使用 GZipStream 计算进度（条）

Question

我正在从一些慢速源（如 FTP 服务器）读取 .gz 文件，并立即处理接收到的数据。 看起来像这样：

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)
  {
    ...
  }
}

我的问题是显示准确的进度条。 我可以提前获得压缩的 .gz 文件大小，但我不知道未压缩的内容有多大。 逐行读取文件我很清楚读取了多少未压缩字节，但我不知道这与压缩文件大小有何关系。

那么，有没有办法从 GZipStream 获取文件指针前进到压缩文件中的距离？ 我只需要当前位置，即在读取文件之前可以获取的 gz 文件大小。

Answer 1

您可以在其中插入一个流，计算 GZipStream 已读取的字节数。

  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.
  }
}

Answer 2

我建议您看一下以下代码：

public static readonly byte[] symbols = new byte[8 * 1024];

public static void Decompress(FileInfo inFile, FileInfo outFile)
{
    using (var inStream = inFile.OpenRead())
    {
        using (var zipStream = new GZipStream(inStream, CompressionMode.Decompress))
        {
            using (var outStream = outFile.OpenWrite())
            {
                var total = 0;
                do
                {
                    var async = zipStream.BeginRead(symbols, 0, symbols.Length, null, null);
                    total = zipStream.EndRead(async);
                    if (total != 0)
                    {
                        // Report progress. Read total bytes (8K) from the zipped file.
                        outStream.Write(symbols, 0, total);
                    }
                } while (total != 0);
            }
        }
    }
}

Answer 3

我重新审视了我的代码并进行了一些测试。 恕我直言，达林是对的。 不过，我认为可以仅读取压缩流的标头（大小？）并找出结果文件的大小。 （WinRar 在不解压整个 zip 存档的情况下“知道”解压文件的大小。它从存档的标头中读取此信息。）如果您找到结果文件大小，此代码将帮助您报告精确的进度。

public static readonly byte[] symbols = new byte[8 * 1024];

public static void Decompress(FileInfo inFile, FileInfo outFile, double size, Action<double> progress)
{
    var percents = new List<double>(100);

    using (var inStream = inFile.OpenRead())
    {
        using (var zipStream = new GZipStream(inStream, CompressionMode.Decompress))
        {
            using (var outStream = outFile.OpenWrite())
            {
                var current = 0;

                var total = 0;
                while ((total = zipStream.Read(symbols, 0, symbols.Length)) != 0)
                {
                    outStream.Write(symbols, 0, total);
                    current += total;

                    var p = Math.Round(((double)current / size), 2) * 100;
                    if (!percents.Contains(p))
                    {
                        if (progress != null)
                        {
                            progress(p);
                        }
                        percents.Add(p);
                    }
                }
            }
        }
    }
}

我希望这有帮助。

Answer 4

作为解压缩进度的代理，您可以尝试使用以下方法从底层流获取文件下载进度的信息：

var percentageProgress = ftpStream.Position / (double)ftpWebResponse.ContentLength;

或者

var percentageProgress = ftpStream.Position / (double)ftpStream.Length;

它适用于 FileStream 并且它应该在 GetResponseStream() 前提是它实现了 Position 属性，FTP 服务器返回有关下载文件长度的信息：http://msdn.microsoft.com/en-us/库/system.net.ftpwebresponse.contentlength(v=vs.110).aspx