werkzeug中服务器处理请求的实现
当成功建立好服务器后，接下来就是等待请求并处理请求通过路由分配给相应的视图函数了，以下是函数调用过程
-> self._handle_request_noblock()
/usr/lib/python2.7/SocketServer.py(295)_handle_request_noblock()
-> self.process_request(request, client_address)
/usr/lib/python2.7/SocketServer.py(321)process_request()
-> self.finish_request(request, client_address)
/usr/lib/python2.7/SocketServer.py(334)finish_request()
-> self.RequestHandlerClass(request, client_address, self)
/usr/lib/python2.7/SocketServer.py(649)__init__()
-> self.handle()
/home/steinliber/flask-source-code/env/local/lib/python2.7/site-packages/werkzeug/serving.py(217)handle()
-> rv = BaseHTTPRequestHandler.handle(self)
/usr/lib/python2.7/BaseHTTPServer.py(340)handle()
-> self.handle_one_request()
/home/steinliber/flask-source-code/env/local/lib/python2.7/site-packages/werkzeug/serving.py(252)handle_one_request()
-> return self.run_wsgi()
/home/steinliber/flask-source-code/env/local/lib/python2.7/site-packages/werkzeug/serving.py(194)run_wsgi()
-> execute(self.server.app)
/home/steinliber/flask-source-code/env/local/lib/python2.7/site-packages/werkzeug/serving.py(184)execute()
-> for data in application_iter:
/home/steinliber/flask-source-code/env/local/lib/python2.7/site-packages/werkzeug/debug/__init__.py(199)debug_application()
首先在刚建立的HTTPServer上会对发来的请求进行处理，得到请求的内容，headers，method等，并通过初始化HTTPBASERequestHandler将这些值都设为HTTPBASERequestHandler的属性。因为WSGIRequestHandler是继承HTTPBASERequestHandler的，所以他也可以使用这些属性来构建APP运行的environ。接着HTTPServer会调用handle方法，WSGIRequestHandler的源码如下
class WSGIRequestHandler(BaseHTTPRequestHandler, object): """A request handler that implements WSGI dispatching.""" @property def server_version(self): return 'Werkzeug/' + werkzeug.__version__ def make_environ(self): request_url = url_parse(self.path) def shutdown_server(): self.server.shutdown_signal = True url_scheme = self.server.ssl_context is None and 'http' or 'https' path_info = url_unquote(request_url.path) environ = { 'wsgi.version': (1, 0), 'wsgi.url_scheme': url_scheme, 'wsgi.input': self.rfile, 'wsgi.errors': sys.stderr, 'wsgi.multithread': self.server.multithread, 'wsgi.multiprocess': self.server.multiprocess, 'wsgi.run_once': False, 'werkzeug.server.shutdown': shutdown_server, 'SERVER_SOFTWARE': self.server_version, 'REQUEST_METHOD': self.command, 'SCRIPT_NAME': '', 'PATH_INFO': wsgi_encoding_dance(path_info), 'QUERY_STRING': wsgi_encoding_dance(request_url.query), 'CONTENT_TYPE': self.headers.get('Content-Type', ''), 'CONTENT_LENGTH': self.headers.get('Content-Length', ''), 'REMOTE_ADDR': self.client_address[0], 'REMOTE_PORT': self.client_address[1], 'SERVER_NAME': self.server.server_address[0], 'SERVER_PORT': str(self.server.server_address[1]), 'SERVER_PROTOCOL': self.request_version } for key, value in self.headers.items(): key = 'HTTP_' + key.upper().replace('-', '_') if key not in ('HTTP_CONTENT_TYPE', 'HTTP_CONTENT_LENGTH'): environ[key] = value if request_url.netloc: environ['HTTP_HOST'] = request_url.netloc return environ def run_wsgi(self): if self.headers.get('Expect', '').lower().strip() == '100-continue': self.wfile.write(b'HTTP/1.1 100 Continue\r\n\r\n') self.environ = environ = self.make_environ() headers_set = [] headers_sent = [] def write(data): assert headers_set, 'write() before start_response' if not headers_sent: status, response_headers = headers_sent[:] = headers_set try: code, msg = status.split(None, 1) except ValueError: code, msg = status, "" self.send_response(int(code), msg) header_keys = set() for key, value in response_headers: self.send_header(key, value) key = key.lower() header_keys.add(key) if 'content-length' not in header_keys: self.close_connection = True self.send_header('Connection', 'close') if 'server' not in header_keys: self.send_header('Server', self.version_string()) if 'date' not in header_keys: