Lib/SocketServer.py

   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     - shutdown_request(request)
 172     - close_request(request)
 173     - handle_error()
 174
 175     Methods for derived classes:
 176
 177     - finish_request(request, client_address)
 178
 179     Class variables that may be overridden by derived classes or
 180     instances:
 181
 182     - timeout
 183     - address_family
 184     - socket_type
 185     - allow_reuse_address
 186
 187     Instance variables:
 188
 189     - RequestHandlerClass
 190     - socket
 191
 192     """
 193
 194     timeout = None
 195
 196     def __init__(self, server_address, RequestHandlerClass):
 197         """Constructor.  May be extended, do not override."""
 198         self.server_address = server_address
 199         self.RequestHandlerClass = RequestHandlerClass
 200         self.__is_shut_down = threading.Event()
 201         self.__serving = False
 202
 203     def server_activate(self):
 204         """Called by constructor to activate the server.
 205
 206         May be overridden.
 207
 208         """
 209         pass
 210
 211     def serve_forever(self, poll_interval=0.5):
 212         """Handle one request at a time until shutdown.
 213
 214         Polls for shutdown every poll_interval seconds. Ignores
 215         self.timeout. If you need to do periodic tasks, do them in
 216         another thread.
 217         """
 218         self.__serving = True
 219         self.__is_shut_down.clear()
 220         while self.__serving:
 221             # XXX: Consider using another file descriptor or
 222             # connecting to the socket to wake this up instead of
 223             # polling. Polling reduces our responsiveness to a
 224             # shutdown request and wastes cpu at all other times.
 225             r, w, e = select.select([self], [], [], poll_interval)
 226             if r:
 227                 self._handle_request_noblock()
 228         self.__is_shut_down.set()
 229
 230     def shutdown(self):
 231         """Stops the serve_forever loop.
 232
 233         Blocks until the loop has finished. This must be called while
 234         serve_forever() is running in another thread, or it will
 235         deadlock.
 236         """
 237         self.__serving = False
 238         self.__is_shut_down.wait()
 239
 240     # The distinction between handling, getting, processing and
 241     # finishing a request is fairly arbitrary.  Remember:
 242     #
 243     # - handle_request() is the top-level call.  It calls
 244     #   select, get_request(), verify_request() and process_request()
 245     # - get_request() is different for stream or datagram sockets
 246     # - process_request() is the place that may fork a new process
 247     #   or create a new thread to finish the request
 248     # - finish_request() instantiates the request handler class;
 249     #   this constructor will handle the request all by itself
 250
 251     def handle_request(self):
 252         """Handle one request, possibly blocking.
 253
 254         Respects self.timeout.
 255         """
 256         # Support people who used socket.settimeout() to escape
 257         # handle_request before self.timeout was available.
 258         timeout = self.socket.gettimeout()
 259         if timeout is None:
 260             timeout = self.timeout
 261         elif self.timeout is not None:
 262             timeout = min(timeout, self.timeout)
 263         fd_sets = select.select([self], [], [], timeout)
 264         if not fd_sets[0]:
 265             self.handle_timeout()
 266             return
 267         self._handle_request_noblock()
 268
 269     def _handle_request_noblock(self):
 270         """Handle one request, without blocking.
 271
 272         I assume that select.select has returned that the socket is
 273         readable before this function was called, so there should be
 274         no risk of blocking in get_request().
 275         """
 276         try:
 277             request, client_address = self.get_request()
 278         except socket.error:
 279             return
 280         if self.verify_request(request, client_address):
 281             try:
 282                 self.process_request(request, client_address)
 283             except:
 284                 self.handle_error(request, client_address)
 285                 self.shutdown_request(request)
 286
 287     def handle_timeout(self):
 288         """Called if no new request arrives within self.timeout.
 289
 290         Overridden by ForkingMixIn.
 291         """
 292         pass
 293
 294     def verify_request(self, request, client_address):
 295         """Verify the request.  May be overridden.
 296
 297         Return True if we should proceed with this request.
 298
 299         """
 300         return True
 301
 302     def process_request(self, request, client_address):
 303         """Call finish_request.
