AppPkg/Applications/Python/Python-2.7.2/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.__shutdown_request = 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.__is_shut_down.clear()
 219         try:
 220             while not self.__shutdown_request:
 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 self in r:
 227                     self._handle_request_noblock()
 228         finally:
 229             self.__shutdown_request = False
 230             self.__is_shut_down.set()
 231
 232     def shutdown(self):
 233         """Stops the serve_forever loop.
 234
 235         Blocks until the loop has finished. This must be called while
 236         serve_forever() is running in another thread, or it will
 237         deadlock.
 238         """
 239         self.__shutdown_request = True
 240         self.__is_shut_down.wait()
 241
 242     # The distinction between handling, getting, processing and
 243     # finishing a request is fairly arbitrary.  Remember:
 244     #
 245     # - handle_request() is the top-level call.  It calls
 246     #   select, get_request(), verify_request() and process_request()
 247     # - get_request() is different for stream or datagram sockets
 248     # - process_request() is the place that may fork a new process
 249     #   or create a new thread to finish the request
 250     # - finish_request() instantiates the request handler class;
 251     #   this constructor will handle the request all by itself
 252
 253     def handle_request(self):
 254         """Handle one request, possibly blocking.
 255
 256         Respects self.timeout.
 257         """
 258         # Support people who used socket.settimeout() to escape
 259         # handle_request before self.timeout was available.
 260         timeout = self.socket.gettimeout()
 261         if timeout is None:
 262             timeout = self.timeout
 263         elif self.timeout is not None:
 264             timeout = min(timeout, self.timeout)
 265         fd_sets = select.select([self], [], [], timeout)
 266         if not fd_sets[0]:
 267             self.handle_timeout()
 268             return
 269         self._handle_request_noblock()
 270
 271     def _handle_request_noblock(self):
 272         """Handle one request, without blocking.
 273
 274         I assume that select.select has returned that the socket is
 275         readable before this function was called, so there should be
 276         no risk of blocking in get_request().
 277         """
 278         try:
 279             request, client_address = self.get_request()
 280         except socket.error:
 281             return
 282         if self.verify_request(request, client_address):
 283             try:
 284                 self.process_request(request, client_address)
 285             except:
 286                 self.handle_error(request, client_address)
 287                 self.shutdown_request(request)
 288
 289     def handle_timeout(self):
 290         """Called if no new request arrives within self.timeout.
 291
 292         Overridden by ForkingMixIn.
 293         """
 294         pass
 295
 296     def verify_request(self, request, client_address):
 297         """Verify the request.  May be overridden.
 298
 299         Return True if we should proceed with this request.
 300
 301         """
 302         return True
 303
 304     def process_request(self, request, client_address):
 305         """Call finish_request.
 306
 307         Overridden by ForkingMixIn and ThreadingMixIn.
 308
 309         """
 310         self.finish_request(request, client_address)
 311         self.shutdown_request(request)
 312
 313     def server_close(self):
 314         """Called to clean-up the server.
 315
 316         May be overridden.
 317
 318         """
 319         pass
 320
 321     def finish_request(self, request, client_address):
 322         """Finish one request by instantiating RequestHandlerClass."""
 323         self.RequestHandlerClass(request, client_address, self)
 324
 325     def shutdown_request(self, request):
 326         """Called to shutdown and close an individual request."""
 327         self.close_request(request)
 328
 329     def close_request(self, request):
 330         """Called to clean up an individual request."""
 331         pass
 332
 333     def handle_error(self, request, client_address):
 334         """Handle an error gracefully.  May be overridden.
 335
 336         The default is to print a traceback and continue.
 337
 338         """
 339         print '-'*40
 340         print 'Exception happened during processing of request from',
 341         print client_address
 342         import traceback
 343         traceback.print_exc() # XXX But this goes to stderr!
 344         print '-'*40
 345
 346
 347 class TCPServer(BaseServer):
 348
 349     """Base class for various socket-based server classes.
 350
 351     Defaults to synchronous IP stream (i.e., TCP).
 352
 353     Methods for the caller:
 354
 355     - __init__(server_address, RequestHandlerClass, bind_and_activate=True)
 356     - serve_forever(poll_interval=0.5)
 357     - shutdown()
 358     - handle_request()  # if you don't use serve_forever()
 359     - fileno() -> int   # for select()
 360
 361     Methods that may be overridden:
 362
 363     - server_bind()
 364     - server_activate()
 365     - get_request() -> request, client_address
 366     - handle_timeout()
 367     - verify_request(request, client_address)
 368     - process_request(request, client_address)
 369     - shutdown_request(request)
 370     - close_request(request)
 371     - handle_error()
 372
 373     Methods for derived classes:
 374
 375     - finish_request(request, client_address)
 376
 377     Class variables that may be overridden by derived classes or
 378     instances:
 379
 380     - timeout
 381     - address_family
 382     - socket_type
 383     - request_queue_size (only for stream sockets)
 384     - allow_reuse_address
 385
 386     Instance variables:
 387
 388     - server_address
 389     - RequestHandlerClass
 390     - socket
 391
 392     """
 393
 394     address_family = socket.AF_INET
 395
 396     socket_type = socket.SOCK_STREAM
 397
 398     request_queue_size = 5
 399
 400     allow_reuse_address = False
 401
 402     def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):
 403         """Constructor.  May be extended, do not override."""
