1 """Generic socket server classes.

     2 

     3 This module tries to capture the various aspects of defining a server:

     4 

     5 For socket-based servers:

     6 

     7 - address family:

     8         - AF_INET{,6}: IP (Internet Protocol) sockets (default)

     9         - AF_UNIX: Unix domain sockets

    10         - others, e.g. AF_DECNET are conceivable (see <socket.h>

    11 - socket type:

    12         - SOCK_STREAM (reliable stream, e.g. TCP)

    13         - SOCK_DGRAM (datagrams, e.g. UDP)

    14 

    15 For request-based servers (including socket-based):

    16 

    17 - client address verification before further looking at the request

    18         (This is actually a hook for any processing that needs to look

    19          at the request before anything else, e.g. logging)

    20 - how to handle multiple requests:

    21         - synchronous (one request is handled at a time)

    22         - forking (each request is handled by a new process)

    23         - threading (each request is handled by a new thread)

    24 

    25 The classes in this module favor the server type that is simplest to

    26 write: a synchronous TCP/IP server.  This is bad class design, but

    27 save some typing.  (There's also the issue that a deep class hierarchy

    28 slows down method lookups.)

    29 

    30 There are five classes in an inheritance diagram, four of which represent

    31 synchronous servers of four types:

    32 

    33         +------------+

    34         | BaseServer |

    35         +------------+

    36               |

    37               v

    38         +-----------+        +------------------+

    39         | TCPServer |------->| UnixStreamServer |

    40         +-----------+        +------------------+

    41               |

    42               v

    43         +-----------+        +--------------------+

    44         | UDPServer |------->| UnixDatagramServer |

    45         +-----------+        +--------------------+

    46 

    47 Note that UnixDatagramServer derives from UDPServer, not from

    48 UnixStreamServer -- the only difference between an IP and a Unix

    49 stream server is the address family, which is simply repeated in both

    50 unix server classes.

    51 

    52 Forking and threading versions of each type of server can be created

    53 using the ForkingMixIn and ThreadingMixIn mix-in classes.  For

    54 instance, a threading UDP server class is created as follows:

    55 

    56         class ThreadingUDPServer(ThreadingMixIn, UDPServer): pass

    57 

    58 The Mix-in class must come first, since it overrides a method defined

    59 in UDPServer! Setting the various member variables also changes

    60 the behavior of the underlying server mechanism.

    61 

    62 To implement a service, you must derive a class from

    63 BaseRequestHandler and redefine its handle() method.  You can then run

    64 various versions of the service by combining one of the server classes

    65 with your request handler class.

    66 

    67 The request handler class must be different for datagram or stream

    68 services.  This can be hidden by using the request handler

    69 subclasses StreamRequestHandler or DatagramRequestHandler.

    70 

    71 Of course, you still have to use your head!

    72 

    73 For instance, it makes no sense to use a forking server if the service

    74 contains state in memory that can be modified by requests (since the

    75 modifications in the child process would never reach the initial state

    76 kept in the parent process and passed to each child).  In this case,

    77 you can use a threading server, but you will probably have to use

    78 locks to avoid two requests that come in nearly simultaneous to apply

    79 conflicting changes to the server state.

    80 

    81 On the other hand, if you are building e.g. an HTTP server, where all

    82 data is stored externally (e.g. in the file system), a synchronous

    83 class will essentially render the service "deaf" while one request is

    84 being handled -- which may be for a very long time if a client is slow

    85 to reqd all the data it has requested.  Here a threading or forking

    86 server is appropriate.

    87 

    88 In some cases, it may be appropriate to process part of a request

    89 synchronously, but to finish processing in a forked child depending on

    90 the request data.  This can be implemented by using a synchronous

    91 server and doing an explicit fork in the request handler class

    92 handle() method.

    93 

    94 Another approach to handling multiple simultaneous requests in an

    95 environment that supports neither threads nor fork (or where these are

    96 too expensive or inappropriate for the service) is to maintain an

    97 explicit table of partially finished requests and to use select() to

    98 decide which request to work on next (or whether to handle a new

    99 incoming request).  This is particularly important for stream services

   100 where each client can potentially be connected for a long time (if

   101 threads or subprocesses cannot be used).

   102 

   103 Future work:

   104 - Standard classes for Sun RPC (which uses either UDP or TCP)

   105 - Standard mix-in classes to implement various authentication

   106   and encryption schemes

   107 - Standard framework for select-based multiplexing

   108 

   109 XXX Open problems:

   110 - What to do with out-of-band data?

