GZipStream压缩无效

Question

我试图读取一个文件并使用GZipStream压缩它，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？

我尝试过在gzipStream.Close()行之后调用fileStream.CopyTo (就像在其他论坛中所建议的那样)，但是这似乎也关闭了outStream，因此使用它的后续代码就结束了。

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，所有的写操作都已经完成，这并不意味着数据已经在MemoryStream中了。您必须先执行gzipStream.Flush()或关闭gzipStream。

示例：

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).
    }
} 

另外，理想的情况是，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。