1"""Generic socket server classes. 2 3This module tries to capture the various aspects of defining a server: 4 5For 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 15For 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 25The classes in this module favor the server type that is simplest to 26write: a synchronous TCP/IP server. This is bad class design, but 27save some typing. (There's also the issue that a deep class hierarchy 28slows down method lookups.) 29 30There are five classes in an inheritance diagram, four of which represent 31synchronous 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 47Note that UnixDatagramServer derives from UDPServer, not from 48UnixStreamServer -- the only difference between an IP and a Unix 49stream server is the address family, which is simply repeated in both 50unix server classes. 51 52Forking and threading versions of each type of server can be created 53using the ForkingMixIn and ThreadingMixIn mix-in classes. For 54instance, a threading UDP server class is created as follows: 55 56 class ThreadingUDPServer(ThreadingMixIn, UDPServer): pass 57 58The Mix-in class must come first, since it overrides a method defined 59in UDPServer! Setting the various member variables also changes 60the behavior of the underlying server mechanism. 61 62To implement a service, you must derive a class from 63BaseRequestHandler and redefine its handle() method. You can then run 64various versions of the service by combining one of the server classes 65with your request handler class. 66 67The request handler class must be different for datagram or stream 68services. This can be hidden by using the request handler 69subclasses StreamRequestHandler or DatagramRequestHandler. 70 71Of course, you still have to use your head! 72 73For instance, it makes no sense to use a forking server if the service 74contains state in memory that can be modified by requests (since the 75modifications in the child process would never reach the initial state 76kept in the parent process and passed to each child). In this case, 77you can use a threading server, but you will probably have to use 78locks to avoid two requests that come in nearly simultaneous to apply 79conflicting changes to the server state. 80 81On the other hand, if you are building e.g. an HTTP server, where all 82data is stored externally (e.g. in the file system), a synchronous 83class will essentially render the service "deaf" while one request is 84being handled -- which may be for a very long time if a client is slow 85to read all the data it has requested. Here a threading or forking 86server is appropriate. 87 88In some cases, it may be appropriate to process part of a request 89synchronously, but to finish processing in a forked child depending on 90the request data. This can be implemented by using a synchronous 91server and doing an explicit fork in the request handler class 92handle() method. 93 94Another approach to handling multiple simultaneous requests in an 95environment that supports neither threads nor fork (or where these are 96too expensive or inappropriate for the service) is to maintain an 97explicit table of partially finished requests and to use select() to 98decide which request to work on next (or whether to handle a new 99incoming request). This is particularly important for stream services 100where each client can potentially be connected for a long time (if 101threads or subprocesses cannot be used). 102 103Future 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 109XXX Open problems: 110- What to do with out-of-band data? 111 112BaseServer: 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__version__ = "0.4" 125 126 127import socket 128import select 129import sys 130import os 131import errno 132try: 133 import threading 134except ImportError: 135 import dummy_threading as threading 136 137__all__ = ["TCPServer","UDPServer","ForkingUDPServer","ForkingTCPServer", 138 "ThreadingUDPServer","ThreadingTCPServer","BaseRequestHandler", 139 "StreamRequestHandler","DatagramRequestHandler", 140 "ThreadingMixIn", "ForkingMixIn"] 141if hasattr(socket, "AF_UNIX"): 142 __all__.extend(["UnixStreamServer","UnixDatagramServer", 143 "ThreadingUnixStreamServer", 144 "ThreadingUnixDatagramServer"]) 145 146def _eintr_retry(func, *args): 147 """restart a system call interrupted by EINTR""" 148 while True: 149 try: 150 return func(*args) 151 except (OSError, select.error) as e: 152 if e.args[0] != errno.EINTR: 153 raise 154 155class BaseServer: 156 157 """Base class for server classes. 