kill off remaining kgio uses

kgio is an extra download and shared object which costs users
bandwidth, disk space, startup time and memory.  Ruby 2.3+
provides `Socket#accept_nonblock(exception: false)' support
in addition to `exception: false' support in IO#*_nonblock
methods from Ruby 2.1.

We no longer distinguish between TCPServer and UNIXServer as
separate classes internally; instead favoring the `Socket' class
of Ruby for both.  This allows us to use `Socket#accept_nonblock'
and get a populated `Addrinfo' object off accept4(2)/accept(2)
without resorting to a getpeername(2) syscall (kgio avoided
getpeername(2) in the same way).

The downside is there's more Ruby-level argument passing and
stack usage on our end with HttpRequest#read_headers (formerly
HttpRequest#read).  I chose this tradeoff since advancements in
Ruby itself can theoretically mitigate the cost of argument
passing, while syscalls are a high fixed cost given modern CPU
vulnerability mitigations.

Note: no benchmarks have been run since I don't have a suitable
system.

13 files changed, 61 insertions, 176 deletions

diff --git a/lib/unicorn.rb b/lib/unicorn.rb
index b817b77..564cb30 100644
--- a/lib/unicorn.rb
+++ b/lib/unicorn.rb
@@ -1,7 +1,6 @@
 # -*- encoding: binary -*-
 require 'etc'
 require 'stringio'
-require 'kgio'
 require 'raindrops'
 require 'io/wait'
 
@@ -112,7 +111,7 @@ module Unicorn
   F_SETPIPE_SZ = 1031 if RUBY_PLATFORM =~ /linux/
 
   def self.pipe # :nodoc:
-    Kgio::Pipe.new.each do |io|
+    IO.pipe.each do |io|
       # shrink pipes to minimize impact on /proc/sys/fs/pipe-user-pages-soft
       # limits.
       if defined?(F_SETPIPE_SZ)
diff --git a/lib/unicorn/http_request.rb b/lib/unicorn/http_request.rb
index 8bca60a..ab3bd6e 100644
--- a/lib/unicorn/http_request.rb
+++ b/lib/unicorn/http_request.rb
@@ -61,7 +61,7 @@ class Unicorn::HttpParser
   # returns an environment hash suitable for Rack if successful
   # This does minimal exception trapping and it is up to the caller
   # to handle any socket errors (e.g. user aborted upload).
-  def read(socket)
+  def read_headers(socket, ai)
     e = env
 
     # From https://www.ietf.org/rfc/rfc3875:
@@ -71,7 +71,7 @@ class Unicorn::HttpParser
     #  identify the client for the immediate request to the server;
     #  that client may be a proxy, gateway, or other intermediary
     #  acting on behalf of the actual source client."
-    e['REMOTE_ADDR'] = socket.kgio_addr
+    e['REMOTE_ADDR'] = ai.unix? ? '127.0.0.1' : ai.ip_address
 
     # short circuit the common case with small GET requests first
     socket.readpartial(16384, buf)
@@ -81,7 +81,7 @@ class Unicorn::HttpParser
       false until add_parse(socket.readpartial(16384))
     end
 
-    check_client_connection(socket) if @@check_client_connection
+    check_client_connection(socket, ai) if @@check_client_connection
 
     e['rack.input'] = 0 == content_length ?
                       NULL_IO : @@input_class.new(socket, self)
@@ -107,8 +107,8 @@ class Unicorn::HttpParser
   if Raindrops.const_defined?(:TCP_Info)
     TCPI = Raindrops::TCP_Info.allocate
 
