Does the HTTP Protocol support multiple content types in response headers?

Question

I\'m wondering if I can return the response header

Content-Type: application/json text/json 

or isn\'t this legal?

The HTTP protoc

Answer 1

No. As pointed out in the accepted answer, the header value itself does not allow for multiple values, and it is also not allowed to send multiple Content-Type headers:

A sender MUST NOT generate multiple header fields with the same field name in a message unless either the entire field value for that header field is defined as a comma-separated list [i.e., #(values)] or the header field is a well-known exception (as noted below).

https://tools.ietf.org/html/rfc7230#section-3.2.2

None of the "escape clauses" holds, because media-type does not allow a comma-separated list of values, and Content-Type evidently is not a well-known exception, either.