AddrWithDefaultLocalhost returns addr with the host set to localhost if it is empty.

NewAddrSetter creates a new pflag.Value raps a address/port configuration option pair and enables setting them both with a single command-line flag.

NewPortRangeSetter creates a new pflag.Value that allows setting a lower and upper bound of a port range with a single setting.

SplitHostPort is like net.SplitHostPort however it supports addresses without a port number.