Add Octokit::Middleware::Retry

Octokit::Middleware::Retry allows incorporating the retry logic without
relying on the default middleware stack.

README.md

@@ -597,7 +597,7 @@ traffic:
 
 ```ruby
 stack = Faraday::RackBuilder.new do |builder|
-  builder.use Faraday::Retry::Middleware, exceptions: Faraday::Request::Retry::DEFAULT_EXCEPTIONS + [Octokit::ServerError] # or Faraday::Request::Retry for Faraday < 2.0
+  builder.use Octokit::Middleware::Retry
   builder.use Octokit::Middleware::FollowRedirects
   builder.use Octokit::Response::RaiseError
   builder.use Octokit::Response::FeedParser

lib/octokit.rb

@@ -76,6 +76,12 @@ def method_missing(method_name, *args, &block)
       super
     end
   end
+
+  module Middleware
+    # In Faraday 2.x, Faraday::Request::Retry was moved to a separate gem
+    # so we use it only when requested.
+    autoload :Retry, 'octokit/middleware/retry'
+  end
 end
 
 Octokit.setup

lib/octokit/middleware/retry.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module Octokit
+  module Middleware
+    base = if defined?(Faraday::Request::Retry)
+             Faraday::Request::Retry
+           else
+             require 'faraday/retry'
+             Faraday::Retry::Middleware
+           end
+
+    # Public: Retries each request a limited number of times.
+    class Retry < base
+      def initialize(app, **kwargs)
+        super(app, **kwargs, exceptions: DEFAULT_EXCEPTIONS + [Octokit::ServerError])
+      end
+    end
+  end
+end

spec/octokit/client_spec.rb

@@ -514,6 +514,27 @@
     end
   end
 
+  describe 'retry' do
+    it 'retries for 504 response' do
+      client = oauth_client
+      client.middleware.insert Octokit::Response::RaiseError, Octokit::Middleware::Retry
+
+      requested = false
+
+      request = stub_get('/foo').to_return do
+        if requested
+          { status: 200 }
+        else
+          requested = true
+          { status: 504 }
+        end
+      end
+
+      client.get('/foo')
+      assert_requested request, times: 2
+    end
+  end
+
   describe 'redirect handling' do
     it 'follows redirect for 301 response' do
       client = oauth_client