XmlDocument无法从ZipArchive条目加载流

Question

I have a zip file that contains an XML file. Using the System.IO.Compression ZipArchive I open the XML file as a Stream (actually a DeflateStream):

Stream xmlStream = null;
using (ZipArchive archive = ZipFile.Open(destPath, ZipArchiveMode.Read))
{
    xmlStream = archive.GetEntry(fileNameXml).Open();
}

Now I can read from the stream using the Stream.Read method:

// This works
byte[] buffer = new byte[10];
int tmp = xmlStream.Read(buffer, 0, 10);

What I really want to do, however, is to load the data into an XmlDocument like this:

XmlDocument xmlDoc = new XmlDocument();
// This throws 'NotSupportedException'
xmlDoc.Load(xmlStream);

But this throws a NotSupportedException with the message "This stream from ZipArchiveEntry does not support reading."

I could of course extract the XML file and open the file, but reading from the stream directly seems to me like a much nicer solution - if I could get it to work!

Answer 1

可能是因为它被包装在一个using中，所以当您实际从流中读取它时，它已经被丢弃了。

Answer 2

This happens when you have a method like this:

    public Stream OpenStream(string filePath)
    {
        using(var zipFile = ZipFile.OpenRead(filePath))
        {
            var entry = zipFile.GetEntry("entryName");
            return entry.Open();
        }
    }

And are using it like this:

    using(var stream = OpenStream(filePath))        
    {
        // NotSupportedException: This stream from ZipArchiveEntry does not support reading.
        // because zipFile is already disposed before reading the entry stream
    }

What we really want to happen is to Dispose of the zipFile at the same time we dispose of the Stream returned by entry.Open() . There's a few approaches to this and depending on your design it might be simple. One of those approaches is to create a wrapper class around the stream and dispose of both streams at the same time.

public class OnDisposeStream : Stream
{
    private readonly Stream _stream;
    private readonly Action _onDispose;

    public OnDisposeStream(Stream stream, Action onDispose)
    {
        _stream = stream;
        _onDispose = onDispose;
    }

    protected override void Dispose(bool disposing)
    {
        base.Dispose(disposing);
        _onDispose();
    }

    public override void Flush()
    {
        _stream.Flush();
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        return _stream.Seek(offset, origin);
    }

    public override void SetLength(long value)
    {
        _stream.SetLength(value);
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        return _stream.Read(buffer, offset, count);
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        _stream.Write(buffer, offset, count);
    }

    public override bool CanRead => _stream.CanRead;
    public override bool CanSeek => _stream.CanSeek;
    public override bool CanWrite => _stream.CanWrite;
    public override long Length => _stream.Length;

    public override long Position
    {
        get { return _stream.Position; }
        set { _stream.Position = value; }
    }
}

Then change our original method like this:

    public Stream OpenStream(string filePath)
    {
        var zipFile = ZipFile.OpenRead(filePath);
        var entry = zipFile.GetEntry("entryName");
        return new OnDisposeStream(entry.Open(), () => zipFile.Dispose());
    }        

Hopefully that'll help someone one day.

Answer 3

OK - figured out a workaround that I can live with.

I don't know how the XML document is trying to read the DeflateStream, since all ways I have tried to read from the stream manually has worked.

I used this workaround to keep the data in a stream and load that stream into my XmlDocument:

MemoryStream readerStream = new MemoryStream();
xmlStream.CopyTo(readerStream);
readerStream.Position = 0;
xmlDoc.Load(readerStream);

If anyone has an explanation for the strange behavior exhibited by the DeflateStream or has a better way to get the data from the DeflateStream into the xml document I would be interested in hearing that