AppPkg/Applications/Python/Python-2.7.10/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 read 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 import errno
 137 try:
 138     import threading
 139 except ImportError:
 140     import dummy_threading as threading
 141
 142 __all__ = ["TCPServer","UDPServer","ForkingUDPServer","ForkingTCPServer",
 143            "ThreadingUDPServer","ThreadingTCPServer","BaseRequestHandler",
 144            "StreamRequestHandler","DatagramRequestHandler",
 145            "ThreadingMixIn", "ForkingMixIn"]
 146 if hasattr(socket, "AF_UNIX"):
 147     __all__.extend(["UnixStreamServer","UnixDatagramServer",
 148                     "ThreadingUnixStreamServer",
 149                     "ThreadingUnixDatagramServer"])
 150
 151 def _eintr_retry(func, *args):
 152     """restart a system call interrupted by EINTR"""
 153     while True:
 154         try:
 155             return func(*args)
 156         except (OSError, select.error) as e:
 157             if e.args[0] != errno.EINTR:
 158                 raise
 159
 160 class BaseServer:
 161
 162     """Base class for server classes.
 163
 164     Methods for the caller:
 165
 166     - __init__(server_address, RequestHandlerClass)
 167     - serve_forever(poll_interval=0.5)
 168     - shutdown()
 169     - handle_request()  # if you do not use serve_forever()
 170     - fileno() -> int   # for select()
 171
 172     Methods that may be overridden:
 173
 174     - server_bind()
 175     - server_activate()
 176     - get_request() -> request, client_address
 177     - handle_timeout()
 178     - verify_request(request, client_address)
 179     - server_close()
 180     - process_request(request, client_address)
 181     - shutdown_request(request)
 182     - close_request(request)
 183     - handle_error()
 184
 185     Methods for derived classes:
 186
 187     - finish_request(request, client_address)
 188
 189     Class variables that may be overridden by derived classes or
 190     instances:
 191
 192     - timeout
 193     - address_family
 194     - socket_type
 195     - allow_reuse_address
 196
 197     Instance variables:
 198
 199     - RequestHandlerClass
 200     - socket
 201
 202     """
 203
 204     timeout = None
 205
 206     def __init__(self, server_address, RequestHandlerClass):
 207         """Constructor.  May be extended, do not override."""
 208         self.server_address = server_address
 209         self.RequestHandlerClass = RequestHandlerClass
 210         self.__is_shut_down = threading.Event()
 211         self.__shutdown_request = False
 212
 213     def server_activate(self):
 214         """Called by constructor to activate the server.
 215
 216         May be overridden.
 217
 218         """
 219         pass
 220
 221     def serve_forever(self, poll_interval=0.5):
 222         """Handle one request at a time until shutdown.
 223
 224         Polls for shutdown every poll_interval seconds. Ignores
 225         self.timeout. If you need to do periodic tasks, do them in
 226         another thread.
 227         """
 228         self.__is_shut_down.clear()
 229         try:
 230             while not self.__shutdown_request:
 231                 # XXX: Consider using another file descriptor or
 232                 # connecting to the socket to wake this up instead of
 233                 # polling. Polling reduces our responsiveness to a
 234                 # shutdown request and wastes cpu at all other times.
 235                 r, w, e = _eintr_retry(select.select, [self], [], [],
 236                                        poll_interval)
 237                 if self in r:
 238                     self._handle_request_noblock()
 239         finally:
 240             self.__shutdown_request = False
 241             self.__is_shut_down.set()
 242
 243     def shutdown(self):
 244         """Stops the serve_forever loop.
 245
 246         Blocks until the loop has finished. This must be called while
 247         serve_forever() is running in another thread, or it will
 248         deadlock.
 249         """
 250         self.__shutdown_request = True
 251         self.__is_shut_down.wait()
 252
 253     # The distinction between handling, getting, processing and
 254     # finishing a request is fairly arbitrary.  Remember:
 255     #
 256     # - handle_request() is the top-level call.  It calls
 257     #   select, get_request(), verify_request() and process_request()
 258     # - get_request() is different for stream or datagram sockets
 259     # - process_request() is the place that may fork a new process
 260     #   or create a new thread to finish the request
 261     # - finish_request() instantiates the request handler class;
 262     #   this constructor will handle the request all by itself
 263
 264     def handle_request(self):
 265         """Handle one request, possibly blocking.
 266
 267         Respects self.timeout.
 268         """
 269         # Support people who used socket.settimeout() to escape
 270         # handle_request before self.timeout was available.
