Feature: Expression support in saga

[wt-better]

Saga is a distributed transaction processing mode used to ensure consistency in distributed systems.The state machine mode of saga implemented in seata java, it`s needs to be support in seata go.

The saga state machine is composed of state nodes, among which the choice node type determines the routing branch based on the expression result. We can also use expressions to obtain values ​​in the input and output parameters of the state.

Example:

{
            "Type": "Choice",
            "Choices":[
                {
                    "Expression":"[a] == 1",
                    "Next":"SecondState"
                },
                {
                    "Expression":"[a] == 2",
                    "Next":"ThirdState"
                }
            ],
            "Default":"Fail"
        }

{
            "Type": "ServiceTask",
            "ServiceName": "demoService",
            "ServiceMethod": "bar",
            "Input": [
                {
                    "barInput": "$.[fooResult]"
                }
            ],
            "Output": {
                "result": "$.result"
            },
            "Next": "Succeed"
        }

We need to implement expression execution and parsing. Considering the development trend of Seata in multiple languages, we need to choose a language-independent and neutral expression engine. For example, Google's Cel. You can also refer to other frameworks such as Argo and Lamba to make a selection and development.

[wt-better]

link: #640

[wt-better]

There has been one history implementation, corresponding to the branch: feature/saga, but the details need to be completed. you can develop on this branch.

[kaori-seasons]

i want to try