Bug 66114

Created attachment 81311 [details] [review]
[PATCH] DBus Specification: unknown key in match rule must be  ignored

Created attachment 81313 [details] [review]
[PATCH v2] DBus Specification: unknown key in match rule must be  ignored

As I said on the mailing list, match rule keys are not header field codes.

This is a feature request: "change the D-Bus Specification so that unknown match rule keys are ignored". It would make all known versions of dbus-daemon instantly non-compliant with that specification.

(In reply to comment #3)
> As I said on the mailing list, match rule keys are not header field codes.

Yes, I known that, just want to say this is just like the message header situation, sorry for my english skill.

> 
> This is a feature request: "change the D-Bus Specification so that unknown
> match rule keys are ignored". It would make all known versions of
> dbus-daemon instantly non-compliant with that specification.

I'm so happy to see that you agree with me.

>On 24/06/13 08:26, Yang Chengwei wrote:
>> Hi List,
>
>No need to Cc me - oddly enough, the person who has done most of the
>D-Bus releases in the last 2 years does read the mailing list :-)
>
>> I just found that the *new* dbus-monitor can't run with the *old" 
>> dbus-daemon.
>
>"Old" here means 1.4, which is older than the current stable branch. I

Yes, that is 1.4.18 on ubuntu.

>don't support older-than-current-stable D-Bus versions, except for
>non-intrusive security fixes.
>
>> Error: Unknown key "eavesdrop" in match rule
>> 
>> This is cause by "eavesdrop" is newly added to dbus to fix an
>> issue: https://bugs.freedesktop.org/show_bug.cgi?id=37890
>
>The right way to fix this would be to do the AddMatch with eavesdrop,
>and if it fails, try again without it - like Bustle does[1]. I'd
>accept a patch that did this, if you think compatibility with D-Bus
>1.4 is really that important.
>
>[1] http://cgit.freedesktop.org/bustle/tree/c-sources/pcap-monitor.c
>

Sure, will do so for dbus-monitor.

>> Again, if an implementation sees a header field code that it does
>> not expect, it must ignore that field, as it will be part of a new
>> (but compatible) version of this specification.
>
>This is specifically talking about header fields: if it was meant to
>be about other constructs, it would say so.
>
>> So I think it's applicable to the match rule, say: ignore unknown
>> keys in match rule.
>
>If you think the D-Bus Specification should have similar wording about
>match rules too, that's a reasonable request to consider.

Yes, that's what I did mean.

>
>In general, adding keys to a match rule makes it narrower, so in
>general, adding an unrecognised key would result in the client
>receiving more messages than it had intended to. In principle, clients
>should consider match rules to be advisory, not mandatory, so in
>principle, it should be prepared to ignore those extra messages. In
>practice, there have been clients that are buggy if they receive
>unwanted messages.
>
>So, it's a question of which of these is more valuable:
>
>* making it fractionally easier to add more match rule keys (clients
>  wouldn't have to "guard" their AddMatch calls, if they can depend on
>  a D-Bus version new enough that it ignores unknown keys)
>
>* minimizing how much we break the expectations of clients that wrongly
>  expect their match rules to be exclusive

Yes, as you said, it's *wrongly*.

>
>If we make this change to the specification, it won't change the
>behaviour of currently-deployed copies of D-Bus, so clients using new
>match rules will *still* have to "guard" AddMatch calls until they can
>depend on a new enough D-Bus version that it has the "ignore unknown
>match rules" behaviour. I think that's the sort of behavioural change
>that should go through a development branch (1.7), meaning it won't be
>widespread until 1.8.

That's fine for me.

As you said in comment 3, we'll adopt this change, although this change will make all distributed dbus-daemon not compliant with the new specification.

>
>    S

(In reply to comment #5)
> As you said in comment 3, we'll adopt this change

I didn't say that, I said this was a feature request. There are two possible resolutions for a feature request: "yes, add it" and "no, we don't want that".

I'm not going to make this change until/unless people have had a chance to respond on the mailing list. I don't have any particular objection to it, but the other maintainers might.

Several patches for dbus-monitor uploaded at #bug66107, includes the one keep backwards compatibility with old dbus which hasn't eavesdropping as a match rule key.

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