[fpc-pascal] FPC and IPv6, and BSD

Mark Morgan Lloyd markMLl.fpc-pascal at telemetry.co.uk
Mon Jul 23 23:24:55 CEST 2012

Mark Morgan Lloyd wrote:
> I'm trying to write a simple finger daemon, capable of both IP4 and IP6. 
> At present it's using an unprivileged socket so as to avoid problems on 
> unix platforms.
> I appear to be having problems at the bind() call for IP6 (returns -1), 
> which I suspect is down to my incomplete understanding of the new 
> sockaddr_in6 structure. Has anybody done this successfully?

On Linux >= 2.4.21 attempting to bind a v6 socket also binds the 
corresponding v4. Appears to need

   bindrc := 1;
   fpsetsockopt(socket6, IPPROTO_IPV6, IPV6_V6ONLY, @bindrc, 

to get them to work individually.

> As a subsidiary question: noting that a client has to be aware of this:
>   sockaddr_in6 = packed Record
>     {$ifdef SOCK_HAS_SINLEN}  // as per RFC 2553
>       sin6_len    : cuint8;
>     {$endif}
>     sin6_family   : sa_family_t;
> ..
> so that it initialises the sin6_len field if present (some BSD 
> variants?), does it see that conditional automatically if defined? 
> Otherwise how best to do it?


Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]

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