Cocoa/Flask_Internal.html at master · csrgxtu/Cocoa · GitHub

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<!DOCTYPE html>
<html>
  <head>
    <title>Title</title>
    <meta charset="utf-8">
    <style>
      @import url(https://fonts.googleapis.com/css?family=Yanone+Kaffeesatz);
      @import url(https://fonts.googleapis.com/css?family=Droid+Serif:400,700,400italic);
      @import url(https://fonts.googleapis.com/css?family=Ubuntu+Mono:400,700,400italic);

      body { font-family: 'Droid Serif'; }
      h1, h2, h3 {
        font-family: 'Yanone Kaffeesatz';
        font-weight: normal;
      }
      .remark-code, .remark-inline-code { font-family: 'Ubuntu Mono'; }
    </style>
  </head>
  <body>
    <textarea id="source">

class: center, middle

# Flask 实现原理
archer.li@shopeemobile.com


---
## 目录
* #### 历史
* #### 通用网关接口
* #### 并发机制
* #### 处理流程
* #### 会话机制
* #### 路由机制
* #### 请求上下文
* #### 模板引擎

---

## 历史

* #### Armin Ronacher  [@mitsuhiko](@mitsuhiko), Pocoo
* #### Deny

```python
# a deny application
from deny import *

@route('/')
def welcome():
  return "welcome to deny"

if __name__ == '__main__':
  run()
```
---
* ### Flask

```Python
from flask import Flask

app = Flask(__name__)

@app.route('/')
def welcome():
  return "welcome to flask"

if __name__ == '__main__':
  run()
```

---
### 问题
1, 请求是如何被传递，处理并且返回？
```bash
http://localhost/
```
```Python
def welcome():
  return 'welcome to Flask'
```

2, 会话机制在Flask中是如何串通的？
```Python
from flask import Flask, session
app = Flask(__name__)
app.serect = 'secret'
session[user_id] = {}
```
---

## 通用网关接口

#### 网站服务器
* Gunicorn
* wsgiref
* Nginx + mod_wsgi
* etc

#### 网站应用
* Django
* Flask
* web.py
* etc

---
#### WSGI -- PEP333
> WSGI specifies a proposed standard interface between web servers and Python web applications or frameworks, to promote web application **portability** across a variety of web servers.

<br/>
<br/>
<br/>
#### Flask 的入口函数
```Python
def wsgi_app(environ, start_response):
  with RequestContext(environ):
    rv = dispatch_request()
    response = make_response(rv)
    response = process_response(response)
    return response(environ, start_response)

```
---
## Flask处理流程
<!-- ![flask request process flow](https://user-images.githubusercontent.com/5053620/29756205-97236942-8bd4-11e7-9531-9d55c7033981.png =250x20) -->
<img src="https://user-images.githubusercontent.com/5053620/29756205-97236942-8bd4-11e7-9531-9d55c7033981.png" alt="Drawing" style="width: 400px;"/>
---
## 并发机制

* 线程全局变量
* 线程局部变量
* ThreadLocal
* Werkzeug.Local

```Python
_request_ctx_stack = LocalStack()
request = _request_ctx_stack.top.request
```
---
## Session 机制

#### 无状态的HTTP
```bash
GET /api/v1/orders/{order_id}/
```
A的订单信息
```json
{
  'orderid': 13937,
  'userid': 297045,
  'buyer_address': {},
  'seller_address': {},
  ...
}
```
B的订单信息
```json
{
  'orderid': 13938,
  'userid': 297043,
  'buyer_address': {},
  'seller_address': {},
  ...
}
```
---
登陆成功后
* session id
* 服务端端存储
* 客户端存储

```json
{
  '9PhQ4YMRDwAcYjNyuZEyTeCslww': {
    'user_name': 'kenseller',
    'userid': 170854,
    'avatar': 'https://s.sg/th.jpg',
    'email': 'kenseller@shopeemobile.com'
    ....
  }
}
```

```bash
http --session=/tmp/flask_session.json GET http://localhost:5000/login/archer

HTTP/1.0 200 OK
Content-Length: 16
Content-Type: text/html; charset=utf-8
Date: Tue, 08 Aug 2017 04:16:12 GMT
Server: Werkzeug/0.12.2 Python/2.7.6
Set-Cookie: session='9PhQ4YMRDwAcYjNyuZEyTeCslww'
```
---
### 数据模型
Werkzeug.Local类型的全局变量
```Python
# context locals, flask line 662
_request_ctx_stack = LocalStack()
session = _request_ctx_stack.top.session
```

```Python
from flask import session

app.secret_key = 'blablabla'

# set session
session[user_id] = {}

# remove session
session.pop(user_id)
```
---
#### 载入会话信息
```Python
class RequestContext(object):
  def __init__(self, app, environ):
    self.session = app.open_session(self.request)

def open_session(self, request):
  key = self.secret_key
  if key is not None:
    return SecureCookie.load_cookie(request, self.session_cookie_name, secret_key)
```

