Reg sdbusplus - async handlers - D-Bus error not getting reflected

[Lei YU]

On Wed, Jun 26, 2019 at 12:19 AM Thomaiyar, Richard Marian
<richard.marian.thomaiyar at linux.intel.com> wrote:
>
> Hi,
>
> In sdbusplus code, async_send_handler callback() uses the
> sdbusplus::message::message.get_errorno()
> https://github.com/openbmc/sdbusplus/blob/master/sdbusplus/asio/detail/async_send_handler.hpp#L66
> function to instantiate the boost::system::error_code. Unfortunately,
> none of our D-Bus exception throwing functionality sets the error_no to
> a proper one, but instead updates only the error_message field
> https://github.com/openbmc/sdbusplus/blob/master/tools/sdbusplus/templates/method.mako.prototype.hpp.in#L171
> causing the error_code instance to always return a generic error code
> value, instead of a proper one. Because of this applications which uses
> the asio logic will not be able to differentiate between exceptions
> thrown / errors from D-Bus.
>
> Planning to fix the same in 2 step,
>
> 1. To make all D-Bus exception to set the errorno properly using
> sd_bus_error_set_errno and getting the error from the yaml if available
> else return generic one (so that no change in existing daemon will be
> required).
>
> 2. make change in async_send_handler_callaback, such that derived class
> of boost::system::error_code is returned, which will hold the error
> message too. Any daemon which uses asio logic, can depend on ec.value()
> as primary exception identifier or ec.message() for any detailed
> exception thrown.
>
> Let me know your thoughts , and if agree, will start implementing the same.
>
> Regards,
>
> Richard

I am glad that you feel the same way!
The patch https://gerrit.openbmc-project.xyz/c/openbmc/sdbusplus/+/21611 was
submitted trying to resolve the issue.
And during review, it's noticed that there is a better way to achieve the goal,
that the DBus error is returned by the message.

So we have https://gerrit.openbmc-project.xyz/c/openbmc/sdbusplus/+/22481

Now in sdbusplus, message::get_error() is added, and the caller could get the
sd_bus_error* from the returned message, and get the DBus exception details
from the sd_bus_error.

See examples at
https://github.com/openbmc/bmcweb/blob/e4a4b9a95622b8e1c1bae93718699ad19f4882ac/include/openbmc_dbus_rest.hpp#L1385-L1403
https://github.com/openbmc/bmcweb/blob/e4a4b9a95622b8e1c1bae93718699ad19f4882ac/include/openbmc_dbus_rest.hpp#L1882-L1893