self.send_header('Date', self.date_time_string()) self.end_headers() assert isinstance(data, bytes), 'applications must write bytes' self.wfile.write(data) self.wfile.flush() def start_response(status, response_headers, exc_info=None): if exc_info: try: if headers_sent: reraise(*exc_info) finally: exc_info = None elif headers_set: raise AssertionError('Headers already set') headers_set[:] = [status, response_headers] return write def execute(app): application_iter = app(environ, start_response) try: for data in application_iter: write(data) if not headers_sent: write(b'') finally: if hasattr(application_iter, 'close'): application_iter.close() application_iter = None try: execute(self.server.app) except (socket.error, socket.timeout) as e: self.connection_dropped(e, environ) except Exception: if self.server.passthrough_errors: raise from werkzeug.debug.tbtools import get_current_traceback traceback = get_current_traceback(ignore_system_exceptions=True) try: # if we haven't yet sent the headers but they are set # we roll back to be able to set them again. if not headers_sent: del headers_set[:] execute(InternalServerError()) except Exception: pass self.server.log('error', 'Error on request:\n%s', traceback.plaintext) def handle(self): """Handles a request ignoring dropped connections.""" rv = None try: rv = BaseHTTPRequestHandler.handle(self) except (socket.error, socket.timeout) as e: self.connection_dropped(e) except Exception: if self.server.ssl_context is None or not is_ssl_error(): raise if self.server.shutdown_signal: self.initiate_shutdown() return rv def initiate_shutdown(self): """A horrible, horrible way to kill the server for Python 2.6 and later. It's the best we can do. """ # Windows does not provide SIGKILL, go with SIGTERM then. sig = getattr(signal, 'SIGKILL', signal.SIGTERM) # reloader active if os.environ.get('WERKZEUG_RUN_MAIN') == 'true': os.kill(os.getpid(), sig) # python 2.7 self.server._BaseServer__shutdown_request = True # python 2.6 self.server._BaseServer__serving = False def connection_dropped(self, error, environ=None): """Called if the connection was closed by the client. By default nothing happens. """ def handle_one_request(self): """Handle a single HTTP request.""" self.raw_requestline = self.rfile.readline() if not self.raw_requestline: self.close_connection = 1 elif self.parse_request(): return self.run_wsgi() def send_response(self, code, message=None): """Send the response header and log the response code.""" self.log_request(code) if message is None: message = code in self.responses and self.responses[code][0] or '' if self.request_version != 'HTTP/0.9': hdr = "%s %d %s\r\n" % (self.protocol_version, code, message) self.wfile.write(hdr.encode('ascii')) def version_string(self): return BaseHTTPRequestHandler.version_string(self).strip() def address_string(self): return self.environ['REMOTE_ADDR'] def log_request(self, code='-', size='-'): self.log('info', '"%s" %s %s', self.requestline, code, size) def log_error(self, *args): self.log('error', *args) def log_message(self, format, *args): self.log('info', format, *args) def log(self, type, message, *args): _log(type, '%s - - [%s] %s\n' % (self.address_string(), self.log_date_time_string(), message % args))
在其中的handle方法会包装了BASERequestHandler的handle方法，如果socket出现错误或超时，它会继续尝试链接，initiate_shutdown是当收到关闭信号时，将服务器强制关闭，这个handle方法在官方文档描述会返回handle_one_request方法，他得到一个HTTP请求，并调用run_wsgi方法进行处理，在run_wsgi中，先将先前设为类属性的Request环境变量储存在environ字典中。这是WSGI的规范，服务器要向app提供environ和start_response两个参数，start_response方法会设置status和reponse_headers，具体可看PEP333规范。然后，会尝试运行excute，如果发生了除socket.error或socket.timeout之外的错误，在debug模式下会返回调试页面。
再接下来的excute函数中，他调用APP并传递environ和start_response两个参数，根据WSGI规范，它应该得到可迭代的对象，然后就调用write将这些数据写出去。在write方法中，他会首先确定start_response先被调用，首先若还没有发送headers，会先将headers_set中的status以及response_header发送出去，之后再将得到的数据发送出去，这样，服务器端的任务基本就完成了。
