Added TemporaryFile implementation, provides a simple abstraction around temporary files

2 files changed, 119 insertions, 3 deletions

diff --git a/zenstore/basicfile.cpp b/zenstore/basicfile.cpp
index fe54184cf..233efa11c 100644
--- a/zenstore/basicfile.cpp
+++ b/zenstore/basicfile.cpp
@@ -36,11 +36,16 @@ void
 BasicFile::Open(std::filesystem::path FileName, bool IsCreate, std::error_code& Ec)
 {
 	const DWORD dwCreationDisposition = IsCreate ? CREATE_ALWAYS : OPEN_EXISTING;
-	const DWORD dwDesiredAccess		  = GENERIC_READ | GENERIC_WRITE;
+	DWORD		dwDesiredAccess		  = GENERIC_READ | GENERIC_WRITE;
 	const DWORD dwShareMode			  = FILE_SHARE_READ;
 	const DWORD dwFlagsAndAttributes  = FILE_ATTRIBUTE_NORMAL;
 	HANDLE		hTemplateFile		  = nullptr;
 
+	if (IsCreate)
+	{
+		dwDesiredAccess |= DELETE;
+	}
+
 	HANDLE FileHandle = CreateFile(FileName.c_str(),
 								   dwDesiredAccess,
 								   dwShareMode,
@@ -63,6 +68,7 @@ BasicFile::Close()
 	if (m_FileHandle)
 	{
 		::CloseHandle(m_FileHandle);
+		m_FileHandle = nullptr;
 	}
 }
 
@@ -158,6 +164,51 @@ BasicFile::FileSize()
 	return uint64_t(liFileSize.QuadPart);
 }
 
+//////////////////////////////////////////////////////////////////////////
+
+TemporaryFile::~TemporaryFile()
+{
+	Close();
+}
+
+void
+TemporaryFile::Close()
+{
+	if (m_FileHandle)
+	{
+		// Mark file for deletion when final handle is closed
+
+		FILE_DISPOSITION_INFO Fdi{.DeleteFile = TRUE};
+
+		SetFileInformationByHandle(m_FileHandle, FileDispositionInfo, &Fdi, sizeof Fdi);
+
+		BasicFile::Close();
+	}
+}
+
+void
+TemporaryFile::CreateTemporary(std::filesystem::path TempDirName, std::error_code& Ec)
+{
+	StringBuilder<64> TempName;
+	Oid::NewOid().ToString(TempName);
+
+	m_TempPath = TempDirName / TempName.c_str();
+
+	const bool IsCreate = true;
+
+	Open(m_TempPath, IsCreate, Ec);
+}
+
+void
+TemporaryFile::MoveTemporaryIntoPlace(std::filesystem::path FinalFileName, std::error_code& Ec)
+{
+	// We intentionally call the base class Close() since otherwise we'll end up
+	// deleting the temporary file
+	BasicFile::Close();
+
+	std::filesystem::rename(m_TempPath, FinalFileName, Ec);
+}
+
 #if ZEN_WITH_TESTS
 
 TEST_CASE("BasicFile")
@@ -171,6 +222,37 @@ TEST_CASE("BasicFile")
 	CHECK(File1.FileSize() == 4);
 }
 
+TEST_CASE("TemporaryFile")
+{
+	ScopedCurrentDirectoryChange _;
+
+	SUBCASE("DeleteOnClose")
+	{
+		TemporaryFile	TmpFile;
+		std::error_code Ec;
+		TmpFile.CreateTemporary(std::filesystem::current_path(), Ec);
+		CHECK(!Ec);
+		CHECK(std::filesystem::exists(TmpFile.GetPath()));
+		TmpFile.Close();
+		CHECK(std::filesystem::exists(TmpFile.GetPath()) == false);
+	}
+
+	SUBCASE("MoveIntoPlace")
+	{
+		TemporaryFile	TmpFile;
+		std::error_code Ec;
+		TmpFile.CreateTemporary(std::filesystem::current_path(), Ec);
+		CHECK(!Ec);
+		std::filesystem::path TempPath	= TmpFile.GetPath();
+		std::filesystem::path FinalPath = std::filesystem::current_path() / "final";
+		CHECK(std::filesystem::exists(TempPath));
+		TmpFile.MoveTemporaryIntoPlace(FinalPath, Ec);
+		CHECK(!Ec);
+		CHECK(std::filesystem::exists(TempPath) == false);
+		CHECK(std::filesystem::exists(FinalPath));
+	}
+}
+
 void
 basicfile_forcelink()
 {
diff --git a/zenstore/include/zenstore/basicfile.h b/zenstore/include/zenstore/basicfile.h
index d4d65b366..8a11ea98a 100644
--- a/zenstore/include/zenstore/basicfile.h
+++ b/zenstore/include/zenstore/basicfile.h
@@ -26,6 +26,10 @@ class BasicFile
 public:
 	BasicFile() = default;
 	~BasicFile();
+
+	BasicFile(const BasicFile&) = delete;
+	BasicFile& operator=(const BasicFile&) = delete;
+
 	void	 Open(std::filesystem::path FileName, bool IsCreate);
 	void	 Open(std::filesystem::path FileName, bool IsCreate, std::error_code& Ec);
 	void	 Close();
@@ -35,13 +39,43 @@ public:
 	void	 Write(const void* Data, uint64_t Size, uint64_t FileOffset);
 	void	 Flush();
 	uint64_t FileSize();
-	void*	 Handle() { return m_FileHandle; }
 	IoBuffer ReadAll();
 
-private:
+	inline void* Handle() { return m_FileHandle; }
+
+protected:
 	void* m_FileHandle = nullptr;  // This is either null or valid
 };
 
+/**
+ * Simple abstraction for a temporary file
+ *
+ * Works like a regular BasicFile but implements a simple mechanism to allow creating
+ * a temporary file for writing in a directory which may later be moved atomically
+ * into the intended location after it has been fully written to.
+ *
+ */
+
+class TemporaryFile : public BasicFile
+{
+public:
+	TemporaryFile() = default;
+	~TemporaryFile();
+
+	TemporaryFile(const TemporaryFile&) = delete;
+	TemporaryFile& operator=(const TemporaryFile&) = delete;
+
+	void						 Close();
+	void						 CreateTemporary(std::filesystem::path TempDirName, std::error_code& Ec);
+	void						 MoveTemporaryIntoPlace(std::filesystem::path FinalFileName, std::error_code& Ec);
+	const std::filesystem::path& GetPath() const { return m_TempPath; }
+
+private:
+	std::filesystem::path m_TempPath;
+
+	using BasicFile::Open;
+};
+
 ZENCORE_API void basicfile_forcelink();
 
 }  // namespace zen