text: # Copyright 2021 National Technology & Engineering Solutions
  # of Sandia, LLC (NTESS). Under the terms of Contract DE-NA0003525 with NTESS,
  # the U.S. Government retains certain rights in this software.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #    http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  """Functionality for binding to network interfaces."""
  
  import contextlib
  import logging
  import socket
  
  import netifaces
  
  log = logging.getLogger()
  
  def loopback_ip():
      """Return an IP address for localhost."""
      return "127.0.0.1"
  
  
  def public_ip():
      """Return a public-facing IP address."""
      gateway, interface = netifaces.gateways()["default"][netifaces.AF_INET]
      return netifaces.ifaddresses(interface)[netifaces.AF_INET][0]["addr"]
  
  
  def random_port(addr):
      """Return a randomly-chosen open port number for the given address."""
      with contextlib.closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as s:
          s.bind((addr, 0))
          s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
          return s.getsockname()[1]
  
  