app.yaml

runtime: python37
service: default

handlers:
  - url: /api/upload.*
    script: auto
    secure: always
    # login: admin

  - url: /(.*\.(gif|png|jpg|jpeg|ico|css|map|json|js|eot|svg|ttf|woff|woff2|ogg|mp3|wav|ogg|mp4|webm|xml|html|fbx|gltf))$
    static_files: public/\1
    upload: .*\.(gif|png|jpg|jpeg|ico|css|map|json|js|eot|svg|ttf|woff|woff2|ogg|mp3|wav|ogg|mp4|webm|xml|html|fbx|gltf)$

  - url: /api/post.*
    script: auto
    secure: always
    # login: admin

  - url: /api/get.*
    script: auto
    secure: always

  - url: /.*
    static_files: index.html
    upload: index.html
    secure: always

main.py

from flask import Flask, request, redirect
from flask_cors import CORS
from google.cloud import datastore
from google.cloud import storage

CLOUD_STORAGE_BUCKET = 'YOUR-CLOUD-STORAGE-BUCKET-ID'
IMAGE_EXTENSIONS = { 'png', 'jpg', 'jpeg', 'gif' }

ds = datastore.Client()
cs = storage.Client()

bucket = cs.bucket(CLOUD_STORAGE_BUCKET)

def allowed(filename: str):
    return '.' in filename and \
        filename.rsplit('.', 1)[1].lower() in IMAGE_EXTENSIONS

def upload(src: str, contents):
    blob = bucket.blob(src)
    blob.upload_from_string(contents)
    return { 'src': 'https://storage.googleapis.com/{}/{}'.format(CLOUD_STORAGE_BUCKET, src) }

def save(id: str, model):
    key = ds.key('model', id)
    entity = datastore.Entity(key)
    entity.update({ 'body': model })
    ds.put(entity)
    return { 'id': id }

def get(id: str):
    key = ds.key('model', id)
    entity = ds.get(key)
    if entity is None:
        return { 'error': 'API Error: no model found for key: {}'.format(id) }
    else:
        return entity.get('body', {})

#

app = Flask(__name__)
CORS(app)

#

@app.route('/api/get/<id>', methods=['GET'])
def on_get(id=None):
    if not isinstance(id, str):
        return { 'error': 'API Error: key does not exist.' }
    else:
        return get(id)

@app.route('/api/post/<id>', methods=['POST'])
def on_post(id=None):
    if isinstance(id, str) and request.method == 'POST':
        body = request.get_json()
        if body is None:
            return { 'error': 'API Error: body does not exist.' }
        else:
            return save(id, body)
    else:
        return { 'error': 'API Error: post not configured correctly.' }

@app.route('/api/upload/<src>', methods=['POST'])
def on_upload(src=None):
    if isinstance(src, str) and request.method == 'POST':
        if 'file' not in request.files:
            return { 'error': 'API Error: file does not exist.' }
        else:
            file = request.files['file']
            if file.filename == '':
                return { 'error': 'API Error: no file selected.' }
            if file and allowed(file.filename):
                filename = 'assets/{}'.format(src)
                contents = file.read()
                return upload(filename, contents)
            else:
                return { 'error': 'API Error: filetype not permitted.' }
    else:
        return { 'error': 'API Error: upload not configured correctly.' }

if __name__ == '__main__':
    # This is used when running locally only. When deploying to Google App
    # Engine, a webserver process such as Gunicorn will serve the app. You
    # can configure startup instructions by adding `entrypoint` to app.yaml.
    app.run(host='127.0.0.1', port=3000, debug=True)

requirements.txt

Flask==2.0.2
flask-cors==3.0.10
google-cloud-datastore
google-cloud-storage