GZIP file Total length in C#

Question

I have a zipped file having size of several GBs, I want to get the size of Unzipped contents but don't want to actually unzip the file in C#, What might be the Library I can use? When I right click on the .gz file and go to Properties then under the Archive Tab there is a property name TotalLength which is showing this value. But I want to get it Programmatically using C#.. Any idea?

Answer 1

The last 4 bytes of the gz file contains the length.

So it should be something like:

using(var fs = File.OpenRead(path))
{
  fs.Position = fs.Length - 4;
  var b = new byte[4];
  fs.Read(b, 0, 4);
  uint length = BitConverter.ToUInt32(b, 0);
  Console.WriteLine(length);
}

Answer 2

The last for bytes of a .gz file are the uncompressed input size modulo 2^32. If your uncompressed file isn't larger than 4GB, just read the last 4 bytes of the file. If you have a larger file, I'm not sure that it's possible to get without uncompressing the stream.

Answer 3

EDIT: See the answers by Leppie and Gabe; the only reason I'm keeping this (rather than deleting it) is that it may be necessary if you suspect the length is > 4GB

---

For gzip, that data doesn't seem to be directly available - I've looked at GZipStream and the SharpZipLib equivalent - neither works. The best I can suggest is to run it locally:

    long length = 0;
    using(var fs = File.OpenRead(path))
    using (var gzip = new GZipStream(fs, CompressionMode.Decompress)) {
        var buffer = new byte[10240];
        int count;
        while ((count = gzip.Read(buffer, 0, buffer.Length)) > 0) {
            length += count;
        }
    }

If it was a zip, then SharpZipLib:

    long size = 0;
    using(var zip = new ZipFile(path)) {
        foreach (ZipEntry entry in zip) {
            size += entry.Size;
        }
    }

Answer 4

public static long mGetFileLength(string strFilePath)
{
    if (!string.IsNullOrEmpty(strFilePath))
    {
        System.IO.FileInfo info = new System.IO.FileInfo(strFilePath);
        return info.Length;
    }

    return 0; 
}