上一篇《白话tornado源码之待请求阶段》中介绍了tornado框架在客户端请求之前所做的准备（下图1、2部分），本质上就是创建了一个socket服务端，并进行了ip和端口的绑定，但是未执行 socket的accept方法，也就是未获取客户端请求信息。
概述
本篇就来详细介绍tornado服务器（socket服务端）是如何接收用户请求数据以及如果根据用户请求的URL处理并返回数据，也就是上图的3系列所有步骤，如上图【start】是一个死循环，其中利用epoll监听服务端socket句柄，一旦客户端发送请求，则立即调用HttpServer对象的_handle_events方法来进行请求的处理。
对于整个3系列按照功能可以划分为四大部分：
获取用户请求数据（上图3.4）根据用户请求URL进行路由匹配，从而使得某个方法处理具体的请求（上图3.5～3.19）将处理后的数据返回给客户端（上图3.21～3.23）关闭客户端socket（上图3.24～3.26）3.1、HTTPServer对象的_handle_events方法此处代码主要有三项任务：
1、 socket.accept() 接收了客户端请求。
2、创建封装了客户端socket对象和IOLoop对象的IOStream实例（用于之后获取或输出数据）。
3、创建HTTPConnection对象，其内容是实现整个功能的逻辑。
classHTTPServer(object):def_handle_events(self, fd, events):whileTrue:try:#======== 获取客户端请求 =========#connection, address = self._socket.accept()except socket.error, e:
if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
return
raise
if self.ssl_options is not None:
assert ssl, "Python 2.6+ and OpenSSL required for SSL"
try:
connection = ssl.wrap_socket(connection,
server_side=True,
do_handshake_on_connect=False,
**self.ssl_options)
except ssl.SSLError, err:
if err.args[0] == ssl.SSL_ERROR_EOF:
return connection.close()
else:
raise
except socket.error, err:
if err.args[0] == errno.ECONNABORTED:
return connection.close()
else:
raisetry:
#这是的条件是选择https和http请求方式
if self.ssl_options is not None:
stream = iostream.SSLIOStream(connection, io_loop=self.io_loop)
else:
#将客户端socket对象和IOLoop对象封装到IOStream对象中
#IOStream用于从客户端socket中读取请求信息stream = iostream.IOStream(connection, io_loop=self.io_loop)#创建HTTPConnection对象
#address是客户端IPdizhi
#self.request_callback是application对象，其中包含了：url映射关系和配置文件等..
#so，HTTPConnection的构造函数就是下一步处理请求的位置了..HTTPConnection(stream, address, self.request_callback,self.no_keep_alive, self.xheaders)except:
logging.error("Error in connection callback", exc_info=True)
3.2、IOStream的__init__方法此处代码主要两项目任务：
封装客户端socket和其他信息，以便之后执行该对象的其他方法获取客户端请求的数据和响应客户信息将客户端socket对象添加到epoll，并且指定当客户端socket对象变化时，就去执行 IOStream的_handle_events方法（调用socket.send给用户响应数据）class IOStream(object):
def __init__(self, socket, io_loop=None, max_buffer_size=104857600,
read_chunk_size=4096):
#客户端socket对象
self.socket = socket
self.socket.setblocking(False)
self.io_loop = io_loop or ioloop.IOLoop.instance()
self.max_buffer_size = max_buffer_size
self.read_chunk_size = read_chunk_size
self._read_buffer = collections.deque()
self._write_buffer = collections.deque()
self._write_buffer_frozen = False
self._read_delimiter = None
self._read_bytes = None
self._read_callback = None
self._write_callback = None
self._close_callback = None
self._connect_callback = None
