= mime-types for Ruby

home :: https://github.com/mime-types/ruby-mime-types/
code :: https://github.com/mime-types/ruby-mime-types/
bugs :: https://github.com/mime-types/ruby-mime-types/issues
rdoc :: http://rdoc.info/gems/mime-types/
clog :: https://github.com/mime-types/ruby-mime-types/blob/master/History.md
continuous integration :: {<img src="https://github.com/mime-types/ruby-mime-types/actions/workflows/ci.yml/badge.svg" alt="Build Status" />}[https://github.com/mime-types/ruby-mime-types/actions/workflows/ci.yml]
test coverage :: {<img src="https://coveralls.io/repos/mime-types/ruby-mime-types/badge.svg?branch=master&service=github" alt="Coverage Status" />}[https://coveralls.io/github/mime-types/ruby-mime-types?branch=master]

== Description

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.

=== 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}[https://www.iana.org/assignments/media-types/media-types.xhtml], and
user contributions. It conforms to RFCs 2045 and 2231.

=== 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.

== Synopsis

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.provisional?          # => false
   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') # => 'x-appl/x-zip'
   puts MIME::Type.i18n_key('x-appl/x-zip') # => 'x-appl.x-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/x-wingz'

=== Columnar Store

mime-types uses as its primary registry storage format a columnar storage
format reducing the default memory footprint. This is done by selectively
loading the data on a per-attribute basis. When the registry is first loaded
from the columnar store, only the canonical MIME content type and known
extensions and the MIME type will be connected to its loading registry. When
other data about the type is required (including +preferred_extension+,
<tt>obsolete?</tt>, and <tt>registered?</tt>) that data is loaded from its own
column file for all types in the registry.

The load of any column data is performed with a Mutex to ensure that types are
updated safely in a multithreaded environment. Benchmarks show that while
columnar data loading is slower than the JSON store, it cuts the memory use by
a third over the JSON store.

If you prefer to load all the data at once, this can be specified in your
application Gemfile as:

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

Projects that do not use Bundler should +require+ the same:

   require 'mime/types/full'

Libraries that use mime-types are discouraged from choosing the JSON store.

For applications and clients that used mime-types 2.6 when the columnar store
was introduced, the require used previously will still work through at least
{version
4}[https://github.com/mime-types/ruby-mime-types/pull/96#issuecomment-100725400]
and possibly beyond; it is effectively an empty operation. You are recommended
to change your Gemfile as soon as is practical.

   require 'mime/types/columnar'

Note that MIME::Type::Columnar and 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 (MIME::Type and
MIME::Types) only.

=== Cached Storage

mime-types supports a cache of MIME types using <tt>Marshal.dump</tt>. The
cache is invalidated for each version of the mime-types-data gem so that data
version 3.2015.1201 will not be reused with data version 3.2016.0101. 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 caching works with both full stores and columnar stores. Only the data that
has been loaded prior to saving the cache will be stored.

== 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}[http://semver.org/];
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 compatibility, 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, the implied PATCH value will be incremented resulting in
   MAJOR.MINOR.PATCH.

In practical terms, there will be fewer releases of mime-types focussing on
features because of the existence of the
{mime-types-data}[https://github.com/mime-types/mime-types-data] gem, and if
features are marked deprecated in the course of mime-types 3.x, they will not
be removed until mime-types 4.x or possibly later.

{Code of Conduct}[Code-of-Conduct_md.html]

{Contributing}[Contributing_md.html]

{Licence}[Licence_md.html]