 404         BaseServer.__init__(self, server_address, RequestHandlerClass)
 405         self.socket = socket.socket(self.address_family,
 406                                     self.socket_type)
 407         if bind_and_activate:
 408             self.server_bind()
 409             self.server_activate()
 410
 411     def server_bind(self):
 412         """Called by constructor to bind the socket.
 413
 414         May be overridden.
 415
 416         """
 417         if self.allow_reuse_address:
 418             self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
 419         self.socket.bind(self.server_address)
 420         self.server_address = self.socket.getsockname()
 421
 422     def server_activate(self):
 423         """Called by constructor to activate the server.
 424
 425         May be overridden.
 426
 427         """
 428         self.socket.listen(self.request_queue_size)
 429
 430     def server_close(self):
 431         """Called to clean-up the server.
 432
 433         May be overridden.
 434
 435         """
 436         self.socket.close()
 437
 438     def fileno(self):
 439         """Return socket file number.
 440
 441         Interface required by select().
 442
 443         """
 444         return self.socket.fileno()
 445
 446     def get_request(self):
 447         """Get the request and client address from the socket.
 448
 449         May be overridden.
 450
 451         """
 452         return self.socket.accept()
 453
 454     def shutdown_request(self, request):
 455         """Called to shutdown and close an individual request."""
 456         try:
 457             #explicitly shutdown.  socket.close() merely releases
 458             #the socket and waits for GC to perform the actual close.
 459             request.shutdown(socket.SHUT_WR)
 460         except socket.error:
 461             pass #some platforms may raise ENOTCONN here
 462         self.close_request(request)
 463
 464     def close_request(self, request):
 465         """Called to clean up an individual request."""
 466         request.close()
 467
 468
 469 class UDPServer(TCPServer):
 470
 471     """UDP server class."""
 472
 473     allow_reuse_address = False
 474
 475     socket_type = socket.SOCK_DGRAM
 476
 477     max_packet_size = 8192
 478
 479     def get_request(self):
 480         data, client_addr = self.socket.recvfrom(self.max_packet_size)
 481         return (data, self.socket), client_addr
 482
 483     def server_activate(self):
 484         # No need to call listen() for UDP.
 485         pass
 486
 487     def shutdown_request(self, request):
 488         # No need to shutdown anything.
 489         self.close_request(request)
 490
 491     def close_request(self, request):
 492         # No need to close anything.
 493         pass
 494
 495 class ForkingMixIn:
 496
 497     """Mix-in class to handle each request in a new process."""
 498
 499     timeout = 300
 500     active_children = None
 501     max_children = 40
 502
 503     def collect_children(self):
 504         """Internal routine to wait for children that have exited."""
 505         if self.active_children is None: return
 506         while len(self.active_children) >= self.max_children:
 507             # XXX: This will wait for any child process, not just ones
 508             # spawned by this library. This could confuse other
 509             # libraries that expect to be able to wait for their own
 510             # children.
 511             try:
 512                 pid, status = os.waitpid(0, 0)
 513             except os.error:
 514                 pid = None
 515             if pid not in self.active_children: continue
 516             self.active_children.remove(pid)
 517
 518         # XXX: This loop runs more system calls than it ought
 519         # to. There should be a way to put the active_children into a
 520         # process group and then use os.waitpid(-pgid) to wait for any
 521         # of that set, but I couldn't find a way to allocate pgids
 522         # that couldn't collide.
 523         for child in self.active_children:
 524             try:
 525                 pid, status = os.waitpid(child, os.WNOHANG)
 526             except os.error:
 527                 pid = None
 528             if not pid: continue
 529             try:
 530                 self.active_children.remove(pid)
 531             except ValueError, e:
 532                 raise ValueError('%s. x=%d and list=%r' % (e.message, pid,
 533                                                            self.active_children))
 534
 535     def handle_timeout(self):
 536         """Wait for zombies after self.timeout seconds of inactivity.
 537
 538         May be extended, do not override.
 539         """
 540         self.collect_children()
 541
 542     def process_request(self, request, client_address):
 543         """Fork a new subprocess to process the request."""
 544         self.collect_children()
 545         pid = os.fork()
 546         if pid:
 547             # Parent process
 548             if self.active_children is None:
 549                 self.active_children = []
 550             self.active_children.append(pid)
 551             self.close_request(request) #close handle in parent process
 552             return
 553         else:
 554             # Child process.
 555             # This must never return, hence os._exit()!
 556             try:
 557                 self.finish_request(request, client_address)
 558                 self.shutdown_request(request)
 559                 os._exit(0)
 560             except:
 561                 try:
 562                     self.handle_error(request, client_address)
 563                     self.shutdown_request(request)
 564                 finally:
 565                     os._exit(1)
 566
 567
 568 class ThreadingMixIn:
 569     """Mix-in class to handle each request in a new thread."""
