Add Rack::Logger.

lib/rack/contrib.rb

@@ -30,6 +30,7 @@ def self.release
   autoload :LazyConditionalGet,         "rack/contrib/lazy_conditional_get"
   autoload :LighttpdScriptNameFix,      "rack/contrib/lighttpd_script_name_fix"
   autoload :Locale,                     "rack/contrib/locale"
+  autoload :Logger,                     "rack/contrib/logger"
   autoload :MailExceptions,             "rack/contrib/mailexceptions"
   autoload :PostBodyContentTypeParser,  "rack/contrib/post_body_content_type_parser"
   autoload :ProcTitle,                  "rack/contrib/proctitle"

lib/rack/logger.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require 'logger'
+
+require 'rack/constants'
+
+module Rack
+  # Sets up rack.logger to write to rack.errors stream
+  class Logger
+    def initialize(app, level = ::Logger::INFO)
+      @app, @level = app, level
+    end
+
+    def call(env)
+      logger = ::Logger.new(env[RACK_ERRORS])
+      logger.level = @level
+
+      env[RACK_LOGGER] = logger
+      @app.call(env)
+    end
+  end
+end

test/spec_logger.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require 'minitest/autorun'
+require 'rack/logger'
+
+describe Rack::Logger do
+  app = lambda { |env|
+    log = env['rack.logger']
+    log.debug("Created logger")
+    log.info("Program started")
+    log.warn("Nothing to do!")
+
+    [200, { 'content-type' => 'text/plain' }, ["Hello, World!"]]
+  }
+
+  it "conform to Rack::Lint" do
+    errors = StringIO.new
+    a = Rack::Lint.new(Rack::Logger.new(app))
+    Rack::MockRequest.new(a).get('/', 'rack.errors' => errors)
+    errors.string.must_match(/INFO -- : Program started/)
+    errors.string.must_match(/WARN -- : Nothing to do/)
+  end
+end