WSGI学习系列eventlet.wsgi

WSGI是Web Service Gateway Interface的缩写。

WSGI标准在PEP(Python Enhancement Proposal)中定义并被许多框架实现，其中包括现广泛使用的django框架。

PythonWeb服务器接口（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, 它已基本达成它的可移植性方面的目标。

Nova使用了eventlet.wsgi接口。

"""This is a simple example of running a wsgi application with eventlet.
For a more fully-featured server which supports multiple processes,
multiple threads, and graceful code reloading, see:

http://pypi.python.org/pypi/Spawning/
"""

import eventlet
from eventlet import wsgi

def hello_world(env, start_response):
    if env['PATH_INFO'] != '/':
        start_response('404 Not Found', [('Content-Type', 'text/plain')])
        return ['Not Found\r\n']
    start_response('200 OK', [('Content-Type', 'text/plain')])
    return ['Hello, World!\r\n']

wsgi.server(eventlet.listen(('', 8090)), hello_world)

SSL方式(Secure Socket Layer)

wsgi.server(eventlet.wrap_ssl(eventlet.listen(('', 8090)),
                              certfile='cert.crt',
                              keyfile='private.key',
                              server_side=True),
            hello_world)

流程描述：

服务器开一个socket等待客户端连接；请求来了，服务器会读出传来的数据，然后根据HTTP协议做一些初步的封装，

接着就可以调用事先注册的应用程序了，并将请求的数据塞进去；等响应处理完毕了再把数据通过socket发出去

server参数介绍：

def server(sock,  # Server socket, must be already bound to a port and listening(IP和端口并开启监听).
           site,  # WSGI application function(事件处理函数，发送start_response响应头然后返回响应内容)
           log=None,  # File-like object that logs should be written to.If not specified, sys.stderr is used.(日志处理，默认为sys.stderr用来重定向标准错误信息的)
           environ=None,  # Additional parameters that go into the environ dictionary of every request(每次请求的参数，写入一个字典中)
           max_size=None,  #Maximum number of client connections opened at any time by this server.(默认为1024)
           max_http_version=DEFAULT_MAX_HTTP_VERSION,  # Set to "HTTP/1.0" to make the server pretend it only supports HTTP 1.0.
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　# This can help with applications or clients that don't behave properly using HTTP 1.1.(HTTP协议版本,默认为HTTP/1.1)
           protocol=HttpProtocol,  # Protocol class.（协议类，默认为HttpProtocol）
           server_event=None,  # Used to collect the Server object(搜集服务器对象信息)
           minimum_chunk_size=None,  # Minimum size in bytes for http chunks.  This can be used to improve performance of applications which yield many small strings, though
　　　　　　　　　　　　　　　　　　　　　 # using it technically violates the WSGI spec. This can be overridden on a per request basis by setting environ['eventlet.minimum_write_chunk_size'].
　　　　　　　　　　　　　　　　　　　　　 # 设置最小的Chunk大小，可以通过设置environ['eventlet.minimum_write_chunk_size']来覆盖.Chunk表示服务器发送给客户端的分块传输编码（Chunked transfer encoding）
           log_x_forwarded_for=True,  # If True (the default), logs the contents of the x-forwarded-for header in addition to the actual client ip address in the 'client_ip' field of the log line.
　　　　　　　　　　　　　　　　　　　　　　# 默认为True,记录客户端IP日志,X-Forwarded-For(XFF)是用来识别通过HTTP代理或负载均衡方式连接到Web服务器的客户端最原始的IP地址的HTTP请求头字段。
           custom_pool=None,  # A custom GreenPool instance which is used to spawn client green threads.If this is supplied, max_size is ignored.(协程池，如果启用则可以忽略前面的max_size参数)
           keepalive=True,  # If set to False, disables keepalives on the server; all connections will be closed after serving one request.（控制客户端连接数是否保持alive）
           log_output=True,  # A Boolean indicating if the server will log data or not.(确定服务端是否输出日志)
           log_format=DEFAULT_LOG_FORMAT,  # A python format string that is used as the template to generate log lines.(日志输出格式)
           url_length_limit=MAX_REQUEST_LINE,  # A maximum allowed length of the request url. If exceeded, 414 error is returned.（最大的url长度限制，默认为8192）
           debug=True, # True if the server should send exception tracebacks to the clients on 500 errors.If False, the server will respond with empty bodies.(是否发送调式信息给客户端)
           socket_timeout=None,  # Timeout for client connections' socket operations. Default None means wait forever.(Socket超时时间设置，单位是秒)
           capitalize_response_headers=True)  # Normalize response headers' names to Foo-Bar(是否标准化相应头)