Add support of results for workflow triggers

[antho1404]

The workflow is now listening to the following streams

• Events
• Executions (filtered by completed executions only)

If it receives a matching even, it creates an execution with the event hash and the event data
If it receives a matching execution, it creates an execution with the parent execution hash and the output of the parent execution

To test:

Current workflow implemented:

engine/workflow/workflow.go

Lines 95 to 103 in f358719

	return []*workflow{
	{ // When result of taskA() -> (a string, b string), execute taskB(a string, b bool)
	Trigger: trigger{InstanceHash: instanceHash, Type: Result, Key: "taskA"},
	Task: task{InstanceHash: instanceHash, TaskKey: "taskB"},
	},
	{ // When event started(a string), execute taskA(a string)
	Trigger: trigger{InstanceHash: instanceHash, Type: Event, Key: "started"},
	Task: task{InstanceHash: instanceHash, TaskKey: "taskA"},
	},

Service here

• Create the service
• Listen for executions (do not start the service yet)
• Start the instance (with --env EVENT_INTERVAL=0 to remove useless logs)

You should see 2 executions, one with the evenHash (event start) and the other with a parentHash (result of taskA)

You can trigger another one with
mesg-cli service:execute test-workflow taskA --data a=hello

And see again 2 executions, one from the CLI (with an eventHash) the second from the workflow (with an parentHash)

[NicolasMahe]

I really think all the Engine should be based on event and it will be simpler to have only one type of data to pass consensus on the network.

[antho1404]

Based on the last meeting, we continue with this implementation but we simplify it.

• Executions don't need an event, either they have an event hash OR a parent hash
• Removing the event from the exection.Create function and pass inputs directly