SOAP defines a binding to the HTTP protocol. This binding to the HTTP protocol describes the relationship between parts of the SOAP request message and various HTTP headers. All SOAP requests use the HTTP POST method and specify at least three HTTP headers:

Content-Type

Content-Length and

a custom header SOAPAction

The actual SOAP message is passed as the body of the request or response.

The Content-Type header for SOAP requests and responses specifies the MIME type for the message and is always text/xml. It may also specify the character encoding used for the XML body of the HTTP request or response.

The Content-Length header for SOAP requests and responses is set to the number of bytes in the body of the request or response.

The SOAP Action header indicates to the HTTP server that the request is a SOAP request. The value of the header is a URI.And its value is undefined.