Autoload IPAddr instead of requiring it eagerly

lib/openssl/ssl.rb

@@ -15,7 +15,11 @@
 if defined?(OpenSSL::SSL)
 
 require "io/nonblock"
-require "ipaddr"
+# Only OpenSSL::SSL.verify_certificate_identity uses IPAddr, and only for
+# certificates carrying an iPAddress SAN. Autoloading keeps ipaddr (and the
+# socket library it pulls in) off the require path for everyone else, while
+# leaving the IPAddr constant resolvable as before.
+autoload :IPAddr, "ipaddr"
 require "socket"
 
 module OpenSSL

test/openssl/test_require.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+require_relative "utils"
+
+class OpenSSL::TestRequire < OpenSSL::TestCase
+  IPADDR_LOADED = '$LOADED_FEATURES.any? { |f| File.basename(f) == "ipaddr.rb" }'
+
+  def subprocess(script)
+    lib = File.expand_path("../../lib", __dir__)
+    IO.popen([RbConfig.ruby, "-I", lib, "-e", script], &:read)
+  end
+
+  def test_requiring_openssl_does_not_load_ipaddr
+    assert_equal "false", subprocess("require 'openssl'; print #{IPADDR_LOADED}")
+  end
+
+  def test_ipaddr_is_still_reachable_after_requiring_openssl
+    assert_equal "127.0.0.1", subprocess("require 'openssl'; print IPAddr.new('127.0.0.1').to_s")
+  end
+
+  def test_referencing_ipaddr_loads_it
+    script = "require 'openssl'; IPAddr.new('127.0.0.1'); print #{IPADDR_LOADED}"
+    assert_equal "true", subprocess(script)
+  end
+end