Faraday::Conductivity

Extra Faraday Middleware! Geared towards a service oriented architecture.

These middlewares are currently included:

• user_agent, adds a dynamic User-Agent header to the request, so you know which server and process the request is coming from.
• extended_logging, logs all the information of the request.
• request_id, passes along the X-Request-Id header to track API request back to the source.
• request_headers, allows you to specify default request headers used in each request.
• selective_errors, raise errors only on the statuses that you specify.

Further information:

• faraday
• faraday_middleware

Example

Here is an overview of my favorite stack. More information about each middleware is below.

APP_VERSION = IO.popen(["git", "rev-parse", "HEAD", :chdir => Rails.root]).read.chomp

require "faraday_middleware"
require "faraday/conductivity"

connection = Faraday.new(url: "http://widgets.yourapp.com") do |faraday|

  # provided by Faraday itself
  faraday.token_auth "secret"
  faraday.request :multipart
  faraday.request :url_encoded

  # provided by this gem
  faraday.request :user_agent, app: "MarketingSite", version: APP_VERSION
  faraday.request :request_id
  faraday.request :request_headers, accept: "application/vnd.widgets-v2+json"

  # provided by this gem
  faraday.use :extended_logging, logger: Rails.logger

  # provided by faraday_middleware
  faraday.response :json, content_type: /\bjson$/

  # provided by this gem
  faraday.response :selective_errors, on: 425..599, except: 402..499

  faraday.adapter Faraday.default_adapter

end

Installation

Add this line to your application's Gemfile:

gem 'faraday-conductivity'

And then execute:

$ bundle

Or install it yourself as:

$ gem install faraday-conductivity

Usage

Here is an overview of the middleware included in this gem.

Extended Logging

Provides pretty logging, allowing you to inspect every detail of the request and response.

connection = Faraday.new(url: "http://widgets.yourapp.com") do |faraday|
  faraday.use :extended_logging, logger: Rails.logger
end

Be sure to put this middleware after other middleware that add headers, otherwise it will log incomplete requests.

RequestID

Pass on a request ID from your frontend applications to your backend services. This allows for tracking requests over multiple services. Use this in combination with something like the Rails tagged logger and you'll always know what triggered something to happen in your application.

It works by trying to find the request id in Thread.current[:request_id] and setting the X-Request-Id header.

connection = Faraday.new(url: "http://widgets.yourapp.com") do |faraday|
  faraday.request :request_id
end

In order for this to work, you need to make the Request ID globally available. To do this in Rails:

class Application < ActionController::Base
  before_filter Faraday::Conductivity::RequestIdFilter
end

It's a hack, because it uses a thread local variable, but it works really well.

Don't forget to turn on uuid logging in Rails too, by uncommenting the line in config/environments/production.rb:

# Prepend all log lines with the following tags
config.log_tags = [ :uuid ]

User Agent

Which application, on which server, made this request? With this middleware you know! It sets the User-Agent string based on the user, pid and hostname.

connection = Faraday.new(url: "http://widgets.yourapp.com") do |faraday|
  faraday.request :user_agent, app: "MarketingSite", version: "1.1"
end

The User-Agent will looks like this on my machine:

MarketingSite/1.1 (iain.local; iain; 30360) ruby/1.9.3 (327; x86_64-darwin12.2.0)

Repeater

The Repeater will retry your requests until they succeed. This is handy for reaching servers that are not too reliable.

connection = Faraday.new(url: "http://slow.website.com") do |faraday|
  faraday.use :repeater, retries: 6, mode: :rapid
end

The retries parameter specifies how many times to retry before succeeding.

The mode parameter specifies how long to wait before retrying. :rapid will retry instantly, :one, will wait one second between retries, :linear and :exponential will retry longer and longer after every retry.

It's also possible to specify your own pattern by providing a lambda, that returns the number of seconds to wait. For example:

connection = Faraday.new(url: "http://slow.website.com") do |faraday|
  faraday.use :repeater, retries: 6, pattern: ->(n) { rand < 0.5 ? 10 : 2 }
end

You can use the repeater together with the raise_error middleware to also retry after getting 404s and other succeeded requests, but failed statuses.

Selective Errors

The default :raise_error middleware raises errors for every http status above 400. However, status codes like 404 or 422 might not be an actual exceptional condition. This middleware allows you to specify which status codes you do and do not want to raise an error for.

You can pass in an array or a range to the :on argument. This will default to 400...600. You can specify exceptions with the :except argument.

connection = Faraday.new(url: "http://widgets.yourapp.com") do |faraday|
  faraday.response :selective_errors, on: (400...600), except: [404, 409, 410, 412, 422]
end

The errors raised will be the same as Faraday, namely Faraday::Error::ResourceNotFound for 404 errors, Faraday::Error::ConnectionFailed for 407 and Faraday::Error::ClientError for the rest.

If you don't specify the :on or :except options, it will behave exactly like :raise_error. The errors are however "enhanced" with extra information about the request that normally are lost:

begin
  do_failing_request_here
rescue Faraday::Error::ClientError => error
  puts error.request[:url]
  puts error.request[:method]
  puts error.request[:body]
  puts error.request[:headers]

  puts error.response[:status]
  puts error.response[:body]
  puts error.response[:headers]
  puts error.response_time
end

Request Headers

Allows you to set request headers ahead of time, so you don't have to do this each time you make a request. You can override it per request of course.

Usage:

connection = Faraday.new(url: "http://widgets.yourapp.com") do |faraday|
  faraday.request :request_headers, accept: "application/json", x_version_number: "10"
end

Mimetype

This one is deprecated. Use Request Headers instead.

Contributing

1. Fork it
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 new Pull Request