TCPSocket.new supports "local_host" and "local_service".

mrblib/socket.rb

@@ -236,6 +236,12 @@ class TCPSocket
       Addrinfo.foreach(host, service) { |ai|
         begin
           s = Socket._socket(ai.afamily, Socket::SOCK_STREAM, 0)
+          if local_host or local_service
+            local_host ||= (ai.afamily == Socket::AF_INET) ? "0.0.0.0" : "::"
+            local_service ||= "0"
+            bi = Addrinfo.getaddrinfo(local_host, local_service, ai.afamily, ai.socktype)[0]
+            Socket._bind(s, bi.to_sockaddr)
+          end
           Socket._connect(s, ai.to_sockaddr)
           super(s, "r+")
           return