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The io-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.

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 io-mime-types library provides the ability for detailed information about MIME entities (provided as an enumerable collection of MimeType objects) to be determined and used programmatically. There are many types defined by RFCs and vendors, so the list is long but by definition incomplete; don't hesitate to to add additional type definitions (see Contributing). The primary sources for MIME type definitions found in mime-types-io is the IANA collection of registrations (see below for the link), RFCs, and W3C recommendations.

This is release 1.0, ported from the Ruby release (mime-types/ruby-mime-types).


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 MimeType stores the known information about one MIME type.

    plaintext := MimeTypes["text/plain"]
    # returns list(text/plain)
    text := plaintext first

    text mediaType println            # => text
    text subType println              # => plain
    text extensions join(" ") println # => asc c cc h hh…
    text encoding println             # => quoted-printable
    text isBinary println             # => false
    text isAscii println              # => true
    text isObsolete println           # => false
    text isRegistered println         # => true
    text isLike("text/plain") println # => true
    MimeType simplifiedFor("x-appl/x-zip") println
                                      # => "appl/zip"

io-mime-types Modified Semantic Versioning

The io-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).

io-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 io-mime-types 1.x will be backwards compatible; the interfaces marked deprecated will not be removed until at least io-mime-types 2.x or possibly later.


io-mime-types is under the MIT licence. See Licence.


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