恒例

https://firebase.google.com/docs/functions ドキュメントを読んでください

Firebase CLI をインストールする

npm install -g firebase-tools

Coding

mkdir test
cd test
mkdir functions
cd functions
vi package.json

{
  "name": "mytest",
  "description": "mytest",
  "dependencies": {
    "firebase-admin": "~7.1.1",
    "firebase-functions": "^2.2.1"
  },
  "devDependencies": {
    "chai": "^3.5.0",
    "chai-as-promised": "^6.0.0",
    "firebase-functions-test": "0.1.6",
    "mocha": "^5.0.5",
    "sinon": "^4.1.3"
  },
  "scripts": {
    "ci-test": "npm install && npm run test",
    "serve": "firebase serve --only functions",
    "shell": "firebase experimental:functions:shell",
    "start": "npm run shell",
    "deploy": "firebase deploy --only functions",
    "logs": "firebase functions:log"
  },
  "engines": {
    "node": "8"
  },
  "private": true
}

vi index.js

'use strict';
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.send_data = functions.https.onRequest(async (req, res) => {

  const time = req.query.time;
  const text = req.query.temp;

  const snapshot = await admin.database().ref('/test').push({time:time,text:text});

  res.redirect(303, snapshot.ref.toString());
});

exports.read_data = functions.https.onRequest((req, res) => {

    var ref = admin.database().ref("test");
    return ref.orderByChild("time").limitToLast(10).once('value').then(function(snapshot) {
      res.send(snapshot.val());
    });

});

Deploy

cd functions && npm install && cd ..
firebase deploy

送信方法

https://us-central1-[MY_PROJECT].cloudfunctions.net/send_data?time=20200218&text=uppercaseme をアクセスする

DATAを読み取る方法

https://us-central1-[MY_PROJECT].cloudfunctions.net/read_data をアクセスする