Who should be responsible for closing a stream

Question

I'm writing an application that creates a "Catalog" of files, which can be attributed with other meta data files such as attachments and thumbnails.

I'm trying to abstract the interface to a catalog to the point where a consumer of a catalog does not need to know about the underlying file system used to store the files. So I've created an interface called IFileSystemAdaptor which is shown below.

public interface IFileSystemAdaptor:IDisposable
{
    void WriteFileData(string fileName, Stream data);
    Stream ReadFileData(string filename);
    void DeleteFileData(string filename);
    void ClearAllData();
    void WriteMetaFileData(string filename, string path, Stream data);
    Stream ReadMetaFileData(string filename, string path);
    void DeleteMetaFileData(string filename, string path);
    void ClearMetaFilesData(string filename);
}

Essentially my IFileSystemAdaptor interface exposes a flat list of files, that can also be associated with additional meta data files.

As you can see I'm using references to generic Stream objects to abstract the interface to a file's data. This way one implementation of a Catalog could return files from a hard disk, while another could return the data from a web server.

Now I'm trying to figure out how to keep my program from leaving streams open. Is there a rule of thumb for what members should close streams? Should the consumer of a stream close it, or should the member that original created the stream be responsible for closing it.

Answer 1

My Rules:

Should the consumer of a stream close it

1. If I return a stream from a method, the consumer is responsible. I'm giving it to you, It's your responsilibity.

2. If I accept a stream as a parameter in a method, I don't close it. When exiting the method, I don't know if the calling method still needs it. It's your stream, I'm just borrowing it, and I don't want to mess you up.

3. If I create a stream and pass it to another method, my method closes it (or tries to) when I am done with it. I don't know what you are going to do with it, but it's my stream, so I am responsible for it.

Answer 2

My spontaneous thought in this case is that the consumer should hold the responsibility for closing the streams. An IFileSystemAdaptor can't know when the consumer is done using the stream, so it also can't decide when to close it.

Answer 3

In effect the last object to use the stream should be responsible for closing it, and that is generally the caller.

Enjoy!