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