Issue 6477 - separate done and error callbacks in IFileSystem::Read

src/DefaultFileSystem.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 183 matching lines @@
     }
   }
 }
 
 DefaultFileSystem::DefaultFileSystem(const Scheduler& scheduler, std::unique_ptr<DefaultFileSystemSync> syncImpl)
   : scheduler(scheduler), syncImpl(std::move(syncImpl))
 {
 }
 
 void DefaultFileSystem::Read(const std::string& fileName,
-                             const ReadCallback& callback) const
+                             const ReadCallback& doneCallback,
+                             const Callback& errorCallback) const
 {
-  scheduler([this, fileName, callback]
+  scheduler([this, fileName, doneCallback, errorCallback]
   {
     std::string error;
     try
     {
-      auto data = syncImpl->Read(Resolve(fileName));
-      callback(std::move(data), error);
+      doneCallback(syncImpl->Read(Resolve(fileName)));
       return;
     }
     catch (std::exception& e)
     {
       error = e.what();
     }
     catch (...)
     {
       error =  "Unknown error while reading from " + fileName + " as " + Resolve(fileName);
     }
-    callback(IOBuffer(), error);
+
+    try
+    {
+      errorCallback(error);
+    }
+    catch (...)
+    {
+      // there is no way to catch an exception thrown from the error callback.
+    }
   });
 }
 
 void DefaultFileSystem::Write(const std::string& fileName,
                               const IOBuffer& data,
                               const Callback& callback)
 {
   scheduler([this, fileName, data, callback]
   {
     std::string error;
@@ skipping 79 matching lines @@
       error = "Unknown error while calling stat on " + fileName + " as " + Resolve(fileName);
     }
     callback(StatResult(), error);
   });
 }
 
 std::string DefaultFileSystem::Resolve(const std::string& fileName) const
 {
   return syncImpl->Resolve(fileName);
 }