/Doc/library/socket.rst
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1:mod:`socket` --- Low-level networking interface 2================================================ 3 4.. module:: socket 5 :synopsis: Low-level networking interface. 6 7 8This module provides access to the BSD *socket* interface. It is available on 9all modern Unix systems, Windows, MacOS, OS/2, and probably additional 10platforms. 11 12.. note:: 13 14 Some behavior may be platform dependent, since calls are made to the operating 15 system socket APIs. 16 17.. index:: object: socket 18 19The Python interface is a straightforward transliteration of the Unix system 20call and library interface for sockets to Python's object-oriented style: the 21:func:`socket` function returns a :dfn:`socket object` whose methods implement 22the various socket system calls. Parameter types are somewhat higher-level than 23in the C interface: as with :meth:`read` and :meth:`write` operations on Python 24files, buffer allocation on receive operations is automatic, and buffer length 25is implicit on send operations. 26 27 28.. seealso:: 29 30 Module :mod:`socketserver` 31 Classes that simplify writing network servers. 32 33 Module :mod:`ssl` 34 A TLS/SSL wrapper for socket objects. 35 36 37Socket families 38--------------- 39 40Depending on the system and the build options, various socket families 41are supported by this module. 42 43Socket addresses are represented as follows: 44 45- A single string is used for the :const:`AF_UNIX` address family. 46 47- A pair ``(host, port)`` is used for the :const:`AF_INET` address family, 48 where *host* is a string representing either a hostname in Internet domain 49 notation like ``'daring.cwi.nl'`` or an IPv4 address like ``'100.50.200.5'``, 50 and *port* is an integral port number. 51 52- For :const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo, 53 scopeid)`` is used, where *flowinfo* and *scopeid* represent the ``sin6_flowinfo`` 54 and ``sin6_scope_id`` members in :const:`struct sockaddr_in6` in C. For 55 :mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for 56 backward compatibility. Note, however, omission of *scopeid* can cause problems 57 in manipulating scoped IPv6 addresses. 58 59- :const:`AF_NETLINK` sockets are represented as pairs ``(pid, groups)``. 60 61- Linux-only support for TIPC is available using the :const:`AF_TIPC` 62 address family. TIPC is an open, non-IP based networked protocol designed 63 for use in clustered computer environments. Addresses are represented by a 64 tuple, and the fields depend on the address type. The general tuple form is 65 ``(addr_type, v1, v2, v3 [, scope])``, where: 66 67 - *addr_type* is one of TIPC_ADDR_NAMESEQ, TIPC_ADDR_NAME, or 68 TIPC_ADDR_ID. 69 - *scope* is one of TIPC_ZONE_SCOPE, TIPC_CLUSTER_SCOPE, and 70 TIPC_NODE_SCOPE. 71 - If *addr_type* is TIPC_ADDR_NAME, then *v1* is the server type, *v2* is 72 the port identifier, and *v3* should be 0. 73 74 If *addr_type* is TIPC_ADDR_NAMESEQ, then *v1* is the server type, *v2* 75 is the lower port number, and *v3* is the upper port number. 76 77 If *addr_type* is TIPC_ADDR_ID, then *v1* is the node, *v2* is the 78 reference, and *v3* should be set to 0. 79 80 If *addr_type* is TIPC_ADDR_ID, then *v1* is the node, *v2* is the 81 reference, and *v3* should be set to 0. 82 83- Certain other address families (:const:`AF_BLUETOOTH`, :const:`AF_PACKET`) 84 support specific representations. 85 86 .. XXX document them! 87 88For IPv4 addresses, two special forms are accepted instead of a host address: 89the empty string represents :const:`INADDR_ANY`, and the string 90``'<broadcast>'`` represents :const:`INADDR_BROADCAST`. This behavior is not 91compatible with IPv6, therefore, you may want to avoid these if you intend 92to support IPv6 with your Python programs. 93 94If you use a hostname in the *host* portion of IPv4/v6 socket address, the 95program may show a nondeterministic behavior, as Python uses the first address 96returned from the DNS resolution. The socket address will be resolved 97differently into an actual IPv4/v6 address, depending on the results from DNS 98resolution and/or the host configuration. For deterministic behavior use a 99numeric address in *host* portion. 100 101All errors raise exceptions. The normal exceptions for invalid argument types 102and out-of-memory conditions can be raised; errors related to socket or address 103semantics raise :exc:`socket.error` or one of its subclasses. 