UA Part 6: Mappings - 7.4.3 XML Encoding

7.4.3 XML Encoding

This TransportProtocol implements the OPC UA Services using a SOAP request-response message pattern over an HTTPS connection.

The body of the HTTP Messages shall be a SOAP 1.2 Message (see SOAP Part 1). WS-Addressing headers are optional.

The OPC UA XML Encoding specifies a way to represent an OPC UA Message as an XML element. This element is added to the SOAP Message as the only child of the SOAP body element. If an error occurs in the Server while parsing the request body, the Server may return a SOAP fault or it may return an OPC UA error response.

The SOAP Action associated with an XML encoded request Message always has the form:

http://opcfoundation.org/UA/2008/02/Services.wsdl/<service name>

Where <service name> is the name of the OPC UA Service being invoked.

The SOAP Action associated with an XML encoded response Message always has the form:

http://opcfoundation.org/UA/2008/02/Services.wsdl/<service name>Response

All requests shall be HTTP POST requests. The Content-type shall be "application/soap+xml" and the charset and action parameters shall be specified. The charset parameter shall be "utf-8" and the action parameter shall be the URI for the SOAP action.

An example HTTP request header is:

POST /UA/SampleServer HTTP/1.1

Content-Type: application/soap+xml; charset="utf-8";

action="http://opcfoundation.org/UA/2008/02/Services.wsdl/Read"

Content-Length: nnnn

The action parameter appears on the same line as the Content-Type declaration.

An example request Message:

<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope">

<s:Body>

…

</ReadRequest>

</s:Body>

</s:Envelope>

An example HTTP response header is:

HTTP/1.1 200 OK