self._connecting = False
self._state = self.io_loop.ERROR
with stack_context.NullContext():
#将客户端socket句柄添加的epoll中，并将IOStream的_handle_events方法添加到 Start 的While循环中
#Start 的While循环中监听客户端socket句柄的状态，以便再最后调用IOStream的_handle_events方法把处理后的信息响应给用户
self.io_loop.add_handler(self.socket.fileno(), self._handle_events, self._state)
3.3、HTTPConnections的__init__方法此处代码主要两项任务：
获取请求数据调用 _on_headers 继续处理请求对于获取请求数据，其实就是执行IOStream的read_until函数来完成，其内部通过socket.recv(4096)方法获取客户端请求的数据，并以 【\r\n\r\n】作为请求信息结束符（http请求头和内容通过\r\n\r\n分割）。
class HTTPConnection(object):
def __init__(self, stream, address, request_callback, no_keep_alive=False,xheaders=False):
self.stream = stream#stream是封装了客户端socket和IOLoop实例的IOStream对象
self.address = address#address是客户端IP地址
self.request_callback = request_callback#request_callback是封装了URL映射和配置文件的Application对象。
self.no_keep_alive = no_keep_alive
self.xheaders = xheaders
self._request = None
self._request_finished = False
#获取请求信息（请求头和内容），然后执行 HTTPConnection的_on_headers方法继续处理请求
self._header_callback = stack_context.wrap(self._on_headers)
self.stream.read_until("\r\n\r\n", self._header_callback)
请求数据格式：
GET / HTTP/1.1
Host: localhost:8888
Connection: keep-alive
Cache-Control: max-age=0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko)Chrome/41.0.2272.118 Safari/537.36
Accept-Encoding: gzip, deflate, sdch
Accept-Language: zh-CN,zh;q=0.8,en;q=0.6,zh-TW;q=0.4
If-None-Match: "e02aa1b106d5c7c6a98def2b13005d5b84fd8dc8"
详细代码解析：
classIOStream(object):defread_until(self, delimiter, callback):"""Call callback when we read the given delimiter."""assertnotself._read_callback,"Already reading"#终止界定 \r\n\r\nself._read_delimiter =delimiter#回调函数，即：HTTPConnection的 _on_headers 方法self._read_callback =stack_context.wrap(callback)whileTrue:#代码概述：#先从socket中读取信息并保存到buffer中#然后再读取buffer中的数据，以其为参数执行回调函数（HTTPConnection的 _on_headers 方法）#buffer其实是一个线程安装的双端队列collections.deque#从buffer中读取数据，并执行回调函数。#注意：首次执行时buffer中没有数据ifself._read_from_buffer():returnself._check_closed()#从socket中读取信息到buffer（线程安全的一个双向消息队列）ifself._read_to_buffer() ==0:
breakself._add_io_state(self.io_loop.READ)
IOStream.read_until
classIOStream(object):def_read_to_buffer(self):#省略部分代码chunk =self._read_from_socket()
self._read_buffer.append(chunk)returnlen(chunk)def_read_from_socket(self):#socket对象的recv函数接收数据#read_chunk_size在构造函数中默认设置为：4096chunk =self.socket.recv(self.read_chunk_size)ifnotchunk:
self.close()returnNonereturnchunk
IOStream._read_to_buffer
classIOStream(object):def_read_from_buffer(self):"""Attempts to complete the currently-pending read from the buffer.
