Use Rack::CommonLogger in Sinatra

Question

I have a small web-server that I wrote with Sinatra. I want to be able to log messages to a log file. I've read through http://www.sinatrarb.com/api/index.html and www.sinatrarb.com/intro.html, and I see that Rack has something called Rack::CommonLogger, but I can't find any examples of how it can be accessed and used to log messages. My app is simple so I wrote it as a top-level DSL, but I can switch to subclassing it from SinatraBase if that's part of what's required.

Solution 1

Rack::CommonLogger won't provide a logger to your main app, it will just logs the request like Apache would do.

Check the code by yourself: https://github.com/rack/rack/blob/master/lib/rack/common_logger.rb

All Rack apps have the call method that get's invoked with the HTTP Request env, if you check the call method of this middleware this is what happens:

def call(env)
  began_at = Time.now
  status, header, body = @app.call(env)
  header = Utils::HeaderHash.new(header)
  log(env, status, header, began_at)
  [status, header, body]
end

The @app in this case is the main app, the middleware is just registering the time the request began at, then it class your middleware getting the [status, header, body] triple, and then invoke a private log method with those parameters, returning the same triple that your app returned in the first place.

The logger method goes like:

def log(env, status, header, began_at)
  now = Time.now
  length = extract_content_length(header)

  logger = @logger || env['rack.errors']
  logger.write FORMAT % [
    env['HTTP_X_FORWARDED_FOR'] || env["REMOTE_ADDR"] || "-",
    env["REMOTE_USER"] || "-",
    now.strftime("%d/%b/%Y %H:%M:%S"),
    env["REQUEST_METHOD"],
    env["PATH_INFO"],
    env["QUERY_STRING"].empty? ? "" : "?"+env["QUERY_STRING"],
    env["HTTP_VERSION"],
    status.to_s[0..3],
    length,
    now - began_at ]
end

As you can tell, the log method just grabs some info from the request env, and logs in on a logger that is specified on the constructor call, if there is no logger instance then it goes to the rack.errors logger (it seems there is one by default)

The way to use it (in your config.ru):

logger = Logger.new('log/app.log')

use Rack::CommonLogger, logger
run YourApp

If you want to have a common logger in all your app, you could create a simple logger middleware:

class MyLoggerMiddleware

  def initialize(app, logger)
    @app, @logger = app, logger
  end

  def call(env)
    env['mylogger'] = @logger
    @app.call(env)
  end

end

To use it, on your config.ru:

logger = Logger.new('log/app.log')
use Rack::CommonLogger, logger
use MyLoggerMiddleware, logger
run MyApp

Hope this helps.

Solution 2

In your config.ru:

root = ::File.dirname(__FILE__)
logfile = ::File.join(root,'logs','requests.log')

require 'logger'
class ::Logger; alias_method :write, :<<; end
logger  = ::Logger.new(logfile,'weekly')

use Rack::CommonLogger, logger

require ::File.join(root,'myapp')
run MySinatraApp.new # Subclassed from Sinatra::Application

Solution 3

I followed what I found on this blog post - excerpted below

require 'rubygems'
require 'sinatra'

disable :run
set :env, :production
set :raise_errors, true
set :views, File.dirname(__FILE__) + '/views'
set :public, File.dirname(__FILE__) + '/public'
set :app_file, __FILE__

log = File.new("log/sinatra.log", "a")
STDOUT.reopen(log)
STDERR.reopen(log)

require 'app'
run Sinatra.application

then use puts or print. It worked for me.

Solution 4

class ErrorLogger
  def initialize(file)
    @file = ::File.new(file, "a+")
    @file.sync = true
  end

  def puts(msg)
    @file.puts
    @file.write("-- ERROR -- #{Time.now.strftime("%d %b %Y %H:%M:%S %z")}: ")
    @file.puts(msg)
  end
end


class App < Sinatra::Base

  if production?
    error_logger = ErrorLogger.new('log/error.log')

    before {
      env["rack.errors"] =  error_logger
    }
  end

  ...

end

View more solutions

Comments

[Lawrence I. Siden]

That works, but I'd really like to find out how to use Rack::CommonLogger to send messages formatted with timestamps.

[Lawrence I. Siden]

Shouldn't the first line of MyLoggerMiddleware#call(env) be: env['rack.errors'] = @logger ?

[Lawrence I. Siden]

Also, I don't want to log every request, just warnings and error messages. But I'd like it to be configurable so that I can set the level of logging, as in "debug", "info", "warnings", "errors", ... BTW - My app is not a Rails app. There is no config.ru file. It's a simple Sinatra app. I was hoping to use an existing standard, but can't figure out what that is. Maybe I have to take the CommonLogger you showed me and wing it on my own?

[Chamnap]

i try your solution, and it works. i wonder why it have to be in config.ru?

[jafrog]

config.ru is a configuration file for Rack, not for Rails. Both Sinatra and Rails are Rack-based, so you can use config.ru in Sinatra applications as well.

[Ian Vaughan]

a file things I'm not 100% on there, would you mind commenting on what/why some of the lines are there please?

[Douglas G. Allen]

The file link first posted here has changed. It is currently github.com/rack/rack/blob/master/lib/rack/common_logger.rb

[Andy Jones]

This doesn't work for me. It has no effect on Sinatra or Rack logging.

[iphone007]

Where is the Logger class (used in Logger.new) defined?