当我们用Flask写好一个app后, 运行app.run()表示监听指定的端口, 对收到的request运行app生成response并返回. 现在分析一下, 运行app.run()后具体发生了什么事情
Flask定义的run方法如下:
def run(self, host=None, port=None, debug=None, **options): """
.........
""" from werkzeug.serving import run_simple if host is None: host = '127.0.0.1' if port is None: server_name = self.config['SERVER_NAME'] if server_name and ':' in server_name: port = int(server_name.rsplit(':', 1)[1]) else: port = 5000 if debug is not None: self.debug = bool(debug) options.setdefault('use_reloader', self.debug) options.setdefault('use_debugger', self.debug) try: run_simple(host, port, self, **options) finally: # reset the first request information if the development server # reset normally. This makes it possible to restart the server # without reloader and that stuff from an interactive shell. self._got_first_request = False
在上面的源码中, from werkzeug.serving import run_simple引入run_simple函数, 该函数将定义好的app在指定的host, port上运行，run_simple函数如下：
def run_simple( hostname, port, application, use_reloader=False, use_debugger=False, use_evalex=True, extra_files=None, reloader_interval=1, reloader_type="auto", threaded=False, processes=1, request_handler=None, static_files=None, passthrough_errors=False, ssl_context=None, ): """ ..................... """def inner(): try: fd = int(os.environ["WERKZEUG_SERVER_FD"]) except (LookupError, ValueError): fd = None srv = make_server( hostname, port, application, threaded, processes, request_handler, passthrough_errors, ssl_context, fd=fd, )#第二步
if fd is None: log_startup(srv.socket) srv.serve_forever() #第三步
if use_reloader: # If we're not running already in the subprocess that is the # reloader we want to open up a socket early to make sure the # port is actually available. if not is_running_from_reloader(): if port == 0 and not can_open_by_fd: raise ValueError( "Cannot bind to a random port with enabled " "reloader if the Python interpreter does " "not support socket opening by fd." ) # Create and destroy a socket so that any exceptions are # raised before we spawn a separate Python interpreter and # lose this ability. address_family = select_address_family(hostname, port) server_address = get_sockaddr(hostname, port, address_family) s = socket.socket(address_family, socket.SOCK_STREAM) s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) s.bind(server_address) if hasattr(s, "set_inheritable"): s.set_inheritable(True) # If we can open the socket by file descriptor, then we can just # reuse this one and our socket will survive the restarts. if can_open_by_fd: os.environ["WERKZEUG_SERVER_FD"] = str(s.fileno()) s.listen(LISTEN_QUEUE) log_startup(s) else: s.close() if address_family == af_unix: _log("info", "Unlinking %s" % server_address) os.unlink(server_address) # Do not use relative imports, otherwise "python -m werkzeug.serving" # breaks. from ._reloader import run_with_reloader run_with_reloader(inner, extra_files, reloader_interval, reloader_type) else: inner() # 第一步
run_simple函数一般情况下调用内部定义的inner函数. inner调用make_server创建server实例srv, 然后调用srv.serve_forever.
