ひとまずそれっぽいやつを書いてみたが、時間ないのでまだ動かしていない

Gemfile

@@ -5,6 +5,10 @@ source "http://rubygems.org"
 
 # Add dependencies to develop your gem here.
 # Include everything needed to run rake, tests, features, etc.
+#
+gem 'fluent-logger'
+gem 'rack'
+
 group :development do
   gem "rspec", "~> 2.8.0"
   gem "rdoc", "~> 3.12"

lib/rack-common_logger-fluent.rb

@@ -0,0 +1,2 @@
+# just alias.
+require 'rack/common_logger/fluent'

lib/rack/common_logger/fluent.rb

@@ -0,0 +1,68 @@
+require 'fluent-logger'
+
+module Rack
+  class CommonLogger
+    #
+    # @example
+    #   # in your config.ru
+    #
+    #   require 'fluent-logger'
+    #   require 'rack/common_logger/fluent'
+    #
+    #   logger = Fluent::Logger::FluentLogger.new(nil, :host => 'localhost', :port => 24224)
+    #   use Rack::CommonLogger::Fluent, 'myapp', logger
+    #
+    #   # if you want to customize format
+    #   use Rack::CommonLogger::Fluent, 'myapp', logger do |info|
+    #     result = {}
+    #
+    #     # ...
+    #
+    #     result
+    #   end
+    # 
+    class Fluent
+      def initialize(app, tag, logger=nil, &format)
+        @app = app
+        @logger = logger || Fluent::Logger::FluentLogger.new(nil, :host => 'localhost', :port => 24224)
+        @tag = tag
+        @format = format || lambda do |info|
+          hash = {}
+
+          hash["remote_addr"]    = info[:env]["HTTP_X_FORWARDED_FOR"] || info[:env]["REMOTE_ADDR"] || '-'
+          hash["accessed_at"]    = info[:now].strftime('%d/%b/%Y %H:%M:%S')
+          hash["request_method"] = info[:env]["REQUEST_METHOD"]
+          hash["path_info"]      = info[:env]["PATH_INFO"]
+          hash["query_string"]   = info[:env]["QUERY_STRING"].empty? ? "" : '?' + info[:env]["QUERY_STRING"]
+          hash["http_version"]   = info[:env]["HTTP_VERSION"]
+          hash["http_status"]    = info[:status].to_s[0..3]
+          hash["content_length"] = info[:length]
+          hash["runtime"]        = info[:runtime]
+
+          hash
+        end
+      end
+
+      def call(env)
+        began_at = Time.now
+        status, header, body = @app.call(env)
+        header = Utils::HeaderHash.new(header)
+        body = BodyProxy.new(body) { log(env, status, header, began_at) }
+        [status, header, body]
+      end
+
+      def log(env, status, header, began_at)
+        now = Time.now
+        length = extract_content_length(header)
+        result = @format.call({ :env => env, :status => status, :header => header, :now => now, :runtime => now - began_at, :length => length })
+        @logger.post(result)
+      end
+
+      def extract_content_length(headers)
+        value = headers['Content-Length'] or return '-'
+        value.to_s == '0' ? '-' : value
+      end
+    end
+  end
+end
+