A typical HTTP header of a SOAP 1.1 message
The content type of the message can be text/xml, but there can be other content types in the message. There should be a SOAPAction header in any SOAP 1.1 message. This SOAPAction header can be empty, but it has to be there.
With SOAP 1.2 the identification becomes tricky. As with the SOAP 1.1 specification, the content type can be application/soap+xml, but users can define their own appropriate content types depending on the content. Also the specification does not define any SOAPAction header to be included within HTTP headers. You may include the SOAPAction information into the Content-type header itself. This is not mandatory.