Returns True if the read was completed."""#构造函数中默认设置为Noneifself._read_bytes:ifself._read_buffer_size() >=self._read_bytes:
num_bytes=self._read_bytes
callback=self._read_callback
self._read_callback=None
self._read_bytes=None
self._run_callback(callback, self._consume(num_bytes))returnTrue#_read_delimiter的值为 \r\n\r\nelifself._read_delimiter:#buffer列表首元素合并，合并详细见_merge_PRefix函数_merge_prefix(self._read_buffer, sys.maxint)#获取 \r\n\r\n 所在 buffer 首元素的位置索引loc =self._read_buffer[0].find(self._read_delimiter)ifloc != -1:#如果在请求中找到了 \r\n\r\n#self._read_callback 是HTTPConnection对象的 _on_headers 方法callback =self._read_callback
delimiter_len= len(self._read_delimiter)#获取 \r\n\r\n 的长度self._read_callback =None
self._read_delimiter=None#============ 执行HTTPConnection对象的 _on_headers 方法 =============#self._consume(loc + delimiter_len)用来获取 buffer 的首元素（请求的信息其实就被封装到了buffer的首个元素中）self._run_callback(callback,self._consume(loc +delimiter_len))returnTruereturnFalse
IOStream._read_from_buffer
3.4、HTTPConnnection的 _on_headers 方法（含3.5）上述代码主要有两个任务：
根据获取的请求信息生成响应的请求头键值对，并把信息封装到HttpRequest对象中调用Application的__call__方法，继续处理请求class HTTPConnection(object):
def _on_headers(self, data):
try:
data = native_str(data.decode('latin1'))
eol = data.find("\r\n")
#获取请求的起始行数据，例如：GET / HTTP/1.1
start_line = data[:eol]
try:
#请求方式、请求地址、http版本号
method, uri, version = start_line.split(" ")
except ValueError:
raise _BadRequestException("Malformed HTTP request line")
if not version.startswith("HTTP/"):
raise _BadRequestException("Malformed HTTP version in HTTP Request-Line")
#把请求头信息包装到一个字典中。（不包括第一行）
headers = httputil.HTTPHeaders.parse(data[eol:])
#把请求信息封装到一个HTTPRequest对象中
#注意：self._request = HTTPRequest，
#HTTPRequest中封装了HTTPConnection
#HTTPConnection中封装了stream和application
self._request = HTTPRequest(connection=self, method=method, uri=uri, version=version,headers=headers, remote_ip=self.address[0])
#从请求头中获取 Content-Length
content_length = headers.get("Content-Length")
if content_length:
content_length = int(content_length)
if content_length > self.stream.max_buffer_size:
raise _BadRequestException("Content-Length too long")
if headers.get("Expect") == "100-continue":
self.stream.write("HTTP/1.1 100 (Continue)\r\n\r\n")
self.stream.read_bytes(content_length, self._on_request_body)
return
#**************** 执行Application对象的 __call__ 方法，也就是路由系统的入口 *******************
self.request_callback(self._request)
except _BadRequestException, e:
logging.info("Malformed HTTP request from %s: %s",
self.address[0], e)
self.stream.close()
return
classHTTPRequest(object):def__init__(self, method, uri, version="HTTP/1.0", headers=None,
body=None, remote_ip=None, protocol=None, host=None,
files=None, connection=None):
self.method=method
self.uri=uri
self.version=version
self.headers= headersorhttputil.HTTPHeaders()
self.body= bodyor""ifconnectionandconnection.xheaders:#Squid uses X-Forwarded-For, others use X-Real-Ipself.remote_ip =self.headers.get("X-Real-Ip", self.headers.get("X-Forwarded-For", remote_ip))#AWS uses X-Forwarded-Protoself.protocol =self.headers.get("X-Scheme", self.headers.get("X-Forwarded-Proto", protocol))ifself.protocolnotin("http","https"):
self.protocol="http"else:
self.remote_ip=remote_ipifprotocol:
self.protocol=protocolelifconnectionandisinstance(connection.stream,
iostream.SSLIOStream):
self.protocol="https"else:
self.protocol="http"self.host= hostorself.headers.get("Host")or"127.0.0.1"self.files= filesor{}
self.connection=connection
self._start_time=time.time()
self._finish_time=None
scheme, netloc, path, query, fragment=urlparse.urlsplit(uri)
self.path=path
self.query=query
arguments=cgi.parse_qs(query)
self.arguments={}forname, valuesinarguments.iteritems():
values= [vforvinvaluesifv]ifvalues: self.arguments[name] = values
HTTPRequest.__init__
3.6、Application的__call__方法(含3.7、3.8、3.9)此处代码主要有三个项任务：
根据请求的url和封装在Application对象中的url映射做匹配，获取url所对应的Handler对象。ps：Handlers泛指继承RequestHandler的类创建Handler对象，即：执行Handler的__init__方法执行Handler对象的 _execute 方法注意：
1、执行Application的 __call__ 方法时，其参数request是HTTPRequest对象（其中封装HTTPConnetion、Stream、Application对象、请求头信息）
2、Handler泛指就是我们定义的用于处理请求的类并且她还继承自RequestHandler
class Application(object):
def __call__(self, request):
"""Called by HTTPServer to execute the request."""
