1 files changed, 58 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/tagged_logging.rb b/activesupport/lib/active_support/tagged_logging.rb
new file mode 100644
index 0000000000..5e080df518
--- /dev/null
+++ b/activesupport/lib/active_support/tagged_logging.rb
@@ -0,0 +1,58 @@
+require 'active_support/core_ext/object/blank'
+require 'logger'
+require 'active_support/logger'
+
+module ActiveSupport
+  # Wraps any standard Logger object to provide tagging capabilities.
+  #
+  #   logger = ActiveSupport::TaggedLogging.new(Logger.new(STDOUT))
+  #   logger.tagged("BCX") { logger.info "Stuff" }                            # Logs "[BCX] Stuff"
+  #   logger.tagged("BCX", "Jason") { logger.info "Stuff" }                   # Logs "[BCX] [Jason] Stuff"
+  #   logger.tagged("BCX") { logger.tagged("Jason") { logger.info "Stuff" } } # Logs "[BCX] [Jason] Stuff"
+  #
+  # This is used by the default Rails.logger as configured by Railties to make it easy to stamp log lines
+  # with subdomains, request ids, and anything else to aid debugging of multi-user production applications.
+  module TaggedLogging
+    module Formatter # :nodoc:
+      # This method is invoked when a log event occurs
+      def call(severity, timestamp, progname, msg)
+        super(severity, timestamp, progname, "#{tags_text}#{msg}")
+      end
+
+      def clear!
+        current_tags.clear
+      end
+
+      def current_tags
+        Thread.current[:activesupport_tagged_logging_tags] ||= []
+      end
+
+      private
+      def tags_text
+        tags = current_tags
+        if tags.any?
+          tags.collect { |tag| "[#{tag}] " }.join
+        end
+      end
+    end
+
+    def self.new(logger)
+      logger.formatter.extend Formatter
+      logger.extend(self)
+    end
+
+    def tagged(*new_tags)
+      tags     = formatter.current_tags
+      new_tags = new_tags.flatten.reject(&:blank?)
+      tags.concat new_tags
+      yield self
+    ensure
+      tags.pop(new_tags.size)
+    end
+
+    def flush
+      formatter.clear!
+      super if defined?(super)
+    end
+  end
+end