fix potential partially written files (#2)

* Make sure WriteFile() does not leave incomplete files
* use TemporaryFile and MoveTemporaryIntoPlace to avoid leaving partial files on error

1 files changed, 12 insertions, 3 deletions

diff --git a/src/zenstore/filecas.cpp b/src/zenstore/filecas.cpp
index af0a3a176..428183827 100644
--- a/src/zenstore/filecas.cpp
+++ b/src/zenstore/filecas.cpp
@@ -1179,8 +1179,13 @@ FileCasStrategy::MakeIndexSnapshot()
 			}
 		}
 
-		BasicFile ObjectIndexFile;
-		ObjectIndexFile.Open(IndexPath, BasicFile::Mode::kTruncate);
+		TemporaryFile	ObjectIndexFile;
+		std::error_code Ec;
+		ObjectIndexFile.CreateTemporary(IndexPath.parent_path(), Ec);
+		if (Ec)
+		{
+			throw std::system_error(Ec, fmt::format("Failed to create temp file for index snapshot at '{}'", IndexPath));
+		}
 		filecas::impl::FileCasIndexHeader Header = {.EntryCount = Entries.size(), .LogPosition = IndexLogPosition};
 
 		Header.Checksum = filecas::impl::FileCasIndexHeader::ComputeChecksum(Header);
@@ -1188,7 +1193,11 @@ FileCasStrategy::MakeIndexSnapshot()
 		ObjectIndexFile.Write(&Header, sizeof(filecas::impl::FileCasIndexHeader), 0);
 		ObjectIndexFile.Write(Entries.data(), Entries.size() * sizeof(FileCasIndexEntry), sizeof(filecas::impl::FileCasIndexHeader));
 		ObjectIndexFile.Flush();
-		ObjectIndexFile.Close();
+		ObjectIndexFile.MoveTemporaryIntoPlace(IndexPath, Ec);
+		if (Ec)
+		{
+			throw std::system_error(Ec, fmt::format("Failed to move temp file '{}' to '{}'", ObjectIndexFile.GetPath(), IndexPath));
+		}
 		EntryCount		   = Entries.size();
 		m_LogFlushPosition = IndexLogPosition;
 	}