158 159 Methods for the caller: 160 161 - __init__(server_address, RequestHandlerClass) 162 - serve_forever(poll_interval=0.5) 163 - shutdown() 164 - handle_request() # if you do not use serve_forever() 165 - fileno() -> int # for select() 166 167 Methods that may be overridden: 168 169 - server_bind() 170 - server_activate() 171 - get_request() -> request, client_address 172 - handle_timeout() 173 - verify_request(request, client_address) 174 - server_close() 175 - process_request(request, client_address) 176 - shutdown_request(request) 177 - close_request(request) 178 - handle_error() 179 180 Methods for derived classes: 181 182 - finish_request(request, client_address) 183 184 Class variables that may be overridden by derived classes or 185 instances: 186 187 - timeout 188 - address_family 189 - socket_type 190 - allow_reuse_address 191 192 Instance variables: 193 194 - RequestHandlerClass 195 - socket 196 197 """ 198 199 timeout = None 200 201 def __init__(self, server_address, RequestHandlerClass): 202 """Constructor. May be extended, do not override.""" 203 self.server_address = server_address 204 self.RequestHandlerClass = RequestHandlerClass 205 self.__is_shut_down = threading.Event() 206 self.__shutdown_request = False 207 208 def server_activate(self): 209 """Called by constructor to activate the server. 210 211 May be overridden. 212 213 """ 214 pass 215 216 def serve_forever(self, poll_interval=0.5): 217 """Handle one request at a time until shutdown. 218 219 Polls for shutdown every poll_interval seconds. Ignores 220 self.timeout. If you need to do periodic tasks, do them in 221 another thread. 222 """ 223 self.__is_shut_down.clear() 224 try: 225 while not self.__shutdown_request: 226 # XXX: Consider using another file descriptor or 227 # connecting to the socket to wake this up instead of 228 # polling. Polling reduces our responsiveness to a 229 # shutdown request and wastes cpu at all other times. 230 r, w, e = _eintr_retry(select.select, [self], [], [], 231 poll_interval) 232 # bpo-35017: shutdown() called during select(), exit immediately. 233 if self.__shutdown_request: 234 break 235 if self in r: 236 self._handle_request_noblock() 237 finally: 238 self.__shutdown_request = False 239 self.__is_shut_down.set() 240 241 def shutdown(self): 242 """Stops the serve_forever loop. 243 244 Blocks until the loop has finished. This must be called while 245 serve_forever() is running in another thread, or it will 246 deadlock. 247 """ 248 self.__shutdown_request = True 249 self.__is_shut_down.wait() 250 251 # The distinction between handling, getting, processing and 252 # finishing a request is fairly arbitrary. Remember: 253 # 254 # - handle_request() is the top-level call. It calls 255 # select, get_request(), verify_request() and process_request() 256 # - get_request() is different for stream or datagram sockets 257 # - process_request() is the place that may fork a new process 258 # or create a new thread to finish the request 259 # - finish_request() instantiates the request handler class; 260 # this constructor will handle the request all by itself 261 262 def handle_request(self): 263 """Handle one request, possibly blocking. 264 265 Respects self.timeout. 266 """ 267 # Support people who used socket.settimeout() to escape 268 # handle_request before self.timeout was available. 269 timeout = self.socket.gettimeout() 270 if timeout is None: 271 timeout = self.timeout 272 elif self.timeout is not None: 273 timeout = min(timeout, self.timeout) 274 fd_sets = _eintr_retry(select.select, [self], [], [], timeout) 275 if not fd_sets[0]: 276 self.handle_timeout() 277 return 278 self._handle_request_noblock() 279 280 def _handle_request_noblock(self): 281 """Handle one request, without blocking. 282 283 I assume that select.select has returned that the socket is 284 readable before this function was called, so there should be 285 no risk of blocking in get_request(). 286 """ 287 try: 288 request, client_address = self.get_request() 289 except socket.error: 290 return 291 if self.verify_request(request, client_address): 292 try: 293 self.process_request(request, client_address) 294 except: 295 self.handle_error(request, client_address) 296 self.shutdown_request(request) 297 else: 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 358class 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 484class 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 510class 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 585class 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 613class ForkingUDPServer(ForkingMixIn, UDPServer): pass 614class ForkingTCPServer(ForkingMixIn, TCPServer): pass 615 616class ThreadingUDPServer(ThreadingMixIn, UDPServer): pass 617class ThreadingTCPServer(ThreadingMixIn, TCPServer): pass 618 619if 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 631class 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 other arbitrary instance variables. 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 677class 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 # A 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 720class DatagramRequestHandler(BaseRequestHandler): 721 722 """Define self.rfile and self.wfile for datagram sockets.""" 723 724 def setup(self): 725 try: 726 from cStringIO import StringIO 727 except ImportError: 728 from StringIO import StringIO 729 self.packet, self.socket = self.request 730 self.rfile = StringIO(self.packet) 731 self.wfile = StringIO() 732 733 def finish(self): 734 self.socket.sendto(self.wfile.getvalue(), self.client_address) 735