GZipStream正在切断XML的最后一部分

Question

我创建了一个名为AddGZip的扩展方法,如下所示:

public static void AddGZip(this HttpResponse response)
{
    response.Filter = new GZipStream(response.Filter, CompressionMode.Compress);
    response.AppendHeader("Content-Encoding", "gzip");
}

这是代码的一个非常简化的版本:

var response = HttpContext.Current.Response;
var request = HttpContext.Current.Request;
var result = File.ReadAllText(path);
if (request.SupportsGZip)
{
  response.AddGZip();
}
response.Write(result);
response.Flush();

当您在支持GZip的Web浏览器中查看响应时,会出现如下错误:

"XML解析错误:未关闭的令牌位置:http://webserver1/1234.xml 第78行,第1列:"

当我查看源代码时,它基本上错过了>XML文件末尾的最后一个.所以1或2个字节.

如果我注释掉AddGZip线,它可以正常工作.但是我真的想支持GZip,因为XML可能非常大.

有人对我有建议吗？我已经尝试检查了很多博客,但似乎没有针对此类错误的解决方案.

戴夫

Answer 1

有一个问题(或许是一个我在任何地方都没有看到的非常聪明的特性)DeflateStream(GZipStream构建DeflateStream并继承问题*),其中刷新可能会丢失数据.

Response.Flush()将冲洗过滤器.解决方案是使用一个知道压缩和底层接收器的包装器,并且只刷新后者:

public enum CompressionType
{
    Deflate,
    GZip
}
/// <summary>
/// Provides GZip or Deflate compression, with further handling for the fact that
/// .NETs GZip and Deflate filters don't play nicely with chunked encoding (when
/// Response.Flush() is called or buffering is off.
/// </summary>
public class WebCompressionFilter : Stream
{
    private Stream _compSink;
    private Stream _finalSink;
    public WebCompressionFilter(Stream stm, CompressionType comp)
    {
        switch(comp)
        {
            case CompressionType.Deflate:
                _compSink = new DeflateStream((_finalSink = stm), CompressionMode.Compress);
                break;
            case CompressionType.GZip:
                _compSink = new GZipStream((_finalSink = stm), CompressionMode.Compress);
                break;
        }
    }
    public override bool CanRead
    {
        get
        {
            return false;
        }
    }
    public override bool CanSeek
    {
        get
        {
            return false;
        }
    }
    public override bool CanWrite
    {
        get
        {
            return true;
        }
    }
    public override long Length
    {
        get
        {
            throw new NotSupportedException();
        }
    }
    public override long Position
    {
        get
        {
            throw new NotSupportedException();
        }
        set
        {
            throw new NotSupportedException();
        }
    }
    public override void Flush()
    {
        //We do not flush the compression stream. At best this does nothing, at worse it
        //loses a few bytes. We do however flush the underlying stream to send bytes down the
        //wire.
        _finalSink.Flush();
    }
    public override long Seek(long offset, SeekOrigin origin)
    {
        throw new NotSupportedException();
    }
    public override void SetLength(long value)
    {
        throw new NotSupportedException();
    }
    public override int Read(byte[] buffer, int offset, int count)
    {
        throw new NotSupportedException();
    }
    public override void Write(byte[] buffer, int offset, int count)
    {
        _compSink.Write(buffer, offset, count);
    }
    public override void WriteByte(byte value)
    {
        _compSink.WriteByte(value);
    }
    public override void Close()
    {
        _compSink.Close();
        _finalSink.Close();
        base.Close();
    }
    protected override void Dispose(bool disposing)
    {
        if(disposing)
        {
            _compSink.Dispose();
            _finalSink.Dispose();
        }
        base.Dispose(disposing);
    }
}

值得注意的是,支持gzip编码的大多数用户代理也支持deflate-encoding.虽然使用deflate进行的大小改进可以忽略不计(字面上只有几个字节),但是某些体系结构上的某些库会更好地处理deflate(这适用于压缩和解压缩),所以它总是值得利用HTTP压缩来支持defz over gzip.