   111 

   112 BaseServer:

   113 - split generic "request" functionality out into BaseServer class.

   114   Copyright (C) 2000  Luke Kenneth Casson Leighton <lkcl@samba.org>

   115 

   116   example: read entries from a SQL database (requires overriding

   117   get_request() to return a table entry from the database).

   118   entry is processed by a RequestHandlerClass.

   119 

   120 """

   121 

   122 # Author of the BaseServer patch: Luke Kenneth Casson Leighton

   123 

   124 # XXX Warning!

   125 # There is a test suite for this module, but it cannot be run by the

   126 # standard regression test.

   127 # To run it manually, run Lib/test/test_socketserver.py.

   128 

   129 __version__ = "0.4"

   130 

   131 

   132 import socket

   133 import select

   134 import sys

   135 import os

   136 try:

   137     import threading

   138 except ImportError:

   139     import dummy_threading as threading

   140 

   141 __all__ = ["TCPServer","UDPServer","ForkingUDPServer","ForkingTCPServer",

   142            "ThreadingUDPServer","ThreadingTCPServer","BaseRequestHandler",

   143            "StreamRequestHandler","DatagramRequestHandler",

   144            "ThreadingMixIn", "ForkingMixIn"]

   145 if hasattr(socket, "AF_UNIX"):

   146     __all__.extend(["UnixStreamServer","UnixDatagramServer",

   147                     "ThreadingUnixStreamServer",

   148                     "ThreadingUnixDatagramServer"])

   149 

   150 class BaseServer:

   151 

   152     """Base class for server classes.

   153 

   154     Methods for the caller:

   155 

   156     - __init__(server_address, RequestHandlerClass)

   157     - serve_forever(poll_interval=0.5)

   158     - shutdown()

   159     - handle_request()  # if you do not use serve_forever()

   160     - fileno() -> int   # for select()

   161 

   162     Methods that may be overridden:

   163 

   164     - server_bind()

   165     - server_activate()

   166     - get_request() -> request, client_address

   167     - handle_timeout()

   168     - verify_request(request, client_address)

   169     - server_close()

   170     - process_request(request, client_address)

   171     - close_request(request)

   172     - handle_error()

   173 

   174     Methods for derived classes:

   175 

   176     - finish_request(request, client_address)

   177 

   178     Class variables that may be overridden by derived classes or

   179     instances:

   180 

   181     - timeout

   182     - address_family

   183     - socket_type

   184     - allow_reuse_address

   185 

   186     Instance variables:

   187 

   188     - RequestHandlerClass

   189     - socket

   190 

   191     """

   192 

   193     timeout = None

   194 

   195     def __init__(self, server_address, RequestHandlerClass):

   196         """Constructor.  May be extended, do not override."""

   197         self.server_address = server_address

   198         self.RequestHandlerClass = RequestHandlerClass

   199         self.__is_shut_down = threading.Event()

   200         self.__serving = False

   201 

   202     def server_activate(self):

   203         """Called by constructor to activate the server.

   204 

   205         May be overridden.

   206 

   207         """

   208         pass

   209 

   210     def serve_forever(self, poll_interval=0.5):

   211         """Handle one request at a time until shutdown.

   212 

   213         Polls for shutdown every poll_interval seconds. Ignores

   214         self.timeout. If you need to do periodic tasks, do them in

   215         another thread.

   216         """

   217         self.__serving = True

   218         self.__is_shut_down.clear()

   219         while self.__serving:

   220             # XXX: Consider using another file descriptor or

   221             # connecting to the socket to wake this up instead of

   222             # polling. Polling reduces our responsiveness to a

   223             # shutdown request and wastes cpu at all other times.

   224             r, w, e = select.select([self], [], [], poll_interval)

   225             if r:

   226                 self._handle_request_noblock()

   227         self.__is_shut_down.set()

   228 

   229     def shutdown(self):

   230         """Stops the serve_forever loop.

   231 

   232         Blocks until the loop has finished. This must be called while

   233         serve_forever() is running in another thread, or it will

   234         deadlock.

   235         """

   236         self.__serving = False

   237         self.__is_shut_down.wait()

   238 

   239     # The distinction between handling, getting, processing and

   240     # finishing a request is fairly arbitrary.  Remember:

   241     #

   242     # - handle_request() is the top-level call.  It calls

   243     #   select, get_request(), verify_request() and process_request()

   244     # - get_request() is different for stream or datagram sockets

   245     # - process_request() is the place that may fork a new process

   246     #   or create a new thread to finish the request

   247     # - finish_request() instantiates the request handler class;

   248     #   this constructor will handle the request all by itself

   249 

   250     def handle_request(self):

   251         """Handle one request, possibly blocking.

