fsml

fsml

FSML is a XML based wrapper on top of https://github.com/looplab/fsm.
It provides the capabilities to define state machine of an entity in XML format and also supports features to handle error states and tasks execution on events and successful transition. Here is an example of state machine definition in xml format.

<Schema>
    <States>
        <new>
            <Events>
                <DummyEvent targetState="pending" errorState="error"></DummyEvent>
            </Events>
        </new>
        <pending></pending>
        <error></error>
    </States>
</Schema>

Above statemachine has three states new, pending and error and event named DummyEvent

Schema Definition

Nodes

• Schema Root Node
• States Container Node
  • All the state definitions will be inside this node
• Events Container Node
• Task
• OnStateSet Default Event
• OnAfterEvent Default Event
• OnBeforeEvent Default Event

Default Events

Default events can used inside each state to define default behaviors when state is updated. you can also define global default events.

 <Schema>
    <OnStateSet></OnStateSet>
    <States>
        <new>
            <OnStateSet></OnStateSet>
            <Events>
                <DummyEvent targetState="pending" errorState="error"></DummyEvent>
            </Events>
        </new>
        <pending></pending>
        <error></error>
    </States>
</Schema>

Custom Events

Custom events can be deined inside Events Node. There is an option to define targetState(required) and errorState which will take effect based on transition result

Tasks

Task Node is defined inside Custom Event or Default Event when we want to execute some task on them. If all tasks defined inside event are executed successfully then state will be changed to targetState otherwise it will be errorState

Every task needs to implement fsml.Task interface to be accessible by statemachine. check examples/tasks.go

    type task struct {}
    func (t *task) Name() string {
        return "increment"
    }

    func (t *task) Execute(i interface{}) error {
        entity := i.(*item)
        entity.count++

        return nil
    }

    ......

    statemachine.AddTask(&task{})

    <new>
        <OnStateSet></OnStateSet>
        <Events>
            <DummyEvent targetState="pending" errorState="error">
                <Task>increment</Task>
                <Task>increment</Task>
            </DummyEvent>
        </Events>
    </new>

Code Example examples/basic.go

    import (
        "fmt"
        "strings"

        "github.com/zain-bahsarat/fsml"
    )

    // Every object which is passed to the statemachine has to implement
    // `Stateful` interface otherwise it will throw error
    // create an entity which implements stateful interface
    type order struct {
        state string
        fsml.Stateful
    }

    func (o *order) SetState(state string) error {
        o.state = state
        return nil
    }

    func (o *order) GetState() string {
        return o.state
    }

    func main() {
        statemachineDef := getSimpleStatemachineDef()

        reader := strings.NewReader(statemachineDef)
        sm, err := fsml.New(reader)
        if err != nil {
            fmt.Printf("error= %+v\n", sm)
        }

        o := &order{}
        o.SetState("new")

        if err := sm.Trigger("DummyEvent", o); err != nil {
            fmt.Printf("error= %+v\n", err)
        }

        if !sm.Can("UndefinedEvent", o) {
            fmt.Printf("cannot trigger UndefinedEvent on %+v\n", o)
        }

    }

    // state machine definition
    func getSimpleStatemachineDef() string {
        return `<Schema>
                <States>
                    <new>
                        <Events>
                            <DummyEvent targetState="pending" errorState="error"></DummyEvent>
                        </Events>
                    </new>
                    <pending></pending>
                    <error></error>
                </States>
            </Schema>`
    }

License

FSML is licensed under Apache License 2.0

http://www.apache.org/licenses/LICENSE-2.0