GZipStream 压缩不起作用

Question

我正在尝试读取文件并使用 GZipStream 对其进行压缩，如下所示：

using (var outStream = new MemoryStream())
{
    using (var fileStream = new FileStream(filename, FileMode.Open, FileAccess.Read))
    {
        using (var gzipStream = new GZipStream(outStream, CompressionMode.Compress))
        {
            fileStream.CopyTo(gzipStream);

            Debug.WriteLine(
                "Compressed from {0} to {1} bytes", 
                fileStream.Length, 
                outStream.Length);

            // "outStream" is utilised here (persisted to a NoSql database).
        }
    }
} 

问题是outStream.Length 总是显示 10 个字节。我做错了什么？

我尝试在fileStream.CopyTo 行之后调用gzipStream.Close()（如其他论坛中所建议的那样），但这似乎也关闭了outStream，因此使用它的后续代码会失败。

Answer 1

MSDN 说：The write operation might not occur immediately but is buffered until the buffer size is reached or until the Flush or Close method is called.

换句话说，所有写操作都完成并不意味着数据已经在MemoryStream 中。您必须先执行gzipStream.Flush() 或关闭 gzipStream。

例子：

using (var outStream = new MemoryStream())
{
    using (var fileStream = new FileStream(filename, FileMode.Open, FileAccess.Read))
    {
        using (var gzipStream = new GZipStream(outStream, CompressionMode.Compress))
        {
            fileStream.CopyTo(gzipStream);
        }

        Debug.WriteLine(
                "Compressed from {0} to {1} bytes", 
                fileStream.Length, 
                outStream.Length);

        // "outStream" is utilised here (persisted to a NoSql database).
    }
} 

此外，理想情况下，也将其放在 FileStream 之外 - 您希望尽快关闭文件，而不是等待其他处理完成。