Allow logging of specified environment variables.

README.rdoc

@@ -64,6 +64,10 @@ For activerecord instantiation counts only:
 
   Rails.application.middleware.use( Oink::Middleware, :instruments => :activerecord )
 
+Environment variables can also be logged by specifying `env_vars`. This is especially handy for displaying request ID or REQUEST_URI from the Rails `env` object.
+
+  Rails.application.middleware.use( Oink::Middleware, :env_vars => ['action_dispatch.request_id', 'REQUEST_ID'] )
+
 Note that the previous way of configuring oink, as a set of modules to include into rails controllers, is deprecated.
 
 == Analyzing logs

lib/oink/middleware.rb

@@ -9,6 +9,7 @@ def initialize(app, options = {})
       @app         = app
       @logger      = options[:logger] || Hodel3000CompliantLogger.new("log/oink.log")
       @instruments = options[:instruments] ? Array(options[:instruments]) : [:memory, :activerecord]
+      @env_vars    = options[:env_vars] ? Array(options[:env_vars]) : []
 
       Oink.extend_active_record! if @instruments.include?(:activerecord)
     end
@@ -17,6 +18,7 @@ def call(env)
       status, headers, body = @app.call(env)
 
       log_routing(env)
+      log_environment(env)
       log_memory
       log_activerecord
       log_completed
@@ -36,6 +38,15 @@ def log_routing(env)
       end
     end
 
+    def log_environment(env)
+      return if @env_vars.empty?
+      env_message = @env_vars.map { |key|
+        value = env[key]
+        "#{key.inspect}: #{value.inspect if value && value.respond_to?(:inspect)}"
+      }.join(', ')
+      @logger.info("Environment: {#{env_message}}")
+    end
+
     def log_memory
       if @instruments.include?(:memory)
         memory = Oink::Instrumentation::MemorySnapshot.memory