 271         timeout = self.socket.gettimeout()
 272         if timeout is None:
 273             timeout = self.timeout
 274         elif self.timeout is not None:
 275             timeout = min(timeout, self.timeout)
 276         fd_sets = _eintr_retry(select.select, [self], [], [], timeout)
 277         if not fd_sets[0]:
 278             self.handle_timeout()
 279             return
 280         self._handle_request_noblock()
 281
 282     def _handle_request_noblock(self):
 283         """Handle one request, without blocking.
 284
 285         I assume that select.select has returned that the socket is
 286         readable before this function was called, so there should be
 287         no risk of blocking in get_request().
 288         """
 289         try:
 290             request, client_address = self.get_request()
 291         except socket.error:
 292             return
 293         if self.verify_request(request, client_address):
 294             try:
 295                 self.process_request(request, client_address)
 296             except:
 297                 self.handle_error(request, client_address)
 298                 self.shutdown_request(request)
 299
 300     def handle_timeout(self):
 301         """Called if no new request arrives within self.timeout.
 302
 303         Overridden by ForkingMixIn.
 304         """
 305         pass
 306
 307     def verify_request(self, request, client_address):
 308         """Verify the request.  May be overridden.
 309
 310         Return True if we should proceed with this request.
 311
 312         """
 313         return True
 314
 315     def process_request(self, request, client_address):
 316         """Call finish_request.
 317
 318         Overridden by ForkingMixIn and ThreadingMixIn.
 319
 320         """
 321         self.finish_request(request, client_address)
 322         self.shutdown_request(request)
 323
 324     def server_close(self):
 325         """Called to clean-up the server.
 326
 327         May be overridden.
 328
 329         """
 330         pass
 331
 332     def finish_request(self, request, client_address):
 333         """Finish one request by instantiating RequestHandlerClass."""
 334         self.RequestHandlerClass(request, client_address, self)
 335
 336     def shutdown_request(self, request):
 337         """Called to shutdown and close an individual request."""
 338         self.close_request(request)
 339
 340     def close_request(self, request):
 341         """Called to clean up an individual request."""
 342         pass
 343
 344     def handle_error(self, request, client_address):
 345         """Handle an error gracefully.  May be overridden.
 346
 347         The default is to print a traceback and continue.
 348
 349         """
 350         print '-'*40
 351         print 'Exception happened during processing of request from',
 352         print client_address
 353         import traceback
 354         traceback.print_exc() # XXX But this goes to stderr!
 355         print '-'*40
 356
 357
 358 class TCPServer(BaseServer):
 359
 360     """Base class for various socket-based server classes.
 361
 362     Defaults to synchronous IP stream (i.e., TCP).
 363
 364     Methods for the caller:
 365
 366     - __init__(server_address, RequestHandlerClass, bind_and_activate=True)
 367     - serve_forever(poll_interval=0.5)
 368     - shutdown()
 369     - handle_request()  # if you don't use serve_forever()
 370     - fileno() -> int   # for select()
 371
 372     Methods that may be overridden:
 373
 374     - server_bind()
 375     - server_activate()
 376     - get_request() -> request, client_address
 377     - handle_timeout()
 378     - verify_request(request, client_address)
 379     - process_request(request, client_address)
 380     - shutdown_request(request)
 381     - close_request(request)
 382     - handle_error()
 383
 384     Methods for derived classes:
 385
 386     - finish_request(request, client_address)
 387
 388     Class variables that may be overridden by derived classes or
 389     instances:
 390
 391     - timeout
 392     - address_family
 393     - socket_type
 394     - request_queue_size (only for stream sockets)
 395     - allow_reuse_address
 396
 397     Instance variables:
 398
 399     - server_address
 400     - RequestHandlerClass
 401     - socket
 402
 403     """
 404
 405     address_family = socket.AF_INET
 406
 407     socket_type = socket.SOCK_STREAM
 408
 409     request_queue_size = 5
 410
 411     allow_reuse_address = False
 412
 413     def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):
 414         """Constructor.  May be extended, do not override."""
 415         BaseServer.__init__(self, server_address, RequestHandlerClass)
 416         self.socket = socket.socket(self.address_family,
 417                                     self.socket_type)
 418         if bind_and_activate:
 419             try:
 420                 self.server_bind()
 421                 self.server_activate()
 422             except:
 423                 self.server_close()
 424                 raise
 425
 426     def server_bind(self):
 427         """Called by constructor to bind the socket.
 428
 429         May be overridden.
 430
 431         """
 432         if self.allow_reuse_address:
 433             self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
 434         self.socket.bind(self.server_address)
 435         self.server_address = self.socket.getsockname()
 436
 437     def server_activate(self):
 438         """Called by constructor to activate the server.
 439
 440         May be overridden.
 441
 442         """
 443         self.socket.listen(self.request_queue_size)
 444
 445     def server_close(self):
 446         """Called to clean-up the server.
