ruby/test/resolv/test_dns.rb

# frozen_string_literal: false
require 'test/unit'
require 'resolv'
require 'socket'
require 'tempfile'

class Object # :nodoc:
  def stub name, val_or_callable, &block
    new_name = "__minitest_stub__#{name}"

    metaclass = class << self; self; end

    if respond_to? name and not methods.map(&:to_s).include? name.to_s then
      metaclass.send :define_method, name do |*args|
        super(*args)
      end
    end

    metaclass.send :alias_method, new_name, name

    metaclass.send :define_method, name do |*args|
      if val_or_callable.respond_to? :call then
        val_or_callable.call(*args)
      else
        val_or_callable
      end
    end

    yield self
  ensure
    metaclass.send :undef_method, name
    metaclass.send :alias_method, name, new_name
    metaclass.send :undef_method, new_name
  end unless method_defined?(:stub) # lib/rubygems/test_case.rb also has the same method definition
end

class TestResolvDNS < Test::Unit::TestCase
  def setup
    @save_do_not_reverse_lookup = BasicSocket.do_not_reverse_lookup
    BasicSocket.do_not_reverse_lookup = true
  end

  def teardown
    BasicSocket.do_not_reverse_lookup = @save_do_not_reverse_lookup
  end

  def with_tcp(host, port)
    t = TCPServer.new(host, port)
    begin
      t.listen(1)
      yield t
    ensure
      t.close
    end
  end

  def with_udp(host, port)
    u = UDPSocket.new
    begin
      u.bind(host, port)
      yield u
    ensure
      u.close
    end
  end

  def with_udp_and_tcp(host, port)
    if port == 0
      # Automatic port; we might need to retry until we find a port which is free on both UDP _and_ TCP.
      retries_remaining = 10
      ts = []
      us = []
      begin
        begin
          us << UDPSocket.new
          us.last.bind(host, 0)
          _, udp_port, _, _ = us.last.addr
          ts << TCPServer.new(host, udp_port)
          ts.last.listen(1)
        rescue Errno::EADDRINUSE, Errno::EACCES
          # ADDRINUSE is what should get thrown if we try and bind a port which is already bound on UNIXen,
          # but windows can sometimes throw EACCESS.
          # See: https://stackoverflow.com/questions/48478869/cannot-bind-to-some-ports-due-to-permission-denied
          retries_remaining -= 1
          retry if retries_remaining > 0
          # Windows and MinGW CI can't bind to the same port with ten retries.
          omit if /mswin|mingw/ =~ RUBY_PLATFORM
          raise
        end

        # If we get to this point, we have a valid t & u socket
        yield us.last, ts.last
      ensure
        ts.each(&:close)
        us.each(&:close)
      end
    else
      # Explicitly specified port, don't retry the bind.
      with_udp(host, port) do |u|
        with_tcp(host, port) do |t|
          yield u, t
        end
      end
    end
  end

  # [ruby-core:65836]
  def test_resolve_with_2_ndots
    conf = Resolv::DNS::Config.new :nameserver => ['127.0.0.1'], :ndots => 2
    assert conf.single?

    candidates = []
    conf.resolv('example.com') { |candidate, *args|
      candidates << candidate
      raise Resolv::DNS::Config::NXDomain
    }
    n = Resolv::DNS::Name.create 'example.com.'
    assert_equal n, candidates.last
  end

  def test_query_ipv4_address
    begin
      OpenSSL
    rescue LoadError
      omit 'autoload problem. see [ruby-dev:45021][Bug #5786]'
    end if defined?(OpenSSL)