   252 

   253         Respects self.timeout.

   254         """

   255         # Support people who used socket.settimeout() to escape

   256         # handle_request before self.timeout was available.

   257         timeout = self.socket.gettimeout()

   258         if timeout is None:

   259             timeout = self.timeout

   260         elif self.timeout is not None:

   261             timeout = min(timeout, self.timeout)

   262         fd_sets = select.select([self], [], [], timeout)

   263         if not fd_sets[0]:

   264             self.handle_timeout()

   265             return

   266         self._handle_request_noblock()

   267 

   268     def _handle_request_noblock(self):

   269         """Handle one request, without blocking.

   270 

   271         I assume that select.select has returned that the socket is

   272         readable before this function was called, so there should be

   273         no risk of blocking in get_request().

   274         """

   275         try:

   276             request, client_address = self.get_request()

   277         except socket.error:

   278             return

   279         if self.verify_request(request, client_address):

   280             try:

   281                 self.process_request(request, client_address)

   282             except:

   283                 self.handle_error(request, client_address)

   284                 self.close_request(request)

   285 

   286     def handle_timeout(self):

   287         """Called if no new request arrives within self.timeout.

   288 

   289         Overridden by ForkingMixIn.

   290         """

   291         pass

   292 

   293     def verify_request(self, request, client_address):

   294         """Verify the request.  May be overridden.

   295 

   296         Return True if we should proceed with this request.

   297 

   298         """

   299         return True

   300 

   301     def process_request(self, request, client_address):

   302         """Call finish_request.

   303 

   304         Overridden by ForkingMixIn and ThreadingMixIn.

   305 

   306         """

   307         self.finish_request(request, client_address)

   308         self.close_request(request)

   309 

   310     def server_close(self):

   311         """Called to clean-up the server.

   312 

   313         May be overridden.

   314 

   315         """

   316         pass

   317 

   318     def finish_request(self, request, client_address):

   319         """Finish one request by instantiating RequestHandlerClass."""

   320         self.RequestHandlerClass(request, client_address, self)

   321 

   322     def close_request(self, request):

   323         """Called to clean up an individual request."""

   324         pass

   325 

   326     def handle_error(self, request, client_address):

   327         """Handle an error gracefully.  May be overridden.

   328 

   329         The default is to print a traceback and continue.

   330 

   331         """

   332         print '-'*40

   333         print 'Exception happened during processing of request from',

   334         print client_address

   335         import traceback

   336         traceback.print_exc() # XXX But this goes to stderr!

   337         print '-'*40

   338 

   339 

   340 class TCPServer(BaseServer):

   341 

   342     """Base class for various socket-based server classes.

   343 

   344     Defaults to synchronous IP stream (i.e., TCP).

   345 

   346     Methods for the caller:

   347 

   348     - __init__(server_address, RequestHandlerClass, bind_and_activate=True)

   349     - serve_forever(poll_interval=0.5)

   350     - shutdown()

   351     - handle_request()  # if you don't use serve_forever()

   352     - fileno() -> int   # for select()

   353 

   354     Methods that may be overridden:

   355 

   356     - server_bind()

   357     - server_activate()

   358     - get_request() -> request, client_address

   359     - handle_timeout()

   360     - verify_request(request, client_address)

   361     - process_request(request, client_address)

   362     - close_request(request)

   363     - handle_error()

   364 

   365     Methods for derived classes:

   366 

   367     - finish_request(request, client_address)

   368 

   369     Class variables that may be overridden by derived classes or

   370     instances:

   371 

   372     - timeout

   373     - address_family

   374     - socket_type

   375     - request_queue_size (only for stream sockets)

   376     - allow_reuse_address

   377 

   378     Instance variables:

   379 

   380     - server_address

   381     - RequestHandlerClass

   382     - socket

   383 

   384     """

   385 

   386     address_family = socket.AF_INET

   387 

   388     socket_type = socket.SOCK_STREAM

   389 

   390     request_queue_size = 5

   391 

   392     allow_reuse_address = False

   393 

   394     def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):

   395         """Constructor.  May be extended, do not override."""

