[雲端] backend
===
###### tags: `雲端`, `backend`, `headers`, `accept`, `application/json`

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[TOC]

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# Flask
## 安裝

# flask_cors 是處理 CORS policy
pip install flask flask_cors

- CORS: Cross-Origin Resource Sharing 跨來源資源共用

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## 基本核心

from flask import Flask
import json

app = Flask("backend_server")

def init():
    print('init')

@app.route('/')
def index():
    return 'The backend server works!'

if __name__ == '__main__':
    init()
    app.run(host='0.0.0.0', port=19998, debug=True)

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## 跨站問題

// 不在同一網站上測試，會遇到 CORS policy
response = await fetch('http://10.78.26.241:19998/');

Access to fetch at 'http://10.78.26.241:19998/' from origin 'null' has been 
blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present 
on the requested resource. If an opaque response serves your needs, set the
request's mode to 'no-cors' to fetch the resource with CORS disabled.

GET http://10.78.26.241:19998/ net::ERR_FAILED
(anonymous)

Uncaught TypeError: Failed to fetch

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**處理方式**：使用 `@cross_origin()`

from flask import Flask
from flask_cors import cross_origin
import json

app = Flask("backend_server")

def init():
    print('init')

@app.route('/')
@cross_origin()
def index():
    return 'The backend server works!'

if __name__ == '__main__':
    init()
    app.run(host='0.0.0.0', port=19998, debug=True)


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## GET 參數
> 使用 `request.args.get('XXX')`

from flask import Flask, request
from flask_cors import cross_origin
import json

app = Flask("backend_server")

def init():
    print('init')

@app.route('/')
@cross_origin()
def index():
    return 'The backend server works!'

@app.route('/query')
@cross_origin()
def query():
    name = request.args.get('name')
    age = request.args.get('age')
    if age == None:
        age = 'Unknown'

    return '''
        <b>Name</b>: %(name)s<br>
        <b>Age</b>: %(age)s<br>
        ''' % {'name':name, 'age':age}

if __name__ == '__main__':
    init()
    app.run(host='0.0.0.0', port=19998, debug=True)

執行結果：
- `http://10.78.26.241:19998/query`
- `http://10.78.26.241:19998/query?name=tj_tsai`
- `http://10.78.26.241:19998/query?name=tj_tsai&age=25`

### 參考資料
- [How can I get the named parameters from a URL using Flask?](https://stackoverflow.com/questions/24892035/how-can-i-get-the-named-parameters-from-a-url-using-flask)

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## 其他參考資料
- [靜態檔案](https://medium.com/seaniap/python-web-flask-%E4%BD%BF%E7%94%A8%E9%9D%9C%E6%85%8B%E6%AA%94%E6%A1%88-ac00e863a470)
- [How to get an IP address using Flask in Python](https://www.kite.com/python/answers/how-to-get-an-ip-address-using-flask-in-python)
`flask.request.remote_addr`

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# Javascript
## 後端相關
- ### [How to Use Fetch with async/await](https://dmitripavlutin.com/javascript-fetch-async-await/)