make_server函数如下:
make_server函数返回BaseWSGIServer实例
def make_server( host=None, port=None, app=None, threaded=False, processes=1, request_handler=None, passthrough_errors=False, ssl_context=None, fd=None, ): """Create a new server instance that is either threaded, or forks or just processes one request after another. """ if threaded and processes > 1: raise ValueError("cannot have a multithreaded and multi process server.") elif threaded: return ThreadedWSGIServer( host, port, app, request_handler, passthrough_errors, ssl_context, fd=fd ) elif processes > 1: return ForkingWSGIServer( host, port, app, processes, request_handler, passthrough_errors, ssl_context, fd=fd, ) else: return BaseWSGIServer( host, port, app, request_handler, passthrough_errors, ssl_context, fd=fd )
BaseWSGIServer类
class BaseWSGIServer(HTTPServer, object): """Simple single-threaded, single-process WSGI server.""" multithread = False multiprocess = False request_queue_size = LISTEN_QUEUE def __init__( self, host, port, app, handler=None, passthrough_errors=False, ssl_context=None, fd=None, ): if handler is None: handler = WSGIRequestHandler #第一步 指定BaseServer中的RequestHandlerClass作为处理请求的handler self.address_family = select_address_family(host, port) if fd is not None: real_sock = socket.fromfd(fd, self.address_family, socket.SOCK_STREAM) port = 0 server_address = get_sockaddr(host, int(port), self.address_family) # remove socket file if it already exists if self.address_family == af_unix and os.path.exists(server_address): os.unlink(server_address) HTTPServer.__init__(self, server_address, handler)#第二步 初始化生成HTTPServer实例 self.app = app self.passthrough_errors = passthrough_errors self.shutdown_signal = False self.host = host self.port = self.socket.getsockname()[1] # Patch in the original socket. if fd is not None: self.socket.close() self.socket = real_sock self.server_address = self.socket.getsockname() if ssl_context is not None: if isinstance(ssl_context, tuple): ssl_context = load_ssl_context(*ssl_context) if ssl_context == "adhoc": ssl_context = generate_adhoc_ssl_context() # If we are on Python 2 the return value from socket.fromfd # is an internal socket object but what we need for ssl wrap # is the wrapper around it :( sock = self.socket if PY2 and not isinstance(sock, socket.socket): sock = socket.socket(sock.family, sock.type, sock.proto, sock) self.socket = ssl_context.wrap_socket(sock, server_side=True) self.ssl_context = ssl_context else: self.ssl_context = None def log(self, type, message, *args): _log(type, message, *args) def serve_forever(self):#第三步 self.shutdown_signal = False try: HTTPServer.serve_forever(self)#第四步调用serve_forever
except KeyboardInterrupt: pass finally: self.server_close()
BaseWSGIServer 类中，指定BaseServer中的RequestHandlerClass作为处理请求的handler
HTTPServer初始化，初始化过程中传入handler（WSGIRequestHandler）
然后 在BaseWSGIServer 的 serve_forever方法中，HTTPServer调用serve_forever方法。
因为HTTPServer为BaseServer子类，HTTPServer调用BaseServer的server_forever方法
BaseServer类 server_forever方法如下
class BaseServer: """
.......
""" timeout = None
def __init__(self, server_address, RequestHandlerClass):
"""Constructor. May be extended, do not override."""
self.server_address = server_address
self.RequestHandlerClass = RequestHandlerClass
self.__is_shut_down = threading.Event()
self.__shutdown_request = False
def serve_forever(self, poll_interval=0.5): """Handle one request at a time until shutdown. Polls for shutdown every poll_interval seconds. Ignores self.timeout. If you need to do periodic tasks, do them in another thread. """ self.__is_shut_down.clear() try: # XXX: Consider using another file descriptor or connecting to the # socket to wake this up instead of polling. Polling reduces our # responsiveness to a shutdown request and wastes cpu at all other # times. with _ServerSelector() as selector: selector.register(self, selectors.EVENT_READ) while not self.__shutdown_request: ready = selector.select(poll_interval) # bpo-35017: shutdown() called during select(), exit immediately. if self.__shutdown_request: break if ready: self._handle_request_noblock()#第一步 self.service_actions() finally: self.__shutdown_request = False self.__is_shut_down.set() def _handle_request_noblock(self): """Handle one request, without blocking. I assume that selector.select() has returned that the socket is readable before this function was called, so there should be no risk of blocking in get_request(). """ try: request, client_address = self.get_request() except OSError: return if self.verify_request(request, client_address): try: self.process_request(request, client_address)#第二步 except Exception: self.handle_error(request, client_address) self.shutdown_request(request) except: self.shutdown_request(request) raise else: self.shutdown_request(request) def process_request(self, request, client_address): """Call finish_request. Overridden by ForkingMixIn and ThreadingMixIn. """ self.finish_request(request, client_address)#第三步 self.shutdown_request(request) def finish_request(self, request, client_address): """Finish one request by instantiating RequestHandlerClass.""" self.RequestHandlerClass(request, client_address, self)#第四步WSGIRequestHandler实例化
server_forever方法中调用 _handle_request_noblock处理请求，由上述代码，最后finish_request 方法处理请求，finish_request 方法中 将WSGIRequestHandler实例化，来处理request
(self.RequestHandlerClass就是WSGIRequestHandler)
接下来 解析RequestHandlerClass,由上代码可知RequestHandlerClass即WSGIRequestHandler
WSGIRequestHandler类 WSGIRequestHandler实例化时调用了其父类BaseRequestHandler的__init__方法
WSGIRequestHandler是BaseHTTPRequestHandler子类，BaseHTTPRequestHandler是socketserver.StreamRequestHandler子类
StreamRequestHandler是BaseRequestHandler的子类
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), 'REMOTE_ADDR': self.address_string(), 'REMOTE_PORT': self.port_integer(), '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 = key.upper().replace('-', '_') if key not in ('CONTENT_TYPE', 'CONTENT_LENGTH'): key = 'HTTP_' + key environ[key] = value if environ.get('HTTP_TRANSFER_ENCODING', '').strip().lower() == 'chunked': environ['wsgi.input_terminated'] = True environ['wsgi.input'] = DechunkedInput(environ['wsgi.input']) if request_url.scheme and 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 ') 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, "" code = int(code) self.send_response(code, msg) header_keys = set() for key, value in response_headers: self.send_header(key, value) key = key.lower() header_keys.add(key) if not ('content-length' in header_keys or environ['REQUEST_METHOD'] == 'HEAD' or code < 200 or code in (204, 304)): 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)# Flask 的__call__方法被调用 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: %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()
/usr/lib/python3.7/http/server.py
class BaseHTTPRequestHandler(socketserver.StreamRequestHandler): """
......