    with_udp('127.0.0.1', 0) {|u|
      _, server_port, _, server_address = u.addr
      begin
        client_thread = Thread.new {
          Resolv::DNS.open(:nameserver_port => [[server_address, server_port]]) {|dns|
            dns.getresources("foo.example.org", Resolv::DNS::Resource::IN::A)
          }
        }
        server_thread = Thread.new {
          msg, (_, client_port, _, client_address) = Timeout.timeout(5) {u.recvfrom(4096)}
          id, word2, qdcount, ancount, nscount, arcount = msg.unpack("nnnnnn")
          qr =     (word2 & 0x8000) >> 15
          opcode = (word2 & 0x7800) >> 11
          aa =     (word2 & 0x0400) >> 10
          tc =     (word2 & 0x0200) >> 9
          rd =     (word2 & 0x0100) >> 8
          ra =     (word2 & 0x0080) >> 7
          z =      (word2 & 0x0070) >> 4
          rcode =   word2 & 0x000f
          rest = msg[12..-1]
          assert_equal(0, qr) # 0:query 1:response
          assert_equal(0, opcode) # 0:QUERY 1:IQUERY 2:STATUS
          assert_equal(0, aa) # Authoritative Answer
          assert_equal(0, tc) # TrunCation
          assert_equal(1, rd) # Recursion Desired
          assert_equal(0, ra) # Recursion Available
          assert_equal(0, z) # Reserved for future use
          assert_equal(0, rcode) # 0:No-error 1:Format-error 2:Server-failure 3:Name-Error 4:Not-Implemented 5:Refused
          assert_equal(1, qdcount) # number of entries in the question section.
          assert_equal(0, ancount) # number of entries in the answer section.
          assert_equal(0, nscount) # number of entries in the authority records section.
          assert_equal(0, arcount) # number of entries in the additional records section.
          name = [3, "foo", 7, "example", 3, "org", 0].pack("Ca*Ca*Ca*C")
          assert_operator(rest, :start_with?, name)
          rest = rest[name.length..-1]
          assert_equal(4, rest.length)
          qtype, _ = rest.unpack("nn")
          assert_equal(1, qtype) # A
          assert_equal(1, qtype) # IN
          id = id
          qr = 1
          opcode = opcode
          aa = 0
          tc = 0
          rd = rd
          ra = 1
          z = 0
          rcode = 0
          qdcount = 0
          ancount = 1
          nscount = 0
          arcount = 0
          word2 = (qr << 15) |
                  (opcode << 11) |
                  (aa << 10) |
                  (tc << 9) |
                  (rd << 8) |
                  (ra << 7) |
                  (z << 4) |
                  rcode
          msg = [id, word2, qdcount, ancount, nscount, arcount].pack("nnnnnn")
          type = 1
          klass = 1
          ttl = 3600
          rdlength = 4
          rdata = [192,0,2,1].pack("CCCC") # 192.0.2.1 (TEST-NET address) RFC 3330
          rr = [name, type, klass, ttl, rdlength, rdata].pack("a*nnNna*")
          msg << rr
          u.send(msg, 0, client_address, client_port)
        }
        result, _ = assert_join_threads([client_thread, server_thread])
        assert_instance_of(Array, result)
        assert_equal(1, result.length)
        rr = result[0]
        assert_instance_of(Resolv::DNS::Resource::IN::A, rr)
        assert_instance_of(Resolv::IPv4, rr.address)
        assert_equal("192.0.2.1", rr.address.to_s)
        assert_equal(3600, rr.ttl)
      end
    }
  end

  def test_query_ipv4_address_truncated_tcp_fallback
    begin
      OpenSSL
    rescue LoadError
      skip 'autoload problem. see [ruby-dev:45021][Bug #5786]'
    end if defined?(OpenSSL)

