Autoload Resolv instead of requiring it eagerly

lib/net/http.rb

@@ -22,8 +22,8 @@
 
 require 'net/protocol'
 require 'uri'
-require 'resolv'
 autoload :OpenSSL, 'openssl'
+autoload :Resolv, 'resolv'
 
 module Net   #:nodoc:
 

test/net/http/test_require.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: false
+require 'net/http'
+require 'test/unit'
+
+# Guards the autoload of Resolv in net/http. The checks run in a subprocess
+# because this one has resolv loaded already.
+class HTTPRequireTest < Test::Unit::TestCase
+  RESOLV_LOADED = '$LOADED_FEATURES.any? { |f| File.basename(f) == "resolv.rb" }'
+
+  def subprocess(script)
+    lib = File.expand_path('../../../lib', __dir__)
+    IO.popen([RbConfig.ruby, '-I', lib, '-e', script], &:read)
+  end
+
+  def test_requiring_net_http_does_not_load_resolv
+    assert_equal 'false', subprocess("require 'net/http'; print #{RESOLV_LOADED}")
+  end
+
+  def test_resolv_is_still_reachable_after_requiring_net_http
+    script = "require 'net/http'; print Resolv::IPv4::Regex.is_a?(Regexp)"
+    assert_equal 'true', subprocess(script)
+  end
+
+  def test_referencing_resolv_loads_it
+    script = "require 'net/http'; Resolv::IPv4::Regex; print #{RESOLV_LOADED}"
+    assert_equal 'true', subprocess(script)
+  end
+end