Add cachebusting fingerprints to asset files.

This is using http://avdgaag.github.io/nanoc-cachebuster/.

docs.css had to be moved out of /static because the static datasource
treats all files as binary, and thus no textual filters can be applied
(necessary for rewriting the jumbotron background image URL).

Fixes https://github.com/prometheus/docs/issues/369

Gemfile

@@ -12,3 +12,4 @@ gem 'builder'
 gem 'rb-inotify', :require => false
 gem 'rb-fsevent', :require => false
 gem 'rb-fchange', :require => false
+gem 'nanoc-cachebuster'

Gemfile.lock

@@ -42,6 +42,8 @@ GEM
     multi_json (1.11.2)
     nanoc (3.7.3)
       cri (~> 2.3)
+    nanoc-cachebuster (0.3.1)
+      nanoc (>= 3.3.0)
     nokogiri (1.6.3.1)
       mini_portile (= 0.6.0)
     posix-spawn (0.3.9)
@@ -75,6 +77,7 @@ DEPENDENCIES
   guard-nanoc
   kramdown
   nanoc
+  nanoc-cachebuster
   nokogiri
   pygments.rb
   rb-fchange

Rules

@@ -17,8 +17,13 @@ compile '/assets/*' do
 end
 
 route '/assets/*' do
-  # /assets/foo.html/ → /foo.html
-  item.identifier[0..-2]
+  # Cachebuster currently doesn't fingerprint all needed files (SVG and font
+  # extensions are missing), so we need to differentiate here.
+  if Nanoc::Cachebuster::FILETYPES_TO_FINGERPRINT.include?(item[:extension])
+    item.identifier[0..-(3 + item[:extension].length)] + fingerprint(item[:filename]) + '.' + item[:extension]
+  else
+    item.identifier[0..-2]
+  end
 end
 
 route '/README/' do
@@ -40,7 +45,6 @@ compile '*' do
   if item[:title] == 'README.md'
     # Don't filter; this should propagate verbatim to the output GitHub repository.
   elsif item[:extension] == 'md'
-    #filter :kramdown
     filter :redcarpet, options: {filter_html: true, autolink: true, no_intraemphasis: true, fenced_code_blocks: true, gh_blockcode: true, tables: true}, renderer_options: {with_toc_data: true}
     filter :add_anchors
     filter :bootstrappify
@@ -61,6 +65,8 @@ compile '*' do
   else
     layout 'default'
   end
+
+  filter :cache_buster
 end
 
 route '/blog/' do
@@ -78,7 +84,7 @@ end
 route '*' do
   if item[:extension] == 'css'
     # Write item with identifier /foo/ to /foo.css
-    item.identifier.chop + '.css'
+    item.identifier.chop + fingerprint(item[:filename]) + '.css'
   elsif item.binary?
     # Write item with identifier /foo/ to /foo.ext
     item.identifier.chop + '.' + item[:extension]

layouts/header.html

@@ -39,7 +39,7 @@
     <link href="/assets/bootstrap-3.3.1/css/bootstrap.min.css" rel="stylesheet">
 
     <!-- Custom styles for this template -->
-    <link href="/assets/docs.css" rel="stylesheet">
+    <link href="/css/docs.css" rel="stylesheet">
 
     <!-- Custom Fonts -->
     <link href="/assets/font-awesome-4.2.0/css/font-awesome.min.css" rel="stylesheet" type="text/css">

lib/default.rb

 # All files in the 'lib' directory will be loaded
 # before nanoc starts compiling.
 
+require 'nanoc/cachebuster'
+
 include Nanoc::Helpers::LinkTo
 include Nanoc::Helpers::Rendering
 include Nanoc3::Helpers::Blogging
 include Nanoc3::Helpers::Tagging
+include Nanoc::Helpers::CacheBusting
 
 module BlogHelper
   def get_pretty_date(post)
@@ -18,7 +21,7 @@ module BlogHelper
       "<div class='read-more'><a href='#{post.path}'>Continue reading &rsaquo;</a></div>"
     end
     return content
-  end  
+  end
 end
 
 include BlogHelper