Logging Excon HTTP request/response

24 Jan 2016

I have been using Excon for a while. It’s great for interacting with JSON APIs. One thing I find missing in it is out of the box support for logging HTTP requests and responses. Though Excon has a debug mode which spits detailed request/response information to terminal, it’s handy to have some of that in the log file. While Excon README doesn’t mention anything about logging, this closed issue provided some cues.

Excon supports Active Support Instrumentation, which allows developers to provide hooks which other developers may hook into. Excon adds some events to which you can subscribe. Instrumentation section of Excon README has more details on how to subscribe to its events. For logging request/response, we are interested in excon.request and excon.response events. So let’s get started.

First you need pass instrumentor while creating Excon connection:

connection = Excon.new(@host, instrumentor: ActiveSupport::Notifications)

Then you can log requests/responses by subscribing to Excon events and accessing the payload data:

# config/initializers/notifications.rb

ActiveSupport::Notifications.subscribe('excon.request') do |*_, payload|
  Rails.logger.info("API Request: #{payload[:method]} #{payload[:path]}")
  Rails.logger.info("headers: #{payload[:headers].except('Content-Type', 'Host')}")
  Rails.logger.info("query: #{payload[:query]}") if payload[:query].present?
  Rails.logger.info("body: #{payload[:body]}") if payload[:body].present?

ActiveSupport::Notifications.subscribe('excon.response') do |*_, payload|
  Rails.logger.info("API Response: #{payload[:body]}")

That’s it. Restart the server and Excon requests and responses will get logged.