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"""Generic socket server classes.This module tries to capture the various aspects of defining a server:For socket-based servers:- address family: - AF_INET{,6}: IP (Internet Protocol) sockets (default) - AF_UNIX: Unix domain sockets - others, e.g. AF_DECNET are conceivable (see - socket type: - SOCK_STREAM (reliable stream, e.g. TCP) - SOCK_DGRAM (datagrams, e.g. UDP)For request-based servers (including socket-based):- client address verification before further looking at the request (This is actually a hook for any processing that needs to look at the request before anything else, e.g. logging)- how to handle multiple requests: - synchronous (one request is handled at a time) - forking (each request is handled by a new process) - threading (each request is handled by a new thread)The classes in this module favor the server type that is simplest towrite: a synchronous TCP/IP server. This is bad class design, butsave some typing. (There's also the issue that a deep class hierarchyslows down method lookups.)There are five classes in an inheritance diagram, four of which representsynchronous servers of four types: +------------+ | BaseServer | +------------+ | v +-----------+ +------------------+ | TCPServer |------->| UnixStreamServer | +-----------+ +------------------+ | v +-----------+ +--------------------+ | UDPServer |------->| UnixDatagramServer | +-----------+ +--------------------+Note that UnixDatagramServer derives from UDPServer, not fromUnixStreamServer -- the only difference between an IP and a Unixstream server is the address family, which is simply repeated in bothunix server classes.Forking and threading versions of each type of server can be createdusing the ForkingMixIn and ThreadingMixIn mix-in classes. Forinstance, a threading UDP server class is created as follows: class ThreadingUDPServer(ThreadingMixIn, UDPServer): passThe Mix-in class must come first, since it overrides a method definedin UDPServer! Setting the various member variables also changesthe behavior of the underlying server mechanism.To implement a service, you must derive a class fromBaseRequestHandler and redefine its handle() method. You can then runvarious versions of the service by combining one of the server classeswith your request handler class.The request handler class must be different for datagram or streamservices. This can be hidden by using the request handlersubclasses StreamRequestHandler or DatagramRequestHandler.Of course, you still have to use your head!For instance, it makes no sense to use a forking server if the servicecontains state in memory that can be modified by requests (since themodifications in the child process would never reach the initial statekept in the parent process and passed to each child). In this case,you can use a threading server, but you will probably have to uselocks to avoid two requests that come in nearly simultaneous to applyconflicting changes to the server state.On the other hand, if you are building e.g. an HTTP server, where alldata is stored externally (e.g. in the file system), a synchronousclass will essentially render the service "deaf" while one request isbeing handled -- which may be for a very long time if a client is slowto read all the data it has requested. Here a threading or forkingserver is appropriate.In some cases, it may be appropriate to process part of a requestsynchronously, but to finish processing in a forked child depending onthe request data. This can be implemented by using a synchronousserver and doing an explicit fork in the request handler classhandle() method.Another approach to handling multiple simultaneous requests in anenvironment that supports neither threads nor fork (or where these aretoo expensive or inappropriate for the service) is to maintain anexplicit table of partially finished requests and to use select() todecide which request to work on next (or whether to handle a newincoming request). This is particularly important for stream serviceswhere each client can potentially be connected for a long time (ifthreads or subprocesses cannot be used).Future work:- Standard classes for Sun RPC (which uses either UDP or TCP)- Standard mix-in classes to implement various authentication and encryption schemes- Standard framework for select-based multiplexingXXX Open problems:- What to do with out-of-band data?BaseServer:- split generic "request" functionality out into BaseServer class. Copyright (C) 2000 Luke Kenneth Casson Leighton example: read entries from a SQL database (requires overriding get_request() to return a table entry from the database). entry is processed by a RequestHandlerClass."""# Author of the BaseServer patch: Luke Kenneth Casson Leighton# XXX Warning!# There is a test suite for this module, but it cannot be run by the# standard regression test.# To run it manually, run Lib/test/test_socketserver.py.__version__ = "0.4"import socketimport selectimport sysimport osimport errnotry: import threadingexcept ImportError: import dummy_threading as threading__all__ = ["TCPServer","UDPServer","ForkingUDPServer","ForkingTCPServer", "ThreadingUDPServer","ThreadingTCPServer","BaseRequestHandler", "StreamRequestHandler","DatagramRequestHandler", "ThreadingMixIn", "ForkingMixIn"]if hasattr(socket, "AF_UNIX"): __all__.extend(["UnixStreamServer","UnixDatagramServer", "ThreadingUnixStreamServer", "ThreadingUnixDatagramServer"])def _eintr_retry(func, *args): """restart a system call interrupted by EINTR""" while True: try: return func(*args) except (OSError, select.error) as e: if e.args[0] != errno.EINTR: raiseclass BaseServer: """Base class for server classes. Methods for the caller: - __init__(server_address, RequestHandlerClass) - serve_forever(poll_interval=0.5) - shutdown() - handle_request() # if you do not use serve_forever() - fileno() -> int # for select() Methods that may be overridden: - server_bind() - server_activate() - get_request() -> request, client_address - handle_timeout() - verify_request(request, client_address) - server_close() - process_request(request, client_address) - shutdown_request(request) - close_request(request) - handle_error() Methods for derived classes: - finish_request(request, client_address) Class variables that may be overridden by derived classes or instances: - timeout - address_family - socket_type - allow_reuse_address Instance variables: - RequestHandlerClass - socket """ 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 server_activate(self): """Called by constructor to activate the server. May be overridden. """ pass 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: while not self.