    num_records = 50

    with_udp_and_tcp('127.0.0.1', 0) {|u, t|
      _, server_port, _, server_address = u.addr
      client_thread = Thread.new {
        Resolv::DNS.open(:nameserver_port => [[server_address, server_port]]) {|dns|
          dns.getresources("foo.example.org", Resolv::DNS::Resource::IN::A)
        }
      }
      udp_server_thread = Thread.new {
        msg, (_, client_port, _, client_address) = Timeout.timeout(5) {u.recvfrom(4096)}
        id, word2, qdcount, ancount, nscount, arcount = msg.unpack("nnnnnn")
        qr =     (word2 & 0x8000) >> 15
        opcode = (word2 & 0x7800) >> 11
        aa =     (word2 & 0x0400) >> 10
        tc =     (word2 & 0x0200) >> 9
        rd =     (word2 & 0x0100) >> 8
        ra =     (word2 & 0x0080) >> 7
        z =      (word2 & 0x0070) >> 4
        rcode =   word2 & 0x000f
        rest = msg[12..-1]
        assert_equal(0, qr) # 0:query 1:response
        assert_equal(0, opcode) # 0:QUERY 1:IQUERY 2:STATUS
        assert_equal(0, aa) # Authoritative Answer
        assert_equal(0, tc) # TrunCation
        assert_equal(1, rd) # Recursion Desired
        assert_equal(0, ra) # Recursion Available
        assert_equal(0, z) # Reserved for future use
        assert_equal(0, rcode) # 0:No-error 1:Format-error 2:Server-failure 3:Name-Error 4:Not-Implemented 5:Refused
        assert_equal(1, qdcount) # number of entries in the question section.
        assert_equal(0, ancount) # number of entries in the answer section.
        assert_equal(0, nscount) # number of entries in the authority records section.
        assert_equal(0, arcount) # number of entries in the additional records section.
        name = [3, "foo", 7, "example", 3, "org", 0].pack("Ca*Ca*Ca*C")
        assert_operator(rest, :start_with?, name)
        rest = rest[name.length..-1]
        assert_equal(4, rest.length)
        qtype, _ = rest.unpack("nn")
        assert_equal(1, qtype) # A
        assert_equal(1, qtype) # IN
        id = id
        qr = 1
        opcode = opcode
        aa = 0
        tc = 1
        rd = rd
        ra = 1
        z = 0
        rcode = 0
        qdcount = 0
        ancount = num_records
        nscount = 0
        arcount = 0
        word2 = (qr << 15) |
                (opcode << 11) |
                (aa << 10) |
                (tc << 9) |
                (rd << 8) |
                (ra << 7) |
                (z << 4) |
                rcode
        msg = [id, word2, qdcount, ancount, nscount, arcount].pack("nnnnnn")
        type = 1
        klass = 1
        ttl = 3600
        rdlength = 4
        num_records.times do |i|
          rdata = [192,0,2,i].pack("CCCC") # 192.0.2.x (TEST-NET address) RFC 3330
          rr = [name, type, klass, ttl, rdlength, rdata].pack("a*nnNna*")
          msg << rr
        end
        u.send(msg[0...512], 0, client_address, client_port)
      }
      tcp_server_thread = Thread.new {
        ct = t.accept
        msg = ct.recv(512)
        msg.slice!(0..1) # Size (only for TCP)
        id, word2, qdcount, ancount, nscount, arcount = msg.unpack("nnnnnn")
        qr =     (word2 & 0x8000) >> 15
        opcode = (word2 & 0x7800) >> 11
        aa =     (word2 & 0x0400) >> 10
        tc =     (word2 & 0x0200) >> 9
        rd =     (word2 & 0x0100) >> 8
        ra =     (word2 & 0x0080) >> 7
        z =      (word2 & 0x0070) >> 4
        rcode =   word2 & 0x000f
        rest = msg[12..-1]
        assert_equal(0, qr) # 0:query 1:response
        assert_equal(0, opcode) # 0:QUERY 1:IQUERY 2:STATUS
        assert_equal(0, aa) # Authoritative Answer
        assert_equal(0, tc) # TrunCation
        assert_equal(1, rd) # Recursion Desired
        assert_equal(0, ra) # Recursion Available
        assert_equal(0, z) # Reserved for future use
        assert_equal(0, rcode) # 0:No-error 1:Format-error 2:Server-failure 3:Name-Error 4:Not-Implemented 5:Refused
        assert_equal(1, qdcount) # number of entries in the question section.
        assert_equal(0, ancount) # number of entries in the answer section.
        assert_equal(0, nscount) # number of entries in the authority records section.
        assert_equal(0, arcount) # number of entries in the additional records section.
        name = [3, "foo", 7, "example", 3, "org", 0].pack("Ca*Ca*Ca*C")
        assert_operator(rest, :start_with?, name)
        rest = rest[name.length..-1]
        assert_equal(4, rest.length)
        qtype, _ = rest.unpack("nn")
        assert_equal(1, qtype) # A
        assert_equal(1, qtype) # IN
        id = id
        qr = 1
        opcode = opcode
        aa = 0
        tc = 0
        rd = rd
        ra = 1
        z = 0
        rcode = 0
        qdcount = 0
        ancount = num_records
        nscount = 0
        arcount = 0
        word2 = (qr << 15) |
                (opcode << 11) |
                (aa << 10) |
                (tc << 9) |
                (rd << 8) |
                (ra << 7) |
                (z << 4) |
                rcode
        msg = [id, word2, qdcount, ancount, nscount, arcount].pack("nnnnnn")
        type = 1
        klass = 1
        ttl = 3600
        rdlength = 4
        num_records.times do |i|
          rdata = [192,0,2,i].pack("CCCC") # 192.0.2.x (TEST-NET address) RFC 3330
          rr = [name, type, klass, ttl, rdlength, rdata].pack("a*nnNna*")
          msg << rr
        end
        msg = "#{[msg.bytesize].pack("n")}#{msg}" # Prefix with size
        ct.send(msg, 0)
        ct.close
      }
      result, _ = assert_join_threads([client_thread, udp_server_thread, tcp_server_thread])
      assert_instance_of(Array, result)
      assert_equal(50, result.length)
      result.each_with_index do |rr, i|
        assert_instance_of(Resolv::DNS::Resource::IN::A, rr)
        assert_instance_of(Resolv::IPv4, rr.address)
        assert_equal("192.0.2.#{i}", rr.address.to_s)
        assert_equal(3600, rr.ttl)
      end
    }
  end