104 105Non-blocking mode is supported through :meth:`~socket.setblocking`. A 106generalization of this based on timeouts is supported through 107:meth:`~socket.settimeout`. 108 109 110Module contents 111--------------- 112 113The module :mod:`socket` exports the following constants and functions: 114 115 116.. exception:: error 117 118 .. index:: module: errno 119 120 A subclass of :exc:`IOError`, this exception is raised for socket-related 121 errors. It is recommended that you inspect its ``errno`` attribute to 122 discriminate between different kinds of errors. 123 124 .. seealso:: 125 The :mod:`errno` module contains symbolic names for the error codes 126 defined by the underlying operating system. 127 128 129.. exception:: herror 130 131 A subclass of :exc:`socket.error`, this exception is raised for 132 address-related errors, i.e. for functions that use *h_errno* in the POSIX 133 C API, including :func:`gethostbyname_ex` and :func:`gethostbyaddr`. 134 The accompanying value is a pair ``(h_errno, string)`` representing an 135 error returned by a library call. *h_errno* is a numeric value, while 136 *string* represents the description of *h_errno*, as returned by the 137 :c:func:`hstrerror` C function. 138 139 140.. exception:: gaierror 141 142 A subclass of :exc:`socket.error`, this exception is raised for 143 address-related errors by :func:`getaddrinfo` and :func:`getnameinfo`. 144 The accompanying value is a pair ``(error, string)`` representing an error 145 returned by a library call. *string* represents the description of 146 *error*, as returned by the :c:func:`gai_strerror` C function. The 147 numeric *error* value will match one of the :const:`EAI_\*` constants 148 defined in this module. 149 150 151.. exception:: timeout 152 153 A subclass of :exc:`socket.error`, this exception is raised when a timeout 154 occurs on a socket which has had timeouts enabled via a prior call to 155 :meth:`~socket.settimeout` (or implicitly through 156 :func:`~socket.setdefaulttimeout`). The accompanying value is a string 157 whose value is currently always "timed out". 158 159 160.. data:: AF_UNIX 161 AF_INET 162 AF_INET6 163 164 These constants represent the address (and protocol) families, used for the 165 first argument to :func:`socket`. If the :const:`AF_UNIX` constant is not 166 defined then this protocol is unsupported. More constants may be available 167 depending on the system. 168 169 170.. data:: SOCK_STREAM 171 SOCK_DGRAM 172 SOCK_RAW 173 SOCK_RDM 174 SOCK_SEQPACKET 175 176 These constants represent the socket types, used for the second argument to 177 :func:`socket`. More constants may be available depending on the system. 178 (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be generally 179 useful.) 180 181.. data:: SOCK_CLOEXEC 182 SOCK_NONBLOCK 183 184 These two constants, if defined, can be combined with the socket types and 185 allow you to set some flags atomically (thus avoiding possible race 186 conditions and the need for separate calls). 187 188 .. seealso:: 189 190 `Secure File Descriptor Handling <http://udrepper.livejournal.com/20407.html>`_ 191 for a more thorough explanation. 192 193 Availability: Linux >= 2.6.27. 194 195 .. versionadded:: 3.2 196 197.. data:: SO_* 198 SOMAXCONN 199 MSG_* 200 SOL_* 201 SCM_* 202 IPPROTO_* 203 IPPORT_* 204 INADDR_* 205 IP_* 206 IPV6_* 207 EAI_* 208 AI_* 209 NI_* 210 TCP_* 211 212 Many constants of these forms, documented in the Unix documentation on sockets 213 and/or the IP protocol, are also defined in the socket module. They are 214 generally used in arguments to the :meth:`setsockopt` and :meth:`getsockopt` 215 methods of socket objects. In most cases, only those symbols that are defined 216 in the Unix header files are defined; for a few symbols, default values are 217 provided. 218 219.. data:: SIO_* 220 RCVALL_* 221 222 Constants for Windows' WSAIoctl(). The constants are used as arguments to the 223 :meth:`ioctl` method of socket objects. 224 225 226.. data:: TIPC_* 227 228 TIPC related constants, matching the ones exported by the C socket API. See 229 the TIPC documentation for more information. 230 231 232.. data:: has_ipv6 233 234 This constant contains a boolean value which indicates if IPv6 is supported on 235 this platform. 