GZipStream corrupts file if i pack it in parts (Flush doesn't work)

Question

I've tried to use this code to compress a file in parts

using (var fsIn = new FileStream("test.avi", FileMode.Open))
{
    using (var fsOut = new FileStream("test.avi.gz", FileMode.Create))
    {
        var buf = new byte[1024 * 1024];

        using (var gzip = new GZipStream(fsOut, CompressionMode.Compress, true))
        {
            while (true)
            {
                var readCount = fsIn.Read(buf, 0, buf.Length);
                if (readCount <= 0)
                {
                    break;
                }

                gzip.Write(buf, 0, buf.Length);
                gzip.Flush();
            }
        }
    }
}

but i've got corrupted file after decompression. This code works

using (var fsIn = new FileStream("test.avi", FileMode.Open))
{
    using (var fsOut = new FileStream("test.avi.gz", FileMode.Create))
    {
        var buf = new byte[1024*1024];

        while (true)
        {
            var readCount = fsIn.Read(buf, 0, buf.Length);
            if (readCount <= 0)
            {
                break;
            }

            // This string was transferred into "while" cycle
            using (var gzip = new GZipStream(fsOut, CompressionMode.Compress, true))
            {
                gzip.Write(buf, 0, buf.Length);
            }
        }
    }
}

Why gzip.Flush() doesn't work? Why only gzip.Close() works?

score 1 · Answer 1 · answered Jun 04 '13 at 08:39

new GZipStream(fsOut, CompressionMode.Compress, true) leaves the stream open after disposing, you should change the last parameter to false.

GZipStream Constructor (Stream, CompressionMode, Boolean)

leaveOpen
Type: System.Boolean
true to leave the stream open after disposing the GZipStream object; otherwise, false.

Also Flush() has no effects in GZipStream

The current implementation of this method does not flush the internal buffer. The internal buffer is flushed when the object is disposed.

If i'll write "false" then it will not work, because i need to left fsOut opened in second version. And the default value is false. — Aleksandrov Stas, Jun 04 '13 at 11:50

score 0 · Accepted Answer · answered Jun 04 '13 at 08:40

0

Yuo need to know that gzip.Flush(); is not working

From MSDN - GZipStream.Flush :

The current implementation of this method does not flush the internal buffer. The internal buffer is flushed when the object is disposed.

answered Jun 04 '13 at 08:40

Mzf

5,210
2
24
37

Hm. The built-in method summary tells the opposite. – Aleksandrov Stas Jun 04 '13 at 11:52

score 0 · Answer 3 · answered Jun 25 '14 at 09:53

File is compressed properly. in fact it turns out that the file contains a set of compressed files. Archives number equal to the number parts. At each new iteration, a new file and appended to the file. decision

You need to specify the length of the packaging after the packaging and before burning to file.

Just like that:

Compress:

BitConverter.GetBytes(compressedPart.Length).CopyTo(blockToWrite, 4);

In decompression read this length and choose part of the file is equal to this length for decompression.

GZipStream corrupts file if i pack it in parts (Flush doesn't work)

3 Answers3