""" # The Python system version, truncated to its first component. sys_version = "Python/" + sys.version.split()[0] # The server software version. You may want to override this. # The format is multiple whitespace-separated strings, # where each string is of the form name[/version]. server_version = "BaseHTTP/" + __version__ error_message_format = DEFAULT_ERROR_MESSAGE error_content_type = DEFAULT_ERROR_CONTENT_TYPE # The default request version. This only affects responses up until # the point where the request line is parsed, so it mainly decides what # the client gets back when sending a malformed request line. # Most web servers default to HTTP 0.9, i.e. don't send a status line. default_request_version = "HTTP/0.9" def handle_one_request(self): """Handle a single HTTP request. You normally don't need to override this method; see the class __doc__ string for information on how to handle specific HTTP commands such as GET and POST. """ try: self.raw_requestline = self.rfile.readline(65537) if len(self.raw_requestline) > 65536: self.requestline = '' self.request_version = '' self.command = '' self.send_error(HTTPStatus.REQUEST_URI_TOO_LONG) return if not self.raw_requestline: self.close_connection = True return if not self.parse_request(): # An error code has been sent, just exit return mname = 'do_' + self.command if not hasattr(self, mname): self.send_error( HTTPStatus.NOT_IMPLEMENTED, "Unsupported method (%r)" % self.command) return method = getattr(self, mname) method() self.wfile.flush() #actually send the response if not already done. except socket.timeout as e: #a read or a write timed out. Discard this connection self.log_error("Request timed out: %r", e) self.close_connection = True return def handle(self): """Handle multiple requests if necessary.""" self.close_connection = True self.handle_one_request() while not self.close_connection: self.handle_one_request()
/usr/lib/python3.7/socketserver.py
class StreamRequestHandler(BaseRequestHandler):
rbufsize = -1
wbufsize = 0
# A timeout to apply to the request socket, if not None.
timeout = None
# Disable nagle algorithm for this socket, if True.
# Use only when wbufsize != 0, to avoid small packets.
disable_nagle_algorithm = False
"....."
def finish(self):
if not self.wfile.closed:
try:
self.wfile.flush()
except socket.error:
# A final socket error may have occurred here, such as
# the local error ECONNABORTED.
pass
self.wfile.close()
self.rfile.close()
/usr/lib/python3.7/socketserver.py
class BaseRequestHandler: """Base class for request handler classes. This class is instantiated for each request to be handled. The constructor sets the instance variables request, client_address and server, and then calls the handle() method. To implement a specific service, all you need to do is to derive a class which defines a handle() method. The handle() method can find the request as self.request, the client address as self.client_address, and the server (in case it needs access to per-server information) as self.server. Since a separate instance is created for each request, the handle() method can define other arbitrary instance variables. """ def __init__(self, request, client_address, server): self.request = request self.client_address = client_address self.server = server self.setup() try: self.handle()
finally: self.finish()
当WSGIRequestHandler初始化时，先调用了BaseRequestHandler的 __init__方法中的handle方法，根据继承性质，此时应该调用WSGIRequestHandler的handle() 方法，来处理。