如何使用 gzipstream 将内存流压缩成内存流？

Question

您好，我的问题是，如果可能的话，我需要将 MemoryStream 和 GZipStream 压缩到 MemoryStream 中，然后压缩到该方法作为参数获取的相同 MemoryStream 中。如果这无法实现，我该如何做到这一点，这样它是最节省内存的。

---

这是我当前的方法，它给了我 System.NotSupportedException: 'Stream does not support reading.' for compress.CopyTo

public static void GZipCompress(MemoryStream memoryStream)
{
    using (GZipStream compress = new GZipStream(memoryStream, CompressionMode.Compress))
    {
        compress.CopyTo(memoryStream);
    }
}

Answer 1

您不能将流复制到自身，至少在没有很多 工作的情况下是这样。只需为压缩数据分配一个新的 MemoryStream 就很简单且相当有效。例如

public MemoryStream GZipCompress(MemoryStream memoryStream)
{
    var newStream = new MemoryStream((int)memoryStream.Length / 2); //set to estimate of compression ratio

    using (GZipStream compress = new GZipStream(newStream, CompressionMode.Compress))
    {
        memoryStream.CopyTo(compress);
    }
    newStream.Position = 0;
    return newStream;
}

这是一个关于如何执行 MemoryStream 就地压缩的未经测试的想法。

public void GZipCompress(MemoryStream memoryStream)
{
    var buf = new byte[1024 * 64];
    int writePos = 0;

    using (GZipStream compress = new GZipStream(memoryStream, CompressionMode.Compress))
    {
        while (true)
        {
            var br = compress.Read(buf, 0, buf.Length);
            if (br == 0) //end of stream
            {
                break;
            }
            var readPos = memoryStream.Position;
            memoryStream.Position = writePos;
            memoryStream.Write(buf, 0, br);
            writePos += br;

            if (memoryStream.Position > readPos)
            {
                throw new InvalidOperationException("Overlapping writes corrupted the stream");
            }
            memoryStream.Position = readPos;
        }
    }
    memoryStream.SetLength(writePos);
    memoryStream.Position = 0;
}