-    def check_client_connection(socket) # :nodoc:
-      if Unicorn::TCPClient === socket
+    def check_client_connection(socket, ai) # :nodoc:
+      if ai.ip?
         # Raindrops::TCP_Info#get!, #state (reads struct tcp_info#tcpi_state)
         raise Errno::EPIPE, "client closed connection".freeze,
               EMPTY_ARRAY if closed_state?(TCPI.get!(socket).state)
@@ -152,8 +152,8 @@ class Unicorn::HttpParser
     # Ruby 2.2+ can show struct tcp_info as a string Socket::Option#inspect.
     # Not that efficient, but probably still better than doing unnecessary
     # work after a client gives up.
-    def check_client_connection(socket) # :nodoc:
-      if Unicorn::TCPClient === socket && @@tcpi_inspect_ok
+    def check_client_connection(socket, ai) # :nodoc:
+      if @@tcpi_inspect_ok && ai.ip?
         opt = socket.getsockopt(Socket::IPPROTO_TCP, Socket::TCP_INFO).inspect
         if opt =~ /\bstate=(\S+)/
           raise Errno::EPIPE, "client closed connection".freeze,
diff --git a/lib/unicorn/http_server.rb b/lib/unicorn/http_server.rb
index 2f1eb1b..ed5bbf1 100644
--- a/lib/unicorn/http_server.rb
+++ b/lib/unicorn/http_server.rb
@@ -111,9 +111,7 @@ class Unicorn::HttpServer
 
     @worker_data = if worker_data = ENV['UNICORN_WORKER']
       worker_data = worker_data.split(',').map!(&:to_i)
-      worker_data[1] = worker_data.slice!(1..2).map do |i|
-        Kgio::Pipe.for_fd(i)
-      end
+      worker_data[1] = worker_data.slice!(1..2).map { |i| IO.for_fd(i) }
       worker_data
     end
   end
@@ -243,10 +241,6 @@ class Unicorn::HttpServer
     tries = opt[:tries] || 5
     begin
       io = bind_listen(address, opt)
-      unless Kgio::TCPServer === io || Kgio::UNIXServer === io
-        io.autoclose = false
-        io = server_cast(io)
-      end
       logger.info "listening on addr=#{sock_name(io)} fd=#{io.fileno}"
       LISTENERS << io
       io
@@ -594,9 +588,9 @@ class Unicorn::HttpServer
 
   # once a client is accepted, it is processed in its entirety here
   # in 3 easy steps: read request, call app, write app response
-  def process_client(client)
+  def process_client(client, ai)
     @request = Unicorn::HttpRequest.new
-    env = @request.read(client)
+    env = @request.read_headers(client, ai)
 
     if early_hints
       env["rack.early_hints"] = lambda do |headers|
@@ -708,10 +702,9 @@ class Unicorn::HttpServer
       reopen = reopen_worker_logs(worker.nr) if reopen
       worker.tick = time_now.to_i
       while sock = ready.shift
-        # Unicorn::Worker#kgio_tryaccept is not like accept(2) at all,
-        # but that will return false
-        if client = sock.kgio_tryaccept
-          process_client(client)
+        client_ai = sock.accept_nonblock(exception: false)
+        if client_ai != :wait_readable
+          process_client(*client_ai)
           worker.tick = time_now.to_i
         end
         break if reopen
@@ -809,7 +802,6 @@ class Unicorn::HttpServer
 
   def inherit_listeners!
     # inherit sockets from parents, they need to be plain Socket objects
-    # before they become Kgio::UNIXServer or Kgio::TCPServer
     inherited = ENV['UNICORN_FD'].to_s.split(',')
     immortal = []
 
@@ -825,8 +817,6 @@ class Unicorn::HttpServer
     inherited.map! do |fd|
       io = Socket.for_fd(fd.to_i)
       @immortal << io if immortal.include?(fd)
-      io.autoclose = false
-      io = server_cast(io)
       set_server_sockopt(io, listener_opts[sock_name(io)])
       logger.info "inherited addr=#{sock_name(io)} fd=#{io.fileno}"
       io
@@ -835,11 +825,9 @@ class Unicorn::HttpServer
     config_listeners = config[:listeners].dup
     LISTENERS.replace(inherited)
 
