|
激励自己的话:
在微博上看到一句话:一件事成功的概率只有1%,但是要是做上100遍的话,成功的概率将会是63%,这句话对现在的我真是一个极大的鼓励。
正文:
在nova源码中看到了wsgi这个模块,不懂,于是谷歌去,又全是英文啊!
官方网站:http://wsgi.readthedocs.org/en/latest/index.html
1. 什么是wsgi?
Web服务器网关接口(Python Web Server Gateway Interface,缩写为WSGI)是Python应用程序或框架和Web服务器之间的一种接口,已经被广泛接受, 它已基本达成它了可移植性方面的目标。WSGI 没有官方的实现, 因为WSGI更像一个协议. 只要遵照这些协议,WSGI应用(Application)都可以在任何实现(Server)上运行, 反之亦然。
2. 如何实现WSGI?
看了几个例子,发现有这么几个“角色”:application、server、client,它们之间的关系是client发送请求给server,server转发这个请求给application,然后application进行一系列操作之后,将响应发送给server,server再将响应转发给client,server就起一个转发的作用。
WSGI就在application和server之间发挥作用:
首先是在server中定义了一个start_response(status, response_headers, exc_info=None)方法,返回值是一个write()函数,也就是在必须在执行过start_response()函数之后,才能执行write()方法。还定义了environ变量,即环境变量,里面存放的是server接收到的client端的环境变量。WSGI就是规定了server要将start_response和environ发送给application。
然后就是application就要有接收这两个参数的“接口”了,这个“接口”可以以各种方式实现:方法、函数、类都可以。接受到之后,就要在application端调用start_resopnse()方法,而且这个调用一定要在return之前。WSGI就是规定了application要实现接收这两个参数的“接口”,并且执行start_response()。
server在接收到application的响应之后,就开始write()数据给client,首先要判断start_response()方法执行了没有,如果没有执行,那么就报出:AssertionError("write() before start_response()") 这样的异常。如果执行了start_response(),那么write()就顺利执行。
经过这样的“接口”设计,就可以让application在任何server上运行了?Maybe吧!
3. 如何使用wsgi?
这里具一个简单的例子,是从官网上看到的,觉得很简单,很具有代表性:
查看文本打印
- #! /usr/bin/env python
-
- # Our tutorial's WSGI server
- from wsgiref.simple_server import make_server
-
- def application(environ, start_response):
- “”“这个就是application,实现了接收这两个参数的接口,并且在下面调用了start_response()”“”
- # Sorting and stringifying the environment key, value pairs
- response_body = ['%s: %s' % (key, value)
- for key, value in sorted(environ.items())]
- response_body = '\n'.join(response_body)
-
- status = '200 OK'
- response_headers = [('Content-Type', 'text/plain'),
- ('Content-Length', str(len(response_body)))]
- start_response(status, response_headers)
-
- return [response_body]
-
- # Instantiate the WSGI server.
- # It will receive the request, pass it to the application
- # and send the application's response to the client
- # 这个是server,在它内部定义了start_response()方法和environ变量,并且调用application
- httpd = make_server(
- 'localhost', # The host name.
- 8051, # A port number where to wait for the request.
- application # Our application object name, in this case a function.
- )
-
- # Wait for a single request, serve it and quit.
- httpd.handle_request()
查看文本打印
- #! /usr/bin/env python
-
- # Our tutorial's WSGI server
- from wsgiref.simple_server import make_server
-
- def application(environ, start_response):
- “”“这个就是application,实现了接收这两个参数的接口,并且在下面调用了start_response()”“”
- # Sorting and stringifying the environment key, value pairs
- response_body = ['%s: %s' % (key, value)
- for key, value in sorted(environ.items())]
- response_body = '\n'.join(response_body)
-
- status = '200 OK'
- response_headers = [('Content-Type', 'text/plain'),
- ('Content-Length', str(len(response_body)))]
- start_response(status, response_headers)
-
- return [response_body]
-
- # Instantiate the WSGI server.
- # It will receive the request, pass it to the application
- # and send the application's response to the client
- # 这个是server,在它内部定义了start_response()方法和environ变量,并且调用application
- httpd = make_server(
- 'localhost', # The host name.
- 8051, # A port number where to wait for the request.
- application # Our application object name, in this case a function.
- )
-
- # Wait for a single request, serve it and quit.
