如何将 GZipStream 与 System.IO.MemoryStream 一起使用? [英] How do I use GZipStream with System.IO.MemoryStream?

问题描述

我遇到了这个测试函数的问题，我在内存中取出一个字符串，压缩它，然后解压它.压缩效果很好，但我似乎无法让解压工作.

I am having an issue with this test function where I take an in memory string, compress it, and decompress it. The compression works great, but I can't seem to get the decompression to work.

//Compress
System.IO.MemoryStream outStream = new System.IO.MemoryStream();                
GZipStream tinyStream = new GZipStream(outStream, CompressionMode.Compress);
mStream.Position = 0;
mStream.CopyTo(tinyStream);

//Decompress    
outStream.Position = 0;
GZipStream bigStream = new GZipStream(outStream, CompressionMode.Decompress);
System.IO.MemoryStream bigStreamOut = new System.IO.MemoryStream();
bigStream.CopyTo(bigStreamOut);

//Results:
//bigStreamOut.Length == 0
//outStream.Position == the end of the stream.

我相信 bigStream out 中至少应该有数据，尤其是当我的源流 (outStream) 正在被读取时.这是 MSFT 的错误还是我的错误?

I believe that bigStream out should at least have data in it, especially if my source stream (outStream) is being read. is this a MSFT bug or mine?

推荐答案

在您的代码中发生的情况是您不断打开流，但从未关闭它们.

What happens in your code is that you keep opening streams, but you never close them.

• 在第 2 行中，您创建了一个 GZipStream.这个流不会向底层流写入任何内容，直到它感觉到了合适的时间.您可以通过关闭它来告诉它.

• In line 2, you create a GZipStream. This stream will not write anything to the underlying stream until it feels it’s the right time. You can tell it to by closing it.

但是，如果您关闭它，它也会关闭底层流 (outStream).因此，您不能在其上使用 mStream.Position = 0.

However, if you close it, it will close the underlying stream (outStream) too. Therefore you can’t use mStream.Position = 0 on it.

您应该始终使用 using 来确保关闭所有流.这是您的代码的一个变体.

You should always use using to ensure that all your streams get closed. Here is a variation on your code that works.

var inputString = "" ... "";
byte[] compressed;
string output;

using (var outStream = new MemoryStream())
{
    using (var tinyStream = new GZipStream(outStream, CompressionMode.Compress))
    using (var mStream = new MemoryStream(Encoding.UTF8.GetBytes(inputString)))
        mStream.CopyTo(tinyStream);

    compressed = outStream.ToArray();
}

// "compressed" now contains the compressed string.
// Also, all the streams are closed and the above is a self-contained operation.

using (var inStream = new MemoryStream(compressed))
using (var bigStream = new GZipStream(inStream, CompressionMode.Decompress))
using (var bigStreamOut = new MemoryStream())
{
    bigStream.CopyTo(bigStreamOut);
    output = Encoding.UTF8.GetString(bigStreamOut.ToArray());
}

// "output" now contains the uncompressed string.
Console.WriteLine(output);

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