Keep variable between promises in a function?

Question

On firebase function I need to get data from Paypal and do 4 things :

1. returns an empty HTTP 200 to them.
2. send the complete message back to PayPal using `HTTPS POST`.
3. get back "VERIFIED" message from Paypal.
4. *** write something to my Firebase database only here.

What I do now works but i am having a problem with (4).

   exports.contentServer = functions.https.onRequest((request, response) => {
....

                       let options = {
                          method: 'POST',
                          uri: "https://ipnpb.sandbox.paypal.com/cgi-bin/webscr",
                          body: verificationBody
                           };

                           // ** say 200 to paypal
                           response.status(200).end();

                           // ** send POST to paypal back using npm request-promise
                           return rp(options).then(body => {

                            if (body === "VERIFIED") {

                              //*** problem is here!
                                   return admin.firestore().collection('Users').add({request.body}).then(writeResult => {return console.log("Request completed");});
                                }
                                return console.log("Request completed");
                              })
                              .catch(error => {
                                      return console.log(error);
                              })

As you can see when I get final VERIFIED from Paypal I try to write to the db with admin.firestore().collection('Users')..

I get a warning on compile :

Avoid nesting promises 

for the write line.

How and where should I put this write at that stage of the promise ?

Answer 1

I understand that this HTTPS Cloud Function is called from Paypal.

By doing response.status(200).end(); at the beginning of your HTTP Cloud Function you are terminating it, as explained in the doc:

Important: Make sure that all HTTP functions terminate properly. By terminating functions correctly, you can avoid excessive charges from functions that run for too long. Terminate HTTP functions with res.redirect(), res.send(), or res.end().

This means that in most cases the rest of the code will not be executed at all or the function will be terminated in the middle of the asynchronous work (i.e. the rp() or the add() methods)

You should send the response to the caller only when all the asynchronous work is finished. The following should work:

exports.contentServer = functions.https.onRequest((request, response) => {

    let options = {
        method: 'POST',
        uri: "https://ipnpb.sandbox.paypal.com/cgi-bin/webscr",
        body: verificationBody
    };

    // ** send POST to paypal back using npm request-promise
    return rp(options)
        .then(body => {

            if (body === "VERIFIED") {
                //*** problem is here!
                return admin.firestore().collection('Users').add({ body: request.body });
            } else {
                console.log("Body is not verified");
                throw new Error("Body is not verified");
            }

        })
        .then(docReference => {
            console.log("Request completed");
            response.send({ result: 'ok' }); //Or any other object, or empty
        })
        .catch(error => {
            console.log(error);
            response.status(500).send(error);
        });


});

I would suggest you watch the official Video Series on Cloud Functions from Doug Stevenson (https://firebase.google.com/docs/functions/video-series/) and in particular the first video on Promises titled "Learn JavaScript Promises (Pt.1) with HTTP Triggers in Cloud Functions".