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|woff2|woff|svg)\z/ => Matches files ending in
     the most common web font formats (.eot, .ttf, .otf, .woff2, .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' => '*'}]
       ]
Methods
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Class Public methods
new(app, options={})
# File lib/rack/static.rb, line 86
def initialize(app, options={})
  @app = app
  @urls = options[:urls] || ["/favicon.ico"]
  @index = options[:index]
  @gzip = options[:gzip]
  root = options[:root] || Dir.pwd

  # HTTP Headers
  @header_rules = options[:header_rules] || []
  # Allow for legacy :cache_control option while prioritizing global header_rules setting
  @header_rules.unshift([:all, {CACHE_CONTROL => options[:cache_control]}]) if options[:cache_control]

  @file_server = Rack::File.new(root)
end
Instance Public methods
add_index_root?(path)
# File lib/rack/static.rb, line 101
def add_index_root?(path)
  @index && path =~ /\/$/
end
applicable_rules(path)

Convert HTTP header rules to HTTP headers

# File lib/rack/static.rb, line 154
def applicable_rules(path)
  @header_rules.find_all do |rule, new_headers|
    case rule
    when :all
      true
    when :fonts
      path =~ /\.(?:ttf|otf|eot|woff2|woff|svg)\z/
    when String
      path = ::Rack::Utils.unescape(path)
      path.start_with?(rule) || path.start_with?('/' + rule)
    when Array
      path =~ /\.(#{rule.join('|')})\z/
    when Regexp
      path =~ rule
    else
      false
    end
  end
end
call(env)
# File lib/rack/static.rb, line 117
def call(env)
  path = env[PATH_INFO]

  if can_serve(path)
    if overwrite_file_path(path)
      env[PATH_INFO] = (add_index_root?(path) ? path + @index : @urls[path])
    elsif @gzip && env['HTTP_ACCEPT_ENCODING'] =~ /\bgzip\b/
      path = env[PATH_INFO]
      env[PATH_INFO] += '.gz'
      response = @file_server.call(env)
      env[PATH_INFO] = path

      if response[0] == 404
        response = nil
      else
        if mime_type = Mime.mime_type(::File.extname(path), 'text/plain')
          response[1][CONTENT_TYPE] = mime_type
        end
        response[1]['Content-Encoding'] = 'gzip'
      end
    end

    path = env[PATH_INFO]
    response ||= @file_server.call(env)

    headers = response[1]
    applicable_rules(path).each do |rule, new_headers|
      new_headers.each { |field, content| headers[field] = content }
    end

    response
  else
    @app.call(env)
  end
end
can_serve(path)
# File lib/rack/static.rb, line 113
def can_serve(path)
  route_file(path) || overwrite_file_path(path)
end
overwrite_file_path(path)
# File lib/rack/static.rb, line 105
def overwrite_file_path(path)
  @urls.kind_of?(Hash) && @urls.key?(path) || add_index_root?(path)
end
route_file(path)
# File lib/rack/static.rb, line 109
def route_file(path)
  @urls.kind_of?(Array) && @urls.any? { |url| path.index(url) == 0 }
end