1121 rule bridge properties

[zmstone]

this is a follow up for #9240

[zmstone]

This was originally (#9240) taken from Selected's pub_props atom filed,
which seemed to be wrong because selected element keys are of binary format. (i.e. <<"pub_props">>).

I tried to change to take from the original message, it seemed to work, however it also affects
other events like message.dropped, message.acked, in those events, a user may not necessary
want to keep the properties.

For example, if someone just want to republish a message.dropped event, but only interested in the topic name.

Fixed to pick <<"pub_props">> value from Selected, but try to convert properties to atom keys,
this requires user to explicitly SELECT pub_props (see test case examples).

The "proper" approach is perhaps to treat message properties like qos, retain flag, and payload,
meaning to add another argument here:

emqx/apps/emqx_rule_engine/src/emqx_rule_engine_schema.erl

Lines 139 to 177 in 966e6dd

	fields("republish_args") ->
	[
	{topic,
	?HOCON(
	binary(),
	#{
	desc => ?DESC("republish_args_topic"),
	required => true,
	example => <<"a/1">>
	}
	)},
	{qos,
	?HOCON(
	qos(),
	#{
	desc => ?DESC("republish_args_qos"),
	default => <<"${qos}">>,
	example => <<"${qos}">>
	}
	)},
	{retain,
	?HOCON(
	hoconsc:union([boolean(), binary()]),
	#{
	desc => ?DESC("republish_args_retain"),
	default => <<"${retain}">>,
	example => <<"${retain}">>
	}
	)},
	{payload,
	?HOCON(
	binary(),
	#{
	desc => ?DESC("republish_args_payload"),
	default => <<"${payload}">>,
	example => <<"${payload}">>
	}
	)}
	].

@terry-xiaoyu @kjellwinblad @thalesmg wdyt ?

[terry-xiaoyu]

Yes, we need a 'properties' config in this case.

• If the 'properties' is not configured and it's a PUBLISH message, we republish the message using the original properties.
• If the 'properties' is not configured and it's an event like $events/client_connected, we republish the message without any property.
• If the 'properties' is configured, then we republish using the configured properties.

[kjellwinblad]

The "proper" approach is perhaps to treat message properties like qos, retain flag, and payload,
meaning to add another argument here:

Based on my limited understanding I also think this would be the the proper approach

[thalesmg]

From my very limited knowledge about this, it seems like the props should indeed be a new config; otherwise, it's not obvious that a property should be dropped or not.

[zmstone]

Thank you for your suggestions.
I have added a user_properties republish action argument with default template ${user_properties}.

Decided NOT to fill user_properties with original message's pub_props.'User-Property',
because the code is shared for both message republish and for message events such as message.acked and message.dropped.

In order to republish message with User-Property, a user will have to explicitly select a variable,
or configure with the special value ${pub_props.'User-Property'}.

[kjellwinblad]

Looks good to me (just a few minor comments about sleeps in test cases).

[zmstone]

these three lines duplicates line 113-116, so i merged the two function clauses.
the only special part is the flags field.

[coveralls]

Pull Request Test Coverage Report for Build 3526362825

• 20 of 24 (83.33%) changed or added relevant lines in 3 files are covered.
• 67 unchanged lines in 16 files lost coverage.
• Overall coverage decreased (-0.1%) to 78.132%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/emqx/src/emqx_misc.erl	5	7	71.43%
apps/emqx_rule_engine/src/emqx_rule_actions.erl	12	14	85.71%

Files with Coverage Reduction	New Missed Lines	%
apps/emqx/src/emqx_olp.erl	1	77.78%
apps/emqx/src/emqx_message.erl	1	94.83%
apps/emqx/src/emqx_authentication_config.erl	1	83.62%
apps/emqx_management/src/emqx_mgmt_api_trace.erl	1	80.41%
apps/emqx/src/emqx_connection.erl	1	87.64%
apps/emqx/src/emqx_router_helper.erl	1	86.27%
apps/emqx_conf/src/emqx_conf_schema.erl	1	92.31%
apps/emqx_gateway/src/mqttsn/emqx_sn_channel.erl	1	72.92%
apps/emqx/src/emqx_channel.erl	2	87.38%
apps/emqx_authn/src/emqx_authn.erl	2	75.0%

Totals
Change from base Build 3523358423:	-0.1%
Covered Lines:	20955
Relevant Lines:	26820

---

💛 - Coveralls