  def test_query_ipv4_duplicate_responses
    begin
      OpenSSL
    rescue LoadError
      omit 'autoload problem. see [ruby-dev:45021][Bug #5786]'
    end if defined?(OpenSSL)

    with_udp('127.0.0.1', 0) {|u|
      _, server_port, _, server_address = u.addr
      begin
        client_thread = Thread.new {
          Resolv::DNS.open(:nameserver_port => [[server_address, server_port]], :search => ['bad1.com', 'bad2.com', 'good.com'], ndots: 5, use_ipv6: false) {|dns|
            dns.getaddress("example")
          }
        }
        server_thread = Thread.new {
          3.times do
            msg, (_, client_port, _, client_address) = Timeout.timeout(5) {u.recvfrom(4096)}
            id, flags, qdcount, ancount, nscount, arcount = msg.unpack("nnnnnn")

            qr =     (flags & 0x8000) >> 15
            opcode = (flags & 0x7800) >> 11
            aa =     (flags & 0x0400) >> 10
            tc =     (flags & 0x0200) >> 9
            rd =     (flags & 0x0100) >> 8
            ra =     (flags & 0x0080) >> 7
            z =      (flags & 0x0070) >> 4
            rcode =   flags & 0x000f
            _rest = msg[12..-1]

            questions = msg.bytes[12..-1]
            labels = []
            idx = 0
            while idx < questions.length-5
              size = questions[idx]
              labels << questions[idx+1..idx+size].pack('c*')
              idx += size+1
            end
            hostname = labels.join('.')

            if hostname == "example.good.com"
              id = id
              qr = 1
              opcode = opcode
              aa = 0
              tc = 0
              rd = rd
              ra = 1
              z = 0
              rcode = 0
              qdcount = 1
              ancount = 1
              nscount = 0
              arcount = 0
              word2 = (qr << 15) |
                      (opcode << 11) |
                      (aa << 10) |
                      (tc << 9) |
                      (rd << 8) |
                      (ra << 7) |
                      (z << 4) |
                      rcode
              msg = [id, word2, qdcount, ancount, nscount, arcount].pack("nnnnnn")
              msg << questions.pack('c*')
              type = 1
              klass = 1
              ttl = 3600
              rdlength = 4
              rdata = [52,0,2,1].pack("CCCC")
              rr = [0xc00c, type, klass, ttl, rdlength, rdata].pack("nnnNna*")
              msg << rr
              rdata = [52,0,2,2].pack("CCCC")
              rr = [0xc00c, type, klass, ttl, rdlength, rdata].pack("nnnNna*")
              msg << rr

              u.send(msg, 0, client_address, client_port)
            else
              id = id
              qr = 1
              opcode = opcode
              aa = 0
              tc = 0
              rd = rd
              ra = 1
              z = 0
              rcode = 3
              qdcount = 1
              ancount = 0
              nscount = 0
              arcount = 0
              word2 = (qr << 15) |
                      (opcode << 11) |
                      (aa << 10) |
                      (tc << 9) |
                      (rd << 8) |
                      (ra << 7) |
                      (z << 4) |
                      rcode
              msg = [id, word2, qdcount, ancount, nscount, arcount].pack("nnnnnn")
              msg << questions.pack('c*')

              u.send(msg, 0, client_address, client_port)
              u.send(msg, 0, client_address, client_port)
            end
          end
        }
        result, _ = assert_join_threads([client_thread, server_thread])
        assert_instance_of(Resolv::IPv4, result)
        assert_equal("52.0.2.1", result.to_s)
      end
    }
  end