 447
 448         May be overridden.
 449
 450         """
 451         self.socket.close()
 452
 453     def fileno(self):
 454         """Return socket file number.
 455
 456         Interface required by select().
 457
 458         """
 459         return self.socket.fileno()
 460
 461     def get_request(self):
 462         """Get the request and client address from the socket.
 463
 464         May be overridden.
 465
 466         """
 467         return self.socket.accept()
 468
 469     def shutdown_request(self, request):
 470         """Called to shutdown and close an individual request."""
 471         try:
 472             #explicitly shutdown.  socket.close() merely releases
 473             #the socket and waits for GC to perform the actual close.
 474             request.shutdown(socket.SHUT_WR)
 475         except socket.error:
 476             pass #some platforms may raise ENOTCONN here
 477         self.close_request(request)
 478
 479     def close_request(self, request):
 480         """Called to clean up an individual request."""
 481         request.close()
 482
 483
 484 class UDPServer(TCPServer):
 485
 486     """UDP server class."""
 487
 488     allow_reuse_address = False
 489
 490     socket_type = socket.SOCK_DGRAM
 491
 492     max_packet_size = 8192
 493
 494     def get_request(self):
 495         data, client_addr = self.socket.recvfrom(self.max_packet_size)
 496         return (data, self.socket), client_addr
 497
 498     def server_activate(self):
 499         # No need to call listen() for UDP.
 500         pass
 501
 502     def shutdown_request(self, request):
 503         # No need to shutdown anything.
 504         self.close_request(request)
 505
 506     def close_request(self, request):
 507         # No need to close anything.
 508         pass
 509
 510 class ForkingMixIn:
 511
 512     """Mix-in class to handle each request in a new process."""
 513
 514     timeout = 300
 515     active_children = None
 516     max_children = 40
 517
 518     def collect_children(self):
 519         """Internal routine to wait for children that have exited."""
 520         if self.active_children is None:
 521             return
 522
 523         # If we're above the max number of children, wait and reap them until
 524         # we go back below threshold. Note that we use waitpid(-1) below to be
 525         # able to collect children in size(<defunct children>) syscalls instead
 526         # of size(<children>): the downside is that this might reap children
 527         # which we didn't spawn, which is why we only resort to this when we're
 528         # above max_children.
 529         while len(self.active_children) >= self.max_children:
 530             try:
 531                 pid, _ = os.waitpid(-1, 0)
 532                 self.active_children.discard(pid)
 533             except OSError as e:
 534                 if e.errno == errno.ECHILD:
 535                     # we don't have any children, we're done
 536                     self.active_children.clear()
 537                 elif e.errno != errno.EINTR:
 538                     break
 539
 540         # Now reap all defunct children.
 541         for pid in self.active_children.copy():
 542             try:
 543                 pid, _ = os.waitpid(pid, os.WNOHANG)
 544                 # if the child hasn't exited yet, pid will be 0 and ignored by
 545                 # discard() below
 546                 self.active_children.discard(pid)
 547             except OSError as e:
 548                 if e.errno == errno.ECHILD:
 549                     # someone else reaped it
 550                     self.active_children.discard(pid)
 551
 552     def handle_timeout(self):
 553         """Wait for zombies after self.timeout seconds of inactivity.
 554
 555         May be extended, do not override.
 556         """
 557         self.collect_children()
 558
 559     def process_request(self, request, client_address):
 560         """Fork a new subprocess to process the request."""
 561         self.collect_children()
 562         pid = os.fork()
 563         if pid:
 564             # Parent process
 565             if self.active_children is None:
 566                 self.active_children = set()
 567             self.active_children.add(pid)
 568             self.close_request(request) #close handle in parent process
 569             return
 570         else:
 571             # Child process.
 572             # This must never return, hence os._exit()!
 573             try:
 574                 self.finish_request(request, client_address)
 575                 self.shutdown_request(request)
 576                 os._exit(0)
 577             except:
 578                 try:
 579                     self.handle_error(request, client_address)
 580                     self.shutdown_request(request)
 581                 finally:
 582                     os._exit(1)
 583
 584
 585 class ThreadingMixIn:
 586     """Mix-in class to handle each request in a new thread."""
 587
 588     # Decides how threads will act upon termination of the
 589     # main process
 590     daemon_threads = False
 591
 592     def process_request_thread(self, request, client_address):
 593         """Same as in BaseServer but as a thread.
 594
 595         In addition, exception handling is done here.
 596
 597         """
 598         try:
 599             self.finish_request(request, client_address)
 600             self.shutdown_request(request)
 601         except:
 602             self.handle_error(request, client_address)
 603             self.shutdown_request(request)
 604
 605     def process_request(self, request, client_address):
 606         """Start a new thread to process the request."""
