Message equality

[peterthomassen]

Hi. dns.message.__eq__ says:

        """Two messages are equal if they have the same content in the
        header, question, answer, and authority sections.

        Returns a ``bool``.
        """

As expected, differing EDNS0 options do not affect equality. However, I don't understand how that works from a code perspective. Doesn't the following (from __eq__) also compare the additional section, as it iterates over self.sections?

        for i, section in enumerate(self.sections):
            other_section = other.sections[i]
            for n in section:
                if n not in other_section:
                    return False
            for n in other_section:
                if n not in section:
                    return False
        return True

[bwelling]

The additional section is compared, but the opt isn't stored as part of the additional section; it's broken out into a separate opt field.

I'm not saying that the current behavior is correct; only explaining it.

[peterthomassen]

Ah, I see. So at the very least, the docstring is inaccurate (it seems to imply that the additional section is not compared, even for non-OPT records).

[bwelling]

Sorry, hadn't noticed that. You're right, the docstring does appear to be inaccurate as well.

[peterthomassen]

We're OK with this behavior (and I'll be happy to submit a PR to fix the docstring), but in implementing RFC 9859 (draft), we will start relying on this behavior. (... by comparing the NOTIFY message and its response, which with the current implementation will only differ in the QR flag. The fact that the outgoing message contained a ReportChannelOption and the response doesn't isn't caught by the equality check.)

So it would be good to know if you're foreseeing this logic to be changed or not. Thanks for letting me know!

[rthalley]

I wasn't planning on changing it, as this kind of equality is often the more useful and I view EDNS0's stuff more like metadata than the content of the message. I'd also be happy to add a more complete equality comparison if anyone did need to compare EDNS0 too.