Under the hood, Faraday uses a Rack-inspired middleware stack for making requests. Much of Faraday’s power is unlocked with custom middleware. Some middleware is included with Faraday, and others are in external gems.

Here are some of the features that middleware can provide:

• authentication
• caching responses on disk or in memory
• cookies
• following redirects
• JSON encoding/decoding
• logging

To use these great features, create a Faraday::Connection with Faraday.new and add the correct middleware in a block. For example:

require 'faraday'

conn = Faraday.new do |f|
  f.request :json # encode req bodies as JSON
  f.request :logger # logs request and responses
  f.response :json # decode response bodies as JSON
  f.adapter :net_http # Use the Net::HTTP adapter
end
response = conn.get("http://httpbingo.org/get")

How it Works

A Faraday::Connection uses a Faraday::RackBuilder to assemble a Rack-inspired middleware stack for making HTTP requests. Each middleware runs and passes an Env object around to the next one. After the final middleware has run, Faraday will return a Faraday::Response to the end user.

The order in which middleware is stacked is important. Like with Rack, the first middleware on the list wraps all others, while the last middleware is the innermost one. If you want to use a custom adapter, it must therefore be last.

Using Middleware

Calling use is the most basic way to add middleware to your stack, but most middleware is conveniently registered in the request, response or adapter namespaces. All four methods are equivalent apart from the namespacing.

For example, the Faraday::Request::UrlEncoded middleware registers itself in Faraday::Request so it can be added with request. These two are equivalent:

# add by symbol, lookup from Faraday::Request,
# Faraday::Response and Faraday::Adapter registries
conn = Faraday.new do |f|
  f.request :url_encoded
  f.response :logger
  f.adapter :net_http
end

or:

# identical, but add the class directly instead of using lookups
conn = Faraday.new do |f|
  f.use Faraday::Request::UrlEncoded
  f.use Faraday::Response::Logger
  f.use Faraday::Adapter::NetHttp
end

This is also the place to pass options. For example:

conn = Faraday.new do |f|
  f.request :logger, bodies: true
end

Available Middleware

The Awesome Faraday project has a complete list of useful, well-maintained Faraday middleware. Middleware is often provided by external gems, like the faraday-retry gem.

We also have great documentation for the middleware that ships with Faraday.

Detailed Example

Here’s a more realistic example:

Faraday.new(...) do |conn|
  # POST/PUT params encoder
  conn.request :url_encoded

  # Logging of requests/responses
  conn.response :logger

  # Last middleware must be the adapter
  conn.adapter :net_http
end

This request middleware setup affects POST/PUT requests in the following way:

1. Request::UrlEncoded encodes as “application/x-www-form-urlencoded” if not already encoded or of another type.
2. Response::Logger logs request and response headers, can be configured to log bodies as well.

Swapping middleware means giving the other priority. Specifying the “Content-Type” for the request is explicitly stating which middleware should process it.