 607         t = threading.Thread(target = self.process_request_thread,
 608                              args = (request, client_address))
 609         t.daemon = self.daemon_threads
 610         t.start()
 611
 612
 613 class ForkingUDPServer(ForkingMixIn, UDPServer): pass
 614 class ForkingTCPServer(ForkingMixIn, TCPServer): pass
 615
 616 class ThreadingUDPServer(ThreadingMixIn, UDPServer): pass
 617 class ThreadingTCPServer(ThreadingMixIn, TCPServer): pass
 618
 619 if hasattr(socket, 'AF_UNIX'):
 620
 621     class UnixStreamServer(TCPServer):
 622         address_family = socket.AF_UNIX
 623
 624     class UnixDatagramServer(UDPServer):
 625         address_family = socket.AF_UNIX
 626
 627     class ThreadingUnixStreamServer(ThreadingMixIn, UnixStreamServer): pass
 628
 629     class ThreadingUnixDatagramServer(ThreadingMixIn, UnixDatagramServer): pass
 630
 631 class BaseRequestHandler:
 632
 633     """Base class for request handler classes.
 634
 635     This class is instantiated for each request to be handled.  The
 636     constructor sets the instance variables request, client_address
 637     and server, and then calls the handle() method.  To implement a
 638     specific service, all you need to do is to derive a class which
 639     defines a handle() method.
 640
 641     The handle() method can find the request as self.request, the
 642     client address as self.client_address, and the server (in case it
 643     needs access to per-server information) as self.server.  Since a
 644     separate instance is created for each request, the handle() method
 645     can define arbitrary other instance variariables.
 646
 647     """
 648
 649     def __init__(self, request, client_address, server):
 650         self.request = request
 651         self.client_address = client_address
 652         self.server = server
 653         self.setup()
 654         try:
 655             self.handle()
 656         finally:
 657             self.finish()
 658
 659     def setup(self):
 660         pass
 661
 662     def handle(self):
 663         pass
 664
 665     def finish(self):
 666         pass
 667
 668
 669 # The following two classes make it possible to use the same service
 670 # class for stream or datagram servers.
 671 # Each class sets up these instance variables:
 672 # - rfile: a file object from which receives the request is read
 673 # - wfile: a file object to which the reply is written
 674 # When the handle() method returns, wfile is flushed properly
 675
 676
 677 class StreamRequestHandler(BaseRequestHandler):
 678
 679     """Define self.rfile and self.wfile for stream sockets."""
 680
 681     # Default buffer sizes for rfile, wfile.
 682     # We default rfile to buffered because otherwise it could be
 683     # really slow for large data (a getc() call per byte); we make
 684     # wfile unbuffered because (a) often after a write() we want to
 685     # read and we need to flush the line; (b) big writes to unbuffered
 686     # files are typically optimized by stdio even when big reads
 687     # aren't.
 688     rbufsize = -1
 689     wbufsize = 0
 690
 691     # A timeout to apply to the request socket, if not None.
 692     timeout = None
 693
 694     # Disable nagle algorithm for this socket, if True.
 695     # Use only when wbufsize != 0, to avoid small packets.
 696     disable_nagle_algorithm = False
 697
 698     def setup(self):
 699         self.connection = self.request
 700         if self.timeout is not None:
 701             self.connection.settimeout(self.timeout)
 702         if self.disable_nagle_algorithm:
 703             self.connection.setsockopt(socket.IPPROTO_TCP,
 704                                        socket.TCP_NODELAY, True)
 705         self.rfile = self.connection.makefile('rb', self.rbufsize)
 706         self.wfile = self.connection.makefile('wb', self.wbufsize)
 707
 708     def finish(self):
 709         if not self.wfile.closed:
 710             try:
 711                 self.wfile.flush()
 712             except socket.error:
 713                 # An final socket error may have occurred here, such as
 714                 # the local error ECONNABORTED.
 715                 pass
 716         self.wfile.close()
 717         self.rfile.close()
 718
 719
 720 class DatagramRequestHandler(BaseRequestHandler):
 721
 722     # XXX Regrettably, I cannot get this working on Linux;
 723     # s.recvfrom() doesn't return a meaningful client address.
 724
 725     """Define self.rfile and self.wfile for datagram sockets."""
 726
 727     def setup(self):
 728         try:
 729             from cStringIO import StringIO
 730         except ImportError:
 731             from StringIO import StringIO
 732         self.packet, self.socket = self.request
 733         self.rfile = StringIO(self.packet)
 734         self.wfile = StringIO()
 735
 736     def finish(self):
 737         self.socket.sendto(self.wfile.getvalue(), self.client_address)