transforms = [t(request) for t in self.transforms]
handler = None
args = []
kwargs = {}
#根据请求的目标主机，匹配主机模版对应的正则表达式和Handlers
handlers = self._get_host_handlers(request)
if not handlers:
handler = RedirectHandler(
self, request, url="http://" + self.default_host + "/")
else:
for spec in handlers:
match = spec.regex.match(request.path)
if match:
# None-safe wrapper around url_unescape to handle
# unmatched optional groups correctly
def unquote(s):
if s is None: return s
return escape.url_unescape(s, encoding=None)
handler = spec.handler_class(self, request, **spec.kwargs) #创建RquestHandler对象
# Pass matched groups to the handler. Since
# match.groups() includes both named and unnamed groups,
# we want to use either groups or groupdict but not both.
# Note that args are passed as bytes so the handler can
# decide what encoding to use.
kwargs = dict((k, unquote(v))
for (k, v) in match.groupdict().iteritems())
if kwargs:
args = []
else:
args = [unquote(s) for s in match.groups()]
break
if not handler:
handler = ErrorHandler(self, request, status_code=404)
# In debug mode, re-compile templates and reload static files on every
# request so you don't need to restart to see changes
if self.settings.get("debug"):
if getattr(RequestHandler, "_templates", None):
for loader in RequestHandler._templates.values():
loader.reset()
RequestHandler._static_hashes = {}
#＝＝＝＝ 执行RequestHandler的_execute方法 ＝＝＝＝
handler._execute(transforms, *args, **kwargs)
return handler
classApplication(object):def_get_host_handlers(self, request):#将请求的host和handlers中的主机模型进行匹配host = request.host.lower().split(':')[0]forpattern, handlersinself.handlers:ifpattern.match(host):returnhandlers#Look for default host if not behind load balancer (for debugging)if"X-Real-Ip"notinrequest.headers:forpattern, handlersinself.handlers:ifpattern.match(self.default_host):returnhandlersreturnNone
Application._get_host_handlers
classRequestHandler(object):
SUPPORTED_METHODS= ("GET","HEAD","POST","DELETE","PUT","OPTIONS")def__init__(self, application, request, **kwargs):
self.application=application
self.request=request
self._headers_written=False
self._finished=False
self._auto_finish=True
self._transforms= None#will be set in _execute#获取在application中设置的 ui_modules 和ui_methodself.ui = _O((n, self._ui_method(m))forn, minapplication.ui_methods.iteritems())
self.ui["modules"] = _O((n, self._ui_module(n, m))forn, minapplication.ui_modules.iteritems())
self.clear()#设置服务器、内容类型编码和连接#Check since connection is not available in WSGI#检查连接是否可用，应该是长短连接有关。ifhasattr(self.request,"connection"):
self.request.connection.stream.set_close_callback(self.on_connection_close)
self.initialize(**kwargs)definitialize(self):passdefclear(self):"""Resets all headers and content for this response."""self._headers={"Server":"TornadoServer/%s"%tornado.version,"Content-Type":"text/html; charset=UTF-8",
}ifnotself.request.supports_http_1_1():ifself.request.headers.get("Connection") =="Keep-Alive":
self.set_header("Connection","Keep-Alive")
self._write_buffer=[]
self._status_code= 200
RequestHandler.__init__
上述过程中，首先根据请求的URL去路由规则中匹配，一旦匹配成功，则创建路由相对应的handler的实例。例如：如果请求 的url是【/index/11】则会创建IndexHandler实例，然后再执行该对象的 _execute 方法。由于所有的 xxxHandler 类是RequestHandler的派生类，所以会默认执行 RequestHandler的 _execute 方法。
3.10 RequestHandler的_execute方法 （含有3.11、3.12、3.13）此处代码主要有三项任务：
扩展点，因为self.prepare默认是空方法，所有可以在这里被重写通过反射执行Handler的get/post/put/delete等方法完成请求处理后，执行finish方法class RequestHandler(object):
def _execute(self, transforms, *args, **kwargs):
"""Executes this request with the given output transforms."""