-    # we start out with generic Socket objects that get cast to either
-    # Kgio::TCPServer or Kgio::UNIXServer objects; but since the Socket
-    # objects share the same OS-level file descriptor as the higher-level
-    # *Server objects; we need to prevent Socket objects from being
-    # garbage-collected
+    # we only use generic Socket objects for aggregate Socket#accept_nonblock
+    # return value [ Socket, Addrinfo ].  This allows us to avoid having to
+    # make getpeername(2) syscalls later on to fill in env['REMOTE_ADDR']
     config_listeners -= listener_names
     if config_listeners.empty? && LISTENERS.empty?
       config_listeners << Unicorn::Const::DEFAULT_LISTEN
diff --git a/lib/unicorn/oob_gc.rb b/lib/unicorn/oob_gc.rb
index 91a8e51..db9f2cb 100644
--- a/lib/unicorn/oob_gc.rb
+++ b/lib/unicorn/oob_gc.rb
@@ -65,8 +65,8 @@ module Unicorn::OobGC
   end
 
   #:stopdoc:
-  def process_client(client)
-    super(client) # Unicorn::HttpServer#process_client
+  def process_client(*args)
+    super(*args) # Unicorn::HttpServer#process_client
     env = instance_variable_get(:@request).env
     if OOBGC_PATH =~ env['PATH_INFO'] && ((@@nr -= 1) <= 0)
       @@nr = OOBGC_INTERVAL
diff --git a/lib/unicorn/socket_helper.rb b/lib/unicorn/socket_helper.rb
index c2ba75e..06ec2b2 100644
--- a/lib/unicorn/socket_helper.rb
+++ b/lib/unicorn/socket_helper.rb
@@ -3,32 +3,6 @@
 require 'socket'
 
 module Unicorn
-
-  # Instead of using a generic Kgio::Socket for everything,
-  # tag TCP sockets so we can use TCP_INFO under Linux without
-  # incurring extra syscalls for Unix domain sockets.
-  # TODO: remove these when we remove kgio
-  TCPClient = Class.new(Kgio::Socket) # :nodoc:
-  class TCPSrv < Kgio::TCPServer # :nodoc:
-    def kgio_tryaccept # :nodoc:
-      super(TCPClient)
-    end
-  end
-
-  if IO.instance_method(:write).arity == 1 # Ruby <= 2.4
-    require 'unicorn/write_splat'
-    UNIXClient = Class.new(Kgio::Socket) # :nodoc:
-    class UNIXSrv < Kgio::UNIXServer # :nodoc:
-      include Unicorn::WriteSplat
-      def kgio_tryaccept # :nodoc:
-        super(UNIXClient)
-      end
-    end
-    TCPClient.__send__(:include, Unicorn::WriteSplat)
-  else # Ruby 2.5+
-    UNIXSrv = Kgio::UNIXServer
-  end
-
   module SocketHelper
 
     # internal interface
@@ -105,7 +79,7 @@ module Unicorn
     def set_server_sockopt(sock, opt)
       opt = DEFAULTS.merge(opt || {})
 
-      TCPSocket === sock and set_tcp_sockopt(sock, opt)
+      set_tcp_sockopt(sock, opt) if sock.local_address.ip?
 
       rcvbuf, sndbuf = opt.values_at(:rcvbuf, :sndbuf)
       if rcvbuf || sndbuf
@@ -149,7 +123,9 @@ module Unicorn
         end
         old_umask = File.umask(opt[:umask] || 0)
         begin
-          UNIXSrv.new(address)
+          s = Socket.new(:UNIX, :STREAM)
+          s.bind(Socket.sockaddr_un(address))
+          s
         ensure
           File.umask(old_umask)
         end
@@ -177,8 +153,7 @@ module Unicorn
         sock.setsockopt(:SOL_SOCKET, :SO_REUSEPORT, 1)
       end
       sock.bind(Socket.pack_sockaddr_in(port, addr))
-      sock.autoclose = false
-      TCPSrv.for_fd(sock.fileno)
+      sock
     end
 