  def test_query_ipv4_address_timeout
    with_udp('127.0.0.1', 0) {|u|
      _, port , _, host = u.addr
      start = nil
      rv = Resolv::DNS.open(:nameserver_port => [[host, port]]) {|dns|
        dns.timeouts = 0.1
        start = Time.now
        dns.getresources("foo.example.org", Resolv::DNS::Resource::IN::A)
      }
      t2 = Time.now
      diff = t2 - start
      assert rv.empty?, "unexpected: #{rv.inspect} (expected empty)"
      assert_operator 0.1, :<=, diff

      rv = Resolv::DNS.open(:nameserver_port => [[host, port]]) {|dns|
        dns.timeouts = [ 0.1, 0.2 ]
        start = Time.now
        dns.getresources("foo.example.org", Resolv::DNS::Resource::IN::A)
      }
      t2 = Time.now
      diff = t2 - start
      assert rv.empty?, "unexpected: #{rv.inspect} (expected empty)"
      assert_operator 0.3, :<=, diff
    }
  end

  def test_no_server
    omit if /mswin/ =~ RUBY_PLATFORM && ENV.key?('GITHUB_ACTIONS') # not working from the beginning
    u = UDPSocket.new
    u.bind("127.0.0.1", 0)
    _, port, _, host = u.addr
    u.close
    # A race condition here.
    # Another program may use the port.
    # But no way to prevent it.
    begin
      Timeout.timeout(5) do
        Resolv::DNS.open(:nameserver_port => [[host, port]]) {|dns|
          assert_equal([], dns.getresources("test-no-server.example.org", Resolv::DNS::Resource::IN::A))
        }
      end
    rescue Timeout::Error
      if RUBY_PLATFORM.match?(/mingw/)
        # cannot repo locally
        omit 'Timeout Error on MinGW CI'
      else
        raise Timeout::Error
      end
    end
  end

  def test_invalid_byte_comment
    bug9273 = '[ruby-core:59239] [Bug #9273]'
    Tempfile.create('resolv_test_dns_') do |tmpfile|
      tmpfile.print("\xff\x00\x40")
      tmpfile.close
      assert_nothing_raised(ArgumentError, bug9273) do
        Resolv::DNS::Config.parse_resolv_conf(tmpfile.path)
      end
    end
  end

  def test_resolv_conf_by_command
    Dir.mktmpdir do |dir|
      Dir.chdir(dir) do
        assert_raise(Errno::ENOENT, Errno::EINVAL) do
          Resolv::DNS::Config.parse_resolv_conf("|echo foo")
        end
      end
    end
  end

  def test_dots_diffences
    name1 = Resolv::DNS::Name.create("example.org")
    name2 = Resolv::DNS::Name.create("ex.ampl.eo.rg")
    assert_not_equal(name1, name2, "different dots")
  end

  def test_case_insensitive_name
    bug10550 = '[ruby-core:66498] [Bug #10550]'
    lower = Resolv::DNS::Name.create("ruby-lang.org")
    upper = Resolv::DNS::Name.create("Ruby-Lang.org")
    assert_equal(lower, upper, bug10550)
  end

  def test_ipv6_name
    addr = Resolv::IPv6.new("\0"*16)
    labels = addr.to_name.to_a
    expected = (['0'] * 32 + ['ip6', 'arpa']).map {|label| Resolv::DNS::Label::Str.new(label) }
    assert_equal(expected, labels)
  end

  def test_ipv6_create
    ref = '[Bug #11910] [ruby-core:72559]'
    assert_instance_of Resolv::IPv6, Resolv::IPv6.create('::1'), ref
    assert_instance_of Resolv::IPv6, Resolv::IPv6.create('::1:127.0.0.1'), ref
  end

  def test_ipv6_to_s
    test_cases = [
      ["2001::abcd:abcd:abcd", "2001::ABcd:abcd:ABCD"],
      ["2001:db8::1", "2001:db8::0:1"],
      ["::", "0:0:0:0:0:0:0:0"],
      ["2001::", "2001::0"],
      ["2001:db8:0:1:1:1:1:1", "2001:db8:0:1:1:1:1:1"], # RFC 5952 Section 4.2.2.
      ["2001:db8::1:1:1:1", "2001:db8:0:0:1:1:1:1"],
      ["1::1:0:0:0:1", "1:0:0:1:0:0:0:1"],
      ["1::1:0:0:1", "1:0:0:0:1:0:0:1"],
    ]

