Resuming an engine seems to lose services

[petermorlion]

I'm looking for a way to configure a fairly complex flow behind a HTML form submission. The flow is hard-coded now but for our customers, we want to make it configurable. I'm making a POC but am stumbling on the user tasks. What I want is an Express app that uses the BPMN to navigate through the screens.

This is a simple BPMN I have now:

<?xml version="1.0" encoding="UTF-8"?>
<definitions id="testProcess" xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <process id="theProcess1" isExecutable="true">
    <startEvent id="theStart" />
    <userTask id="loginPage" />
    <exclusiveGateway id="checkLogin" />
    <serviceTask id="invalidLogin" implementation="{environment.service.invalidLogin}" />
    <serviceTask id="validLogin" implementation="{environment.service.validLogin}" />

    <sequenceFlow id="flow1" sourceRef="theStart" targetRef="loginPage" />
    <sequenceFlow id="flow2" sourceRef="loginPage" targetRef="checkLogin" />
    <sequenceFlow id="flow3a" sourceRef="checkLogin" targetRef="invalidLogin">
        <conditionExpression xsi:type="tFormalExpression">\${environment.services.isFalse(environment.variables.isValidLogin)}</conditionExpression>
    </sequenceFlow>
    <sequenceFlow id="flow3b" sourceRef="checkLogin" targetRef="validLogin">
        <conditionExpression xsi:type="tFormalExpression">\${environment.services.isTrue(environment.variables.isValidLogin)}</conditionExpression>
    </sequenceFlow>
    <sequenceFlow id="flow4" sourceRef="validLogin" targetRef="end1" />
    <sequenceFlow id="flow5" sourceRef="invalidLogin" targetRef="end2" />

    <endEvent id="end1" />
    <endEvent id="end2" />
  </process>
</definitions>

When I GET the root URL, my app starts the engine:

app.get('/', async (req, res) => {
    const id = Math.floor(Math.random() * 10000);
    engine = new Engine({
        name: 'execution example',
        source,
        variables: {
            id
        },
        listener,
        services: {
            req,
            res,
            isTrue: (val) => val === true,
            isFalse: (va) => val === false
        }
    });

    await engine.execute();
});

The listener listens to several events, but this is the important one:

listener.on('activity.wait', async (api, execution) => {
    if (api.type === "bpmn:UserTask") {
        await userTasks[api.id](api);
    }

    api.stop();
    state = await execution.getState();
});

The userTasks[api.id](api) basically calls the following logic:

function loginPage(api, execution) {
    api.environment.services.res.render('login');
}

Now this works on the GET. The state is stored and the engine is stopped. But when I POST the form, I want to continue the flow where I left off:

app.post('/', async (req, res) => {
    engine = new Engine().recover(state);
    
    await engine.resume({
        listener,
        variables: {
            isValidLogin: true
        },
        services: {
            req,
            res,
            isTrue: (val) => val === true,
            isFalse: (va) => val === false
        }
    })
});

First I was thinking it would take the correct flow after the loginPage task, but it seems it continues inside the loginPage task. Makes sense, as I haven't ended that activity yet.

So I was going to inspect the request object which I pass to the services option. However, on resuming my engine, I see that all services are undefined (req, res, isTrue and `isFalse).

What is the correct way to resume an engine and include the necessary services again so I can continue "as if nothing happened"?

[petermorlion]

If this should be moved to the bpmn-engine repository, let me know and I'll recreate there. I realized I may have used the wrong repo.

[petermorlion]

For anyone looking at this (including the author): I finally managed to achieve what I wanted. You can see my current POC here. For this specifically, I declared my services outside my Express handlers.