Added Metadata Plugin and documentation.

docs/plugin-use.md

@@ -39,6 +39,34 @@
 
 **Example**: `(gh-pages :cname t)`
 
+## SEO and Social Metadata
+
+**Description**: Adds description and keywords metadata for SEO purposes.
+  Adds both Open Graph and Twitter Cards metadata for sharing posts as well.
+  `:twitter` keyword argument sets "site" property of Twitter.
+  Twitter Card specific metadata will be omitted if this property is not set.
+  `:card` keyword argument sets the type of Twitter card created.
+  Possible types are `:summary` and `:image`. Defaults to `:summary`.
+  
+  Five *optional* tags for post file header are added.
+
+  `keywords:` comma, seperated, seo, keywords.
+  They will be generated from tags if empty.
+
+  `description:` Description to be used in SEO and
+  Open Graph description tags. If empty, Open Graph description will be generated
+  from content while SEO description metadata will be omitted.
+
+  `image:` either an absolute (`http://www.example.com/image.png`)
+  or a root-relative (`/static/image.png`) image URL.
+
+  `card:` Overrides Twitter Card type defined in plugin activation.
+  Possible values are either `image` or `summary`.
+
+  `creator:` Twitter username of the content creator.
+
+**Example**: `(metadata :twitter "twitter_account" :card :summary)`
+
 ## Incremental Builds
 
 **Description**: Primarily a performance enhancement. Caches the

plugins/metadata.lisp

@@ -0,0 +1,81 @@
+(eval-when (:compile-toplevel :load-toplevel)
+  (ql:quickload 's-xml))
+
+(defpackage :coleslaw-metadata
+  (:use :cl :coleslaw)
+  (:import-from :coleslaw
+                #:title
+                #:domain
+                #:tag-name
+                #:page-url
+                #:content-tags
+                #:content-text
+                #:keywords-of
+                #:description-of
+                #:image-of
+                #:card-format
+                #:creator-of)
+    (:import-from :s-xml
+                #:xml-parser-state
+                #:start-parse-xml)
+  (:export #:enable))
+
+(in-package :coleslaw-metadata)
+
+(defparameter *description-length* 200)
+
+(defvar *metadata-header*
+  "
+<meta name=\"keywords\" content=\"~A\" />~@[
+<meta name=\"description\" content=\"~A\" />~]~:[~*~*~;~:*
+<meta name=\"twitter:site\" content=\"@~A\" />
+<meta name=\"twitter:card\" content=\"~:[summary~;summary_large_image~]\" />~@[
+<meta name=\"twitter:creator\" content=\"@~A\" />~]~]
+<meta property=\"og:title\" content=\"~A\" />
+<meta property=\"og:site_name\" content=\"~A\" />
+<meta property=\"og:url\" content=\"~A\" />
+<meta property=\"og:description\" content=\"~A\" />~@[
+<meta property=\"og:image\" content=\"~A\" />~]
+")
+
+(defun remove-markup (text)
+  (with-input-from-string (in text)
+    (let* ((state (make-instance 'xml-parser-state
+                                 :text-hook #'(lambda (string seed) (cons string seed))))
+           (result (start-parse-xml in state)))
+      (apply #'concatenate 'string (nreverse result)))))
+
+(defun shorten-text (text)
+  (if (< *description-length* (length text))
+      (subseq text 0 (- *description-length* 1)) text))
+
+(defun compile-description (text)
+  (shorten-text (remove #\" (remove-markup text))))
+
+(defun root-relative-url-p (url)
+  (eq (elt url 0) #\/))
+
+(defun compile-url (url)
+  (if (root-relative-url-p url)
+      (concatenate 'string (domain *config*) url)
+      url))
+
+(defun compile-metadata (post twitter card)
+  (format nil *metadata-header*
+          (or (keywords-of post)
+              (format nil "~{~A~^, ~}" (mapcar #'tag-name (content-tags post))))
+          (description-of post)
+          twitter
+          (eq (or (card-format post) card) :image)
+          (creator-of post)
+          (title-of post)
+          (title *config*)
+          (concatenate 'string (domain *config*) "/" (namestring (page-url post)))
+          (or (description-of post)
+              (compile-description (content-text post)))
+          (when (image-of post) (compile-url (image-of post)))))
+
+(defun enable (&key twitter card)
+  (flet ((inject-p (x)
+           (when (typep x 'post) (compile-metadata x twitter card))))
+    (add-injection #'inject-p :head)))

src/posts.lisp

@@ -3,15 +3,27 @@
 (defclass post (content)
   ((title  :initarg :title  :reader title-of)
    (author :initarg :author :reader author-of)
-   (format :initarg :format :reader post-format))
+   (format :initarg :format :reader post-format)
-  (:default-initargs :author nil))
+   (keywords :initarg :keywords :reader keywords-of)
+   (description :initarg :description :reader description-of)
+   (image :initarg :image :reader image-of)
+   (card :initarg :card :reader card-format)
+   (creator :initarg :creator :reader creator-of))
+  (:default-initargs
+   :author nil
+   :keywords nil
+   :description nil
+   :image nil
+   :card nil
+   :creator nil))
 
 (defmethod initialize-instance :after ((object post) &key)
-  (with-slots (url title author format text) object
+  (with-slots (url title author format card text) object
     (setf url (compute-url object (slugify title))
           format (make-keyword (string-upcase format))
           text (render-text text format)
-          author (or author (author *config*)))))
+          author (or author (author *config*))
+          card (if card (make-keyword (string-upcase card))))))
 
 (defmethod render ((object post) &key prev next)
   (funcall (theme-fn 'post) (list :config *config*