AttachmentSaveFunc

Specifies the type of the function passed to save_to_callback.

It is called once for each block of bytes that is "written" by save_to_callback. If successful it should return true. If an error occurs it should set throws and return false, in which case save_to_callback will fail with the same error.

Parameters:

buf	buffer containing bytes to be written.
count	number of bytes in buf.
data	user data passed to save_to_callback

Returns:

true if successful, false (with throws set) if failed.