 570
 571     # Decides how threads will act upon termination of the
 572     # main process
 573     daemon_threads = False
 574
 575     def process_request_thread(self, request, client_address):
 576         """Same as in BaseServer but as a thread.
 577
 578         In addition, exception handling is done here.
 579
 580         """
 581         try:
 582             self.finish_request(request, client_address)
 583             self.shutdown_request(request)
 584         except:
 585             self.handle_error(request, client_address)
 586             self.shutdown_request(request)
 587
 588     def process_request(self, request, client_address):
 589         """Start a new thread to process the request."""
 590         t = threading.Thread(target = self.process_request_thread,
 591                              args = (request, client_address))
 592         if self.daemon_threads:
 593             t.setDaemon (1)
 594         t.start()
 595
 596
 597 class ForkingUDPServer(ForkingMixIn, UDPServer): pass
 598 class ForkingTCPServer(ForkingMixIn, TCPServer): pass
 599
 600 class ThreadingUDPServer(ThreadingMixIn, UDPServer): pass
 601 class ThreadingTCPServer(ThreadingMixIn, TCPServer): pass
 602
 603 if hasattr(socket, 'AF_UNIX'):
 604
 605     class UnixStreamServer(TCPServer):
 606         address_family = socket.AF_UNIX
 607
 608     class UnixDatagramServer(UDPServer):
 609         address_family = socket.AF_UNIX
 610
 611     class ThreadingUnixStreamServer(ThreadingMixIn, UnixStreamServer): pass
 612
 613     class ThreadingUnixDatagramServer(ThreadingMixIn, UnixDatagramServer): pass
 614
 615 class BaseRequestHandler:
 616
 617     """Base class for request handler classes.
 618
 619     This class is instantiated for each request to be handled.  The
 620     constructor sets the instance variables request, client_address
 621     and server, and then calls the handle() method.  To implement a
 622     specific service, all you need to do is to derive a class which
 623     defines a handle() method.
 624
 625     The handle() method can find the request as self.request, the
 626     client address as self.client_address, and the server (in case it
 627     needs access to per-server information) as self.server.  Since a
 628     separate instance is created for each request, the handle() method
 629     can define arbitrary other instance variariables.
 630
 631     """
 632
 633     def __init__(self, request, client_address, server):
 634         self.request = request
 635         self.client_address = client_address
 636         self.server = server
 637         self.setup()
 638         try:
 639             self.handle()
 640         finally:
 641             self.finish()
 642
 643     def setup(self):
 644         pass
 645
 646     def handle(self):
 647         pass
 648
 649     def finish(self):
 650         pass
 651
 652
 653 # The following two classes make it possible to use the same service
 654 # class for stream or datagram servers.
 655 # Each class sets up these instance variables:
 656 # - rfile: a file object from which receives the request is read
 657 # - wfile: a file object to which the reply is written
 658 # When the handle() method returns, wfile is flushed properly
 659
 660
 661 class StreamRequestHandler(BaseRequestHandler):
 662
 663     """Define self.rfile and self.wfile for stream sockets."""
 664
 665     # Default buffer sizes for rfile, wfile.
 666     # We default rfile to buffered because otherwise it could be
 667     # really slow for large data (a getc() call per byte); we make
 668     # wfile unbuffered because (a) often after a write() we want to
 669     # read and we need to flush the line; (b) big writes to unbuffered
 670     # files are typically optimized by stdio even when big reads
 671     # aren't.
 672     rbufsize = -1
 673     wbufsize = 0
 674
 675     # A timeout to apply to the request socket, if not None.
 676     timeout = None
 677
 678     # Disable nagle algorithm for this socket, if True.
 679     # Use only when wbufsize != 0, to avoid small packets.
 680     disable_nagle_algorithm = False
 681
 682     def setup(self):
 683         self.connection = self.request
 684         if self.timeout is not None:
 685             self.connection.settimeout(self.timeout)
 686         if self.disable_nagle_algorithm:
 687             self.connection.setsockopt(socket.IPPROTO_TCP,
 688                                        socket.TCP_NODELAY, True)
 689         self.rfile = self.connection.makefile('rb', self.rbufsize)
 690         self.wfile = self.connection.makefile('wb', self.wbufsize)
 691
 692     def finish(self):
 693         if not self.wfile.closed:
 694             self.wfile.flush()
 695         self.wfile.close()
 696         self.rfile.close()
 697
 698
 699 class DatagramRequestHandler(BaseRequestHandler):
 700
 701     # XXX Regrettably, I cannot get this working on Linux;
 702     # s.recvfrom() doesn't return a meaningful client address.
 703
 704     """Define self.rfile and self.wfile for datagram sockets."""
 705
 706     def setup(self):
 707         try:
 708             from cStringIO import StringIO
 709         except ImportError:
 710             from StringIO import StringIO
 711         self.packet, self.socket = self.request
 712         self.rfile = StringIO(self.packet)
 713         self.wfile = StringIO()
 714
 715     def finish(self):
 716         self.socket.sendto(self.wfile.getvalue(), self.client_address)