   396         BaseServer.__init__(self, server_address, RequestHandlerClass)

   397         self.socket = socket.socket(self.address_family,

   398                                     self.socket_type)

   399         if bind_and_activate:

   400             self.server_bind()

   401             self.server_activate()

   402 

   403     def server_bind(self):

   404         """Called by constructor to bind the socket.

   405 

   406         May be overridden.

   407 

   408         """

   409         if self.allow_reuse_address:

   410             self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

   411         self.socket.bind(self.server_address)

   412         self.server_address = self.socket.getsockname()

   413 

   414     def server_activate(self):

   415         """Called by constructor to activate the server.

   416 

   417         May be overridden.

   418 

   419         """

   420         self.socket.listen(self.request_queue_size)

   421 

   422     def server_close(self):

   423         """Called to clean-up the server.

   424 

   425         May be overridden.

   426 

   427         """

   428         self.socket.close()

   429 

   430     def fileno(self):

   431         """Return socket file number.

   432 

   433         Interface required by select().

   434 

   435         """

   436         return self.socket.fileno()

   437 

   438     def get_request(self):

   439         """Get the request and client address from the socket.

   440 

   441         May be overridden.

   442 

   443         """

   444         return self.socket.accept()

   445 

   446     def close_request(self, request):

   447         """Called to clean up an individual request."""

   448         request.close()

   449 

   450 

   451 class UDPServer(TCPServer):

   452 

   453     """UDP server class."""

   454 

   455     allow_reuse_address = False

   456 

   457     socket_type = socket.SOCK_DGRAM

   458 

   459     max_packet_size = 8192

   460 

   461     def get_request(self):

   462         data, client_addr = self.socket.recvfrom(self.max_packet_size)

   463         return (data, self.socket), client_addr

   464 

   465     def server_activate(self):

   466         # No need to call listen() for UDP.

   467         pass

   468 

   469     def close_request(self, request):

   470         # No need to close anything.

   471         pass

   472 

   473 class ForkingMixIn:

   474 

   475     """Mix-in class to handle each request in a new process."""

   476 

   477     timeout = 300

   478     active_children = None

   479     max_children = 40

   480 

   481     def collect_children(self):

   482         """Internal routine to wait for children that have exited."""

   483         if self.active_children is None: return

   484         while len(self.active_children) >= self.max_children:

   485             # XXX: This will wait for any child process, not just ones

   486             # spawned by this library. This could confuse other

   487             # libraries that expect to be able to wait for their own

   488             # children.

   489             try:

   490                 pid, status = os.waitpid(0, options=0)

   491             except os.error:

   492                 pid = None

   493             if pid not in self.active_children: continue

   494             self.active_children.remove(pid)

   495 

   496         # XXX: This loop runs more system calls than it ought

   497         # to. There should be a way to put the active_children into a

   498         # process group and then use os.waitpid(-pgid) to wait for any

   499         # of that set, but I couldn't find a way to allocate pgids

   500         # that couldn't collide.

   501         for child in self.active_children:

   502             try:

   503                 pid, status = os.waitpid(child, os.WNOHANG)

   504             except os.error:

   505                 pid = None

   506             if not pid: continue

   507             try:

   508                 self.active_children.remove(pid)

   509             except ValueError, e:

   510                 raise ValueError('%s. x=%d and list=%r' % (e.message, pid,

   511                                                            self.active_children))

   512 

   513     def handle_timeout(self):

   514         """Wait for zombies after self.timeout seconds of inactivity.

   515 

   516         May be extended, do not override.

   517         """

   518         self.collect_children()

   519 

   520     def process_request(self, request, client_address):

   521         """Fork a new subprocess to process the request."""

   522         self.collect_children()

   523         pid = os.fork()

   524         if pid:

   525             # Parent process

   526             if self.active_children is None:

   527                 self.active_children = []

   528             self.active_children.append(pid)

   529             self.close_request(request)

   530             return

   531         else:

   532             # Child process.

   533             # This must never return, hence os._exit()!

   534             try:

   535                 self.finish_request(request, client_address)

   536                 os._exit(0)

   537             except:

   538                 try:

   539                     self.handle_error(request, client_address)

   540                 finally:

   541                     os._exit(1)

   542 

   543 

   544 class ThreadingMixIn:

   545     """Mix-in class to handle each request in a new thread."""

   546 

   547     # Decides how threads will act upon termination of the

   548     # main process

   549     daemon_threads = False

   550 

   551     def process_request_thread(self, request, client_address):

   552         """Same as in BaseServer but as a thread.