self._transforms = transforms
with stack_context.ExceptionStackContext(
self._stack_context_handle_exception):
if self.request.method not in self.SUPPORTED_METHODS:
raise HTTPError(405)
# If XSRF cookies are turned on, reject form submissions without
# the proper cookie
if self.request.method not in ("GET", "HEAD") and \
self.application.settings.get("xsrf_cookies"):
self.check_xsrf_cookie()
self.prepare()
if not self._finished:
#通过反射的方法，执行 RequestHandler 派生类的的 get、post、put方法
getattr(self, self.request.method.lower())(*args, **kwargs)
if self._auto_finish and not self._finished:
self.finish()
例：用户发送get请求
classMyHandler(tornado.web.RequestHandler):defget(self):
self.write("Hello, world")
MyHandler.get
classRequestHandler(object):defwrite(self, chunk):assertnotself._finishedifisinstance(chunk, dict):
chunk=escape.json_encode(chunk)
self.set_header("Content-Type","text/javascript; charset=UTF-8")
chunk=_utf8(chunk)
self._write_buffer.append(chunk)
RequestHandler.write
上述在执行RequestHandler的write方法时，讲数据保存在Handler对象的 _write_buffer 列表中，在之后执行finish时再讲数据写到IOStream对象的_write_buffer字段中，其类型是双向队列collections.deque()。
3.14、执行RequestHandler的finish此段代码主要有两项任务：
将用户处理请求后返回的数据发送到IOStream的_write_buffer队列中纪录操作日志class RequestHandler：
def finish(self, chunk=None):
"""Finishes this response, ending the HTTP request."""
assert not self._finished
if chunk is not None: self.write(chunk)
if not self._headers_written:
if (self._status_code == 200 and
self.request.method in ("GET", "HEAD") and
"Etag" not in self._headers):
hasher = hashlib.sha1()
for part in self._write_buffer:
hasher.update(part)
etag = '"%s"' % hasher.hexdigest()
inm = self.request.headers.get("If-None-Match")
if inm and inm.find(etag) != -1:
self._write_buffer = []
self.set_status(304)
else:
self.set_header("Etag", etag)
if "Content-Length" not in self._headers:
content_length = sum(len(part) for part in self._write_buffer)
self.set_header("Content-Length", content_length)
if hasattr(self.request, "connection"):
self.request.connection.stream.set_close_callback(None)
if not self.application._wsgi:
＃将处理请求返回的数据发送到IOStream的_write_buffer队列中
self.flush(include_footers=True)
self.request.finish()
＃纪录日志
self._log()
self._finished = True
3.15、执行RequestHandler的flush方法此处代码主要有一项任务：
将处理请求返回的数据发送到IOStream的_write_buffer队列中def flush(self, include_footers=False):
"""Flushes the current output buffer to the network."""
