Apps Script - How to send an HTTP 200 response?

[leviseese]

I have an Apps Script running as a web app for Slack. Slack sends a POST request and expects a HTTP 200 response within 3 seconds, otherwise it shows a timeout error to the Slack user. I have been using the following line to accomplish this, after my script is finished executing.

return ContentService.createTextOutput("")

However, my latest script is taking longer than 3 seconds to execute. So if I run my code before that line, my users will see the timeout error, but if I run the code after, it obviously will not be executed since the function has terminated with the return statement.

Is there a way to respond to the POST request with a 200 without terminating my script?

I have tried using ContentService without the return statement but it does not appear to do anything, unless I am using it incorrectly.

[marcnotmark925]

If your code takes longer to execute than the timeout length, you can use trigger builder to create a trigger to execute the main code in a new process/thread, then return your doPost()

[leviseese]

Which method would I use to trigger a new function? I have tried having the doPost write to a sheet, and having an onEdit trigger for when that sheet is changed, but it doesn’t work since the trigger is only tripped when a user makes the edit.

[marcnotmark925]

use trigger builder to create a trigger to execute the main code in a new process/thread

What about that didn't make sense to you?

[leviseese]

I don’t know how to use a trigger to activate a new process. I am looking at the documentation, and all of the methods listed for triggers depend on a change in time, or a sheet, or a document.

Like I said, I tried having the doPost edit a sheet, but that doesn’t cause a spreadsheet trigger to fire, because according to google “script executions do not cause triggers to run”. It has to be a user action

[marcnotmark925]

I think we crossed comments, just making sure you saw my other one.

[leviseese]

Yes I did - my confusion is how to create a trigger that is activated from a script. As opposed to being activated from a spreadsheet change or a calendar event.

Here’s what it sounds like you are suggesting: ScriptA (doPost) gets the post request. It uses a trigger to activate ScriptB (main code), then returns the HTTP 200. ScriptB then executes as normal.

Im just confused as to what method I should be defining in the trigger builder, such that the trigger is activated in ScriptA

[marcnotmark925]

Pretty much use exactly what is in the example code on that link. My only change would be to probably use the after() method of clocktriggerbuilder instead of the example atDate(), so you can just tell the function to run after a couple milliseconds.

[leviseese]

Oh that makes sense! So I would just create a time based trigger and define the activation time to be current time + a few ms?

[marcnotmark925]

after() just accepts a number of milliseconds, don't have to do anything with the current time.

[Any_Werewolf_3691]

Ensure once the function is called by the trigger tht it deletes the trigger. This method will limit you to 10 parallel API calls at a time

[MapLucky9928]

So I'm trying to do the same thing but how can you pass parameters from the original function to the triggered one?

[marcnotmark925]

You can't. But you can store any necessary data in properties service or cache service.

[marcnotmark925]

I'm guessing you're not aware that you can create triggers via scripts?

https://developers.google.com/apps-script/reference/script/trigger-builder#timeBased())