Parsing dbus introspect

[Patrick Venture]

On Thu, Oct 17, 2019 at 7:46 PM William Kennington <wak at google.com> wrote:
>
> Looks like systemd doesn't even use an xml parser
> https://github.com/systemd/systemd/blob/cee97d57687e93e07a8ee36edf0e0d0f3317fccc/src/busctl/busctl-introspect.c

I'm thinking I'll just regex for what I seek in this case.  Since I
know the lead of the string, and how the surrounding bits should
appear.  I just need the interface name, a good regex use-case. :)

>
> On Thu, Oct 17, 2019 at 7:35 PM Patrick Venture <venture at google.com> wrote:
> >
> > With dbus-sensors, if I follow the Association property, i can find
> > the board that owns the sensor.  However, we have a use-case where we
> > want sensors to be able to have their own EntityId and EntityInstance
> > values configured via the json --
> >
> > This lead to three situations:
> > 1) sensor's board doesn't implement the Ipmi decoration
> > 2) sensor's board implements the Ipmi decoration
> > 3) sensor's board implements the Ipmi decoration, but the sensor has
> > override values in the sensor dbus object owned by EntityManager.
> >
> > The way I see to do it is to introspect on the dbus path and service,
> > and then search the list of interfaces to find one that starts
> > "xyz.openbmc_project.Configuration" and then search that interface for
> > an "EntityId" and "EntityInstance" property, and if present, read
> > them.
> >
> > So this leads me to this email:
> > 1) Has anyone already got an XML parser they like and has used it in
> > this way?  Just to save me from figuring out the exact way to wire it
> > up.
> >
> > busctl call xyz.openbmc_project.EntityManager
> > /xyz/openbmc_project/inventory/system/board/18_razorback_card/18_rzbk_temp
> > org.freedesktop.DBus.Introspectable Introspect
> >
> > s "<!DOCTYPE node PUBLIC \"-//freedesktop//DTD D-BUS Object
> > Introspection 1.0//EN\"\n\"http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd\">\n<node>\n
> > <interface name=\"org.freedesktop.DBus.Peer\">\n  <method
> > name=\"Ping\"/>\n  <method name=\"GetMachineId\">\n   <arg type=\"s\"
> > name=\"machine_uuid\" direction=\"out\"/>\n  </method>\n
> > </interface>\n <interface
> > name=\"org.freedesktop.DBus.Introspectable\">\n  <method
> > name=\"Introspect\">\n   <arg name=\"data\" type=\"s\"
> > direction=\"out\"/>\n  </method>\n </interface>\n <interface
> > name=\"org.freedesktop.DBus.Properties\">\n  <method name=\"Get\">\n
> > <arg name=\"interface\" direction=\"in\" type=\"s\"/>\n   <arg
> > name=\"property\" direction=\"in\" type=\"s\"/>\n   <arg
> > name=\"value\" direction=\"out\" type=\"v\"/>\n  </method>\n  <method
> > name=\"GetAll\">\n   <arg name=\"interface\" direction=\"in\"
> > type=\"s\"/>\n   <arg name=\"properties\" direction=\"out\"
> > type=\"a{sv}\"/>\n  </method>\n  <method name=\"Set\">\n   <arg
> > name=\"interface\" direction=\"in\" type=\"s\"/>\n   <arg
> > name=\"property\" direction=\"in\" type=\"s\"/>\n   <arg
> > name=\"value\" direction=\"in\" type=\"v\"/>\n  </method>\n  <signal
> > name=\"PropertiesChanged\">\n   <arg type=\"s\" name=\"interface\"/>\n
> >   <arg type=\"a{sv}\" name=\"changed_properties\"/>\n   <arg
> > type=\"as\" name=\"invalidated_properties\"/>\n  </signal>\n
> > </interface>\n <interface
> > name=\"xyz.openbmc_project.Configuration.TMP421\">\n  <property
> > name=\"Address\" type=\"t\" access=\"read\">\n  </property>\n
> > <property name=\"Bus\" type=\"t\" access=\"read\">\n  </property>\n
> > <property name=\"Name\" type=\"s\" access=\"read\">\n  </property>\n
> > <property name=\"Type\" type=\"s\" access=\"read\">\n  </property>\n
> > </interface>\n</node>\n"
> >
> > It's pretty easy -- it takes no parameters and returns a string that I
> > feed into an XML parser, and then walk the nodes --> but has anyone
> > already done this? Maybe I can use their code as a snippet or if it's
> > in a common OpenBMC library?
> >
> > If nobody else has done this yet, I'll reply to this email with the
> > patch that does it :)  I'm definitely interested in suggestions on a
> > favored c++ XML parser.
> >
> > Thanks
> > Patrick