if self.application._wsgi:
raise Exception("WSGI applications do not support flush()")
chunk = "".join(self._write_buffer)
self._write_buffer = []
if not self._headers_written:
self._headers_written = True
for transform in self._transforms:
self._headers, chunk = transform.transform_first_chunk(
self._headers, chunk, include_footers)
headers = self._generate_headers()
else:
for transform in self._transforms:
chunk = transform.transform_chunk(chunk, include_footers)
headers = ""
# Ignore the chunk and only write the headers for HEAD requests
if self.request.method == "HEAD":
if headers: self.request.write(headers)
return
if headers or chunk:
#执行HTTPReqeust的write方法
self.request.write(headers + chunk)
classHTTPRequest(object):defwrite(self, chunk):"""Writes the given chunk to the response stream."""assertisinstance(chunk, str)#执行HTTPConnection的write方法self.connection.write(chunk)
HTTPRequest.write
classIOStream(object):defwrite(self, data, callback=None):
self._check_closed()#将数据保存到collections.deque()类型的双向队列中_write_buffer中self._write_buffer.append(data)
self._add_io_state(self.io_loop.WRITE)
self._write_callback= stack_context.wrap(callback)
IOStream.write
以上代码执行完成之后，请求的处理基本上就完成了。下面就是等待监听客户端socket句柄的epoll触发，然后执行IOStream的_handle_event方法来将 响应数据发送给客户端。
3.20、执行RequestHandler的_log方法此处代码主要有一项任务：
记录操作日志（利用logging模块）class RequestHandler：
def _log(self):
self.application.log_request(self)
classApplication：deflog_request(self, handler):if"log_function"inself.settings:
self.settings["log_function"](handler)returnifhandler.get_status() < 400:
log_method=logging.infoelifhandler.get_status() < 500:
log_method=logging.warningelse:
log_method=logging.error
request_time= 1000.0 *handler.request.request_time()
log_method("%d %s %.2fms", handler.get_status(),
handler._request_summary(), request_time)
Application.log_request
3.21、IOStream的Handle_event方法由于epoll中不但监听了服务器socket句柄还监听了客户端sokcet句柄，所以当客户端socket对象变化时，就会去调用之前指定的IOStream的_handler_events方法。
此段代码主要有一项任务：
将处理之后的响应数据发送给客户端class IOStream(object):
def _handle_events(self, fd, events):
if not self.socket:
logging.warning("Got events for closed stream %d", fd)
return
try:
if events & self.io_loop.READ:
self._handle_read()
if not self.socket:
return
if events & self.io_loop.WRITE:
if self._connecting:
self._handle_connect()
#执行_handle_write方法，内部调用socket.send将数据响应给客户端
self._handle_write()
if not self.socket:
return
if events & self.io_loop.ERROR:
self.close()
return
state = self.io_loop.ERROR
if self.reading():
state |= self.io_loop.READ
if self.writing():
state |= self.io_loop.WRITE
if state != self._state:
self._state = state
self.io_loop.update_handler(self.socket.fileno(), self._state)
except:
logging.error("Uncaught exception, closing connection.",
exc_info=True)
self.close()
raise
3.22、IOStream的_handle_write方法此段代码主要有两项任务：
调用socket.send给客户端发送响应数据执行回调函数HTTPConnection的_on_write_complete方法class IOStream(object):
def _handle_write(self):
while self._write_buffer:
try:
if not self._write_buffer_frozen:
_merge_prefix(self._write_buffer, 128 * 1024)
#调用客户端socket对象的send方法发送数据
num_bytes = self.socket.send(self._write_buffer[0])
self._write_buffer_frozen = False
_merge_prefix(self._write_buffer, num_bytes)
self._write_buffer.popleft()
except socket.error, e:
if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
self._write_buffer_frozen = True
break
else:
logging.warning("Write error on %d: %s",
self.socket.fileno(), e)
self.close()
return
if not self._write_buffer and self._write_callback:
callback = self._write_callback
self._write_callback = None
#执行回调函数关闭客户端socket连接（HTTPConnection的_on_write_complete方法）
self._run_callback(callback)
classIOStream(object):def_run_callback(self, callback, *args, **kwargs):try:
with stack_context.NullContext():
callback(*args, **kwargs)except:
logging.error("Uncaught exception, closing connection.",
exc_info=True)
self.close()raise
IOStream._run_callback
注：IOStream的_run_callback方法内部调用了HTTPConnection的_on_write_complete方法
3.23、执行HTTPConnection的_on_write_complete方法此处代码主要有一项任务：
更新客户端socket所在epoll中的状态为【READ】，以便之后执行3.24时关闭socket客户端。class HTTPConnection(object):
