Maximum length of a MIME Content-Type header field?

email mime
Ian Nelson picture Ian Nelson · Aug 21, 2008 · Viewed 17.5k times · Source

I'm just designing the schema for a database table which will hold details of email attachments - their size in bytes, filename and content-type (i.e. "image/jpg", "audio/mp3", etc).

Does anybody know the maximum length that I can expect a content-type to be?

Answer

speaker picture speaker · Dec 4, 2009

I hope I havn't misread, but it looks like the length is max 127/127 or 255 total.

RFC 4288 has a reference in 4.2 (page 6):

Type and subtype names MUST conform to the following ABNF:

   type-name = reg-name
   subtype-name = reg-name

   reg-name = 1*127reg-name-chars
   reg-name-chars = ALPHA / DIGIT / "!" /
                   "#" / "$" / "&" / "." /
                   "+" / "-" / "^" / "_"

It is not clear to me if the +suffix can add past the 127, but it appears not.

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