236 237 238.. function:: create_connection(address[, timeout[, source_address]]) 239 240 Convenience function. Connect to *address* (a 2-tuple ``(host, port)``), 241 and return the socket object. Passing the optional *timeout* parameter will 242 set the timeout on the socket instance before attempting to connect. If no 243 *timeout* is supplied, the global default timeout setting returned by 244 :func:`getdefaulttimeout` is used. 245 246 If supplied, *source_address* must be a 2-tuple ``(host, port)`` for the 247 socket to bind to as its source address before connecting. If host or port 248 are '' or 0 respectively the OS default behavior will be used. 249 250 .. versionchanged:: 3.2 251 *source_address* was added. 252 253 .. versionchanged:: 3.2 254 support for the :keyword:`with` statement was added. 255 256 257.. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0) 258 259 Translate the *host*/*port* argument into a sequence of 5-tuples that contain 260 all the necessary arguments for creating a socket connected to that service. 261 *host* is a domain name, a string representation of an IPv4/v6 address 262 or ``None``. *port* is a string service name such as ``'http'``, a numeric 263 port number or ``None``. By passing ``None`` as the value of *host* 264 and *port*, you can pass ``NULL`` to the underlying C API. 265 266 The *family*, *type* and *proto* arguments can be optionally specified 267 in order to narrow the list of addresses returned. Passing zero as a 268 value for each of these arguments selects the full range of results. 269 The *flags* argument can be one or several of the ``AI_*`` constants, 270 and will influence how results are computed and returned. 271 For example, :const:`AI_NUMERICHOST` will disable domain name resolution 272 and will raise an error if *host* is a domain name. 273 274 The function returns a list of 5-tuples with the following structure: 275 276 ``(family, type, proto, canonname, sockaddr)`` 277 278 In these tuples, *family*, *type*, *proto* are all integers and are 279 meant to be passed to the :func:`socket` function. *canonname* will be 280 a string representing the canonical name of the *host* if 281 :const:`AI_CANONNAME` is part of the *flags* argument; else *canonname* 282 will be empty. *sockaddr* is a tuple describing a socket address, whose 283 format depends on the returned *family* (a ``(address, port)`` 2-tuple for 284 :const:`AF_INET`, a ``(address, port, flow info, scope id)`` 4-tuple for 285 :const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect` 286 method. 287 288 The following example fetches address information for a hypothetical TCP 289 connection to ``www.python.org`` on port 80 (results may differ on your 290 system if IPv6 isn't enabled):: 291 292 >>> socket.getaddrinfo("www.python.org", 80, proto=socket.SOL_TCP) 293 [(2, 1, 6, '', ('82.94.164.162', 80)), 294 (10, 1, 6, '', ('2001:888:2000:d::a2', 80, 0, 0))] 295 296 .. versionchanged:: 3.2 297 parameters can now be passed as single keyword arguments. 298 299.. function:: getfqdn([name]) 300 301 Return a fully qualified domain name for *name*. If *name* is omitted or empty, 302 it is interpreted as the local host. To find the fully qualified name, the 303 hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the 304 host, if available. The first name which includes a period is selected. In 305 case no fully qualified domain name is available, the hostname as returned by 306 :func:`gethostname` is returned. 307 308 309.. function:: gethostbyname(hostname) 310 311 Translate a host name to IPv4 address format. The IPv4 address is returned as a 312 string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself 313 it is returned unchanged. See :func:`gethostbyname_ex` for a more complete 314 interface. :func:`gethostbyname` does not support IPv6 name resolution, and 315 :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support. 316 317 318.. function:: gethostbyname_ex(hostname) 319 320 Translate a host name to IPv4 address format, extended interface. Return a 321 triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary 322 host name responding to the given *ip_address*, *aliaslist* is a (possibly 323 empty) list of alternative host names for the same address, and *ipaddrlist* is 324 a list of IPv4 addresses for the same interface on the same host (often but not 325 always a single address). :func:`gethostbyname_ex` does not support IPv6 name 326 resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual 327 stack support. 328 329 330.. function:: gethostname() 331 332 Return a string containing the hostname of the machine where the Python 333 interpreter is currently executing. 