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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.

This is release 2.99.1, the first scheduled data update for mime-types 2.x. As of mime-types 2.99. deprecation warnings are noisy and data that has been deprecated is now no longer available. The data is both dropped from the data files and is stubbed out as empty or nil values as appropriate.

mime-types-2.6 was the last version of mime-types 2.x with newly available features, and mime-types 2.99 will only receive quarterly updates to the IANA registered MIME media types plus any security updates that may be required.

If the loss of the deprecated data matters, be sure to set your dependency appropriately:

gem 'mime-types', '~> 2.6, < 2.99'

About MIME Media Types

MIME content types are used in MIME-compliant communications, as in e-mail or HTTP traffic, to indicate the type of content which is transmitted. The mime-types library provides the ability for detailed information about MIME entities (provided as an enumerable collection of MIME::Type objects) to be determined and used. There are many types defined by RFCs and vendors, so the list is long but by definition incomplete; don't hesitate to add additional type definitions. MIME type definitions found in mime-types are from RFCs, W3C recommendations, the IANA Media Types registry, and user contributions. It conforms to RFCs 2045 and 2231.

mime-types 1.x End of Life

mime-types 1.x has reached end of life and is no longer supported as of 2015-10-27 and will receive no updates at all.

mime-types 2.x End of Life

mime-types 2.x is supported as 2.99.x receiving quarterly updates of the IANA registry and security updates for two years. It will reach full end of life on 2017-11-21.

mime-types 3.x

Users are encouraged to upgrade to mime-types 3.x as soon as is practical. mime-types 3.x requires Ruby 2.0 compatibility and a simpler licensing scheme.


MIME types are used in MIME entities, as in email or HTTP traffic. It is useful at times to have information available about MIME types (or, inversely, about files). A MIME::Type stores the known information about one MIME type.

require 'mime/types'

plaintext = MIME::Types['text/plain'] # => [ text/plain ]
text = plaintext.first
puts text.media_type            # => 'text'
puts text.sub_type              # => 'plain'

puts text.extensions.join(' ')  # => 'txt asc c cc h hh cpp hpp dat hlp'
puts text.preferred_extension   # => 'txt'
puts text.friendly              # => 'Text Document'
puts text.i18n_key              # => 'text.plain'

puts text.encoding              # => quoted-printable
puts text.default_encoding      # => quoted-printable
puts text.binary?               # => false
puts text.ascii?                # => true
puts text.obsolete?             # => false
puts text.registered?           # => true
puts text.complete?             # => true

puts text                       # => 'text/plain'

puts text == 'text/plain'       # => true
puts 'text/plain' == text       # => true
puts text == 'text/x-plain'     # => false
puts 'text/x-plain' == text     # => false

puts MIME::Type.simplified('x-appl/x-zip') # => 'appl/zip'
puts MIME::Type.i18n_key('x-appl/x-zip') # => 'appl.zip'

puts text.like?('text/x-plain') # => true
puts text.like?(MIME::Type.new('x-text/x-plain')) # => true

puts text.xrefs.inspect # => { "rfc" => [ "rfc2046", "rfc3676", "rfc5147" ] }
puts text.xref_urls # => [ "http://www.iana.org/go/rfc2046",
                    #      "http://www.iana.org/go/rfc3676",
                    #      "http://www.iana.org/go/rfc5147" ]

xtext = MIME::Type.new('x-text/x-plain')
puts xtext.media_type # => 'text'
puts xtext.raw_media_type # => 'x-text'
puts xtext.sub_type # => 'plain'
puts xtext.raw_sub_type # => 'x-plain'
puts xtext.complete? # => false

puts MIME::Types.any? { |type| type.content_type == 'text/plain' } # => true
puts MIME::Types.all?(&:registered?) # => false

# Various string representations of MIME types
qcelp = MIME::Types['audio/QCELP'].first # => audio/QCELP
puts qcelp.content_type         # => 'audio/QCELP'
puts qcelp.simplified           # => 'audio/qcelp'

xwingz = MIME::Types['application/x-Wingz'].first # => application/x-Wingz
puts xwingz.content_type        # => 'application/x-Wingz'
puts xwingz.simplified          # => 'application/wingz'

Columnar Store

mime-types 2.6 introduced an experimental columnar storage format that reduces the default memory footprint. It does this by selectively loading data. When a registry is first loaded from a columnar store, only the canonical MIME type and registered extensions will be loaded and the MIME type will be connected to its registry. When extended data is required (including registered, obsolete, and use_instead), that data is loaded from its own column file for all types in the registry. This load is done with a Mutex to ensure that the types are updated safely in a multithreaded environment.

Columnar storage is slated to become the default storage format for mime-types 3.0, but until that is released, the default is still to use the JSON storage format. As such, columnar storage can only currently be loaded at an application level with the following specification in the application Gemfile:

gem 'mime-types', require: 'mime/types/columnar'

Projects that do not use Bundler, and libraries that wish to suggest this behaviour to applications are encouraged to require this directly, but only if you specify a dependency on mime-types 2.6.

require 'mime/types/columnar'

Although this require will not be necessary after mime-types 3, it will work through at least version 4 and possibly beyond.

Note that the new Columnar class (MIME::Type::Columnar) and module (MIME::Types::Columnar) are considered private variant implementations of MIME::Type and MIME::Types and the specific implementation should not be relied upon by consumers of the mime-types library. Instead, depend on the public implementations only.

Cached Storage

Since version 2.0, mime-types has supported a cache of MIME types based on Marshal.dump. The cache is invalidated for each released version of mime-types so that version 2.5 is not reused for version 2.6. If the environment variable RUBY_MIME_TYPES_CACHE is set to a cache file, mime-types will attempt to load the MIME type registry from the cache file. If it cannot, it will load the types normally and then saves the registry to the cache file.

The current mime-types cache is not compatible with the columnar storage format. This will be resolved for mime-types 3.

mime-types Modified Semantic Versioning

The mime-types library has one version number, but this single version number tracks both API changes and registry data changes; this is not wholly compatible with all aspects of Semantic Versioning; removing a MIME type from the registry could be considered a breaking change under some interpretations of semantic versioning (as lookups for that particular type would no longer work by default).

mime-types uses a modified semantic versioning scheme. Given the version MAJOR.MINOR:

  1. If an incompatible API (code) change is made, the MAJOR version will be incremented, MINOR will be set to zero, and PATCH will be reset to the implied zero.

  2. If an API (code) feature is added that does not break compatibilty OR if there are MIME types added, removed, or changed in the registry, the MINOR version will be incremented and PATCH will be reset to the implied zero.

  3. If there is a bugfix to a feature added in the most recent MAJOR.MINOR release, OR if purely typographical errors are fixed in MIME types, the implied PATCH value will be incremented resulting in MAJOR.MINOR.PATCH.

In practical terms, there should be a MINOR release roughly monthly to track updated or changed MIME types from the official IANA registry. This does not indicate when new API features have been added, but all minor versions of mime-types 2.x will be backwards compatible; the interfaces marked deprecated will be removed in mime-types 3.x.

:include: Code-of-Conduct.rdoc

:include: Contributing.rdoc

:include: Licence.rdoc