simple attempt in crystal to use getnameinfo()

dns-test.cr

require "socket"

# taken from
# /Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/netdb.h
@[Flags]
enum NetDB::Flags
  NI_NOFQDN       = 0x00000001
  NI_NUMERICHOST  = 0x00000002
  NI_NAMEREQD     = 0x00000004
  NI_NUMERICSERV  = 0x00000008
  NI_DGRAM        = 0x00000010
  NI_WITHSCOPEID  = 0x00000020
  NI_NUMERICSCOPE = 0x00000100
end

module DNS
  NI_MAXHOST = LibC::SocklenT.new(1025)

  def self.getnameinfo(addr : Socket::Address, service : String, flags : NetDB::Flags)
    host_ptr = Pointer.malloc(NI_MAXHOST, 0_u8)
    host_slice = Slice.new(host_ptr, NI_MAXHOST)
    addr_len = LibC::SocklenT.new(sizeof(typeof(addr)))
    service_len = LibC::SocklenT.new(service.bytesize)
    STDERR.puts "calling getnameinfo(addr: #{addr.inspect}, addr_len: #{addr_len}, host_slice: #{host_slice.size}, NI_MAXHOST: #{NI_MAXHOST}, service: #{service.inspect}, service_len: #{service_len}, flags: #{flags})"
    result = LibC.getnameinfo(addr, addr_len, host_ptr, NI_MAXHOST, service, service_len, flags)
    STDERR.puts "result: #{result}: #{String.new(LibC.gai_strerror(result))}"
  end
end

DNS.getnameinfo addr: Socket::IPAddress.new("8.8.8.8", 8080), service: "80", flags: NetDB::Flags::None