   553 

   554         In addition, exception handling is done here.

   555 

   556         """

   557         try:

   558             self.finish_request(request, client_address)

   559             self.close_request(request)

   560         except:

   561             self.handle_error(request, client_address)

   562             self.close_request(request)

   563 

   564     def process_request(self, request, client_address):

   565         """Start a new thread to process the request."""

   566         t = threading.Thread(target = self.process_request_thread,

   567                              args = (request, client_address))

   568         if self.daemon_threads:

   569             t.setDaemon (1)

   570         t.start()

   571 

   572 

   573 class ForkingUDPServer(ForkingMixIn, UDPServer): pass

   574 class ForkingTCPServer(ForkingMixIn, TCPServer): pass

   575 

   576 class ThreadingUDPServer(ThreadingMixIn, UDPServer): pass

   577 class ThreadingTCPServer(ThreadingMixIn, TCPServer): pass

   578 

   579 if hasattr(socket, 'AF_UNIX'):

   580 

   581     class UnixStreamServer(TCPServer):

   582         address_family = socket.AF_UNIX

   583 

   584     class UnixDatagramServer(UDPServer):

   585         address_family = socket.AF_UNIX

   586 

   587     class ThreadingUnixStreamServer(ThreadingMixIn, UnixStreamServer): pass

   588 

   589     class ThreadingUnixDatagramServer(ThreadingMixIn, UnixDatagramServer): pass

   590 

   591 class BaseRequestHandler:

   592 

   593     """Base class for request handler classes.

   594 

   595     This class is instantiated for each request to be handled.  The

   596     constructor sets the instance variables request, client_address

   597     and server, and then calls the handle() method.  To implement a

   598     specific service, all you need to do is to derive a class which

   599     defines a handle() method.

   600 

   601     The handle() method can find the request as self.request, the

   602     client address as self.client_address, and the server (in case it

   603     needs access to per-server information) as self.server.  Since a

   604     separate instance is created for each request, the handle() method

   605     can define arbitrary other instance variariables.

   606 

   607     """

   608 

   609     def __init__(self, request, client_address, server):

   610         self.request = request

   611         self.client_address = client_address

   612         self.server = server

   613         try:

   614             self.setup()

   615             self.handle()

   616             self.finish()

   617         finally:

   618             sys.exc_traceback = None    # Help garbage collection

   619 

   620     def setup(self):

   621         pass

   622 

   623     def handle(self):

   624         pass

   625 

   626     def finish(self):

   627         pass

   628 

   629 

   630 # The following two classes make it possible to use the same service

   631 # class for stream or datagram servers.

   632 # Each class sets up these instance variables:

   633 # - rfile: a file object from which receives the request is read

   634 # - wfile: a file object to which the reply is written

   635 # When the handle() method returns, wfile is flushed properly

   636 

   637 

   638 class StreamRequestHandler(BaseRequestHandler):

   639 

   640     """Define self.rfile and self.wfile for stream sockets."""

   641 

   642     # Default buffer sizes for rfile, wfile.

   643     # We default rfile to buffered because otherwise it could be

   644     # really slow for large data (a getc() call per byte); we make

   645     # wfile unbuffered because (a) often after a write() we want to

   646     # read and we need to flush the line; (b) big writes to unbuffered

   647     # files are typically optimized by stdio even when big reads

   648     # aren't.

   649     rbufsize = -1

   650     wbufsize = 0

   651 

   652     def setup(self):

   653         self.connection = self.request

   654         self.rfile = self.connection.makefile('rb', self.rbufsize)

   655         self.wfile = self.connection.makefile('wb', self.wbufsize)

   656 

   657     def finish(self):

   658         if not self.wfile.closed:

   659             self.wfile.flush()

   660         self.wfile.close()

   661         self.rfile.close()

   662 

   663 

   664 class DatagramRequestHandler(BaseRequestHandler):

   665 

   666     # XXX Regrettably, I cannot get this working on Linux;

   667     # s.recvfrom() doesn't return a meaningful client address.

   668 

   669     """Define self.rfile and self.wfile for datagram sockets."""

   670 

   671     def setup(self):

   672         try:

   673             from cStringIO import StringIO

   674         except ImportError:

   675             from StringIO import StringIO

   676         self.packet, self.socket = self.request

   677         self.rfile = StringIO(self.packet)

   678         self.wfile = StringIO()

   679 

   680     def finish(self):

   681         self.socket.sendto(self.wfile.getvalue(), self.client_address)