    test_cases.each do |expected, ipv6|
      assert_equal expected, Resolv::IPv6.create(ipv6).to_s
    end
  end

  def test_ipv6_should_be_16
    ref = '[rubygems:1626]'

    broken_message =
      "\0\0\0\0\0\0\0\0\0\0\0\1" \
      "\x03ns2\bdnsimple\x03com\x00" \
      "\x00\x1C\x00\x01\x00\x02OD" \
      "\x00\x10$\x00\xCB\x00 I\x00\x01\x00\x00\x00\x00"

    e = assert_raise_with_message(Resolv::DNS::DecodeError, /IPv6 address must be 16 bytes/, ref) do
      Resolv::DNS::Message.decode broken_message
    end
    assert_kind_of(ArgumentError, e.cause)
  end

  def test_too_big_label_address
    n = 2000
    m = Resolv::DNS::Message::MessageEncoder.new {|msg|
      2.times {
        n.times {|i| msg.put_labels(["foo#{i}"]) }
      }
    }
    Resolv::DNS::Message::MessageDecoder.new(m.to_s) {|msg|
      2.times {
        n.times {|i|
          assert_equal(["foo#{i}"], msg.get_labels.map {|label| label.to_s })
        }
      }
    }
    assert_operator(2**14, :<, m.to_s.length)
  end

  def test_too_long_address
    too_long_address_message = [0, 0, 1, 0, 0, 0].pack("n*") + "\x01x" * 129 + [0, 0, 0].pack("cnn")
    assert_raise_with_message(Resolv::DNS::DecodeError, /name label data exceed 255 octets/) do
      Resolv::DNS::Message.decode too_long_address_message
    end
  end

  def assert_no_fd_leak
    socket = assert_throw(self) do |tag|
      Resolv::DNS.stub(:bind_random_port, ->(s, *) {throw(tag, s)}) do
        yield.getname("8.8.8.8")
      end
    end

    assert_predicate(socket, :closed?, "file descriptor leaked")
  end

  def test_no_fd_leak_connected
    assert_no_fd_leak {Resolv::DNS.new(nameserver_port: [['127.0.0.1', 53]])}
  end

  def test_no_fd_leak_unconnected
    assert_no_fd_leak {Resolv::DNS.new}
  end

  def test_each_name
    dns = Resolv::DNS.new
    def dns.each_resource(name, typeclass)
      yield typeclass.new(name)
    end

    dns.each_name('127.0.0.1') do |ptr|
      assert_equal('1.0.0.127.in-addr.arpa', ptr.to_s)
    end
    dns.each_name(Resolv::IPv4.create('127.0.0.1')) do |ptr|
      assert_equal('1.0.0.127.in-addr.arpa', ptr.to_s)
    end
    dns.each_name('::1') do |ptr|
      assert_equal('1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa', ptr.to_s)
    end
    dns.each_name(Resolv::IPv6.create('::1')) do |ptr|
      assert_equal('1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa', ptr.to_s)
    end
    dns.each_name(Resolv::DNS::Name.create('1.0.0.127.in-addr.arpa.')) do |ptr|
      assert_equal('1.0.0.127.in-addr.arpa', ptr.to_s)
    end
    assert_raise(Resolv::ResolvError) { dns.each_name('example.com') }
  end

  def test_unreachable_server
    unreachable_ip = '127.0.0.1'
    sock = UDPSocket.new
    sock.connect(unreachable_ip, 53)
    begin
      sock.send('1', 0)
    rescue Errno::ENETUNREACH, Errno::EHOSTUNREACH
    else
      omit('cannot test unreachable server, as IP used is reachable')
    end

    config = {
      :nameserver => [unreachable_ip],
      :search => ['lan'],
      :ndots => 1
    }
    r = Resolv.new([Resolv::DNS.new(config)])
    assert_equal([], r.getaddresses('www.google.com'))

    config[:raise_timeout_errors] = true
    r = Resolv.new([Resolv::DNS.new(config)])
    assert_raise(Resolv::ResolvError) { r.getaddresses('www.google.com') }
  ensure
    sock&.close
  end

  def test_multiple_servers_with_timeout_and_truncated_tcp_fallback
    begin
      OpenSSL
    rescue LoadError
      skip 'autoload problem. see [ruby-dev:45021][Bug #5786]'
    end if defined?(OpenSSL)

