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。
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：
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。
class HTTPServer(object):def _handle_events(self, fd, events): while True: 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: raise try: #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)
此处代码主要两项目任务：
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)
此处代码主要两项任务：
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：
class IOStream(object): def read_until(self, delimiter, callback): """Call callback when we read the given delimiter.""" assert not self._read_callback, "Already reading" #终止界定 /r/n/r/n self._read_delimiter = delimiter #回调函数，即：HTTPConnection的 _on_headers 方法 self._read_callback = stack_context.wrap(callback) while True: #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 if self._read_from_buffer(): return self._check_closed() #从socket中读取信息到buffer（线程安全的一个双向消息队列） if self._read_to_buffer() == 0: break self._add_io_state(self.io_loop.READ)
class IOStream(object): def _read_to_buffer(self): #省略部分代码 chunk = self._read_from_socket() self._read_buffer.append(chunk) return len(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：4096 chunk = self.socket.recv(self.read_chunk_size) if not chunk: self.close() return None return chunk
class IOStream(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None if self._read_bytes: if self._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)) return True #_read_delimiter的值为 /r/n/r/n elif self._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) if loc != -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)) return True return False
上述代码主要有两个任务：
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() returnclass HTTPRequest(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 = headers or httputil.HTTPHeaders() self.body = body or "" if connection and connection.xheaders: # Squid uses X-Forwarded-For, others use X-Real-Ip self.remote_ip = self.headers.get( "X-Real-Ip", self.headers.get("X-Forwarded-For", remote_ip)) # AWS uses X-Forwarded-Proto self.protocol = self.headers.get( "X-Scheme", self.headers.get("X-Forwarded-Proto", protocol)) if self.protocol not in ("http", "https"): self.protocol = "http" else: self.remote_ip = remote_ip if protocol: self.protocol = protocol elif connection and isinstance(connection.stream, iostream.SSLIOStream): self.protocol = "https" else: self.protocol = "http" self.host = host or self.headers.get("Host") or "127.0.0.1" self.files = files or {} 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 = {} for name, values in arguments.iteritems(): values = [v for v in values if v] if values: self.arguments[name] = values
此处代码主要有三个项任务：
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 handlerclass Application(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] for pattern, handlers in self.handlers: if pattern.match(host): return handlers # Look for default host if not behind load balancer (for debugging) if "X-Real-Ip" not in request.headers: for pattern, handlers in self.handlers: if pattern.match(self.default_host): return handlers return None
class RequestHandler(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_method self.ui = _O((n, self._ui_method(m)) for n, m in application.ui_methods.iteritems()) self.ui["modules"] = _O((n, self._ui_module(n, m)) for n, m in application.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。 if hasattr(self.request, "connection"): self.request.connection.stream.set_close_callback(self.on_connection_close) self.initialize(**kwargs) def initialize(self): pass def clear(self): """Resets all headers and content for this response.""" self._headers = { "Server": "TornadoServer/%s" % tornado.version, "Content-Type": "text/html; charset=UTF-8", } if not self.request.supports_http_1_1(): if self.request.headers.get("Connection") == "Keep-Alive": self.set_header("Connection", "Keep-Alive") self._write_buffer = [] self._status_code = 200
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。
此处代码主要有三项任务：
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
class MyHandler(tornado.web.RequestHandler): def get(self): self.write("Hello, world")
class RequestHandler(object): def write(self, chunk): assert not self._finished if isinstance(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)
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()。
此段代码主要有两项任务：
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此处代码主要有一项任务：
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)class HTTPRequest(object): def write(self, chunk): """Writes the given chunk to the response stream.""" assert isinstance(chunk, str) #执行HTTPConnection的write方法 self.connection.write(chunk)
class IOStream(object): def write(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)
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。
此处代码主要有一项任务：
class RequestHandler： def _log(self): self.application.log_request(self)
class Application： def log_request(self, handler): if "log_function" in self.settings: self.settings["log_function"](handler) return if handler.get_status() < 400: log_method = logging.info elif handler.get_status() < 500: log_method = logging.warning else: 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)
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：
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此段代码主要有两项任务：
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)class IOStream(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
注：IOStream的_run_callback方法内部调用了HTTPConnection的_on_write_complete方法
此处代码主要有一项任务：
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)class IOStream(object): def read_until(self, delimiter, callback): """Call callback when we read the given delimiter.""" assert not self._read_callback, "Already reading" self._read_delimiter = delimiter self._read_callback = stack_context.wrap(callback) while True: # See if we've already got the data from a previous read if self._read_from_buffer(): return self._check_closed() if self._read_to_buffer() == 0: break #更新为READ self._add_io_state(self.io_loop.READ)
class IOStream(object): def _add_io_state(self, state): if self.socket is None: # connection has been closed, so there can be no future events return if not self._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)
class IOLoop(object): def update_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)
此段代码主要有一项任务：
class 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() raiseclass IOStream(object): def _handle_read(self): while True: 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() except Exception: self.close() return if result == 0: break else: if self._read_from_buffer(): return
class IOStream(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) except socket.error, e: if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN): return None else: raise if not chunk: #执行close方法 self.close() return None return chunk
class IOStream(object): def close(self): """Close this stream.""" if self.socket is not None: #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socket self.socket.close() #将socket置空 self.socket = None if self._close_callback: self._run_callback(self._close_callback)
class IOLoop(object): def remove_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)
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！！！
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