ClickHouse/dbms/include/DB/IO/WriteBufferFromFileDescriptor.h

#pragma once

#include <DB/IO/WriteBufferFromFileBase.h>


namespace DB
{

/** Use ready file descriptor. Does not open or close a file.
  */
class WriteBufferFromFileDescriptor : public WriteBufferFromFileBase
{
protected:
	int fd;

	void nextImpl() override;

	/// Name or some description of file.
	std::string getFileName() const override;

public:
	WriteBufferFromFileDescriptor(
		int fd_ = -1,
		size_t buf_size = DBMS_DEFAULT_BUFFER_SIZE,
		char * existing_memory = nullptr,
		size_t alignment = 0);

	/** Could be used before initialization if needed 'fd' was not passed to constructor.
	  * It's not possible to change 'fd' during work.
	  */
	void setFD(int fd_)
	{
		fd = fd_;
	}

	~WriteBufferFromFileDescriptor() override;

	int getFD() const override
	{
		return fd;
	}

	off_t getPositionInFile() override;

	void sync() override;

private:
	off_t doSeek(off_t offset, int whence) override;

	void doTruncate(off_t length) override;
};

}