    num_records = 50

    with_udp_and_tcp('127.0.0.1', 0) do |u1, t1|
      with_udp_and_tcp('127.0.0.1', 0) do |u2,t2|
        u2.close # XXX: u2 UDP socket is not used, but using #with_udp_and_tcp to enable Windows EACCES workaround
        _, server1_port, _, server1_address = u1.addr
        _, server2_port, _, server2_address = t2.addr

        client_thread = Thread.new do
          Resolv::DNS.open(nameserver_port: [[server1_address, server1_port], [server2_address, server2_port]]) do |dns|
            dns.timeouts = [0.1, 0.2]
            dns.getresources('foo.example.org', Resolv::DNS::Resource::IN::A)
          end
        end

        udp_server1_thread = Thread.new do
          msg, (_, client_port, _, client_address) = Timeout.timeout(5) { u1.recvfrom(4096) }
          id, word2, _qdcount, _ancount, _nscount, _arcount = msg.unpack('nnnnnn')
          opcode = (word2 & 0x7800) >> 11
          rd = (word2 & 0x0100) >> 8
          name = [3, 'foo', 7, 'example', 3, 'org', 0].pack('Ca*Ca*Ca*C')
          qr = 1
          aa = 0
          tc = 1
          ra = 1
          z = 0
          rcode = 0
          qdcount = 0
          ancount = num_records
          nscount = 0
          arcount = 0
          word2 = (qr << 15) |
                  (opcode << 11) |
                  (aa << 10) |
                  (tc << 9) |
                  (rd << 8) |
                  (ra << 7) |
                  (z << 4) |
                  rcode
          msg = [id, word2, qdcount, ancount, nscount, arcount].pack('nnnnnn')
          type = 1
          klass = 1
          ttl = 3600
          rdlength = 4
          num_records.times do |i|
            rdata = [192, 0, 2, i].pack('CCCC') # 192.0.2.x (TEST-NET address) RFC 3330
            rr = [name, type, klass, ttl, rdlength, rdata].pack('a*nnNna*')
            msg << rr
          end
          u1.send(msg[0...512], 0, client_address, client_port)
        end

        tcp_server1_thread = Thread.new do
          # Keep this socket open so that the client experiences a timeout
          t1.accept
        end

        tcp_server2_thread = Thread.new do
          ct = t2.accept
          msg = ct.recv(512)
          msg.slice!(0..1) # Size (only for TCP)
          id, word2, _qdcount, _ancount, _nscount, _arcount = msg.unpack('nnnnnn')
          rd = (word2 & 0x0100) >> 8
          opcode = (word2 & 0x7800) >> 11
          name = [3, 'foo', 7, 'example', 3, 'org', 0].pack('Ca*Ca*Ca*C')
          qr = 1
          aa = 0
          tc = 0
          ra = 1
          z = 0
          rcode = 0
          qdcount = 0
          ancount = num_records
          nscount = 0
          arcount = 0
          word2 = (qr << 15) |
                  (opcode << 11) |
                  (aa << 10) |
                  (tc << 9) |
                  (rd << 8) |
                  (ra << 7) |
                  (z << 4) |
                  rcode
          msg = [id, word2, qdcount, ancount, nscount, arcount].pack('nnnnnn')
          type = 1
          klass = 1
          ttl = 3600
          rdlength = 4
          num_records.times do |i|
            rdata = [192, 0, 2, i].pack('CCCC') # 192.0.2.x (TEST-NET address) RFC 3330
            rr = [name, type, klass, ttl, rdlength, rdata].pack('a*nnNna*')
            msg << rr
          end
          msg = "#{[msg.bytesize].pack('n')}#{msg}" # Prefix with size
          ct.send(msg, 0)
          ct.close
        end
        result, _, tcp_server1_socket, = assert_join_threads([client_thread, udp_server1_thread, tcp_server1_thread, tcp_server2_thread])
        assert_instance_of(Array, result)
        assert_equal(50, result.length)
        result.each_with_index do |rr, i|
          assert_instance_of(Resolv::DNS::Resource::IN::A, rr)
          assert_instance_of(Resolv::IPv4, rr.address)
          assert_equal("192.0.2.#{i}", rr.address.to_s)
          assert_equal(3600, rr.ttl)
        end
      ensure
        tcp_server1_socket&.close
      end
    end
  end
end