Why “Data at the root level is invalid. Line 1, po

问题:

I am using a third-party DLL which transmits an XML document over the internet.

Why would the DLL be throwing the following exception?

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

Here are the first few lines of the XML Document:

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

Exception:

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:

回答1:

I eventually figured out there was a byte mark exception and removed it using this code:

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

回答2:

I can give you two advices:

1. It seems you are using "LoadXml" instead of "Load" method. In some cases, it helps me.
2. You have an encoding problem. Could you check the encoding of the XML file and write it?

回答3:

Remove everything before <?xml version="1.0" encoding="utf-8"?>

Sometimes, there is some "invisible" (not visible in all text editors). Some programs add this.

It's called BOM, you can read more about it here: https://en.wikipedia.org/wiki/Byte_order_mark#Representations_of_byte_order_marks_by_encoding

回答4:

if you are using XDocument.Load(url); to fetch xml from another domain, it's possible that the host will reject the request and return and unexpected (non-xml) result, which results in the above XmlException

See my solution to this eventuality here: XDocument.Load(feedUrl) returns "Data at the root level is invalid. Line 1, position 1."