     # returns rfc2732-style (e.g. "[::1]:666") addresses for IPv6
@@ -194,10 +169,6 @@ module Unicorn
     def sock_name(sock)
       case sock
       when String then sock
-      when UNIXServer
-        Socket.unpack_sockaddr_un(sock.getsockname)
-      when TCPServer
-        tcp_name(sock)
       when Socket
         begin
           tcp_name(sock)
@@ -210,16 +181,5 @@ module Unicorn
     end
 
     module_function :sock_name
-
-    # casts a given Socket to be a TCPServer or UNIXServer
-    def server_cast(sock)
-      begin
-        Socket.unpack_sockaddr_in(sock.getsockname)
-        TCPSrv.for_fd(sock.fileno)
-      rescue ArgumentError
-        UNIXSrv.for_fd(sock.fileno)
-      end
-    end
-
   end # module SocketHelper
 end # module Unicorn
diff --git a/lib/unicorn/worker.rb b/lib/unicorn/worker.rb
index ad5814c..4af31be 100644
--- a/lib/unicorn/worker.rb
+++ b/lib/unicorn/worker.rb
@@ -71,8 +71,8 @@ class Unicorn::Worker
   end
 
   # this only runs when the Rack app.call is not running
-  # act like a listener
-  def kgio_tryaccept # :nodoc:
+  # act like Socket#accept_nonblock(exception: false)
+  def accept_nonblock(*_unused) # :nodoc:
     case buf = @to_io.read_nonblock(4, exception: false)
     when String
       # unpack the buffer and trigger the signal handler
@@ -82,7 +82,7 @@ class Unicorn::Worker
     when nil # EOF: master died, but we are at a safe place to exit
       fake_sig(:QUIT)
     when :wait_readable # keep waiting
-      return false
+      return :wait_readable
     end while true # loop, as multiple signals may be sent
   end
 
diff --git a/t/oob_gc.ru b/t/oob_gc.ru
index c253540..224cb06 100644
--- a/t/oob_gc.ru
+++ b/t/oob_gc.ru
@@ -7,9 +7,6 @@ $gc_started = false
 
 # Mock GC.start
 def GC.start
-  ObjectSpace.each_object(Kgio::Socket) do |x|
-    x.closed? or abort "not closed #{x}"
-  end
   $gc_started = true
 end
 run lambda { |env|
diff --git a/t/oob_gc_path.ru b/t/oob_gc_path.ru
index af8e3b9..7f40601 100644
--- a/t/oob_gc_path.ru
+++ b/t/oob_gc_path.ru
@@ -7,9 +7,6 @@ $gc_started = false
 
 # Mock GC.start
 def GC.start
-  ObjectSpace.each_object(Kgio::Socket) do |x|
-    x.closed? or abort "not closed #{x}"
-  end
   $gc_started = true
 end
 run lambda { |env|
diff --git a/test/unit/test_request.rb b/test/unit/test_request.rb
index 7f22b24..53ae944 100644
--- a/test/unit/test_request.rb
+++ b/test/unit/test_request.rb
@@ -10,14 +10,9 @@ include Unicorn
 
 class RequestTest < Test::Unit::TestCase
 
-  class MockRequest < StringIO
-    alias_method :readpartial, :sysread
-    alias_method :kgio_read!, :sysread
-    alias_method :read_nonblock, :sysread
-    def kgio_addr
-      '127.0.0.1'
-    end
-  end
+  MockRequest = Class.new(StringIO)
+
+  AI = Addrinfo.new(Socket.sockaddr_un('/unicorn/sucks'))
 
