context.df.isReplaying is always undefined

[Kosmonaft]

context.df.isReplaying is always undefined

[WhataHeckinName]

I've encountered this as well but I've discovered more information when testing with the basic "Hello" activity template. Instead of yielding to an array, I changed it to yield to it's own variable.

const activityName = "DurableFunctionsHelloActivity";
const orchestratorName = "DurableFunctionsOrchestrator";

export const durableFunctionsOrchestrator: OrchestrationHandler = function* (context: OrchestrationContext) {
    logIfNotReplaying(context, `Received request to orchestrator ${orchestratorName}`);

    const output1 = yield context.df.callActivity(activityName, "Tokyo"); // line 7
    const output2 = yield context.df.callActivity(activityName, "Seattle"); // line 8
    const output3 = yield context.df.callActivity(activityName, "Cairo"); // line 9

    logIfNotReplaying(context, `Processed orchestrator with outputs ${output1} ${output2} ${output3}`);

    return [output1, output2, output3];
};

const logIfNotReplaying = (context: OrchestrationContext, message: string): void => {
    const isReplayString = context.triggerMetadata.isReplaying as string;
    if (isReplayString == 'False') {
        context.log(message);
    }
};

df.app.orchestration(orchestratorName, durableFunctionsOrchestrator);

context.triggerMetadata.isReplaying is 'False' until after the first callActivity and then for the rest of the orchestrator's life (line 8 and on) it is set to 'True' regardless of whether it has handled the next activity yet or not. So this is not a reliable replacement.

context.df.isReplaying is undefined until after a callActivity processes. So put a break point on line 8. First time that break point is hit, it changes to false. After the 2nd time it hits the break point (meaning 2nd callActivity processed and intends to go to the 3rd callActivity) then it changes to true but only during the breakpoint on line 8. A second break point on line 9 would show the value immediately go back to false.

So there's definitely a bug to this context.df.isReplaying value. I've confirmed this with durable-functions version 3.0.0 and latest.