解码为MemoryStream的XML附件不起作用

Question

我的应用会读取Gmail的附件。附件是一种XML文件（特别是.tcx）。当我将它们解码为MemoryStream时，我收到错误

XDocument.Load(stream): 

System.Xml.XmlException
  HResult=0x80131940
  Message=Root element is missing.
  Source=System.Private.Xml
  StackTrace:
   at System.Xml.XmlTextReaderImpl.Throw(Exception e)
   at System.Xml.XmlTextReaderImpl.ParseDocumentContent()
   at System.Xml.XmlTextReaderImpl.Read()
   at System.Xml.Linq.XDocument.Load(XmlReader reader, LoadOptions options)
   at System.Xml.Linq.XDocument.Load(Stream stream, LoadOptions options)
   at System.Xml.Linq.XDocument.Load(Stream stream)

但是当我将它解码为FileStream时，一切都还可以。

失败的代码：

foreach (var attachment in message.Attachments)
{
    var stream = new MemoryStream();

    if (attachment is MessagePart rfc822)
    {
        rfc822.Message.WriteTo(stream);
    }
    else
    {
        var part = (MimePart)attachment;
        part.Content.DecodeTo(stream);
    }
    XDocument xDocument = XDocument.Load(stream);
}

但是如果我使用FIleStream，它可以工作：

using (var stream = File.Create(fileName))
{
    if (attachment is MessagePart rfc822)
    {
        rfc822.Message.WriteTo(stream);
    }
    else
    {
        var part = (MimePart)attachment;
        part.Content.DecodeTo(stream);
    }
}

XDocument xDocument = XDocument.Load(File.Open(fileName, 
FileMode.OpenOrCreate));  

Answer 1

在尝试加载流之前，需要将流回滚到开头。

换句话说，这样做：

stream.Position = 0;
XDocument xDocument = XDocument.Load(stream);