udp.cr

require "socket"

lib LibC
  ifdef darwin
  else
    SO_BINDTODEVICE = 25
  end
end


server = UDPSocket.new
iface = "lo"
res = LibC.setsockopt(server.fd, LibC::SOL_SOCKET, LibC::SO_BINDTODEVICE, pointerof(iface) as Void*, iface.size)

# % strace -qq -f -e trace=setsockopt -e 'signal=!all' crystal run udp.cr
# [pid 25840] setsockopt(8, SOL_SOCKET, SO_BINDTODEVICE, "\270x", 2) = -1 EPERM (Operation not permitted)