   def setup
     @request = HttpRequest.new
@@ -30,7 +25,7 @@ class RequestTest < Test::Unit::TestCase
   def test_options
     client = MockRequest.new("OPTIONS * HTTP/1.1\r\n" \
                              "Host: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal '', env['REQUEST_PATH']
     assert_equal '', env['PATH_INFO']
     assert_equal '*', env['REQUEST_URI']
@@ -40,7 +35,7 @@ class RequestTest < Test::Unit::TestCase
   def test_absolute_uri_with_query
     client = MockRequest.new("GET http://e:3/x?y=z HTTP/1.1\r\n" \
                              "Host: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal '/x', env['REQUEST_PATH']
     assert_equal '/x', env['PATH_INFO']
     assert_equal 'y=z', env['QUERY_STRING']
@@ -50,7 +45,7 @@ class RequestTest < Test::Unit::TestCase
   def test_absolute_uri_with_fragment
     client = MockRequest.new("GET http://e:3/x#frag HTTP/1.1\r\n" \
                              "Host: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal '/x', env['REQUEST_PATH']
     assert_equal '/x', env['PATH_INFO']
     assert_equal '', env['QUERY_STRING']
@@ -61,7 +56,7 @@ class RequestTest < Test::Unit::TestCase
   def test_absolute_uri_with_query_and_fragment
     client = MockRequest.new("GET http://e:3/x?a=b#frag HTTP/1.1\r\n" \
                              "Host: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal '/x', env['REQUEST_PATH']
     assert_equal '/x', env['PATH_INFO']
     assert_equal 'a=b', env['QUERY_STRING']
@@ -73,7 +68,7 @@ class RequestTest < Test::Unit::TestCase
     %w(ssh+http://e/ ftp://e/x http+ssh://e/x).each do |abs_uri|
       client = MockRequest.new("GET #{abs_uri} HTTP/1.1\r\n" \
                                "Host: foo\r\n\r\n")
-      assert_raises(HttpParserError) { @request.read(client) }
+      assert_raises(HttpParserError) { @request.read_headers(client, AI) }
     end
   end
 
@@ -81,7 +76,7 @@ class RequestTest < Test::Unit::TestCase
     client = MockRequest.new("GET / HTTP/1.1\r\n" \
                              "X-Forwarded-Proto: https\r\n" \
                              "Host: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal "https", env['rack.url_scheme']
     assert_kind_of Array, @lint.call(env)
   end
@@ -90,7 +85,7 @@ class RequestTest < Test::Unit::TestCase
     client = MockRequest.new("GET / HTTP/1.1\r\n" \
                              "X-Forwarded-Proto: http\r\n" \
                              "Host: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal "http", env['rack.url_scheme']
     assert_kind_of Array, @lint.call(env)
   end
@@ -99,14 +94,14 @@ class RequestTest < Test::Unit::TestCase
     client = MockRequest.new("GET / HTTP/1.1\r\n" \
                              "X-Forwarded-Proto: ftp\r\n" \
                              "Host: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal "http", env['rack.url_scheme']
     assert_kind_of Array, @lint.call(env)
   end
 
   def test_rack_lint_get
     client = MockRequest.new("GET / HTTP/1.1\r\nHost: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal "http", env['rack.url_scheme']
     assert_equal '127.0.0.1', env['REMOTE_ADDR']
     assert_kind_of Array, @lint.call(env)
@@ -114,7 +109,7 @@ class RequestTest < Test::Unit::TestCase
 
   def test_no_content_stringio
     client = MockRequest.new("GET / HTTP/1.1\r\nHost: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal StringIO, env['rack.input'].class
   end
 
@@ -122,7 +117,7 @@ class RequestTest < Test::Unit::TestCase
     client = MockRequest.new("PUT / HTTP/1.1\r\n" \
                              "Content-Length: 0\r\n" \
                              "Host: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal StringIO, env['rack.input'].class
   end
 
@@ -130,7 +125,7 @@ class RequestTest < Test::Unit::TestCase
     client = MockRequest.new("PUT / HTTP/1.1\r\n" \
                              "Content-Length: 1\r\n" \
                              "Host: foo\r\n\r\n")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert_equal Unicorn::TeeInput, env['rack.input'].class
   end
 
