The Art of SQL Server FILESTREAM - Red Gate Software

Chapter 3: Accessing FILESTREAM Data from Client ApplicationsNote that FILESTREAM data can be accessed using the OpenSqlFilestream() functiononly if the application connects to SQL Server using Windows authentication.If OpenSqlFilestream()succeeds, it returns a valid handle to the FILESTREAM datafile associated with the logical path name passed into the function as the first parameter.If the function fails, it returns INVALID_HANDLE_VALUE. The handle value returnedby this function can be used to manipulate the FILESTREAM data associated withthe handle. The Win32 API functions below can be used on the handle returned byOpenSqlFilestream() function.• ReadFile() – Reads information from the FILESTREAM data file.• WriteFile() – Writes information into the FILESTREAM data file.• TransmitFile() – Used to transmit FILESTREAM data over a socket.• SetFilePointer() – Moves the file pointer to a desired location in the diskfile associated with the handle. The next read/write operation will start from thenew location.• SetEndOfFile() – Truncates the file at the current file pointer position.• FlushFileBuffers() – Writes the data in all the buffers associated with a file intothe disk.• CloseHandle() – Closes the FILESTREAM file handle. If the table has UPDATEtriggers, they will be fired when the FILESTREAM file handle is closed.Note that the FILESTREAM data handle cannot be used with any Win32 APIs other thanthose listed above. If you pass the handle to any other Win32 API function, you will get anERROR_ACCESS_DENIED error.The FILESTREAM file handle should be closed by calling CloseHandle() before the currenttransaction is committed or rolled back.129