__shutdown_request: # 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. r, w, e = _eintr_retry(select.select, [self], [], [], poll_interval) if self in r: self._handle_request_noblock() finally: self.__shutdown_request = False self.__is_shut_down.set() def shutdown(self): """Stops the serve_forever loop. Blocks until the loop has finished. This must be called while serve_forever() is running in another thread, or it will deadlock. """ self.__shutdown_request = True self.__is_shut_down.wait() # The distinction between handling, getting, processing and # finishing a request is fairly arbitrary. Remember: # # - handle_request() is the top-level call. It calls # select, get_request(), verify_request() and process_request() # - get_request() is different for stream or datagram sockets # - process_request() is the place that may fork a new process # or create a new thread to finish the request # - finish_request() instantiates the request handler class; # this constructor will handle the request all by itself def handle_request(self): """Handle one request, possibly blocking. Respects self.timeout. """ # Support people who used socket.settimeout() to escape # handle_request before self.timeout was available. timeout = self.socket.gettimeout() if timeout is None: timeout = self.timeout elif self.timeout is not None: timeout = min(timeout, self.timeout) fd_sets = _eintr_retry(select.select, [self], [], [], timeout) if not fd_sets[0]: self.handle_timeout() return self._handle_request_noblock() def _handle_request_noblock(self): """Handle one request, without blocking. I assume that select.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 socket.error: return if self.verify_request(request, client_address): try: self.process_request(request, client_address) except: self.handle_error(request, client_address) self.shutdown_request(request) def handle_timeout(self): """Called if no new request arrives within self.timeout. Overridden by ForkingMixIn. """ pass def verify_request(self, request, client_address): """Verify the request. May be overridden. Return True if we should proceed with this request. """ return True def process_request(self, request, client_address): """Call finish_request. Overridden by ForkingMixIn and ThreadingMixIn. """ self.finish_request(request, client_address) self.shutdown_request(request) def server_close(self): """Called to clean-up the server. May be overridden. """ pass def finish_request(self, request, client_address): """Finish one request by instantiating RequestHandlerClass.""" self.RequestHandlerClass(request, client_address, self) def shutdown_request(self, request): """Called to shutdown and close an individual request.""" self.close_request(request) def close_request(self, request): """Called to clean up an individual request.""" pass def handle_error(self, request, client_address): """Handle an error gracefully. May be overridden. The default is to print a traceback and continue. """ print '-'*40 print 'Exception happened during processing of request from', print client_address import traceback traceback.print_exc() # XXX But this goes to stderr! print '-'*40class TCPServer(BaseServer): """Base class for various socket-based server classes. Defaults to synchronous IP stream (i.e., TCP). Methods for the caller: - __init__(server_address, RequestHandlerClass, bind_and_activate=True) - serve_forever(poll_interval=0.5) - shutdown() - handle_request() # if you don't use serve_forever() - fileno() -> int # for select() Methods that may be overridden: - server_bind() - server_activate() - get_request() -> request, client_address - handle_timeout() - verify_request(request, client_address) - process_request(request, client_address) - shutdown_request(request) - close_request(request) - handle_error() Methods for derived classes: - finish_request(request, client_address) Class variables that may be overridden by derived classes or instances: - timeout - address_family - socket_type - request_queue_size (only for stream sockets) - allow_reuse_address Instance variables: - server_address - RequestHandlerClass - socket """ address_family = socket.AF_INET socket_type = socket.SOCK_STREAM request_queue_size = 5 allow_reuse_address = False def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True): """Constructor. May be extended, do not override.""" BaseServer.__init__(self, server_address, RequestHandlerClass) self.socket = socket.socket(self.address_family, self.socket_type) if bind_and_activate: try: self.server_bind() self.server_activate() except: self.server_close() raise def server_bind(self): """Called by constructor to bind the socket. May be overridden. """ if self.allow_reuse_address: self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) self.socket.bind(self.server_address) self.server_address = self.socket.getsockname() def server_activate(self): """Called by constructor to activate the server. May be overridden. """ self.socket.listen(self.request_queue_size) def server_close(self): """Called to clean-up the server. May be overridden. """ self.socket.close() def fileno(self): """Return socket file number. Interface required by select(). """ return self.socket.fileno() def get_request(self): """Get the request and client address from the socket. May be overridden. """ return self.socket.accept() def shutdown_request(self, request): """Called to shutdown and close an individual request.""" try: #explicitly shutdown. socket.close() merely releases #the socket and waits for GC to perform the