#### 设置会话信息
```Python
def process_response(self, response):
  session = _request_ctx_stack.top.session
  if session is not None:
      self.save_session(session, response)
  return response

def save_session(self, session, response):
    if session is not None:
        session.save_cookie(response, self.session_cookie_name)
```

---
## 路由机制
#### 数据模型
```Python
class Flask(object):
  def __init__(self, package_name):
    self.view_functions = {}
    self.url_map = Map()
```

![route](https://user-images.githubusercontent.com/5053620/29773537-80faf138-8c30-11e7-8da9-9de34a80b2be.png)

---
#### 构建路由表 -- 装饰器
```Python
def route(self, rule, **options):
 def decorator(f):
   self.add_url_rule(rule, f.__name__, **options)
   self.view_functions[f.__name__] = f
 return decorator
```

```Python
@app.route('/')
def welcome():
  return 'welcome ya'
```

```Python
url_map('/', 'welcome', **options)

view_functions = {
  'welcome': welcome
}
```
---
#### 查找路由
```Python
def dispatch_request(self):
   try:
     endpoint, values = self.match_request()
     return self.view_functions[endpoint](**values)
```

* 根据url从url_map中找到对应的视图函数名称
* 根据名称从view_functions里面找到函数对象
---
## 请求上下文

#### 数据模型
```Python
class _RequestContext(object):
    def __init__(self, app, environ):
        self.app = app
        self.url_adapter = app.url_map.bind_to_environ(environ)
        self.request = app.request_class(environ)
        self.session = app.open_session(self.request)
        self.g = _RequestGlobals()
        self.flashes = None

    def __enter__(self):
        _request_ctx_stack.push(self)

    def __exit__(self, exc_type, exc_value, tb):
        if tb is None or not self.app.debug:
            _request_ctx_stack.pop()

request = LocalProxy(lambda: _request_ctx_stack.top.request)
```
```Python
from flask import request

request.args.get('username')
```
---
## 模板引擎
#### 为什么需要模板引擎?
* 逻辑处理较多
* 文本处理较多

#### 目标
```html
<html>
  <head><title>Template</title></head>
  <body>
    <h3>Hello {{username}}</h3>
  </body>
</html>
```

```Python
{{%if%}}
{{%for%}}
{{%endif%}}
{{%endfor%}}
```
---
### 方法
* 字符串替换
  * % operator
  * .format
  * .replace
* 代码执行
  * 模板
  * 字面量
  * 对象
  * 带参数执行

```Python
CodeBuilder.add_line('result.apend("<html>\nHello ") ')
CodeBuilder.add_line(str(username))
```
---

```Python
#!/usr/bin/env python

# string format
func_str = """
def render_function(**kwargs):
    result = []

    result.append('<html>\n<head><title>Template</title></head>\n<body>\n<h3>')
    result.append(str(user_name))
    result.append('</h3>\n</body>\n</html>')

    return ''.join(result)
"""
namespace = {}
exec(func_str, namespace) # will put render_function as a function into namespace, like JS's evil eval which will execute a string as a statements
html = namespace.get('render_function')({'username': 'code execution'})
print html
```
---
class: center, middle
# 谢谢

---
## 参考
[Flask, A simple history](https://github.com/csrgxtu/Cocoa/wiki/Flask,-a-simple-history)

[Web server and web application](https://github.com/csrgxtu/Cocoa/wiki/Web-Server-and-Web-app)

[Flask Session](https://github.com/csrgxtu/Cocoa/wiki/Flask-Session)

[Flask URL Routing](https://github.com/csrgxtu/Cocoa/wiki/Flask-URL-Routing)

[Flask Context](https://github.com/csrgxtu/Cocoa/wiki/Flask-Request-Context)

[Template Engine](https://github.com/csrgxtu/TemplateEngine/issues/1)


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