Escape multipart type parameter value in Content-Type header ## Summary Multipart responses do not quote/escape the value of their type parameter (the subtype) even though it always contains at least one special character (the slash "/"), which confuses standard-compliant HTTP clients. ## Details The Content-Type header in HTTP is in RFC 7231, Section 3.1.1.5: https://tools.ietf.org/html/rfc7231#section-3.1.1.5 The section defers to the media type section (3.1.1.1) for the syntax of the media type: https://tools.ietf.org/html/rfc7231#section-3.1.1.1 This states that a parameter value can be quoted: parameter = token "=" ( token / quoted-string ) A parameter value that matches the token production can be transmitted either as a token or within a quoted-string. The quoted and unquoted values are equivalent. Tokens are defined in RFC 7230, Section 3.2.6 (via RFC 7231, appendix C): https://tools.ietf.org/html/rfc7231#appendix-C https://tools.ietf.org/html/rfc7230#section-3.2.6 Here we observe that tokens cannot contain a slash "/" character: token = 1*tchar tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA ; any VCHAR, except delimiters Delimiters are chosen from the set of US-ASCII visual characters not allowed in a token (DQUOTE and "(),/:;<=>?@[\]{}"). However, the current implementation does not quote/escape the value of the type parameter: multipart/related; type=application/dicom Instead, it should be: multipart/related; type="application/dicom" All of this also seems to apply to the MIME Content-Type header definition, even though it is a little different: https://www.iana.org/assignments/message-headers https://tools.ietf.org/html/rfc2045#section-5.1 https://tools.ietf.org/html/rfc2387