I used 0. Didn't work.

Probably because your protoype is wrong.

This: my $f = Win32::API->new('kernel32', 'PeekNamedPipe', 'LLLLLL', 'L')

Should be this: my $f = Win32::API->new('kernel32', 'PeekNamedPipe', 'LPLPPP', 'L')

Fix that, and your 'fix' above is unnecessary.

Just another hack at a module that worked fine for the most part before people start trying 'fix it' without enough knowledge to do so.

I wouldn't call it excitement. More depression when I see people proffering this kind unnecessary complexity:

sub get_pv { local $^W; unpack 'L!', pack 'P', $_[0] }

BEGIN {
   # BOOL PeekNamedPipe(
   #    HANDLE  hNamedPipe,
   #    LPVOID  lpBuffer,
   #    DWORD   nBufferSize,
   #    LPDWORD lpBytesRead,
   #    LPDWORD lpTotalBytesAvail,
   #    LPDWORD lpBytesLeftThisMessage
   # )

   my $f = Win32::API->new('kernel32', 'PeekNamedPipe', 'LLLLLL', 'L')
      or die $^E;

   sub PeekNamedPipe {
      my $nBytesRead;
      my $nTotalBytesAvail;
      my $nBytesLeftThisMessage;

      $nBytesRead            = pack('L!', $_[3]) if defined $_[3];
      $nTotalBytesAvail      = pack('L!', $_[4]) if defined $_[4];
      $nBytesLeftThisMessage = pack('L!', $_[5]) if defined $_[5];

      my $rv = $f->Call(
         $_[0],
         get_pv($_[1]),
         $_[2],
         get_pv($nBytesRead),
         get_pv($nTotalBytesAvail),
         get_pv($nBytesLeftThisMessage),
      );

      $_[3] = unpack('L!', $nBytesRead           ) if defined $_[3];
      $_[4] = unpack('L!', $nTotalBytesAvail     ) if defined $_[4];
      $_[5] = unpack('L!', $nBytesLeftThisMessage) if defined $_[5];

      return $rv;
   }
}
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for the sake of a little reading, and a couple of zeros. The icing on the cake is when they try to claim the technical high ground as justifiction for it.

My original code, the one with the problem, was

Win32::API->Import(
   'kernel32',
   'BOOL PeekNamedPipe(
      HANDLE  hNamedPipe,
      LPVOID  lpBuffer,
      DWORD   nBufferSize,
      LPDWORD lpBytesRead,
      LPDWORD lpTotalBytesAvail,
      LPDWORD lpBytesLeftThisMessage
   )',
);
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There's no way to pass NULL when using that syntax. Using that syntax is what sets has_proto. I may not have found the optimal *workaround*, but that doesn't mean the bug isn't there. I didn't use LPLPPP because I assumed it was buggy too.

More depression when I see people proffering this kind unnecessary complexity:

If you think LPLPPP is shorter...

BEGIN {
   # BOOL WINAPI PeekNamedPipe(
   #    __in       HANDLE hNamedPipe,
   #    __out_opt  LPVOID lpBuffer,
   #    __in       DWORD nBufferSize,
   #    __out_opt  LPDWORD lpBytesRead,
   #    __out_opt  LPDWORD lpTotalBytesAvail,
   #    __out_opt  LPDWORD lpBytesLeftThisMessage
   # )

   my $f = Win32::API->new('kernel32', 'PeekNamedPipe', 'LPLPPP', 'L')
      or die $^E;

   sub PeekNamedPipe {
      my $vBuffer           = defined($_[1]) ? $vBuffer          : 0;
      my $nBytesRead        = defined($_[3]) ? pack('L!', $_[3]) : 0;
      my $nTotalBytesAvail  = defined($_[4]) ? pack('L!', $_[4]) : 0;
      my $nBytesLeftThisMsg = defined($_[5]) ? pack('L!', $_[5]) : 0;

      my $rv = $f->Call(
         $_[0],
         $vBuffer,
         $_[2],
         $nBytesRead,
         $nTotalBytesAvail,
         $nBytesLeftThisMsg,
      );

      $_[1] = $vBuffer                         if defined $_[1];
      $_[3] = unpack('L!', $nBytesRead       ) if defined $_[3];
      $_[4] = unpack('L!', $nTotalBytesAvail ) if defined $_[4];
      $_[5] = unpack('L!', $nBytesLeftThisMsg) if defined $_[5];

      return $rv;      
   }
}
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That's why I prefer to use the prototype approach. It's much simpler. It handles packing pointers. It just doesn't handle NULL.

I agree with you. Avoiding this complexity would be much better, but a bug is preventing me.