XmlSerialize 直接到 GZipStream 在解压缩时抛出幻数异常

Question

我正在尝试将一个对象序列化为 XML，但是我的对象是一个包含许多记录的通用列表，并导致序列化程序消耗大量内存。因此，我尝试使用以下代码直接序列化为 GZipStream：

Dim formatter As XmlSerializer = XmlSerializerFactory.GetSerializerForType(_type)
Using _ms As New MemoryStream()
    Using gzStream As New GZipStream(_ms, CompressionMode.Compress, True)

        _ms.Position = 0
        formatter.Serialize(gzStream, obj)
        _ms.Position = 0
        gzStream.Flush()
        gzStream.Close()
    End Using

    _ms.Position = 0
    Dim decompressData() As Byte
    Using gzStream As New GZipStream(_ms, CompressionMode.Decompress)
        ReDim decompressData(9000 - 1) 'this number doesn't matter, the data in my test sample is small
        Dim Len As Integer = gzStream.Read(decompressData, 0, decompressData.Length)
    End Using
End Using

但是，我遇到了 InvalidDataException GZip 标头中的幻数不正确。当尝试将数据读入 decompressData 数组时，请确保传入 GZip 流。。

当我首先序列化到单独的内存流，然后压缩该流时，例如：

Dim formatter As XmlSerializer = XmlSerializerFactory.GetSerializerForType(_type)
Using _ms As New MemoryStream()
    Dim uc_fileBytes() As Byte
    Dim uc_len As Integer
    Using _ms101 As New MemoryStream()
        formatter.Serialize(_ms101, obj)
        uc_fileBytes = _ms101.GetBuffer()
        uc_len = _ms101.Length
    End Using
    Using gzStream As New GZipStream(_ms, CompressionMode.Compress, True)
        _ms.Position = 0
        gzStream.Write(uc_fileBytes, 0, uc_len)
        gzStream.Flush()
        gzStream.Close()
    End Using

    Dim decompressData() As Byte
    Using gzStream As New GZipStream(_ms, CompressionMode.Decompress)
        ReDim decompressData(9000 - 1)
        Dim Len As Integer = gzStream.Read(decompressData, 0, decompressData.Length)
    End Using
End Using

它工作正常，没有错误。但是为什么当我直接序列化到 GZipStream 时会失败？

Answer 1

问题的原因是 GZipStream 在写入时的行为与 MemoryStream 不同（显然）。它不能很好地处理分页写入。