334 335 If you want to know the current machine's IP address, you may want to use 336 ``gethostbyname(gethostname())``. This operation assumes that there is a 337 valid address-to-host mapping for the host, and the assumption does not 338 always hold. 339 340 Note: :func:`gethostname` doesn't always return the fully qualified domain 341 name; use ``getfqdn()`` (see above). 342 343 344.. function:: gethostbyaddr(ip_address) 345 346 Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the 347 primary host name responding to the given *ip_address*, *aliaslist* is a 348 (possibly empty) list of alternative host names for the same address, and 349 *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same 350 host (most likely containing only a single address). To find the fully qualified 351 domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports 352 both IPv4 and IPv6. 353 354 355.. function:: getnameinfo(sockaddr, flags) 356 357 Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending 358 on the settings of *flags*, the result can contain a fully-qualified domain name 359 or numeric address representation in *host*. Similarly, *port* can contain a 360 string port name or a numeric port number. 361 362 363.. function:: getprotobyname(protocolname) 364 365 Translate an Internet protocol name (for example, ``'icmp'``) to a constant 366 suitable for passing as the (optional) third argument to the :func:`socket` 367 function. This is usually only needed for sockets opened in "raw" mode 368 (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen 369 automatically if the protocol is omitted or zero. 370 371 372.. function:: getservbyname(servicename[, protocolname]) 373 374 Translate an Internet service name and protocol name to a port number for that 375 service. The optional protocol name, if given, should be ``'tcp'`` or 376 ``'udp'``, otherwise any protocol will match. 377 378 379.. function:: getservbyport(port[, protocolname]) 380 381 Translate an Internet port number and protocol name to a service name for that 382 service. The optional protocol name, if given, should be ``'tcp'`` or 383 ``'udp'``, otherwise any protocol will match. 384 385 386.. function:: socket([family[, type[, proto]]]) 387 388 Create a new socket using the given address family, socket type and protocol 389 number. The address family should be :const:`AF_INET` (the default), 390 :const:`AF_INET6` or :const:`AF_UNIX`. The socket type should be 391 :const:`SOCK_STREAM` (the default), :const:`SOCK_DGRAM` or perhaps one of the 392 other ``SOCK_`` constants. The protocol number is usually zero and may be 393 omitted in that case. 394 395 396.. function:: socketpair([family[, type[, proto]]]) 397 398 Build a pair of connected socket objects using the given address family, socket 399 type, and protocol number. Address family, socket type, and protocol number are 400 as for the :func:`socket` function above. The default family is :const:`AF_UNIX` 401 if defined on the platform; otherwise, the default is :const:`AF_INET`. 402 Availability: Unix. 403 404 .. versionchanged:: 3.2 405 The returned socket objects now support the whole socket API, rather 406 than a subset. 407 408 409.. function:: fromfd(fd, family, type[, proto]) 410 411 Duplicate the file descriptor *fd* (an integer as returned by a file object's 412 :meth:`fileno` method) and build a socket object from the result. Address 413 family, socket type and protocol number are as for the :func:`socket` function 414 above. The file descriptor should refer to a socket, but this is not checked --- 415 subsequent operations on the object may fail if the file descriptor is invalid. 416 This function is rarely needed, but can be used to get or set socket options on 417 a socket passed to a program as standard input or output (such as a server 418 started by the Unix inet daemon). The socket is assumed to be in blocking mode. 419 420 421.. function:: ntohl(x) 422 423 Convert 32-bit positive integers from network to host byte order. On machines 424 where the host byte order is the same as network byte order, this is a no-op; 425 otherwise, it performs a 4-byte swap operation. 426 427 428.. function:: ntohs(x) 429 430 Convert 16-bit positive integers from network to host byte order. On machines 431 where the host byte order is the same as network byte order, this is a no-op; 432 otherwise, it performs a 2-byte swap operation. 433 434 435.. function:: htonl(x) 436 437 Convert 32-bit positive integers from host to network byte order. On machines 438 where the host byte order is the same as network byte order, this is a no-op; 439 otherwise, it performs a 4-byte swap operation. 