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/compactcas.cpp b/src/zenstore/compactcas.cpp
index c8fb41ffc..17cf20e35 100644
--- a/src/zenstore/compactcas.cpp
+++ b/src/zenstore/compactcas.cpp
@@ -910,8 +910,13 @@ CasContainerStrategy::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));
+		}
 		CasDiskIndexHeader Header = {.EntryCount	   = Entries.size(),
 									 .LogPosition	   = IndexLogPosition,
 									 .PayloadAlignment = gsl::narrow<uint32_t>(m_PayloadAlignment)};
@@ -921,7 +926,11 @@ CasContainerStrategy::MakeIndexSnapshot()
 		ObjectIndexFile.Write(&Header, sizeof(CasDiskIndexHeader), 0);
 		ObjectIndexFile.Write(Entries.data(), Entries.size() * sizeof(CasDiskIndexEntry), sizeof(CasDiskIndexHeader));
 		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;
 	}