+;;; atom.el --- Create an Atom feed
+
+;; Copyright (C) 2011 Frédéric Perrin
+
+;; Author: Frédéric Perrin <frederic.perrin@resel.fr>
+;; Keywords: www, hypermedia, atom, rss
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This is a library for creating an Atom feed from a Lisp program.
+;; The normal usage is to create a feed with `atom-create', giving it
+;; a title and a Web address. Once the feed has been created, entries
+;; may be added to the feed, by specifying (at the minimum) a title, a
+;; permanent link and the content of the entry. Text-only, HTML and
+;; XHTML entries are supported.
+
+;; A feed is really a Lisp structure as used by the `xml.el' package,
+;; without the parent `feed' element.
+
+;; A typical usage would look like this:
+
+;; (let ((my-atom-feed (atom-create "My feed" "http://example.org")))
+;; ; A simple, text-only entry
+;; (atom-add-text-entry
+;; my-atom-feed
+;; "Hello world"
+;; "http://example.org/hello"
+;; "Hello the world!")
+;;
+;; ; A text-only entry, with all the optional pieces of data
+;; (atom-add-text-entry
+;; my-atom-feed
+;; "Bonjour"
+;; "http://example.org/bonjour"
+;; "Bonjour à tout le monde !"
+;; ;; optional: the last modification time
+;; (date-to-time "2011-01-30 23:40:12")
+;; ;; optional: an identifier for this entry; a common way to generate it is
+;; ;; to use the domain name and the creation date of the entry.
+;; (atom-generate-id "http://example.org"
+;; (date-to-time "2011-01-30 10:01:05"))
+;; ;; optional: a summary for this entry
+;; "Bonjour, monde.")
+;;
+;; (atom-add-xhtml-entry
+;; my-atom-feed
+;; "An XHTML example"
+;; "http://example.org/html-example"
+;; "<p>One can also use <acronym>XHTML</acronym> in the entries.</p>")
+;; (atom-print my-atom-feed))
+
+;;; Code:
+
+(require 'xml)
+
+(defun atom-create (title link &optional self id author updated)
+ "Create a new atom structure.
+
+TITLE is the title for the feed, a short, text-only, human
+readable string.
+
+LINK is the URL of a page responible for the content of this
+feed.
+
+SELF is the canonical URL to this feed.
+
+ID is a unique identifier for this feed. If not given, it
+defaults to SELF.
+
+AUTHOR is the author of the feed. See `atom-massage-author' for
+the possible ways to specify it.
+
+UPDATED is the date the feed was last updated. If not given,
+`(current-time)' is used."
+ (let ((atom-feed (list (list 'title nil title))))
+ (atom-modify-entry atom-feed 'link `(((href . ,link))))
+ (atom-modify-entry atom-feed 'author (atom-massage-author author))
+ (if self (atom-modify-entry atom-feed 'link
+ `(((href . ,self) (rel . "self")
+ (type . "application/atom+xml")))))
+ (atom-modify-entry atom-feed 'updated (atom-format-time updated))
+ (atom-modify-entry atom-feed 'id (or id self link))
+ atom-feed))
+
+(defun atom-push-entry (atom entry)
+ "Add the entry ENTRY to the feed ATOM."
+ (nconc atom (list `(entry nil ,@entry))))
+
+(defun atom-modify-entry (entry name val)
+ "Set the NAME element of ENTRY to VAL. A true MULTIPLE means
+to add a new element instead of updating it when it already exists."
+ (let ((elem (if (stringp val)
+ (list name nil val)
+ (cons name val))))
+ (nconc entry (list elem))))
+
+(defun atom-add-entry (atom title link content
+ &optional updated id summary)
+ "Add an entry to the atom flux ATOM. Return the newly added
+entry.
+
+TITLE is a short, text-only, human readable string.
+
+LINK is a permanent link for this entry. For a given entry, LINK
+may change between successive generations of the atom feed.
+
+CONTENT is the content of the entry; use `atom-add-html-entry'
+or `atom-add-xhtml-entry' when CONTENT is not text-only.
+
+If SUMMARY is not given, the entry will not contain any summary.
+
+UPDATED defaults to `(current-time)' if omitted, which is
+probably not a very good default.
+
+ID defaults to LINK, which is not optimal; see `atom-generate-id'
+for a way to create good identifiers. For a given entry, it must
+not change between successive generations of the atom feed, even
+when the content of the entry ."