440 441 442.. function:: htons(x) 443 444 Convert 16-bit positive integers from host to network byte order. On machines 445 where the host byte order is the same as network byte order, this is a no-op; 446 otherwise, it performs a 2-byte swap operation. 447 448 449.. function:: inet_aton(ip_string) 450 451 Convert an IPv4 address from dotted-quad string format (for example, 452 '123.45.67.89') to 32-bit packed binary format, as a bytes object four characters in 453 length. This is useful when conversing with a program that uses the standard C 454 library and needs objects of type :c:type:`struct in_addr`, which is the C type 455 for the 32-bit packed binary this function returns. 456 457 :func:`inet_aton` also accepts strings with less than three dots; see the 458 Unix manual page :manpage:`inet(3)` for details. 459 460 If the IPv4 address string passed to this function is invalid, 461 :exc:`socket.error` will be raised. Note that exactly what is valid depends on 462 the underlying C implementation of :c:func:`inet_aton`. 463 464 :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used 465 instead for IPv4/v6 dual stack support. 466 467 468.. function:: inet_ntoa(packed_ip) 469 470 Convert a 32-bit packed IPv4 address (a bytes object four characters in 471 length) to its standard dotted-quad string representation (for example, 472 '123.45.67.89'). This is useful when conversing with a program that uses the 473 standard C library and needs objects of type :c:type:`struct in_addr`, which 474 is the C type for the 32-bit packed binary data this function takes as an 475 argument. 476 477 If the byte sequence passed to this function is not exactly 4 bytes in 478 length, :exc:`socket.error` will be raised. :func:`inet_ntoa` does not 479 support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual 480 stack support. 481 482 483.. function:: inet_pton(address_family, ip_string) 484 485 Convert an IP address from its family-specific string format to a packed, 486 binary format. :func:`inet_pton` is useful when a library or network protocol 487 calls for an object of type :c:type:`struct in_addr` (similar to 488 :func:`inet_aton`) or :c:type:`struct in6_addr`. 489 490 Supported values for *address_family* are currently :const:`AF_INET` and 491 :const:`AF_INET6`. If the IP address string *ip_string* is invalid, 492 :exc:`socket.error` will be raised. Note that exactly what is valid depends on 493 both the value of *address_family* and the underlying implementation of 494 :c:func:`inet_pton`. 495 496 Availability: Unix (maybe not all platforms). 497 498 499.. function:: inet_ntop(address_family, packed_ip) 500 501 Convert a packed IP address (a bytes object of some number of characters) to its 502 standard, family-specific string representation (for example, ``'7.10.0.5'`` or 503 ``'5aef:2b::8'``). :func:`inet_ntop` is useful when a library or network protocol 504 returns an object of type :c:type:`struct in_addr` (similar to :func:`inet_ntoa`) 505 or :c:type:`struct in6_addr`. 506 507 Supported values for *address_family* are currently :const:`AF_INET` and 508 :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the 509 specified address family, :exc:`ValueError` will be raised. A 510 :exc:`socket.error` is raised for errors from the call to :func:`inet_ntop`. 511 512 Availability: Unix (maybe not all platforms). 513 514 515.. 516 XXX: Are sendmsg(), recvmsg() and CMSG_*() available on any 517 non-Unix platforms? The old (obsolete?) 4.2BSD form of the 518 interface, in which struct msghdr has no msg_control or 519 msg_controllen members, is not currently supported. 520 521.. function:: CMSG_LEN(length) 522 523 Return the total length, without trailing padding, of an ancillary 524 data item with associated data of the given *length*. This value 525 can often be used as the buffer size for :meth:`~socket.recvmsg` to 526 receive a single item of ancillary data, but :rfc:`3542` requires 527 portable applications to use :func:`CMSG_SPACE` and thus include 528 space for padding, even when the item will be the last in the 529 buffer. Raises :exc:`OverflowError` if *length* is outside the 530 permissible range of values. 531 532 Availability: most Unix platforms, possibly others. 