The Content-Type entity header is used to indicate the media type of the resource. In responses, a Content-Type header tells the client what the content type of the returned content actually is. Browsers will do MIME sniffing in some cases and will not necessarily follow the value of this header; to prevent this behavior, the header X-Content-Type-Options can be set to nosniff. I have to validate the Content-Type header value before passing it to HTTP request. Is there a specific list for all the possible values of Content-Type? Otherwise, is there a way to validate the. Stack Overflow. Log In Sign Up. What are all the possible values for HTTP “Content-Type” header? Header class for Content-Type header. The header class sip_content_type_class defines how a SIP Content-Type header is parsed and printed. It also contains methods used by SIP parser and other functions to manipulate the sip_content_type_t header structure.