Isolate method to create a WriteFileHandler

Summary: This diff isolates a few lines of code that can be useful to create a WriteFileHandler from a name using the FileHandlerFactory. This will be used down the stack.

Reviewed By: hanghu

Differential Revision: D67329236

fbshipit-source-id: 8b1b4b59ccc980d008fc72b09a79e0ba2e9a058f

vrs/FileHandlerFactory.cpp

@@ -193,4 +193,10 @@ FileDelegator* FileHandlerFactory::getFileDelegator(const string& name) {
   return (delegator == fileDelegatorMap_.end()) ? nullptr : delegator->second.get();
 }
 
+unique_ptr<WriteFileHandler> WriteFileHandler::make(const string& fileHandlerName) {
+  unique_ptr<WriteFileHandler> file{dynamic_cast<WriteFileHandler*>(
+      FileHandlerFactory::getInstance().getFileHandler(fileHandlerName).release())};
+  return file;
+}
+
 } // namespace vrs

vrs/RecordFileWriter.cpp

@@ -808,8 +808,7 @@ int RecordFileWriter::createFile(const string& filePath, bool splitHead) {
 
   if (file_->getFileHandlerName() == DiskFile::staticName() &&
       spec.fileHandlerName != DiskFile::staticName()) {
-    unique_ptr<WriteFileHandler> writeFile{dynamic_cast<WriteFileHandler*>(
-        FileHandlerFactory::getInstance().getFileHandler(spec.fileHandlerName).release())};
+    unique_ptr<WriteFileHandler> writeFile = WriteFileHandler::make(spec.fileHandlerName);
     if (!writeFile) {
       XR_LOGE("Found no WriteFileHandler named {}.", spec.fileHandlerName);
       return INVALID_FILE_SPEC;

vrs/WriteFileHandler.h

@@ -44,6 +44,9 @@ class WriteFileHandler : public FileHandler {
  public:
   WriteFileHandler() = default;
 
+  /// Create a new WriteFileHandler from a name.
+  static unique_ptr<WriteFileHandler> make(const string& fileHandlerName);
+
   /// Create a new file for writing, using a spec.
   /// The path of the file to create is expected to be in the first chunk.
   /// Optional URI parameters might be provided in the spec' extras.