing,
     });
   };
 }