file-types Manual

file-types is a simplistic approach to identify types of files based on their names (e.g. no magic numbers like UNIX's file(1)). It exposes a way to find the common MIME type of a file but also comes with a novel file tag system.

file-mime may be used to get the MIME type for a file e.g.:

(file-mime #P"foo.sh") ⇒ ("application" "x-sh")

file-tags on the other hand exposes access to the file tagging system. When invoked with a single filename argument it will return a list of keywords, each being an increasingly specific description of the file's type. If invoked with a keyword as the second parameter, file-tags will act as a predicate to test if the file has the tag designated by the supplied keyword.

(file-tags #P"test.lisp") ⇒ (:TEXT :COMMON-LISP)
(file-tags #P"Makefile") ⇒ (:TEXT :MAKE-FILE)

(and (file-tags #P"test.lisp" :text)
     (file-tags #P"Makefile" :text))
  ⇒ true

The file-types database is created at compile time. It is sourced from two Lisp files—types.lisp and names.lisp. The former contains a special parameter variable *file-type-list* which stores a list of pathname-type to file tag and MIME type assignments. In specific, filenames whose pathname-type are equalp to one of the pathname-type strings in an assignment will inherit the tags and MIME type of that assignment.

(defparameter *file-type-list*
  '(;; Text files
    (("txt")                   ; List of PATHNAME-TYPEs.
     :tags (:text)             ; Tags.
     :mime ("text" "plain")))) ; MIME type as returned by FILE-MIME.

Now the file tag definition format has one special rule: Multiple assignments to a single type are valid and the specified tags will be appended in the database (MIME types will be superseded). Consider an exended version of the example above.

(defparameter *file-type-list* '(

   ;; Text file class
   (("txt" "lisp" "asd" "html" "htm")
    :tags (:text)
    :mime ("text" "plain"))

   ;; HTML file class
   (("html" "htm")
    :tags (:hyper-text-markup-language)
    :mime ("text" "html"))

   ;; Lisp file class
   (("lisp" "asd")
    :tags (:common-lisp))

   ;; ASDF file class
   (("asd")
    :tags (:asdf-system-definition))

))

We specify a set of pathname-types to designate plain text files. Further down we specialize on some of those types. For instance, html and htm get assigned their tag :hyper-text-markup-language and their correct MIME type. Then we define lisp and asd to be :common-lisp files but let them retain the plain text MIME type. Then we fan out further among the lisp files and append the asdf-system-definition tag to the asd type.

"txt"  ("text" "plain") (:TEXT)
"lisp" ("text" "plain") (:TEXT :COMMON-LISP)
"asd"  ("text" "plain") (:TEXT :COMMON-LISP :ASDF-SYSTEM-DEFINITION)
"html" ("text" "html")  (:TEXT :HYPER-TEXT-MARKUP-LANGUAGE)
"htm"  ("text" "html")  (:TEXT :HYPER-TEXT-MARKUP-LANGUAGE)

The second file is name.lisp. It contains the special parameter variable *file-name-list* which stores simple euqalp mappings from pathname-names to pathname-types. Some types of files share a conventional name but have no type suffix—for instance consider Makefiles. In this case file-types will try to match the pathname-name against the names in names.lisp and if successful continue with the type recommended.

(defparameter *file-name-list*
  '(;; Conventions
    ("README" "txt")
    ("Makefile" "mk")
    ;; Init files
    (".emacs" "el")
    (".clisprc" "lisp")
    (".sbclrc" "lisp")))