Using a struct[enum] as an sdbusplus D-Bus method arg?

[Patrick Williams]

On Wed, Jan 08, 2020 at 01:32:49PM -0600, Matt Spinler wrote:

Hi Matt,

> I'm designing a phosphor-dbus-interfaces D-Bus method where I think the
> ideal interface has YAML like:
> 
> - name : CreateStuff
>   parameters:
>     - name: Data
>       type: array[struct[enum[self.Types], uint32]]
> 
> But that doesn't compile using an enum in the struct, and fails because
> sdbus++ creates code like:
> 
> server.cpp:
> 
>     // Uses enum<self.Types>
>     std::vector<std::tuple<enum<self.Types>, uint8_t>> data{};
>     m.read(data);
>     auto o = static_cast<Create*>(context);
>     o->createStuff(data);
> 
> What I'm trying to do is a valid D-Bus definition, correct? Or should I just
> use a string instead
> of an enum?

Enums are not actually a DBus concept, but something we added to
sdbusplus specifically.  What happens is that at the DBus level we send
them between processes as fully-qualified strings[1].  In the sdbusplus
generated code we know that this was defined in the YAML as an enum and
so we look the string up in a map<string, enum> to get you the enum
value (and throw an exception if an invalid enum was given).

I wouldn't recommend using a string instead because you are just
bypassing this enum-string checking code.

> It doesn't seem very straightforward to fix, as the vector that gets passed
> to o->createStuff()
> is a std::vector<std::tuple<Types, uint32_t>>, but the vector passed to
> m.read() is a
> std::vector<std::tuple<std::string, uint32_t>>.

This is a bug / missing feature in the header generator.  I'd have to
look into the code but it seems like it is not re-cursing inside the
tuple correctly.  We handle this case fine for raw enums.  The
definition of data's type looks like a start of the problem
(enum<self.Types> doesn't seem correct to me).  It's possible though
that the m.read generated function is wrong in that it is missing the
conversion from self.Types <-> std::string.

[1] A fully-qualified string is something like
    xyz.openbmc-project.InterfaceClass.EnumType.EnumValue.
-- 
Patrick Williams
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