@@ -141,7 +136,7 @@ class RequestTest < Test::Unit::TestCase
       "Content-Length: 5\r\n" \
       "\r\n" \
       "abcde")
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert ! env.include?(:http_body)
     assert_kind_of Array, @lint.call(env)
   end
@@ -152,14 +147,6 @@ class RequestTest < Test::Unit::TestCase
     buf = (' ' * bs).freeze
     length = bs * count
     client = Tempfile.new('big_put')
-    def client.kgio_addr; '127.0.0.1'; end
-    def client.kgio_read(*args)
-      readpartial(*args)
-    rescue EOFError
-    end
-    def client.kgio_read!(*args)
-      readpartial(*args)
-    end
     client.syswrite(
       "PUT / HTTP/1.1\r\n" \
       "Host: foo\r\n" \
@@ -167,7 +154,7 @@ class RequestTest < Test::Unit::TestCase
       "\r\n")
     count.times { assert_equal bs, client.syswrite(buf) }
     assert_equal 0, client.sysseek(0)
-    env = @request.read(client)
+    env = @request.read_headers(client, AI)
     assert ! env.include?(:http_body)
     assert_equal length, env['rack.input'].size
     count.times {
diff --git a/test/unit/test_socket_helper.rb b/test/unit/test_socket_helper.rb
index 62d5a3a..a446f06 100644
--- a/test/unit/test_socket_helper.rb
+++ b/test/unit/test_socket_helper.rb
@@ -24,7 +24,8 @@ class TestSocketHelper < Test::Unit::TestCase
     port = unused_port @test_addr
     @tcp_listener_name = "#@test_addr:#{port}"
     @tcp_listener = bind_listen(@tcp_listener_name)
-    assert TCPServer === @tcp_listener
+    assert Socket === @tcp_listener
+    assert @tcp_listener.local_address.ip?
     assert_equal @tcp_listener_name, sock_name(@tcp_listener)
   end
 
@@ -38,10 +39,10 @@ class TestSocketHelper < Test::Unit::TestCase
       { :backlog => 16, :rcvbuf => 4096, :sndbuf => 4096 }
     ].each do |opts|
       tcp_listener = bind_listen(tcp_listener_name, opts)
-      assert TCPServer === tcp_listener
+      assert tcp_listener.local_address.ip?
       tcp_listener.close
       unix_listener = bind_listen(unix_listener_name, opts)
-      assert UNIXServer === unix_listener
+      assert unix_listener.local_address.unix?
       unix_listener.close
     end
   end
@@ -52,11 +53,13 @@ class TestSocketHelper < Test::Unit::TestCase
     @unix_listener_path = tmp.path
     File.unlink(@unix_listener_path)
     @unix_listener = bind_listen(@unix_listener_path)
-    assert UNIXServer === @unix_listener
+    assert Socket === @unix_listener
+    assert @unix_listener.local_address.unix?
     assert_equal @unix_listener_path, sock_name(@unix_listener)
     assert File.readable?(@unix_listener_path), "not readable"
     assert File.writable?(@unix_listener_path), "not writable"
     assert_equal 0777, File.umask
+    assert_equal @unix_listener, bind_listen(@unix_listener)
   ensure
     File.umask(old_umask)
   end
@@ -67,7 +70,6 @@ class TestSocketHelper < Test::Unit::TestCase
     @unix_listener_path = tmp.path
     File.unlink(@unix_listener_path)
     @unix_listener = bind_listen(@unix_listener_path, :umask => 077)
-    assert UNIXServer === @unix_listener
     assert_equal @unix_listener_path, sock_name(@unix_listener)
     assert_equal 0140700, File.stat(@unix_listener_path).mode
     assert_equal 0777, File.umask
@@ -75,28 +77,6 @@ class TestSocketHelper < Test::Unit::TestCase
     File.umask(old_umask)
   end
 
-  def test_bind_listen_unix_idempotent
-    test_bind_listen_unix
-    a = bind_listen(@unix_listener)
-    assert_equal a.fileno, @unix_listener.fileno
-    unix_server = server_cast(@unix_listener)
-    assert UNIXServer === unix_server
-    a = bind_listen(unix_server)
-    assert_equal a.fileno, unix_server.fileno
-    assert_equal a.fileno, @unix_listener.fileno
-  end
-
-  def test_bind_listen_tcp_idempotent
-    test_bind_listen_tcp
-    a = bind_listen(@tcp_listener)
-    assert_equal a.fileno, @tcp_listener.fileno
-    tcp_server = server_cast(@tcp_listener)
-    assert TCPServer === tcp_server
-    a = bind_listen(tcp_server)
-    assert_equal a.fileno, tcp_server.fileno
-    assert_equal a.fileno, @tcp_listener.fileno
-  end
-
   def test_bind_listen_unix_rebind
     test_bind_listen_unix
     new_listener = nil
@@ -107,14 +87,18 @@ class TestSocketHelper < Test::Unit::TestCase
     File.unlink(@unix_listener_path)
     new_listener = bind_listen(@unix_listener_path)
 
