WSGI 的全称是 Web Server Gateway Interface, 是为 Python 语言定义的 Web 服务器和 Web 应用程序之间的一种简单而通用的接口。类似的协议还有 CGI, FastCGI, uWSGI 等。该协议保证了 Python Web 应用和服务器之间的交互的通用性。有关WSGI的功能解释用一张图就可以解释。
WSGi 可以很好的将服务器和 Web 应用解耦开来，服务器负责解析 HTTP，应用负责处理业务逻辑。这里需要说明的是，Werkzeug 是 flask 本身自己的 Web Server；Tornado本身又可以作 Server 又可以作 Framework，可以不走 wsgi；Nginx可以提供更加强悍的网关功能，包括静态文件处理、负载均衡等，所以通常会暴露在 wsgi server 的外面。还要补充的一点是 wsgi 应用是同步IO的，即回调函数运行完后，才会进行下一个请求的操作，因此通常这种网络架构的并发问题由 server 和 proxy 部分完成，比如多线程的从 accept 池中获得请求并递交 application，当然如果对并发有更高的要求，则要再开多个进程，来利用更多的 CPU 资源。
简单说明一下 wsgi 的用法。作为一种通信的协议，往往靠标准来传递数据进行交互。wsgi通过两个参数来完成这个工作，一个是 environ，另一个则是 start_response。
environ：是一系列的环境变量，包含 wsgi 本身的信息和解析出来的HTTP请求信息、客户端信息。
start_response：是回调函数。它包含两个参数， 一个是status，另一个则是response_headers，分别代表着HTTP请求状态和响应请求的头信息。
通过 wsgi 将参数传给 application 之后，在处理完毕后，application运行回调函数传递相关信息之外，同时返回请求的回复信息，即response。接下来的工作则继续由 server 返给客户端。至此一个请求从接收到回答处理完毕。wsgi则很好的将有关网络的工作和有关业务的工作拆分开来。
附上一段wsgi的应用代码。不需要详细说明。
一个小的wsgi server：
# Tested with Python 2.7.9, Linux & Mac OS X
import socket
import StringIO
import sys
class WSGIServer(object):
address_family = socket.AF_INET
socket_type = socket.SOCK_STREAM
request_queue_size = 1
def __init__(self, server_address):
# Create a listening socket
self.listen_socket = listen_socket = socket.socket(
self.address_family,
self.socket_type
)
# Allow to reuse the same address
listen_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
# Bind
listen_socket.bind(server_address)
# Activate
listen_socket.listen(self.request_queue_size)
# Get server host name and port
host, port = self.listen_socket.getsockname()[:2]
self.server_name = socket.getfqdn(host)
self.server_port = port
# Return headers set by Web framework/Web application
self.headers_set = []
def set_app(self, application):
self.application = application
def serve_forever(self):
listen_socket = self.listen_socket
while True:
# New client connection
self.client_connection, client_address = listen_socket.accept()
# Handle one request and close the client connection. Then
# loop over to wait for another client connection
self.handle_one_request()
def handle_one_request(self):
self.request_data = request_data = self.client_connection.recv(1024)
# Print formatted request data a la 'curl -v'
print(''.join(
'< {line}\n'.format(line=line)
for line in request_data.splitlines()
))
self.parse_request(request_data)
# Construct environment dictionary using request data
env = self.get_environ()
# It's time to call our application callable and get
# back a result that will become HTTP response body
result = self.application(env, self.start_response)
# Construct a response and send it back to the client
self.finish_response(result)
def parse_request(self, text):
request_line = text.splitlines()[0]
request_line = request_line.rstrip('\r\n')
# Break down the request line into components
(self.request_method, # GET
self.path, # /hello
self.request_version # HTTP/1.1
) = request_line.split()
def get_environ(self):
env = {}
# The following code snippet does not follow PEP8 conventions
# but it's formatted the way it is for demonstration purposes
# to emphasize the required variables and their values
#
# Required WSGI variables
env['wsgi.version'] = (1, 0)
env['wsgi.url_scheme'] = 'http'
env['wsgi.input'] = StringIO.StringIO(self.request_data)
env['wsgi.errors'] = sys.stderr
env['wsgi.multithread'] = False
env['wsgi.multiprocess'] = False
env['wsgi.run_once'] = False
# Required CGI variables
env['REQUEST_METHOD'] = self.request_method # GET
env['PATH_INFO'] = self.path # /hello
env['SERVER_NAME'] = self.server_name # localhost
env['SERVER_PORT'] = str(self.server_port) # 8888
return env
def start_response(self, status, response_headers, exc_info=None):
# Add necessary server headers
server_headers = [
('Date', 'Tue, 31 Mar 2015 12:54:48 GMT'),
('Server', 'WSGIServer 0.2'),
]
self.headers_set = [status, response_headers + server_headers]
# To adhere to WSGI specification the start_response must return
# a 'write' callable. We simplicity's sake we'll ignore that detail
# for now.
# return self.finish_response
def finish_response(self, result):
try:
status, response_headers = self.headers_set
response = 'HTTP/1.1 {status}\r\n'.format(status=status)
for header in response_headers:
response += '{0}: {1}\r\n'.format(*header)
response += '\r\n'
for data in result:
response += data
# Print formatted response data a la 'curl -v'
print(''.join(
'> {line}\n'.format(line=line)
for line in response.splitlines()
))
self.client_connection.sendall(response)
finally:
self.client_connection.close()
SERVER_ADDRESS = (HOST, PORT) = '', 8888
def make_server(server_address, application):
server = WSGIServer(server_address)
server.set_app(application)
return server
if __name__ == '__main__':
if len(sys.argv) < 2:
sys.exit('Provide a WSGI application object as module:callable')
app_path = sys.argv[1]
module, application = app_path.split(':')
module = __import__(module)
application = getattr(module, application)
httpd = make_server(SERVER_ADDRESS, application)
print('WSGIServer: Serving HTTP on port {port} ...\n'.format(port=PORT))
httpd.serve_forever()
一个小的flask app：
from flask import Flask
from flask import Response
flask_app = Flask('flaskapp')
@flask_app.route('/hello')
def hello_world():
return Response(
'Hello world from Flask!\n',
mimetype='text/plain'
)
app = flask_app.wsgi_app
代码来源：https://ruslanspivak.com/lsbaws-part2/
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