def _on_write_complete(self):
if self._request_finished:
self._finish_request()
def _finish_request(self):
if self.no_keep_alive:
disconnect = True
else:
connection_header = self._request.headers.get("Connection")
if self._request.supports_http_1_1():
disconnect = connection_header == "close"
elif ("Content-Length" in self._request.headers
or self._request.method in ("HEAD", "GET")):
disconnect = connection_header != "Keep-Alive"
else:
disconnect = True
self._request = None
self._request_finished = False
if disconnect:
self.stream.close()
return
self.stream.read_until("\r\n\r\n", self._header_callback)
classIOStream(object):defread_until(self, delimiter, callback):"""Call callback when we read the given delimiter."""assertnotself._read_callback,"Already reading"self._read_delimiter=delimiter
self._read_callback=stack_context.wrap(callback)whileTrue:#See if we've already got the data from a previous readifself._read_from_buffer():returnself._check_closed()ifself._read_to_buffer() ==0:
break#更新为READself._add_io_state(self.io_loop.READ)
IOStream.read_until
classIOStream(object):def_add_io_state(self, state):ifself.socketisNone:#connection has been closed, so there can be no future eventsreturnifnotself._state &state:
self._state= self._state |state#执行IOLoop对象的update_handler方法self.io_loop.update_handler(self.socket.fileno(), self._state)
IOStream._add_io_state
classIOLoop(object):defupdate_handler(self, fd, events):"""Changes the events we listen for fd."""#self._impl就是epoll对象self._impl.modify(fd, events | self.ERROR)
IOLoop.update_handler
3.24、IOStream的_handle_write方法（含3.25、3.26）此段代码主要有一项任务：
关闭客户端socketclass IOStream(object):
def _handle_events(self, fd, events):
if not self.socket:
logging.warning("Got events for closed stream %d", fd)
return
try:
#由于在 2.23 步骤中已经将epoll的状态更新为READ，所以这次会执行_handle_read方法
if events & self.io_loop.READ:
self._handle_read()
#执行完_handle_read后，客户端socket被关闭且置空，所有此处就会执行return
if not self.socket:
return
#===============================终止===========================
if events & self.io_loop.WRITE:
if self._connecting:
self._handle_connect()
self._handle_write()
if not self.socket:
return
if events & self.io_loop.ERROR:
self.close()
return
state = self.io_loop.ERROR
if self.reading():
state |= self.io_loop.READ
if self.writing():
state |= self.io_loop.WRITE
if state != self._state:
self._state = state
self.io_loop.update_handler(self.socket.fileno(), self._state)
except:
logging.error("Uncaught exception, closing connection.",
exc_info=True)
self.close()
raise
classIOStream(object):def_handle_read(self):whileTrue:try:#Read from the socket until we get EWOULDBLOCK or equivalent.#SSL sockets do some internal buffering, and if the data is#sitting in the SSL object's buffer select() and friends#can't see it; the only way to find out if it's there is to#try to read it.result =self._read_to_buffer()exceptException:
self.close()returnifresult ==0:
breakelse:ifself._read_from_buffer():return
IOStream._handle_read
classIOStream(object):def_read_from_socket(self):"""Attempts to read from the socket.
Returns the data read or None if there is nothing to read.
May be overridden in subclasses."""try:
chunk=self.socket.recv(self.read_chunk_size)exceptsocket.error, e:ife.args[0]in(errno.EWOULDBLOCK, errno.EAGAIN):returnNoneelse:raiseifnotchunk:#执行close方法self.close()returnNonereturnchunk
IOStream._read_from_socket
classIOStream(object):defclose(self):"""Close this stream."""ifself.socketisnotNone:#将客户端socket句柄在epoll中的移除，即：不再监听此客户端请求。self.io_loop.remove_handler(self.socket.fileno())#关闭客户端socketself.socket.close()#将socket置空self.socket =Noneifself._close_callback:
self._run_callback(self._close_callback)
IOStream.close
classIOLoop(object):defremove_handler(self, fd):"""Stop listening for events on fd."""self._handlers.pop(fd, None)
self._events.pop(fd, None)try:
self._impl.unregister(fd)except(OSError, IOError):
logging.debug("Error deleting fd from IOLoop", exc_info=True)
IOLoop.remove_handler
结束语以上就是tornado源码针对请求的主要内容，另外，大家可能注意到我们返回给用户的只是一个简单的“hello world”，tornado返回复杂的内容时又需要使用模板语言，至于如何生成复杂的页面，我们会在下一篇再会剖析。
读者如果觉得那里错误或不适，请与我联系！！！