rand-api.p6

#!/usr/bin/env perl6
use NativeCall;

my %*SUB-MAIN-OPTS =
  :named-anywhere,
;

#| http://man7.org/linux/man-pages/man2/getrandom.2.html
#| https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
sub MAIN (
  UInt  $bytes = 8, #= Number of random bytes (defaults to 8)
  UInt :$flags = 0,
  --> Nil
) {
  my Buf $buf.=allocate: $bytes;
  LEAVE $buf.say;

  if $*DISTRO.is-win {
    rand-api( Nil, $buf, $bytes, 2 );
  }
  else {
    given rand-api( $buf, $bytes, $flags ) {
      when -1 {
        die sub strerror( long --> Str ) is native {*}(
          cglobal |( 'c', v6; 'errno'; long ) );
      }
      when * < $bytes { die 'got fewer bytes than requested' }
    }
  }
}

my &rand-api = $*DISTRO.is-win
  ?? sub ( Pointer, Buf, size_t, ulong --> ulong )
    is symbol('BCryptGenRandom')
    is native('bcrypt') {*}
  !! sub ( Buf, size_t, ulong --> ssize_t )
    is symbol('getrandom')
    is native('c', v6) {*};