Debugging event-triggered functions

Support
1

I’m implementing a fetch call inside the submission-created event:

exports.handler = async (event, context, callback) => {

   // validate the event.body.payload here
   ...

   try {
     // call an API to get a JSON Web Token
     fetch('urlToJWTapi', {
          headers: new Headers({
             'Authenticate': 'username:password'
          })
     })
     .then(token => {
         console.log("Did we get a response? ", token)
         return token.json()
     })
     .then(jsonToken => {
         console.log(JSON.stringify(jsonToken))
         // do another fetch here to POST the comment to a different API
         ...
     })
     .catch(error => {
         console.log("error: ", error);
         throw new Error('Something bad happened.', error)
     })

 } catch (e) {
     callback(null, {
         statusCode: 500,
         body: "Internal Server Error: " + e
     })
 }

The problem is I can’t see the result of the fetch call. The function fails silently.

Ideally, I would like to output the result of the fetch call inside the callback feature of the AWS Lambda function except that I was informed that you can’t access event-trigger Lambda functions directly through using the ./netlify/functions/{nameOfFunction} path. You run into a problem with access and authorization.

I imagine it might be possible to use a Webhook to send the form submission payload to a different function but I’m not sure what that URL would look like. https://mysite.com/.netlify/functions/{nameOfOtherFunction} ? Would I assume the POST data (form submission payload) will just be accessible somehow? Maybe globally?

Thanks for any help you can provide.

2

Hi David,

We’re working on updating our docs around event-triggered functions - to make it clearer that they are only accessible as called in response to an event. If you want to test it yourself, two options:

  1. make a copy of it and name it something different; then you can access it directly by URL
  2. deploy a copy of it on a branch, and test on that branch using real form submissions from that branch. That won’t affect whatever setup you have in production now.

Do make sure that your return returns JSON - we’ll throw other errors in case you are returning plain text (and those errors - I’m not sure if you can see them or not! I think so but it probably depends on how you’re returning them and whether your function logs before it meets an untimely end, in case it is crashing or timing out.)

3

i just made this pr to improve the local testing story on netlify dev: [feature] add functions:invoke command by sw-yx · Pull Request #213 · netlify/netlify-dev-plugin · GitHub

however i think your “fails silently” issue is due to a slight misunderstanding of how function signatures work. you’re using async (event, context, callback) syntax, which is a footgun because when you’re using async, callback is never called. furhter, you also do not return the result of your fetch call with a statuscode or body. basically try to make sure you follow a signature like this netlify-dev-plugin/hello-world.js at master · netlify/netlify-dev-plugin · GitHub