Re: Speaking of DNS server software...

[Tom Beecher via NANOG <nanog () lists nanog org>]

> For Python to access a DNS packet, the programmer must pack
> and unpack an array of bytes using complex software of their own
> devising. You can't just tell Python, "This is the complex data
> structure these bytes contain, let me access the data without
> unpacking it."


Yes you can.

https://docs.python.org/3/library/socket.html

With these data structures you can:
> header = (struct ipv4_header*) byte_buffer;
> printf ("Don't fragment bit is: %s\n",
> header->dont_fragment?"set":"unset");
>
> Not only is that code simple, the amount of work the CPU has to do to
> execute that code is trivial.



    df_status = s.getsockopt(socket.IPPROTO_IP, socket.IP_DONTFRAG)
    print(f"Don't Fragment flag status: {df_status}")


On Sun, Aug 10, 2025 at 9:31 PM William Herrin via NANOG <
nanog () lists nanog org> wrote:

> On Sun, Aug 10, 2025 at 5:56 PM John Levine <johnl () iecc com> wrote:
> > It appears that William Herrin via NANOG <nanog () lists nanog org> said:
> > > Python doesn't work this way. Its memory management is abstracted away
> > > from the programmer and the programmer does not control its precise
> > > structure. For Python to access a DNS packet, the programmer must pack
> > > and unpack an array of bytes using complex software of their own
> > > devising. You can't just tell Python, "This is the complex data
> > > structure these bytes contain, let me access the data without
> > > unpacking it."
> >
> > The python struct module is pretty fast, since it's written in C.
>
> Hi John,
>
> That's the difference. In Python you have a complex software library
> which can shuttle data back and forth between Python's internal data
> management process and an arbitrary byte-oriented data structure. In
> C, that arbitrary data structure is a first class citizen in the core
> language and no translation is needed.
>
> You could pull apart a DNS packet in a Bash shell script if you really
> wanted to. The code complexity would be out of sight and it would run
> orders of magnitude slower than Python or C, but it can be done. Just
> because a thing can be done doesn't mean the language is an optimal
> choice for the task.
>
> Regards,
> Bill Herrin
>
>
> --
> William Herrin
> bill () herrin us
> https://bill.herrin.us/
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>
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