+ (let ((entry (list (list 'title nil title))))
+ (atom-modify-entry entry 'link (list (list (cons 'href link))))
+ (atom-modify-entry entry 'id (or id link))
+ (atom-modify-entry entry 'updated (atom-format-time updated))
+ (if summary (atom-modify-entry entry 'summary summary))
+ (atom-modify-entry entry 'content content)
+ (atom-push-entry atom entry)
+ entry))
+
+(defalias 'atom-add-text-entry 'atom-add-entry
+ "Add an entry to ATOM, with a textual content. See
+`atom-add-entry' for details.")
+
+(defun atom-add-html-entry (atom title link content
+ &optional updated id summary)
+ "Add an entry to ATOM, with some HTML content. CONTENT should
+be a string enconding a valid HTML fragment. See `atom-add-entry'
+for additional details."
+ (atom-add-entry atom
+ title link (atom-massage-html content)
+ updated id (and summary (atom-massage-html summary))))
+
+(defun atom-add-xhtml-entry (atom title link content
+ &optional updated id summary)
+ "Add an entry to ATOM, with some XHTML content. CONTENT may be
+given either as a string, or as an XML tree, of a valid XHTML
+fragment. See `atom-add-entry' for additional details."
+ (atom-add-entry atom
+ title link (atom-massage-xhtml content)
+ updated id (and summary (atom-massage-xhtml summary))))
+
+(defun atom-print (atom)
+ "Print the Atom feed ATOM in the current buffer."
+ (insert "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n")
+ (insert "<feed xmlns=\"http://www.w3.org/2005/Atom\">\n")
+ (xml-print atom)
+ (insert "\n</feed>"))
+
+(defun atom-write-file (atom filename)
+ "Writes the feed ATOM to FILENAME."
+ (with-temp-buffer
+ (atom-print atom)
+ (write-region (point-min) (point-max) filename)))
+
+\f
+(defun atom-format-time (&optional time)
+ "Format a time according to RFC3339."
+ ;; The time zone must be specified in numeric form, but with a colon between
+ ;; the hour and minute parts.
+ (replace-regexp-in-string
+ "\\(..\\)$"
+ ":\\1"
+ (format-time-string "%Y-%m-%dT%T%z" time)))
+
+(defun atom-massage-html (content)
+ "Massage CONTENT so it can be used as an HTML fragment in an
+Atom feed. CONTENT must be a string."
+ (list '((type . "html")) content))
+
+(defun atom-string-to-xml (string)
+ "Convert STRING into a Lisp structure as used by `xml.el'."
+ (with-temp-buffer
+ (insert "<div xmlns=\"http://www.w3.org/1999/xhtml\">")
+ (insert string)
+ (insert "</div>")
+ (xml-parse-region (point-min) (point-max))))
+
+(defun atom-massage-xhtml (content)
+ "Massage CONTENT so it can be used as an XHTML fragment in an
+Atom feed."
+ `(((type . "xhtml"))
+ ,@(or (and (stringp content)
+ (atom-string-to-xml content))
+ content)))
+
+(defun atom-massage-author (author)
+ "Return an XML node representing the author. AUTHOR can be:
+- nil, in which case `user-full-name' and `user-mail-address' are
+ used;
+- a single string, the full name of the author;
+- a list with two elements, the full name and the email address
+ of the author;
+- something else, assumed to be a complete `atomPersonConstruct'."
+ `(nil ,@(cond
+ ((null author) `((name nil ,user-full-name)
+ (email nil ,user-mail-address)))
+ ((stringp author) `((name nil ,author)))
+ ((= 2 (length author)) `((name nil ,(car author))
+ (email nil ,(cadr author))))
+ (t `(author nil ,author)))))
+
+(require 'url-parse)
+
+(defun atom-generate-id (link creation-date)
+ "Generate a string suitable for use as an atom:id element. This
+implements Mark Pilgrom's tag: URI method, using the
+CREATION-DATE of the entry, and the domain part of LINK."
+ (format "tag:%s,%s:/%s"
+ (url-host (url-generic-parse-url link))
+ (format-time-string "%Y-%m-%d" creation-date)
+ (format-time-string "%Y%m%d%H%M%S" creation-date)))
+
+(provide 'atom)
+;;; atom.el ends here
projects / atom.git / blobdiff