DotNetZip - Cannot access a closed Stream

Question

None of the similar questions are quite what I'm looking for!

What's wrong with the following code? files is a text array of file contents, and fileNames is the corresponding filename array.

This code always fails at the second-last line with the Save method, but I can't see why the stream would be closed!

result = new MemoryStream();

using (ZipFile zipFile = new ZipFile())
{
    for (int i = 0; i < files.Count(); i++)
    {
        System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
        Byte[] bytes = encoding.GetBytes(files[i]);
        using (MemoryStream fs = new MemoryStream(bytes))
        {
            zipFile.AddEntry(fileNames[i], fs);
        }
    }
    zipFile.Save(result);
}

Thanks for any help - getting desperate here!

This is my solution based on @spender's first comment, although his solution posted below is possibly nicer.

        try
        {
            result = new MemoryStream();
            List<Stream> streams = new List<Stream>();

            if (files.Count > 0)
            {
                using (ZipFile zipFile = new ZipFile())
                {
                    for (int i = 0; i < files.Count(); i++)
                    {

                        System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
                        Byte[] bytes = encoding.GetBytes(files[i]);
                        streams.Add(new MemoryStream(bytes));
                        zipFile.AddEntry(fileNames[i], streams[i]);
                    }
                    zipFile.Save(result);
                }
            }
        }
        catch (Exception ex)
        {
            throw;
        }

What's in the `files` array? I think that the stream `fs` is not read until `Save` is called, at which point you've already disposed of it. — spender, Jul 11 '13 at 00:39
The stream is being closed when you exit the `using(MemoryStream..){}` block. Expand it to include the `.Save`. — Nick Gotch, Jul 11 '13 at 00:39
Nick - only the streams for loading into the zip are closed, not the one saved to. Do you think that's the problem? — CompanyDroneFromSector7G, Jul 11 '13 at 00:41
You're adding the fs to the zipFile as an entry. I'd suspect it's trying to access that stream when it does the Save. — Nick Gotch, Jul 11 '13 at 00:42
Yup @spender is exactly right. Thanks a lot that's a big help. If you post it as an answer I'll accept. — CompanyDroneFromSector7G, Jul 11 '13 at 00:48

spender · Accepted Answer · 2013-07-11T00:49:17.027

It seems that calling Save is the point when the source streams are read. This means you have to keep them undisposed until after the save. Abandon using statement in this case as it is impossible to extend its scope beyond the loop. Instead, collect your IDisposables and dispose of them once the save is completed.

result = new MemoryStream();

using (ZipFile zipFile = new ZipFile())
{
    List<IDisposable> memStreams = new List<IDisposable>();
    try
    {
        for (int i = 0; i < files.Count(); i++)
        {
            System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
            Byte[] bytes = encoding.GetBytes(files[i]);
            MemoryStream fs = new MemoryStream(bytes);
            zipFile.AddEntry(fileNames[i], fs);
            memStreams.Add(fs);
        }
        zipFile.Save(result);
    }
    finally
    {
        foreach(var x in memStreams)
        {
            x.Dispose();
        }
    }
}

That's almost exactly what I did when I read your comment. I used a list to track the streams! However I think your explicit disposing is a bit better. Thanks :) — CompanyDroneFromSector7G, Jul 11 '13 at 00:50
@bukko: Thinking about it, it's actually completely unnecessary to dispose of MemoryStream instances, as they don't hold onto any resources. The IDisposable interface is inherited from Stream with the assumption that all streams are IO related... MemoryStream is the exception. I think the answer is still good as a general answer to your problem though. — spender, Jul 11 '13 at 01:13

score 1 · Answer 2 · answered Aug 09 '18 at 15:17

@spender answer is spot on but as my 2 cents if you want to be more synonymous with using pattern you can do something like

class

public class DisposableBucket : IDisposable
{
    readonly List<IDisposable> listOfDisposables = new List<IDisposable>();

    public TClass Using<TClass>(TClass disposable) where TClass : IDisposable
    {
        listOfDisposables.Add(disposable);
        return disposable;
    }

    public void Dispose()
    {
        foreach (var listOfDisposable in listOfDisposables)
        {
            listOfDisposable.Dispose();
        }

    }
}

How to use

result = new MemoryStream();
using(var bucket = new DisposableBucket())
{
    using (var zipFile = new ZipFile())
    {
        List<IDisposable> memStreams = new List<IDisposable>();

        for (int i = 0; i < files.Count(); i++)
        {
            System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
            Byte[] bytes = encoding.GetBytes(files[i]);

            var fs = bucket.Using(new MemoryStream(bytes));
            zipFile.AddEntry(fileNames[i], fs);

        }
        zipFile.Save(result);

    }
}

DotNetZip - Cannot access a closed Stream

2 Answers2