-    assert UNIXServer === new_listener
     assert new_listener.fileno != @unix_listener.fileno
     assert_equal sock_name(new_listener), sock_name(@unix_listener)
     assert_equal @unix_listener_path, sock_name(new_listener)
     pid = fork do
-      client = server_cast(new_listener).accept
-      client.syswrite('abcde')
-      exit 0
+      begin
+        client, _ = new_listener.accept
+        client.syswrite('abcde')
+        exit 0
+      rescue => e
+        warn "#{e.message} (#{e.class})"
+        exit 1
+      end
     end
     s = unix_socket(@unix_listener_path)
     IO.select([s])
@@ -123,32 +107,6 @@ class TestSocketHelper < Test::Unit::TestCase
     assert status.success?
   end
 
-  def test_server_cast
-    test_bind_listen_unix
-    test_bind_listen_tcp
-    unix_listener_socket = Socket.for_fd(@unix_listener.fileno)
-    assert Socket === unix_listener_socket
-    @unix_server = server_cast(unix_listener_socket)
-    assert_equal @unix_listener.fileno, @unix_server.fileno
-    assert UNIXServer === @unix_server
-    assert_equal(@unix_server.path, @unix_listener.path,
-                 "##{@unix_server.path} != #{@unix_listener.path}")
-    assert File.socket?(@unix_server.path)
-    assert_equal @unix_listener_path, sock_name(@unix_server)
-
-    tcp_listener_socket = Socket.for_fd(@tcp_listener.fileno)
-    assert Socket === tcp_listener_socket
-    @tcp_server = server_cast(tcp_listener_socket)
-    assert_equal @tcp_listener.fileno, @tcp_server.fileno
-    assert TCPServer === @tcp_server
-    assert_equal @tcp_listener_name, sock_name(@tcp_server)
-  end
-
-  def test_sock_name
-    test_server_cast
-    sock_name(@unix_server)
-  end
-
   def test_tcp_defer_accept_default
     return unless defined?(TCP_DEFER_ACCEPT)
     port = unused_port @test_addr
diff --git a/test/unit/test_stream_input.rb b/test/unit/test_stream_input.rb
index 2a14135..7986ca7 100644
--- a/test/unit/test_stream_input.rb
+++ b/test/unit/test_stream_input.rb
@@ -9,7 +9,7 @@ class TestStreamInput < Test::Unit::TestCase
     @rs = "\n"
     $/ == "\n" or abort %q{test broken if \$/ != "\\n"}
     @env = {}
-    @rd, @wr = Kgio::UNIXSocket.pair
+    @rd, @wr = UNIXSocket.pair
     @rd.sync = @wr.sync = true
     @start_pid = $$
   end
diff --git a/test/unit/test_tee_input.rb b/test/unit/test_tee_input.rb
index 6f5bc8a..607ce87 100644
--- a/test/unit/test_tee_input.rb
+++ b/test/unit/test_tee_input.rb
@@ -10,7 +10,7 @@ end
 
 class TestTeeInput < Test::Unit::TestCase
   def setup
-    @rd, @wr = Kgio::UNIXSocket.pair
+    @rd, @wr = UNIXSocket.pair
     @rd.sync = @wr.sync = true
     @start_pid = $$
     @rs = "\n"
diff --git a/unicorn.gemspec b/unicorn.gemspec
index 7bb1154..85183d9 100644
--- a/unicorn.gemspec
+++ b/unicorn.gemspec
@@ -36,7 +36,6 @@ Gem::Specification.new do |s|
   # won't have descriptive text, only the numeric status.
   s.add_development_dependency(%q<rack>)
 
-  s.add_dependency(%q<kgio>, '~> 2.6')
   s.add_dependency(%q<raindrops>, '~> 0.7')
 
   s.add_development_dependency('test-unit', '~> 3.0')