Add exponential backoff to bundler retries

bundler/lib/bundler/retry.rb

@@ -6,6 +6,8 @@ class Retry
     attr_accessor :name, :total_runs, :current_run
 
     class << self
+      attr_accessor :default_base_delay
+
       def default_attempts
         default_retries + 1
       end
@@ -16,11 +18,17 @@ def default_retries
       end
     end
 
-    def initialize(name, exceptions = nil, retries = self.class.default_retries)
+    # Set default base delay for exponential backoff
+    self.default_base_delay = 1.0
+
+    def initialize(name, exceptions = nil, retries = self.class.default_retries, opts = {})
       @name = name
       @retries = retries
       @exceptions = Array(exceptions) || []
       @total_runs = @retries + 1 # will run once, then upto attempts.times
+      @base_delay = opts[:base_delay] || self.class.default_base_delay
+      @max_delay = opts[:max_delay] || 60.0
+      @jitter = opts[:jitter] || 0.5
     end
 
     def attempt(&block)
@@ -48,9 +56,23 @@ def fail_attempt(e)
         Bundler.ui.info "" unless Bundler.ui.debug?
         raise e
       end
-      return true unless name
-      Bundler.ui.info "" unless Bundler.ui.debug? # Add new line in case dots preceded this
-      Bundler.ui.warn "Retrying #{name} due to error (#{current_run.next}/#{total_runs}): #{e.class} #{e.message}", true
+      if name
+        Bundler.ui.info "" unless Bundler.ui.debug? # Add new line in case dots preceded this
+        Bundler.ui.warn "Retrying #{name} due to error (#{current_run.next}/#{total_runs}): #{e.class} #{e.message}", true
+      end
+      backoff_sleep if @base_delay > 0
+      true
+    end
+
+    def backoff_sleep
+      # Exponential backoff: delay = base_delay * 2^(attempt - 1)
+      # Add jitter to prevent thundering herd: random value between 0 and jitter seconds
+      delay = @base_delay * (2**(@current_run - 1))
+      delay = [@max_delay, delay].min
+      jitter_amount = rand * @jitter
+      total_delay = delay + jitter_amount
+      Bundler.ui.debug "Sleeping for #{total_delay.round(2)} seconds before retry"
+      sleep(total_delay)
     end
 
     def keep_trying?

bundler/spec/bundler/retry_spec.rb

@@ -78,4 +78,108 @@
       end
     end
   end
+
+  context "exponential backoff" do
+    it "can be disabled by setting base_delay to 0" do
+      attempts = 0
+      expect do
+        Bundler::Retry.new("test", [], 2, base_delay: 0).attempt do
+          attempts += 1
+          raise "error"
+        end
+      end.to raise_error(StandardError)
+
+      # Verify no sleep was called (implicitly - if sleep was called, timing would be different)
+      expect(attempts).to eq(3)
+    end
+
+    it "is enabled by default with 1 second base delay" do
+      attempts = 0
+      sleep_times = []
+
+      allow_any_instance_of(Bundler::Retry).to receive(:sleep) do |_instance, delay|
+        sleep_times << delay
+      end
+
+      expect do
+        Bundler::Retry.new("test", [], 2, jitter: 0).attempt do
+          attempts += 1
+          raise "error"
+        end
+      end.to raise_error(StandardError)
+
+      expect(attempts).to eq(3)
+      expect(sleep_times.length).to eq(2)
+      # First retry: 1.0 * 2^0 = 1.0
+      expect(sleep_times[0]).to eq(1.0)
+      # Second retry: 1.0 * 2^1 = 2.0
+      expect(sleep_times[1]).to eq(2.0)
+    end
+
+    it "sleeps with exponential backoff when base_delay is set" do
+      attempts = 0
+      sleep_times = []
+
+      allow_any_instance_of(Bundler::Retry).to receive(:sleep) do |_instance, delay|
+        sleep_times << delay
+      end
+
+      expect do
+        Bundler::Retry.new("test", [], 2, base_delay: 1.0, jitter: 0).attempt do
+          attempts += 1
+          raise "error"
+        end
+      end.to raise_error(StandardError)
+
+      expect(attempts).to eq(3)
+      expect(sleep_times.length).to eq(2)
+      # First retry: 1.0 * 2^0 = 1.0
+      expect(sleep_times[0]).to eq(1.0)
+      # Second retry: 1.0 * 2^1 = 2.0
+      expect(sleep_times[1]).to eq(2.0)
+    end
+
+    it "respects max_delay" do
+      sleep_times = []
+
+      allow_any_instance_of(Bundler::Retry).to receive(:sleep) do |_instance, delay|
+        sleep_times << delay
+      end
+
+      expect do
+        Bundler::Retry.new("test", [], 3, base_delay: 10.0, max_delay: 15.0, jitter: 0).attempt do
+          raise "error"
+        end
+      end.to raise_error(StandardError)
+
+      # First retry: 10.0 * 2^0 = 10.0
+      expect(sleep_times[0]).to eq(10.0)
+      # Second retry: 10.0 * 2^1 = 20.0, capped at 15.0
+      expect(sleep_times[1]).to eq(15.0)
+      # Third retry: 10.0 * 2^2 = 40.0, capped at 15.0
+      expect(sleep_times[2]).to eq(15.0)
+    end
+
+    it "adds jitter to delay" do
+      sleep_times = []
+
+      allow_any_instance_of(Bundler::Retry).to receive(:sleep) do |_instance, delay|
+        sleep_times << delay
+      end
+
+      expect do
+        Bundler::Retry.new("test", [], 2, base_delay: 1.0, jitter: 0.5).attempt do
+          raise "error"
+        end
+      end.to raise_error(StandardError)
+
+      expect(sleep_times.length).to eq(2)
+      # First retry should be between 1.0 and 1.5 (base + jitter)
+      expect(sleep_times[0]).to be >= 1.0
+      expect(sleep_times[0]).to be <= 1.5
+      # Second retry should be between 2.0 and 2.5
+      expect(sleep_times[1]).to be >= 2.0
+      expect(sleep_times[1]).to be <= 2.5
+    end
+  end
 end

bundler/spec/spec_helper.rb

@@ -93,6 +93,9 @@ def self.ruby=(ruby)
     require_relative "support/rubygems_ext"
     Spec::Rubygems.test_setup
 
+    # Disable retry delays in tests to speed them up
+    Bundler::Retry.default_base_delay = 0
+
     # Simulate bundler has not yet been loaded
     ENV.replace(ENV.to_hash.delete_if {|k, _v| k.start_with?(Bundler::EnvironmentPreserver::BUNDLER_PREFIX) })