服务器 或 getway 每次收到 http客户端 发出的请求都会调用一次相应的 应用程序callable . 举例来说, 这里有一个简单的 CGI getway, 以一个接受一个应用程序对象作为参数的函数来实现的. 值得注意的是这个简单的例子还拥有有限的错误处理功能, 因为未捕捉的异常默认会写到 sys.error 里并被web服务器记录下来.
The server or gateway invokes the application callable once for each request it receives from an HTTP client, that is directed at the application. To illustrate, here is a simple CGI gateway, implemented as a function taking an application object. Note that this simple example has limited error handling, because by default an uncaught exception will be dumped to sys.stderr and logged by the web server.
示例
1 import os, sys
2
3 def run_with_cgi(application):
4
5 environ = dict(os.environ.items())
6 environ['wsgi.input'] = sys.stdin
7 environ['wsgi.errors'] = sys.stderr
8 environ['wsgi.version'] = (1,0)
9 environ['wsgi.multithread'] = False
10 environ['wsgi.multiprocess'] = True
11 environ['wsgi.run_once'] = True
12
13 if environ.get('HTTPS','off') in ('on','1'):
14 environ['wsgi.url_scheme'] = 'https'
15 else:
16 environ['wsgi.url_scheme'] = 'http'
17
18 headers_set = []
19 headers_sent = []
20
21 def write(data):
22 if not headers_set:
23 raise AssertionError("write() before start_response()")
24
25 elif not headers_sent:
26 # Before the first output, send the stored headers
27 status, response_headers = headers_sent[:] = headers_set
28 sys.stdout.write('Status: %s\r\n' % status)
29 for header in response_headers:
30 sys.stdout.write('%s: %s\r\n' % header)
31 sys.stdout.write('\r\n')
32
33 sys.stdout.write(data)
34 sys.stdout.flush()
35
36 def start_response(status,response_headers,exc_info=None):
37 if exc_info:
38 try:
39 if headers_sent:
40 # Re-raise original exception if headers sent
41 raise exc_info[0], exc_info[1], exc_info[2]
42 finally:
43 exc_info = None # avoid dangling circular ref
44 elif headers_set:
45 raise AssertionError("Headers already set!")
46
47 headers_set[:] = [status,response_headers]
48 return write
49
50 result = application(environ, start_response)
51 try:
52 for data in result:
53 if data: # don't send headers until body appears
54 write(data)
55 if not headers_sent:
56 write('') # send headers now if body was empty
57 finally:
58 if hasattr(result,'close'):
59 result.close()