 304
 305         Overridden by ForkingMixIn and ThreadingMixIn.
 306
 307         """
 308         self.finish_request(request, client_address)
 309         self.shutdown_request(request)
 310
 311     def server_close(self):
 312         """Called to clean-up the server.
 313
 314         May be overridden.
 315
 316         """
 317         pass
 318
 319     def finish_request(self, request, client_address):
 320         """Finish one request by instantiating RequestHandlerClass."""
 321         self.RequestHandlerClass(request, client_address, self)
 322
 323     def shutdown_request(self, request):
 324         """Called to shutdown and close an individual request."""
 325         self.close_request(request)
 326
 327     def close_request(self, request):
 328         """Called to clean up an individual request."""
 329         pass
 330
 331     def handle_error(self, request, client_address):
 332         """Handle an error gracefully.  May be overridden.
 333
 334         The default is to print a traceback and continue.
 335
 336         """
 337         print '-'*40
 338         print 'Exception happened during processing of request from',
 339         print client_address
 340         import traceback
 341         traceback.print_exc() # XXX But this goes to stderr!
 342         print '-'*40
 343
 344
 345 class TCPServer(BaseServer):
 346
 347     """Base class for various socket-based server classes.
 348
 349     Defaults to synchronous IP stream (i.e., TCP).
 350
 351     Methods for the caller:
 352
 353     - __init__(server_address, RequestHandlerClass, bind_and_activate=True)
 354     - serve_forever(poll_interval=0.5)
 355     - shutdown()
 356     - handle_request()  # if you don't use serve_forever()
 357     - fileno() -> int   # for select()
 358
 359     Methods that may be overridden:
 360
 361     - server_bind()
 362     - server_activate()
 363     - get_request() -> request, client_address
 364     - handle_timeout()
 365     - verify_request(request, client_address)
 366     - process_request(request, client_address)
 367     - shutdown_request(request)
 368     - close_request(request)
 369     - handle_error()
 370
 371     Methods for derived classes:
 372
 373     - finish_request(request, client_address)
 374
 375     Class variables that may be overridden by derived classes or
 376     instances:
 377
 378     - timeout
 379     - address_family
 380     - socket_type
 381     - request_queue_size (only for stream sockets)
 382     - allow_reuse_address
 383
 384     Instance variables:
 385
 386     - server_address
 387     - RequestHandlerClass
 388     - socket
 389
 390     """
 391
 392     address_family = socket.AF_INET
 393
 394     socket_type = socket.SOCK_STREAM
 395
 396     request_queue_size = 5
 397
 398     allow_reuse_address = False
 399
 400     def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):
 401         """Constructor.  May be extended, do not override."""
 402         BaseServer.__init__(self, server_address, RequestHandlerClass)
 403         self.socket = socket.socket(self.address_family,
 404                                     self.socket_type)
 405         if bind_and_activate:
 406             self.server_bind()
 407             self.server_activate()
 408
 409     def server_bind(self):
 410         """Called by constructor to bind the socket.
 411
 412         May be overridden.
 413
 414         """
 415         if self.allow_reuse_address:
 416             self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
 417         self.socket.bind(self.server_address)
 418         self.server_address = self.socket.getsockname()
 419
 420     def server_activate(self):
 421         """Called by constructor to activate the server.
 422
 423         May be overridden.
 424
 425         """
 426         self.socket.listen(self.request_queue_size)
 427
 428     def server_close(self):
 429         """Called to clean-up the server.
 430
 431         May be overridden.
 432
 433         """
 434         self.socket.close()
 435
 436     def fileno(self):
 437         """Return socket file number.
 438
 439         Interface required by select().
 440
 441         """
 442         return self.socket.fileno()
 443
 444     def get_request(self):
 445         """Get the request and client address from the socket.
 446
 447         May be overridden.
 448
 449         """
 450         return self.socket.accept()
 451
 452     def shutdown_request(self, request):
 453         """Called to shutdown and close an individual request."""
 454         try:
 455             #explicitly shutdown.  socket.close() merely releases
 456             #the socket and waits for GC to perform the actual close.
 457             request.shutdown(socket.SHUT_WR)
 458         except socket.error:
 459             pass #some platforms may raise ENOTCONN here
 460         self.close_request(request)
 461
 462     def close_request(self, request):
 463         """Called to clean up an individual request."""
