Write to gzip file from MemoryStream using XmlWriter and GZipStream

Question

I am tring to write generate a gzipped XML file from a MemoryStream. Here is what I have so far -

XmlWriterSettings settings = new XmlWriterSettings();
settings.Indent = true;

MemoryStream ms = new MemoryStream();
using (XmlWriter writer = XmlWriter.Create(ms, settings))
{
    // CREATE XML
}

Then I want to take that stream, and save it to a compressed file. I've seen many examples using GZipStream, but none exactly match this.

You might want to look at just controlling your gzip compression at the server level. You can have all xml responses gzip compressed at the IIS level. — Brian Ogden, Jul 19 '13 at 21:20

Jim Mischel · Accepted Answer · 2013-07-22T19:30:06.477

To save a document to a compressed file, you have to create two streams:

using (var fs = File.Create(fileName))
{
    using (var gz = new GZipStream(fs, CompressionMode.Compress))
    {
        doc.Save(gz);
    }
}

It assumes that you've created an XmlDocument. It then calls the XmlDocument.Save(Stream) method.

If you want to write XML directly to a compressed file, you can write:

using (var fs = File.Create(fileName))
{
    using (var gz = new GZipStream(fs, CompressionMode.Compress))
    {
        XmlWriterSettings settings = new XmlWriterSettings();
        settings.Indent = true;
        using (var writer = XmlWriter.Create(gz, settings))
        {
            // write xml here
        }
    }
}

That's the way that I'd suggest if you just want to write a gzip compressed XML file.

If you really want to go to a MemoryStream first, and then to a compressed file, you create the memory stream as you show in your question, and then you write it like this.

using (var fs = File.Create(fileName))
{
    using (var gz = new GZipStream(fs, CompressionMode.Compress))
    {
        ms.CopyTo(gz);
    }
}

Remember to set ms.Position = 0 before you do the copy.

Hey Jim, I saw you made a comment in the other anwser, I would rather just take the memory stream, and write it to a compressed file. Maybe I misunderstood your answer. Is that what you were saying to do? One thing that I didn't understand was `doc.Save(gz)` in your answer. You didn't define doc. — A Bogus, Jul 22 '13 at 18:35
@ABogus: See my updated answer, in particular the second example. — Jim Mischel, Jul 22 '13 at 19:30

Ehsan · Answer 2 · 2013-07-22T12:51:23.330

0

First of all save this to a file

 XmlDocument doc = new XmlDocument();
 doc.Save(writer);

Then use the zip methods to compress it. For compressing

    byte[] b;
using (FileStream f = new FileStream("filename", FileMode.Open))
{
    b = new byte[f.Length];
    f.Read(b, 0, (int)f.Length);
}

using (FileStream f2 = new FileStream(fileName, FileMode.Create))
using (GZipStream gz = new GZipStream(f2, CompressionMode.Compress, false))
{
    gz.Write(b, 0, b.Length);
}

edited Jul 22 '13 at 12:51

answered Jul 19 '13 at 21:18

Ehsan

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Hey Ehsan, What is "b" in your gz.Write statment? A byte array, correct? How should it be declared? Do I need to initialize it to anything? Thanks! – A Bogus Jul 22 '13 at 12:48
This works, Ehsan, except... when I uncompress the file, it seems I am losing the file type, the fact that is was an XML file is lost. Any idea why? Thanks so much for all your help! – A Bogus Jul 22 '13 at 13:03
Nevermind, Ehsan. Turns out I have to name the file like this, fileName.xml.gz to maintain the file name. Thanks again! – A Bogus Jul 22 '13 at 13:06
@ABogus: I'm curious why you would want to save the file to disk, read it back, and then save it compressed rather than just saving it compressed in the first place. – Jim Mischel Jul 22 '13 at 13:13
Hey Jim, I would like to just compress it in the first place. I would like that solution better if you know how to do it. – A Bogus Jul 22 '13 at 18:32

Write to gzip file from MemoryStream using XmlWriter and GZipStream

2 Answers2