如何使用 Firebase 云功能向客户端（Swift）发送条带响应

Question

我正在使用 Stripe 和 Firebase 作为后端制作像 Airbnb 这样的 iOS 应用。我正在关注这个文件。 https://medium.com/firebase-developers/go-serverless-manage-payments-in-your-apps-with-cloud-functions-for-firebase-3528cfad770。
正如文档所述，这是我到目前为止所做的工作流程。（假设用户想要购买东西）
1。用户将支付信息发送到 Firebase 实时数据库，例如金额货币和卡令牌）
2。 Firebase 触发一个向 Stripe 发送收费请求（stripe.charge.create）的函数。
3。得到响应后，将其写回 Firebase 数据库。如果响应失败，则将错误消息写入数据库（参见 index.js 中的 userFacingMessage 函数）
4.在客户端（Swift）中，观察 Firebase 数据库以检查响应。
5. 如果响应成功，向用户显示成功消息。如果出现任何错误，例如（支付失败，因为信用卡过期），向用户显示失败消息（同时显示“请重试”消息）

我想这不是正确的方法，因为我认为一旦firebase从Stripe获得响应，用户应该知道响应（如果成功或失败）。换句话说，客户端（Swift）应该在得到响应后立即得到响应，然后再写回Firebase数据库？知道如何向客户端发送响应吗？
任何帮助将不胜感激

ChargeViewController.swift（客户端）

  func didTapPurchase(for amountCharge: String, for cardId: String) {
    print("coming from purchas button", amountCharge, cardId)

    guard let uid = Auth.auth().currentUser?.uid else {return}

    guard let cardId = defaultCardId else {return}
    let amount = amountCharge
    let currency = "usd"

    let value = ["source": cardId, "amount": amount, "currency": currency] as [String: Any]

    let ref = Database.database().reference().child("users").child(uid).child("charges")
    ref.childByAutoId().updateChildValues(value) { (err, ref) in
        if let err = err {
            print("failed to inserted charge into db", err)
        }

        print("successfully inserted charge into db")

       //Here, I want to get the response and display messages to user whether the response was successful or not.

    }

}

index.js(云函数) 语言：node.js

exports.createStripeCharge = functions.database
.ref(‘users/{userId}/charges/{id}’)
.onCreate(async (snap, context) => {
const val = snap.data();
try {
// Look up the Stripe customer id written in createStripeCustomer
const snapshot = await admin.database()
.ref(`users/stripe/${context.params.userId}/stripe_customer_id`)
.once('value');

const snapval = snapshot.data();
const customer = snapval.stripe_customer_id;
// Create a charge using the pushId as the idempotency key
// protecting against double charges
const amount = val.amount;
const idempotencyKey = context.params.id;
const charge = {amount, currency, customer};
if (val.source !== null) {
   charge.source = val.source;
}
const response = await stripe.charges
    .create(charge, {idempotency_key: idempotencyKey});
// If the result is successful, write it back to the database
//*I want to send this response to the client side but not sure how if I can do it nor not*
return snap.ref.set(response);
} catch(error) {
    await snap.ref.set(error: userFacingMessage(error));
}
});
    // Sanitize the error message for the user
function userFacingMessage(error) {
  return error.type ? error.message : 'An error occurred, developers have been alerted';
}

Answer 1

基于Franks's post here，我决定等待 Firebase 数据库的更改。下面是工作流程和代码（index.js 文件没有变化）：

1. 用户在 /users/{userId}/charges 路径下向 Firebase 实时数据库发送支付信息，例如金额货币和卡令牌）
2. Firebase 触发向 Stripe 发送充电请求（stripe.charge.create）的函数。
3. 得到响应后，将其写回 Firebase 数据库。如果响应失败，则将错误消息写入数据库（请参阅 index.js 中的 userFacingMessage 函数）
4.在客户端（Swift），等待Firebase数据库的变化，使用Observe(.childChanged)检查响应是否成功（见Swift代码）
5. 如果响应成功，向用户显示成功消息。如果有任何错误，例如（由于信用卡过期而支付失败），向用户显示失败消息（同时显示“请重试”消息）

ChargeViewController.swift

func didTapPurchase(for amountCharge: String, for cardId: String) {
print("coming from purchas button", amountCharge, cardId)

guard let uid = Auth.auth().currentUser?.uid else {return}

guard let cardId = defaultCardId else {return}
let amount = amountCharge
let currency = "usd"

let value = ["source": cardId, "amount": amount, "currency": currency] as [String: Any]

let ref = Database.database().reference().child("users").child(uid).child("charges")
ref.childByAutoId().updateChildValues(value) { (err, ref) in
    if let err = err {
        print("failed to inserted charge into db", err)
    }

    print("successfully inserted charge into db")

   //Here, Wait for the response that has been changed
   waitForResponseBackFromStripe(uid: uid)

  }

 }

func waitForResponseBackFromStripe(uid: String) {

    let ref = Database.database().reference().child("users").child(uid).child("charges")
    ref.observe(.childChanged, with: { (snapshot) in

        guard let dictionary = snapshot.value as? [String: Any] else {return}

        if let errorMessage = dictionary["error"] {
            print("there's an error happening so display error message")
            let alertController = UIAlertController(title: "Sorry:(\n \(errorMessage)", message: "Please try again", preferredStyle: .alert)
            alertController.addAction(UIAlertAction(title: "Ok", style: .cancel, handler: nil))
            //alertController.addAction(UIAlertAction(title: "Ok", style: .cancel, handler: nil))
            self.present(alertController, animated: true, completion: nil)
            return

        } else {
            let alertController = UIAlertController(title: "Success!", message: "The charge was Successful", preferredStyle: .alert)
            alertController.addAction(UIAlertAction(title: "Ok", style: .cancel, handler: nil))
            self.present(alertController, animated: true, completion: nil)
        }
    }) { (err) in
        print("failed to fetch charge data", err.localizedDescription)
        return
    }
}

如果我在逻辑上做错了什么，请告诉我。但到目前为止它对我有用
希望这对正在集成 Firebase 和 Stripe 支付的人有所帮助