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.

6 files changed, 27 insertions, 80 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