Better socket_timeout handling (#977)

Better socket_timeout handling by using Socket's connect_timeout (available since Ruby 3.0) instead of Timeout when possible.

lib/dalli/socket.rb

@@ -88,21 +88,40 @@ class TCP < TCPSocket
       # options - supports enhanced logging in the case of a timeout
       attr_accessor :options
 
-      def self.open(host, port, options = {})
-        Timeout.timeout(options[:socket_timeout]) do
-          sock = new(host, port)
+      if RUBY_VERSION >= '3.0'
+        def self.open(host, port, options = {})
+          sock = new(host, port, connect_timeout: options[:socket_timeout])
           sock.options = { host: host, port: port }.merge(options)
           init_socket_options(sock, options)
 
           options[:ssl_context] ? wrapping_ssl_socket(sock, host, options[:ssl_context]) : sock
         end
+      else
+        def self.open(host, port, options = {})
+          Timeout.timeout(options[:socket_timeout]) do
+            sock = new(host, port)
+            sock.options = { host: host, port: port }.merge(options)
+            init_socket_options(sock, options)
+
+            options[:ssl_context] ? wrapping_ssl_socket(sock, host, options[:ssl_context]) : sock
+          end
+        end
       end
 
       def self.init_socket_options(sock, options)
         sock.setsockopt(::Socket::IPPROTO_TCP, ::Socket::TCP_NODELAY, true)
         sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_KEEPALIVE, true) if options[:keepalive]
         sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_RCVBUF, options[:rcvbuf]) if options[:rcvbuf]
         sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_SNDBUF, options[:sndbuf]) if options[:sndbuf]
+
+        return unless options[:socket_timeout]
+
+        seconds, fractional = options[:socket_timeout].divmod(1)
+        microseconds = fractional * 1_000_000
+        timeval = [seconds, microseconds].pack('l_2')
+
+        sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_RCVTIMEO, timeval)
+        sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_SNDTIMEO, timeval)
       end
 
       def self.wrapping_ssl_socket(tcp_socket, host, ssl_context)