- httpd.handle_request()
如果想看server内部是如何实现的话,可以看一下PEP333上的这个例子:
查看文本打印
- import os, sys
-
- def run_with_cgi(application):
-
- environ = dict(os.environ.items())
- environ['wsgi.input'] = sys.stdin
- environ['wsgi.errors'] = sys.stderr
- environ['wsgi.version'] = (1, 0)
- environ['wsgi.multithread'] = False
- environ['wsgi.multiprocess'] = True
- environ['wsgi.run_once'] = True
-
- if environ.get('HTTPS', 'off') in ('on', '1'):
- environ['wsgi.url_scheme'] = 'https'
- else:
- environ['wsgi.url_scheme'] = 'http'
-
- headers_set = []
- headers_sent = []
-
- def write(data):
- if not headers_set:
- raise AssertionError("write() before start_response()")
-
- elif not headers_sent:
- # Before the first output, send the stored headers
- status, response_headers = headers_sent[:] = headers_set
- sys.stdout.write('Status: %s\r\n' % status)
- for header in response_headers:
- sys.stdout.write('%s: %s\r\n' % header)
- sys.stdout.write('\r\n')
-
- sys.stdout.write(data)
- sys.stdout.flush()
-
- def start_response(status, response_headers, exc_info=None):
- if exc_info:
- try:
- if headers_sent:
- # Re-raise original exception if headers sent
- raise exc_info[0], exc_info[1], exc_info[2]
- finally:
- exc_info = None # avoid dangling circular ref
- elif headers_set:
- raise AssertionError("Headers already set!")
-
- headers_set[:] = [status, response_headers]
- return write
-
- result = application(environ, start_response)
- try:
- for data in result:
- if data: # don't send headers until body appears
- write(data)
- if not headers_sent:
- write('') # send headers now if body was empty
- finally:
- if hasattr(result, 'close'):
- result.close()
查看文本打印
- import os, sys
-
- def run_with_cgi(application):
-
- environ = dict(os.environ.items())
- environ['wsgi.input'] = sys.stdin
- environ['wsgi.errors'] = sys.stderr
- environ['wsgi.version'] = (1, 0)
- environ['wsgi.multithread'] = False
- environ['wsgi.multiprocess'] = True
- environ['wsgi.run_once'] = True
-
- if environ.get('HTTPS', 'off') in ('on', '1'):
- environ['wsgi.url_scheme'] = 'https'
- else:
- environ['wsgi.url_scheme'] = 'http'
-
- headers_set = []
- headers_sent = []
-
- def write(data):
- if not headers_set:
- raise AssertionError("write() before start_response()")
-
- elif not headers_sent:
- # Before the first output, send the stored headers
- status, response_headers = headers_sent[:] = headers_set
- sys.stdout.write('Status: %s\r\n' % status)
- for header in response_headers:
- sys.stdout.write('%s: %s\r\n' % header)
- sys.stdout.write('\r\n')
-
- sys.stdout.write(data)
- sys.stdout.flush()
-
- def start_response(status, response_headers, exc_info=None):
- if exc_info:
- try:
- if headers_sent:
- # Re-raise original exception if headers sent
- raise exc_info[0], exc_info[1], exc_info[2]
- finally:
- exc_info = None # avoid dangling circular ref
- elif headers_set:
- raise AssertionError("Headers already set!")
-
- headers_set[:] = [status, response_headers]
- return write
-
- result = application(environ, start_response)
- try:
- for data in result:
- if data: # don't send headers until body appears
- write(data)
- if not headers_sent:
- write('') # send headers now if body was empty
- finally:
- if hasattr(result, 'close'):
- result.close()
4. eventlet中的wsgi
因为nova中用的是eventlet中的wsgi,所以再来看一下wsgi在eventlet中是怎么实现的。其实不用看源码也可以知道evenlet中,将和服务器建立的连接放在了绿色线程中,socket用的也是绿化过的socket。简单的使用,如下示例:
查看文本打印
- from eventlet import wsgi
- import eventlet
-
- def hello_world(env, start_response):
- start_response('200 OK', [('Content-Type', 'text/plain')])
- return ['Hello, World!\r\n']
-
- wsgi.server(eventlet.listen(('', 8090)), hello_world)
查看文本打印
- from eventlet import wsgi
- import eventlet
-
- def hello_world(env, start_response):
- start_response('200 OK', [('Content-Type', 'text/plain')])
- return ['Hello, World!\r\n']
-
- wsgi.server(eventlet.listen(('', 8090)), hello_world)
参考资料:
http://webpython.codepoint.net/wsgi_tutorial
http://www.python.org/dev/peps/pep-0333/
http://eventlet.net/doc/modules/wsgi.html
|
|