 464         request.close()
 465
 466
 467 class UDPServer(TCPServer):
 468
 469     """UDP server class."""
 470
 471     allow_reuse_address = False
 472
 473     socket_type = socket.SOCK_DGRAM
 474
 475     max_packet_size = 8192
 476
 477     def get_request(self):
 478         data, client_addr = self.socket.recvfrom(self.max_packet_size)
 479         return (data, self.socket), client_addr
 480
 481     def server_activate(self):
 482         # No need to call listen() for UDP.
 483         pass
 484
 485     def shutdown_request(self, request):
 486         # No need to shutdown anything.
 487         self.close_request(request)
 488
 489     def close_request(self, request):
 490         # No need to close anything.
 491         pass
 492
 493 class ForkingMixIn:
 494
 495     """Mix-in class to handle each request in a new process."""
 496
 497     timeout = 300
 498     active_children = None
 499     max_children = 40
 500
 501     def collect_children(self):
 502         """Internal routine to wait for children that have exited."""
 503         if self.active_children is None: return
 504         while len(self.active_children) >= self.max_children:
 505             # XXX: This will wait for any child process, not just ones
 506             # spawned by this library. This could confuse other
 507             # libraries that expect to be able to wait for their own
 508             # children.
 509             try:
 510                 pid, status = os.waitpid(0, 0)
 511             except os.error:
 512                 pid = None
 513             if pid not in self.active_children: continue
 514             self.active_children.remove(pid)
 515
 516         # XXX: This loop runs more system calls than it ought
 517         # to. There should be a way to put the active_children into a
 518         # process group and then use os.waitpid(-pgid) to wait for any
 519         # of that set, but I couldn't find a way to allocate pgids
 520         # that couldn't collide.
 521         for child in self.active_children:
 522             try:
 523                 pid, status = os.waitpid(child, os.WNOHANG)
 524             except os.error:
 525                 pid = None
 526             if not pid: continue
 527             try:
 528                 self.active_children.remove(pid)
 529             except ValueError, e:
 530                 raise ValueError('%s. x=%d and list=%r' % (e.message, pid,
 531                                                            self.active_children))
 532
 533     def handle_timeout(self):
 534         """Wait for zombies after self.timeout seconds of inactivity.
 535
 536         May be extended, do not override.
 537         """
 538         self.collect_children()
 539
 540     def process_request(self, request, client_address):
 541         """Fork a new subprocess to process the request."""
 542         self.collect_children()
 543         pid = os.fork()
 544         if pid:
 545             # Parent process
 546             if self.active_children is None:
 547                 self.active_children = []
 548             self.active_children.append(pid)
 549             self.close_request(request) #close handle in parent process
 550             return
 551         else:
 552             # Child process.
 553             # This must never return, hence os._exit()!
 554             try:
 555                 self.finish_request(request, client_address)
 556                 self.shutdown_request(request)
 557                 os._exit(0)
 558             except:
 559                 try:
 560                     self.handle_error(request, client_address)
 561                     self.shutdown_request(request)
 562                 finally:
 563                     os._exit(1)
 564
 565
 566 class ThreadingMixIn:
 567     """Mix-in class to handle each request in a new thread."""
 568
 569     # Decides how threads will act upon termination of the
 570     # main process
 571     daemon_threads = False
 572
 573     def process_request_thread(self, request, client_address):
 574         """Same as in BaseServer but as a thread.
 575
 576         In addition, exception handling is done here.
 577
 578         """
 579         try:
 580             self.finish_request(request, client_address)
 581             self.shutdown_request(request)
 582         except:
 583             self.handle_error(request, client_address)
 584             self.shutdown_request(request)
 585
 586     def process_request(self, request, client_address):
 587         """Start a new thread to process the request."""
