WSGI is a protocal or convention that ensures that your web application can speak with the webserver and more importantly that web applications work nicely together. Source: Tutorial of Werkzeug
服务的代码，包括网络通信部分与业务逻辑部分。为了将两个部分解耦开，业界定义了WSGI协议，让一部分人专注在改进网络通信部分，即开发服务器；一部分人专注在自己的业务逻辑里，即我们市场上能看到的各种网站应用。只要两部分的人都按照WSGI协议开发，就能保证二者能够很好地配合运作起来。
现在我们遵从WSGI协议开发一个HelloWorld的网页应用，文件名是wsgiapp.py。我们需要提供一个函数定义：
def application(environ, start_response):
status = '200 OK'
response_headers = [('Content-Type', 'text/plain')]
start_response(status, response_headers)
return ['Hello World!']这个函数接受两个参数：environ是一个字典，里面包含了所有需要知道的信息；start_response是一个函数，用于生成请求的响应的头部信息。这两个参数由遵从WSGI的服务器提供。网络应用开发者需要提供start_response函数需要的参数，主要是status和response_header，用于表明响应的状态和相应的头信息，application除了给start_response提供这两个参数外，还需要返回响应结果，响应结果是一个list。
我们再来看一个遵从WSGI协议的简单服务器，看服务器和应用是怎么互相配合起来的。从前面的分析可以看出，服务器首先要能够提供environ字典。那么这个字典都包括哪些信息呢？一是客户端提交过来的请求。所以服务器需要有代码写socket，bind，listen这些底层的socket通信命令，用于解析从客户端发过来的HTTP请求，然后存到environ字典里。二是要提供一些服务器的基本信息，比如服务器的名字、端口。三是WSGI协议里要求提供的一些字段，比如wsgi.version，wsgi.input，wsgi.errors等。
然后，服务器需要提供start_response函数，该函数主要接受两个参数，一是响应的status，二是响应的头信息response_headers。
最后，通过提供environ字典和start_response函数，服务从应用那里取到了响应的status，响应的头信息和响应的结果，然后按照HTTP协议把这些信息封装为符合格式的响应，发送给客户端。
那么，服务器的代码和网络应用的代码怎么配合起来？服务器会import网络应用的代码，从而完成二者的交互。一个简单的WSGI服务器代码示例如下，假设文件名为wsgiserver.py：
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()在shell下执行：
python wsgiserver.py wsgiapp:application