Extracted file changes Date modified

Question

When I tried to extract my file using winrar, It retains the date modified of the file inside a .gz. But when I extracted it using a code that is working (I got from other blogs):

 public static void Decompress(FileInfo fileToDecompress)
    {
        using (FileStream originalFileStream = fileToDecompress.OpenRead())
        {
            string currentFileName = fileToDecompress.FullName;
            string date = fileToDecompress.LastWriteTimeUtc.ToString();
            MessageBox.Show(date);
            string newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length);

            using (FileStream decompressedFileStream = File.Create(newFileName))
            {
                using (GZipStream decompressionStream = new GZipStream(originalFileStream, CompressionMode.Decompress))
                {
                    decompressionStream.CopyTo(decompressedFileStream);
                    Console.WriteLine("Decompressed: {0}", fileToDecompress.Name);
                }
            }
        }
    }

It changes the modified date of the extracted file to the current date which is the date and time I extracted it.

How can I able to retain the date modified of the file?

example the file in a .gz is dated as 8/13/2014 using a winrar it didn't change but when I use my code it changes to the current date I extracted it.

score 2 · Accepted Answer · answered Aug 19 '14 at 07:58

2

To be technically correct you are not extracting file but writing decompressed stream to another stream which is file in your case. After you look at it that way is obvious that last write date of file is changed.

If you want to last write time of destination file to be the same as compressed filed, you can use File.SetLastWriteTime method (http://msdn.microsoft.com/en-US/library/system.io.file.setlastwritetime(v=vs.110).aspx):

File.SetLastWriteTimeUtc(newFileName, fileToDecompress.LastWriteTimeUtc);

answered Aug 19 '14 at 07:58

Novakov

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I've done that to my code. And I'm aware that I'm writing / creating new file. Thanks anyway. What I'm really wanna know is how can I able to get the date of the file inside the .gz file since in some cases, .gz date modified is differ from the date modified of the file inside it and I found it impossible for my code. – Kuriyama Mirai Aug 19 '14 at 08:01
What I get is as same as what you're telling me. the LastWriteTime of my fileToDecompress. – Kuriyama Mirai Aug 19 '14 at 08:02
I also find out ,or maybe there is but I'm not into using third party for my application, that my code is the only way I can able to decompress a .gz file. That's why I really cant get the date modified of the file inside it due to what my code do. – Kuriyama Mirai Aug 19 '14 at 08:07
If you want to read metadata from Gzip file, you can use SharpZipLib (http://icsharpcode.github.io/SharpZipLib) library – Novakov Aug 19 '14 at 08:09

score 2 · Answer 2 · answered Nov 17 '15 at 04:40

Using the .gz file's modified time is substandard, as the file has most likely been downloaded over http and may even be a stream in memory.

Following on from Mark Adler's suggestion:

    using (Stream s = File.OpenRead("file.gz"))
    {
        uint timestamp = 0;

        for (int x = 0; x < 4; x++)
            s.ReadByte();

        for (int x = 0; x < 4; x++)
        {
            timestamp += (uint)s.ReadByte() << (8*x);
        }

        DateTime innerFileTime = new DateTime(1970, 1, 1).AddSeconds(timestamp)
            // Gzip times are stored in universal time, I actually needed two calls to get it almost right, and the time was still out by an hour
            .ToLocalTime().ToLocalTime();


        // Reset stream position before decompressing file
        s.Seek(0, SeekOrigin.Begin);
    }

new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc).AddSeconds(timestamp) will solve your two call issue. You need to create a UTC time object, and then add seconds. — Adarsha, Dec 08 '17 at 22:08

score 1 · Answer 3 · edited Oct 07 '21 at 06:11

The modification time and date can be found in the fourth through seventh bytes of the gzip header thusly, least significant byte first:

MTIME (Modification TIME) This gives the most recent modification time of the original file being compressed. The time is in Unix format, i.e., seconds since 00:00:00 GMT, Jan. 1, 1970. (Note that this may cause problems for MS-DOS and other systems that use local rather than Universal time.) If the compressed data did not come from a file, MTIME is set to the time at which compression started. MTIME = 0 means no time stamp is available.

as documented in the GZIP File Format Specification.

You can then use the other answer here to set the modify time of the file written.

Extracted file changes Date modified

3 Answers3