Feature invoke activity

[rameshpolishetti]

This PR implements #69. It enhances rule action function to service. A service is constructed from a gofunction / flogo activity / flogo action.
When a rules fires, corresponding service input expressions would be resolved from tuple scope and then service gets executed (i.e underlying function/activity/action gets executed).

A service definition goes like this:

"services": [
  {
    "name": "ServiceFlowAction",
    "description": "Asynchronous flow action service",
    "type": "action",
    "ref": "github.com/project-flogo/flow",
    "settings": {
      "flowURI": "res://flow:sample_flow"
    }
  }
]

Invoking the service:

"rules": [
  {
    "name": "n1.name == function",
    "conditions": [],
    "actionService": {
      "service": "ServiceFunction",
      "input": {
        "message": "=$.n1.name"
       }
    }
  }
]

An example covering all varients of service is made available at - examples/flogo/invokeservice

[balamg]

I'd like to see support added for invoking a flow as compared to an activity. That would be a general solution

[rameshpolishetti]

@balamg Now I have added support to invoke flogo-action (ex: flow)

[fm-tibco]

Maybe you should consider leaving this as invoke activity? @skothari-tibco is implementing an activity that can invoke actions (not just flows). This way you have a lot more flexibility. If someone wants to invoke a simple rest call, they don't have to setup an entire flow for that.

I guess if you can invoke either activity or action in this implementation it is fine also.

[rameshpolishetti]

Thank you @fm-tibco for sharing your input. Seems my PR message is not conveying enough about rule service in detail. In fact, this PR supports any action (not just flow-action) as rule service, as mentioned below:

"services": [
{
"name": "ServiceFlowAction",
"description": "Asynchronous flow action service",
"type": "action", ==> type can be "function" / "activity" / "action"
"ref": "github.com/project-flogo/flow", ==> It can be any flogo-action / flogo-activity reference
"settings": { ==> action/activity specific settings
"flowURI": "res://flow:sample_flow"
}
}
]
Comprehensive example is made available at: https://github.com/project-flogo/rules/tree/feature-invoke-activity/examples/flogo/invokeservice

Coming back to what to consider here activity vs action OR both - my original plan was to have just activity. As per the @balamg view mentioned above, action (flow) adds more value to rules.

Appreciate your further inputs.

[rameshpolishetti]

closing this PR as an improved version of this feature (invoke activity) is available in develop branch.