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 (at] 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) 717