lib/connection.js
function wrapIPv6Address (host, port) {
  if (!port) {
    if (host.indexOf('[') === 0) return host
    host = host.split(':')
    port = host[1]
    host = host[0]
  }
  return '[' + host + ']:' + port
}
function wrapIPv6Address (host, port) {
  if (!port) {
    if (host.indexOf('[') === 0) return host
    host = host.split(':')
    port = host[1]
    host = host[0]
  }
  return '[' + host + ']:' + port
}
support IPv6 https://www.ietf.org/rfc/rfc2732.txt