How to handle a chain of promises that need to be retried. Reference discussion: https://github.com/GoogleCloudPlatform/google-cloud-node/pull/2144#discussion_r108394699

gistfile1.js

// A)
datastore
  .runTransaction(function(err, transaction) {
    if (err) {
      // Could not start transaction 
      return Promise.reject(err)
    }

    // ...transaction stuff...
    return transaction.commit()
  })
  .then(success)
  .then(doSomethingElse)
  .catch(handleErrors)

// B)
datastore.runTransaction(function(err, tranaction) {
  if (err) {
    // Could not start transaction  
  }
  
  // ...transaction stuff...
  transaction.commit()
    .then(success)
    .then(doSomethingElse)
    .catch(handleErrors)
})

This is for our Cloud Spanner API-- as part of the nature of a Transaction, they can fail rather commonly. The best handling for this (as advised by the API team) is retrying everything. So that means retrying all arbitrary user code up until they are ready to commit the transaction.

To handle this, we have to encapsulate all of that code so that we can easily retry it. That forces us to create a sandbox of sorts, inside of datastore.runTransaction(). We are deciding between two approaches, judging them solely on the basis of what is most intuitive and less prone for error or misconception, given the nature of the situation.

Any thoughts or completely alternative solutions would be very appreciated.

Thanks!