The Rack::Static middleware intercepts requests for static files (javascript files, images, stylesheets, etc) based on the url prefixes or route mappings passed in the options, and serves them using a Rack::File object. This allows a Rack stack to serve both static and dynamic content.

Examples:

Serve all requests beginning with /media from the "media" folder located in the current directory (ie media/*):

    use Rack::Static, :urls => ["/media"]

Serve all requests beginning with /css or /images from the folder "public" in the current directory (ie public/css/* and public/images/*):

    use Rack::Static, :urls => ["/css", "/images"], :root => "public"

Serve all requests to / with "index.html" from the folder "public" in the current directory (ie public/index.html):

    use Rack::Static, :urls => {"/" => 'index.html'}, :root => 'public'

Serve all requests normally from the folder "public" in the current directory but uses index.html as default route for "/"

    use Rack::Static, :urls => [""], :root => 'public', :index =>
    'index.html'

Set custom HTTP Headers for based on rules:

    use Rack::Static, :root => 'public',
        :header_rules => [
          [rule, {header_field => content, header_field => content}],
          [rule, {header_field => content}]
        ]

 Rules for selecting files:

 1) All files
    Provide the :all symbol
    :all => Matches every file

 2) Folders
    Provide the folder path as a string
    '/folder' or '/folder/subfolder' => Matches files in a certain folder

 3) File Extensions
    Provide the file extensions as an array
    ['css', 'js'] or %w(css js) => Matches files ending in .css or .js

 4) Regular Expressions / Regexp
    Provide a regular expression
    %r{\.(?:css|js)\z} => Matches files ending in .css or .js
    /\.(?:eot|ttf|otf|woff|svg)\z/ => Matches files ending in
      the most common web font formats (.eot, .ttf, .otf, .woff, .svg)
      Note: This Regexp is available as a shortcut, using the :fonts rule

 5) Font Shortcut
    Provide the :fonts symbol
    :fonts => Uses the Regexp rule stated right above to match all common web font endings

 Rule Ordering:
   Rules are applied in the order that they are provided.
   List rather general rules above special ones.

 Complete example use case including HTTP header rules:

    use Rack::Static, :root => 'public',
        :header_rules => [
          # Cache all static files in public caches (e.g. Rack::Cache)
          #  as well as in the browser
          [:all, {'Cache-Control' => 'public, max-age=31536000'}],

          # Provide web fonts with cross-origin access-control-headers
          #  Firefox requires this when serving assets using a Content Delivery Network
          [:fonts, {'Access-Control-Allow-Origin' => '*'}]
        ]