D-Bus message header fields

[Felipe Gasper]

> On Sep 18, 2018, at 11:35 AM, Simon McVittie <smcv at collabora.com> wrote:
> 
> On Tue, 18 Sep 2018 at 11:13:44 -0400, Felipe Gasper wrote:
>>> On Sep 18, 2018, at 11:08 AM, Simon McVittie <smcv at collabora.com> wrote:
>>>> 	Is it intended that duplicate headers be used? Or is it safe for a new client implementation to treat the message headers as a dictionary?
>>> 
>>> The reference implementation of D-Bus considers duplicate headers
>>> to be invalid (try `git grep DBUS_INVALID_HEADER_FIELD_APPEARS_TWICE`),
>>> so dbus-daemon will close connections that try to send a message with
>>> duplicate headers. As a result, we'll probably never want to use duplicate
>>> headers - we'd be more likely to define a header whose value is an array.
>> 
>> Would there be any problem, then, with marshaling/unmarshaling headers as “yyyyuua{yv}”?
> 
> Why would you? The spec says the header fields are an array of pairs,
> so unmarshalling them as anything other than an array of pairs seems an
> odd thing to want to do?
> 
> (You don't have to store them in the same way you would present an array
> of pairs to users of your implementation, of course.)

I am new to both the protocol and its specification, but FWIW, it seems like the protocol uses those header fields as a dictionary in practice, as in your previous example of a get_interface() method: look up by index, no dupes allowed.

I suppose it’s implementation-dependent, but it would seem a bit simpler, conceptually as well as in practice, to marshal/unmarshal *as* a dict rather than as an array of pairs that we use as a dict.

-F