Logging middleware for Grape apps
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Latest commit e8a0f6e Aug 22, 2018


A logger for Grape apps

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  • Request path
  • Parameters
  • Endpoint class name and handler
  • Response status
  • Duration of the request
  • Exceptions
  • Error responses from error!


Add this line to your application's Gemfile:

gem 'grape', '>= 0.17'
gem 'grape-middleware-logger'


require 'grape'
require 'grape/middleware/logger'

class API < Grape::API
  # @note Make sure this is above your first +mount+
  insert_after Grape::Middleware::Formatter, Grape::Middleware::Logger

Server requests will be logged to STDOUT by default.

Example output


Started GET "/v1/reports/101" at 2015-12-11 15:40:51 -0800
Processing by ReportsAPI/reports/:id
  Parameters: {"id"=>"101"}
Completed 200 in 6.29ms


Started POST "/v1/reports" at 2015-12-11 15:42:33 -0800
Processing by ReportsAPI/reports
  Parameters: {"name"=>"foo", "password"=>"[FILTERED]"}
  Error: {:error=>"undefined something something bad", :detail=>"Whoops"}
Completed 422 in 6.29ms


The middleware logger can be customized with the following options:

  • The :logger option can be any object that responds to .info(String)
  • The :filter option can be any object that responds to .filter(Hash) and returns a hash.
  • The :headers option can be either :all or array of strings.
    • If :all, all request headers will be output.
    • If array, output will be filtered by names in the array. (case-insensitive)

For example:

insert_after Grape::Middleware::Formatter, Grape::Middleware::Logger, {
  logger: Logger.new(STDERR),
  filter: Class.new { def filter(opts) opts.reject { |k, _| k.to_s == 'password' } end }.new,
  headers: %w(version cache-control)

Using Rails?

Rails.logger and Rails.application.config.filter_parameters will be used automatically as the default logger and param filterer, respectively. This behavior can be overridden by passing the :logger or :filter option when mounting.

You may want to disable Rails logging for API endpoints, so that the logging doesn't double-up. You can achieve this by switching around some middleware. For example:

# config/application.rb
config.middleware.swap 'Rails::Rack::Logger', 'SelectiveLogger'

# config/initializers/selective_logger.rb
class SelectiveLogger
  def initialize(app)
    @app = app

  def call(env)
    if env['PATH_INFO'] =~ %r{^/api}


If you're using the rackup command to run your server in development, pass the -q flag to silence the default rack logger.


Big thanks to jadent's question/answer on stackoverflow for easily logging error responses. Borrowed some motivation from the grape_logging gem and would love to see these two consolidated at some point.


  1. Fork it ( https://github.com/ridiculous/grape-middleware-logger/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request