The mime-types library provides a library and registry for information about
MIME content type definitions. It can be used to determine defined filename
extensions for MIME types, or to use filename extensions to look up the likely
MIME type definitions.
Version 3.0 is a major release that requires Ruby 2.0 compatibility and
removes
deprecated functions. The columnar registry format introduced in 2.6 has been
made the primary format; the registry data has been extracted from this
library
and put into {mime-types-data}[https://github.com/mime-types/mime-types-data].
Additionally, mime-types is now licensed exclusively under the MIT licence and
there is a code of conduct in effect. There are a number of other smaller
changes described in the History file.