在不使用磁盘的情况下动态压缩流

Question

我正在尝试在我的 C# MVC 项目中编写一个方法，该方法从 S3（或任何地方）流式传输文件，并将其动态压缩为 zip 文件，然后再将压缩流发送给用户。到目前为止，我已经找到了几种通过将流保存到磁盘然后正常返回来从流创建 zip 文件的方法，但我想跳过保存到磁盘并使用缓冲区到流的方法。我正在尝试下载一个非常大的文件（4GB+），该文件很容易压缩到其原始大小的一小部分。

到目前为止，我已经避免了磁盘，但似乎首先将整个文件加载到内存中：

using( var memoryStream = new MemoryStream() )
{
    using( var archive = new ZipArchive( memoryStream, ZipArchiveMode.Create, true ) )
    {
        var zipEntry = archive.CreateEntry( File );

        using( var entryStream = zipEntry.Open() )
        {
            S3.StreamFile( File, Bucket ).CopyTo( entryStream );
        }
    }

    return base.File( memoryStream.ToArray(), "application/zip", File + ".zip" );
}

类似的问题（Creating a ZIP Archive in Memory using System.IO. Compression）仅包含涉及写入磁盘的答案。

Answer 1

ZipArchive 类需要一个提供当前位置的流。TrackablePositionStream下面的类通过在发生写入调用时递增字段来保存位置

public class TrackablePositionStream : Stream
{
    private readonly Stream _stream;

    private long _position = 0;

    public TrackablePositionStream(Stream stream)
    {
        this._stream = stream;
    }

    public override void Flush()
    {
        this._stream.Flush();
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        throw new NotImplementedException();
    }

    public override void SetLength(long value)
    {
        throw new NotImplementedException();
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        throw new NotImplementedException();
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        this._position += count;
        this._stream.Write(buffer, offset, count);
    }

    public override bool CanRead => this._stream.CanRead;

    public override bool CanSeek => this._stream.CanSeek;

    public override bool CanWrite => this._stream.CanWrite;

    public override long Length => this._stream.Length;

    public override long Position
    {
        get
        {
            return this._position;
        }
        set
        {
            throw new NotImplementedException();
        }
    }
}

然后在您的操作方法中使用它：

using( var archive = new ZipArchive(new TrackablePositionStream(response.OutputStream), ZipArchiveMode.Create, true ) )
{
    var zipEntry = archive.CreateEntry( File );

    using(var entryStream = zipEntry.Open() )
    {
        S3.StreamFile( File, Bucket ).CopyTo( entryStream );
    }
}

return new EmptyResult();