What are the mechanisms/approaches to validate the UDP payload in case of SIP? SIP message doesn't contain size of header or the body, so how to verify that the payload is valid? In contrast, RTP indicates the size, so given the length value from UDP header it is possible to check RTP for validit and integrity. Can something similar be done for SIP?
Mark.
Your question has two parts:
How do I validate SIP headers? The only way to validate SIP headers is to parse them according to the rules of section 7.3.1 of RFC 3261. There are SIP parsers available for many different languages.
How do I validate the body of SIP messages? There is a mechanism built into SIP: the Content-Length header specifies the size of the body. In the general case, the body can contain an arbitrary MIME type, and no further validation rules apply.
Edit: Per Frank Shearar's comment below, Content-Length is not required for SIP messages conveyed via UDP. But if your UA supports it, you can take advantage of it.
