.net – 为什么“根级别的数据无效.第1行,第1位.“用于XML文档？

我正在使用通过互联网传输XML文档的第三方DLL.

为什么DLL会抛出以下异常？

Data at the root level is invalid. Line 1,position 1. (see below for
full exception text.)

以下是XML文档的前几行：

<?xml version="1.0" encoding="utf-8"?> <REQUEST>   <HEADER>
    <REQUESTID>8a5f6d56-d56d-4b7b-b7bf-afcf89cd970d</REQUESTID>
    <MESSAGETYPE>101</MESSAGETYPE>
    <MESSAGEVERSION>3.0.2</MESSAGEVERSION>

例外：

System.ApplicationException was caught
      Message=Unexpected exception.
      Source=FooSDK
      StackTrace:
           at FooSDK.RequestProcessor.Send(String SocketServerAddress,Int32 port)
           at Foo.ExecuteRequest(Int32 messageID,IPayload payload,Provider prov)
           at Foo.SendOrder(Int32 OrderNo)
      InnerException: System.Xml.XmlException
           LineNumber=1
           LinePosition=1
           Message=Data at the root level is invalid. Line 1,position 1.
           Source=System.Xml
           SourceUri=""
           StackTrace:
                at System.Xml.XmlTextReaderImpl.Throw(Exception e)
                at System.Xml.XmlTextReaderImpl.Throw(String res,String arg)
                at System.Xml.XmlTextReaderImpl.ParseRootLevelWhitespace()
                at System.Xml.XmlTextReaderImpl.ParseDocumentContent()
                at System.Xml.XmlTextReaderImpl.Read()
                at System.Xml.XmlLoader.Load(XmlDocument doc,XmlReader reader,Boolean preserveWhitespace)
                at System.Xml.XmlDocument.Load(XmlReader reader)
                at System.Xml.XmlDocument.LoadXml(String xml)
                at XYZ.RequestProcessor.GetObjectFromXML(String xmlResult)
                at XYZ.RequestProcessor.Send(String SocketServerAddress,Int32 port)
           InnerException:

我最终弄清楚有一个字节标记异常,并使用以下代码将其删除：

string _byteOrderMarkUtf8 = Encoding.UTF8.GetString(Encoding.UTF8.GetPreamble());
    if (xml.StartsWith(_byteOrderMarkUtf8))
    {
        var lastIndexOfUtf8 = _byteOrderMarkUtf8.Length-1;
        xml = xml.Remove(0,lastIndexOfUtf8);
    }