actual close. request.shutdown(socket.SHUT_WR) except socket.error: pass #some platforms may raise ENOTCONN here self.close_request(request) def close_request(self, request): """Called to clean up an individual request.""" request.close()class UDPServer(TCPServer): """UDP server class.""" allow_reuse_address = False socket_type = socket.SOCK_DGRAM max_packet_size = 8192 def get_request(self): data, client_addr = self.socket.recvfrom(self.max_packet_size) return (data, self.socket), client_addr def server_activate(self): # No need to call listen() for UDP. pass def shutdown_request(self, request): # No need to shutdown anything. self.close_request(request) def close_request(self, request): # No need to close anything. passclass ForkingMixIn: """Mix-in class to handle each request in a new process.""" timeout = 300 active_children = None max_children = 40 def collect_children(self): """Internal routine to wait for children that have exited.""" if self.active_children is None: return # If we're above the max number of children, wait and reap them until # we go back below threshold. Note that we use waitpid(-1) below to be # able to collect children in size( ) syscalls instead # of size( ): the downside is that this might reap children # which we didn't spawn, which is why we only resort to this when we're # above max_children. while len(self.active_children) >= self.max_children: try: pid, _ = os.waitpid(-1, 0) self.active_children.discard(pid) except OSError as e: if e.errno == errno.ECHILD: # we don't have any children, we're done self.active_children.clear() elif e.errno != errno.EINTR: break # Now reap all defunct children. for pid in self.active_children.copy(): try: pid, _ = os.waitpid(pid, os.WNOHANG) # if the child hasn't exited yet, pid will be 0 and ignored by # discard() below self.active_children.discard(pid) except OSError as e: if e.errno == errno.ECHILD: # someone else reaped it self.active_children.discard(pid) def handle_timeout(self): """Wait for zombies after self.timeout seconds of inactivity. May be extended, do not override. """ self.collect_children() def process_request(self, request, client_address): """Fork a new subprocess to process the request.""" self.collect_children() pid = os.fork() if pid: # Parent process if self.active_children is None: self.active_children = set() self.active_children.add(pid) self.close_request(request) #close handle in parent process return else: # Child process. # This must never return, hence os._exit()! try: self.finish_request(request, client_address) self.shutdown_request(request) os._exit(0) except: try: self.handle_error(request, client_address) self.shutdown_request(request) finally: os._exit(1)class ThreadingMixIn: """Mix-in class to handle each request in a new thread.""" # Decides how threads will act upon termination of the # main process daemon_threads = False def process_request_thread(self, request, client_address): """Same as in BaseServer but as a thread. In addition, exception handling is done here. """ try: self.finish_request(request, client_address) self.shutdown_request(request) except: self.handle_error(request, client_address) self.shutdown_request(request) def process_request(self, request, client_address): """Start a new thread to process the request.""" t = threading.Thread(target = self.process_request_thread, args = (request, client_address)) t.daemon = self.daemon_threads t.start()class ForkingUDPServer(ForkingMixIn, UDPServer): passclass ForkingTCPServer(ForkingMixIn, TCPServer): passclass ThreadingUDPServer(ThreadingMixIn, UDPServer): passclass ThreadingTCPServer(ThreadingMixIn, TCPServer): passif hasattr(socket, 'AF_UNIX'): class UnixStreamServer(TCPServer): address_family = socket.AF_UNIX class UnixDatagramServer(UDPServer): address_family = socket.AF_UNIX class ThreadingUnixStreamServer(ThreadingMixIn, UnixStreamServer): pass class ThreadingUnixDatagramServer(ThreadingMixIn, UnixDatagramServer): passclass 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 arbitrary other instance variariables. """ 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() def setup(self): pass def handle(self): pass def finish(self): pass# The following two classes make it possible to use the same service# class for stream or datagram servers.# Each class sets up these instance variables:# - rfile: a file object from which receives the request is read# - wfile: a file object to which the reply is written# When the handle() method returns, wfile is flushed properlyclass StreamRequestHandler(BaseRequestHandler): """Define self.rfile and self.wfile for stream sockets.""" # Default buffer sizes for rfile, wfile. # We default rfile to buffered because otherwise it could be # really slow for large data (a getc() call per byte); we make # wfile unbuffered because (a) often after a write() we want to # read and we need to flush the line; (b) big writes to unbuffered # files are typically optimized by stdio even when big reads # aren't. 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 setup(self): self.connection = self.request if self.timeout is not None: self.connection.settimeout(self.timeout) if self.disable_nagle_algorithm: self.connection.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, True) self.rfile = self.connection.makefile('rb', self.rbufsize) self.wfile = self.connection.makefile('wb', self.wbufsize) def finish(self): if not self.wfile.closed: try: self.wfile.flush() except socket.error: # An final socket error may have occurred here, such as # the local error ECONNABORTED. pass self.wfile.close() self.rfile.close()class DatagramRequestHandler(BaseRequestHandler): # XXX Regrettably, I cannot get this working on Linux; # s.recvfrom() doesn't return a meaningful client address. """Define self.rfile and self.wfile for datagram sockets.""" def setup(self): try: from cStringIO import StringIO except ImportError: from StringIO import StringIO self.packet, self.socket = self.request self.rfile = StringIO(self.packet) self.wfile = StringIO() def finish(self): self.socket.sendto(self.wfile.getvalue(), self.client_address)