Logging

# Configuration

Lucky uses Dexter to handle all logging. Log configuration is in config/log.cr.

Lucky sets up a different configuration based on the environment your app is running in.

• In the test environment, the logger uses the DEBUG level, and writes to a temp file (tmp/test.log) instead of STDOUT.
• In production, the logger uses the INFO level, and writes to STDOUT using a json formatter for the output.
• Finally, in development, the logger uses the DEBUG level, and writes to STDOUT using a custom pretty formatter.

All of these settings can be changed in config/log.cr.

When writing to STDOUT, the colors are turned on for development. If you’d like to disable color, open config/colors.cr, and set Colorize.enabled = false.

# Configuration using Dexter

Dexter is a Lucky library that makes it simpler to configure logging in a type-safe way. It also adds some methods and formatters we’ll go into more later in the guide.

{LogClass}.dexter.configure allows for configuring the Severity/level that the log should handle. It also accepts a second optional argument for setting the Log::Backend.

Calling {LogClass}.dexter.configure will configure the Log and all its children.

If the backend argument is not passed, the Log’s backend will not be changed. Instead it will use the Log’s backend for all its children.

backend = Log::IOBackend.new
# Pass a Log::Severity like :error, :none, or :debug.
# You usually want to pass a backend to the top-level `Log` or logs
# will not write to anything.
Log.dexter.configure(:info, Log::IOBackend.new)

# LogToIgnore and its children will not log anything
LogToIgnore.dexter.configure(:none)

# LogEverything and its children will log everything because `:debug`
# is the lowest level severity
LogEverything.dexter.configure(:debug)

# Logging Data

You can access the logger from anywhere in your app by calling info|warn|debug or one of the other Log::Severity levels on Log.

class Dashboard::Index < BrowserAction
  get "/dashboard" do
    # Pass a String to log that message
    Log.info { "#{current_user.email} view the Dashboard" }
    html IndexPage
  end
end

# Lucky/Dexter specific Log methods

It is often useful to log key/value data so that it is easier to parse and search logs in production.

For logging key/value data you can return a NamedTuple or Hash in the block.

  Log.dexter.debug do
    {
      message: "Calling LegacyRedirectHandler",
      last_thing_i_had_for_lunch: "🌮"
    }
  end

# Logger Severity

There are several different severity levels you can choose. These are all defined in the Crystal Log::Severity enum.

# LogHandler

Lucky includes a LogHandler middleware in src/app_server.cr that logs basic request information like the request method, request path, response status, and the duration of the request.

# skip_if

The skip_if option is configured in config/log.cr to allow you to skip logging certain requests that come in to your application.

By default, Lucky will not log requests for static assets.

You might use skip_if to skip logging sensitive data or requests to certain paths.