How to set soap message header element namespace explicitly in .NET WCF

Question

I'm trying to create a ClientInspector that will add some data to outgoing SOAP requests and add it as a endpoint behavior for client services. Something like this:

public class InsertHeaderClientInspector : IClientMessageInspector
{

    public object BeforeSendRequest(ref Message request, System.ServiceModel.IClientChannel channel)
    {
        var HeaderData = new ProcType()
            {
                attr = _correlation
            };

        MessageHeader header = MessageHeader.CreateHeader("HeaderInfo", "http://schemas.tempuri.fi/process/2016/04/", HeaderData);
        request.Headers.Add(header);

        return null;
    }
}

[System.Xml.Serialization.XmlRootAttribute("HeaderInfo", Namespace = "http://schemas.tempuri.fi/process/2016/04/", IsNullable = false)]
public class ProcType
{
    [XmlElement(Namespace = "")]
    public string attr;
}

Inspector is working fine, but the problem is that generated SOAP message will have namespace for ProcType.attr and I want to remove it.

<s:Header>
    <HeaderInfo xmlns="http://schemas.tempuri.fi/process/2016/04/" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
        <attr xmlns="http://schemas.datacontract.org/2004/07/MyService.Behaviors">asdasd</attr>
    </HeaderInfo>
</s:Header>

Instead it should be like

<s:Header>
    <HeaderInfo xmlns="http://schemas.tempuri.fi/process/2016/04/" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
        <attr">asdasd</attr>
    </HeaderInfo>
</s:Header>

XMLElement attribute I've tried to use does not work. So how do I remove this unnecessary namespace?

Answer 1

I ended up fixing this issue by creating custom header element which I insert to request.

public class ProcessGuidHeader : MessageHeader
{
    private string _attr;
    private string _headerName = "HeaderInfo";
    private string _elementName = "ProcType";
    private string _headerNamespace = "http://schemas.tempuri.fi/process/2016/04/";

    public ProcessGuidHeader(string attr)
    {
        _attr = attr;
    }

    public string Attr
    {
        get { return _attr; }
    } 

    public override string Name
    {
        get { return _headerName; }
    }

    public override string Namespace
    {
        get { return _headerNamespace; }
    }

    protected override void OnWriteHeaderContents(XmlDictionaryWriter writer, MessageVersion messageVersion)
    {
        writer.WriteElementString(_elementName, _attr);
    }
}

This does not set any namespace for header child element and solves the issue.