Computing progress (bar) using GZipStream

Question

I'm reading a .gz file from some slow source (like FTP Server) and am processing the received data right away. Looks something like this:

FtpWebResponse response = ftpclientRequest.GetResponse() as FtpWebResponse;
using (Stream ftpStream = response.GetResponseStream())
using (GZipStream unzipped = new GZipStream(ftpStream, CompressionMode.Decompress))
using (StreamReader linereader = new StreamReader(unzipped))
{
  String l;
  while ((l = linereader.ReadLine()) != null)
  {
    ...
  }
}

My problem is showing an accurate progress bar. In advance I can get the compressed .gz file size, but I got no clue how large the content would be uncompressed. Reading the file line by line I know quite well how many uncompressed bytes I read, but I don't know how this does relate to the compressed file size.

So, is there any way to get from GZipStream how far the file pointer is advanced into the compressed file? I only need the current position, the gz file size I can fetch before reading the file.

Answer 1

You can plug a stream in between which counts, how many bytes GZipStream has read.

  public class ProgressStream : Stream
  {
    public long BytesRead { get; set; }
    Stream _baseStream;
    public ProgressStream(Stream s)
    {
      _baseStream = s;
    }
    public override bool CanRead
    {
      get { return _baseStream.CanRead; }
    }
    public override bool CanSeek
    {
      get { return false; }
    }
    public override bool CanWrite
    {
      get { return false; }
    }
    public override void Flush()
    {
      _baseStream.Flush();
    }
    public override long Length
    {
      get { throw new NotImplementedException(); }
    }
    public override long Position
    {
      get
      {
        throw new NotImplementedException();
      }
      set
      {
        throw new NotImplementedException();
      }
    }
    public override int Read(byte[] buffer, int offset, int count)
    {
      int rc = _baseStream.Read(buffer, offset, count);
      BytesRead += rc;
      return rc;
    }
    public override long Seek(long offset, SeekOrigin origin)
    {
      throw new NotImplementedException();
    }
    public override void SetLength(long value)
    {
      throw new NotImplementedException();
    }
    public override void Write(byte[] buffer, int offset, int count)
    {
      throw new NotImplementedException();
    }
  }

// usage
FtpWebResponse response = ftpclientRequest.GetResponse() as FtpWebResponse;
using (Stream ftpStream = response.GetResponseStream())
using (ProgressStream progressStream = new ProgressStream(ftpstream))
using (GZipStream unzipped = new GZipStream(progressStream, CompressionMode.Decompress))
using (StreamReader linereader = new StreamReader(unzipped))
{
  String l;
  while ((l = linereader.ReadLine()) != null)
  {
    progressStream.BytesRead(); // does contain the # of bytes read from FTP so far.
  }
}