server: add Server::ETag

packages/ruby/server/lib/server.rb

@@ -4,10 +4,12 @@ class Server
   require "rack"
   require_relative "server/puma"
   require_relative "server/gzip"
+  require_relative "server/etag"
   require_relative "server/dir"
 
   def self.app(path)
     Rack::Builder.app do
+      use Server::ETag
       run Server::Dir.new(path)
     end
   end

packages/ruby/server/lib/server/dir.rb

@@ -32,7 +32,7 @@ class Server::Dir
       200,
       {"content-type" => mime_types[extn] || Rack::Mime.mime_type(extn),
        "content-length" => body.bytesize},
-      body.each_line
+      body.each_line.to_a
     ]
   end
 

packages/ruby/server/lib/server/etag.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class Server::ETag < Rack::ETag
+  def initialize(app)
+    @app = app
+  end
+
+  def call(env)
+    status, headers, body = super(env)
+    if env["HTTP_IF_NONE_MATCH"] == headers["etag"]
+      [304, headers, [""]]
+    else
+      [status, headers, body]
+    end
+  end
+end