 588         t = threading.Thread(target = self.process_request_thread,
 589                              args = (request, client_address))
 590         if self.daemon_threads:
 591             t.setDaemon (1)
 592         t.start()
 593
 594
 595 class ForkingUDPServer(ForkingMixIn, UDPServer): pass
 596 class ForkingTCPServer(ForkingMixIn, TCPServer): pass
 597
 598 class ThreadingUDPServer(ThreadingMixIn, UDPServer): pass
 599 class ThreadingTCPServer(ThreadingMixIn, TCPServer): pass
 600
 601 if hasattr(socket, 'AF_UNIX'):
 602
 603     class UnixStreamServer(TCPServer):
 604         address_family = socket.AF_UNIX
 605
 606     class UnixDatagramServer(UDPServer):
 607         address_family = socket.AF_UNIX
 608
 609     class ThreadingUnixStreamServer(ThreadingMixIn, UnixStreamServer): pass
 610
 611     class ThreadingUnixDatagramServer(ThreadingMixIn, UnixDatagramServer): pass
 612
 613 class BaseRequestHandler:
 614
 615     """Base class for request handler classes.
 616
 617     This class is instantiated for each request to be handled.  The
 618     constructor sets the instance variables request, client_address
 619     and server, and then calls the handle() method.  To implement a
 620     specific service, all you need to do is to derive a class which
 621     defines a handle() method.
 622
 623     The handle() method can find the request as self.request, the
 624     client address as self.client_address, and the server (in case it
 625     needs access to per-server information) as self.server.  Since a
 626     separate instance is created for each request, the handle() method
 627     can define arbitrary other instance variariables.
 628
 629     """
 630
 631     def __init__(self, request, client_address, server):
 632         self.request = request
 633         self.client_address = client_address
 634         self.server = server
 635         self.setup()
 636         try:
 637             self.handle()
 638         finally:
 639             self.finish()
 640
 641     def setup(self):
 642         pass
 643
 644     def handle(self):
 645         pass
 646
 647     def finish(self):
 648         pass
 649
 650
 651 # The following two classes make it possible to use the same service
 652 # class for stream or datagram servers.
 653 # Each class sets up these instance variables:
 654 # - rfile: a file object from which receives the request is read
 655 # - wfile: a file object to which the reply is written
 656 # When the handle() method returns, wfile is flushed properly
 657
 658
 659 class StreamRequestHandler(BaseRequestHandler):
 660
 661     """Define self.rfile and self.wfile for stream sockets."""
 662
 663     # Default buffer sizes for rfile, wfile.
 664     # We default rfile to buffered because otherwise it could be
 665     # really slow for large data (a getc() call per byte); we make
 666     # wfile unbuffered because (a) often after a write() we want to
 667     # read and we need to flush the line; (b) big writes to unbuffered
 668     # files are typically optimized by stdio even when big reads
 669     # aren't.
 670     rbufsize = -1
 671     wbufsize = 0
 672
 673     # A timeout to apply to the request socket, if not None.
 674     timeout = None
 675
 676     # Disable nagle algoritm for this socket, if True.
 677     # Use only when wbufsize != 0, to avoid small packets.
 678     disable_nagle_algorithm = False
 679
 680     def setup(self):
 681         self.connection = self.request
 682         if self.timeout is not None:
 683             self.connection.settimeout(self.timeout)
 684         if self.disable_nagle_algorithm:
 685             self.connection.setsockopt(socket.IPPROTO_TCP,
 686                                        socket.TCP_NODELAY, True)
 687         self.rfile = self.connection.makefile('rb', self.rbufsize)
 688         self.wfile = self.connection.makefile('wb', self.wbufsize)
 689
 690     def finish(self):
 691         if not self.wfile.closed:
 692             self.wfile.flush()
 693         self.wfile.close()
 694         self.rfile.close()
 695
 696
 697 class DatagramRequestHandler(BaseRequestHandler):
 698
 699     # XXX Regrettably, I cannot get this working on Linux;
 700     # s.recvfrom() doesn't return a meaningful client address.
 701
 702     """Define self.rfile and self.wfile for datagram sockets."""
 703
 704     def setup(self):
 705         try:
 706             from cStringIO import StringIO
 707         except ImportError:
 708             from StringIO import StringIO
 709         self.packet, self.socket = self.request
 710         self.rfile = StringIO(self.packet)
 711         self.wfile = StringIO()
 712
 713     def finish(self):
 714         self.socket.sendto(self.wfile.getvalue(), self.client_address)