Question

Is a client SOAP request simply the use of HTTP POST to send a correctly formatted HTTP header followed by the correctly formatted XML SOAP content to the web service server over a TCP/IP socket connection and then waiting for and parsing the response?

Is it this ‘simple’ or is there more going on behind the scenes?

I ask because of difficulty using gSOAP with C++ for multiple WSDL files and am considering writing a client from scratch.

Answer 1

SOAP can be used over any transport protocol like TCP, HTTP, SMTP etc with HTTP being the most popular.

SOAP over HTTP basically translates to a valid POST HTTP request with a SOAP envelope inside it, there where the form parameters would have been if we were to talk about a classic POST from the browser. The response body also contains a SOAP envelope, there where you would expect the HTML to be as response to the request from the browser.

You just have to use the proper content type for the SOAP version you are using (text/xml for SOAP 1.1 and application/soap+xml for SOAP 1.2) and maybe specify the SOAPAction header if needed (for SOAP 1.1), but that’s about it as HTTP communication is concerned.

Then the receiver of the envelope (be it the server on a request or the client on a response) must make use of the SOAP message, but this has nothing to do with HTTP any more, HTTP just got the message there.