533 534 .. versionadded:: 3.3 535 536 537.. function:: CMSG_SPACE(length) 538 539 Return the buffer size needed for :meth:`~socket.recvmsg` to 540 receive an ancillary data item with associated data of the given 541 *length*, along with any trailing padding. The buffer space needed 542 to receive multiple items is the sum of the :func:`CMSG_SPACE` 543 values for their associated data lengths. Raises 544 :exc:`OverflowError` if *length* is outside the permissible range 545 of values. 546 547 Note that some systems might support ancillary data without 548 providing this function. Also note that setting the buffer size 549 using the results of this function may not precisely limit the 550 amount of ancillary data that can be received, since additional 551 data may be able to fit into the padding area. 552 553 Availability: most Unix platforms, possibly others. 554 555 .. versionadded:: 3.3 556 557 558.. function:: getdefaulttimeout() 559 560 Return the default timeout in seconds (float) for new socket objects. A value 561 of ``None`` indicates that new socket objects have no timeout. When the socket 562 module is first imported, the default is ``None``. 563 564 565.. function:: setdefaulttimeout(timeout) 566 567 Set the default timeout in seconds (float) for new socket objects. When 568 the socket module is first imported, the default is ``None``. See 569 :meth:`~socket.settimeout` for possible values and their respective 570 meanings. 571 572 573.. function:: sethostname(name) 574 575 Set the machine's hostname to *name*. This will raise a 576 :exc:`socket.error` if you don't have enough rights. 577 578 Availability: Unix. 579 580 .. versionadded:: 3.3 581 582 583.. function:: if_nameindex() 584 585 Return a list of network interface information 586 (index int, name string) tuples. 587 :exc:`socket.error` if the system call fails. 588 589 Availability: Unix. 590 591 .. versionadded:: 3.3 592 593 594.. function:: if_nametoindex(if_name) 595 596 Return a network interface index number corresponding to an 597 interface name. 598 :exc:`socket.error` if no interface with the given name exists. 599 600 Availability: Unix. 601 602 .. versionadded:: 3.3 603 604 605.. function:: if_indextoname(if_index) 606 607 Return a network interface name corresponding to a 608 interface index number. 609 :exc:`socket.error` if no interface with the given index exists. 610 611 Availability: Unix. 612 613 .. versionadded:: 3.3 614 615 616.. data:: SocketType 617 618 This is a Python type object that represents the socket object type. It is the 619 same as ``type(socket(...))``. 620 621 622.. _socket-objects: 623 624Socket Objects 625-------------- 626 627Socket objects have the following methods. Except for :meth:`makefile` these 628correspond to Unix system calls applicable to sockets. 629 630 631.. method:: socket.accept() 632 633 Accept a connection. The socket must be bound to an address and listening for 634 connections. The return value is a pair ``(conn, address)`` where *conn* is a 635 *new* socket object usable to send and receive data on the connection, and 636 *address* is the address bound to the socket on the other end of the connection. 637 638 639.. method:: socket.bind(address) 640 641 Bind the socket to *address*. The socket must not already be bound. (The format 642 of *address* depends on the address family --- see above.) 643 644 645.. method:: socket.close() 646 647 Close the socket. All future operations on the socket object will fail. The 648 remote end will receive no more data (after queued data is flushed). Sockets are 649 automatically closed when they are garbage-collected. 650 651 .. note:: 652 :meth:`close()` releases the resource associated with a connection but 653 does not necessarily close the connection immediately. If you want 654 to close the connection in a timely fashion, call :meth:`shutdown()` 655 before :meth:`close()`. 656 657 658.. method:: socket.connect(address) 659 660 Connect to a remote socket at *address*. (The format of *address* depends on the 661 address family --- see above.) 662 663 664.. method:: socket.connect_ex(address) 665 666 Like ``connect(address)``, but return an error indicator instead of raising an 667 exception for errors returned by the C-level :c:func:`connect` call (other 668 problems, such as "host not found," can still raise exceptions). The error 669 indicator is ``0`` if the operation succeeded, otherwise the value of the 670 :c:data:`errno` variable. This is useful to support, for example, asynchronous 671 connects. 672 673 674.. method:: socket.detach() 675 676 Put the socket object into closed state without actually closing the 677 underlying file descriptor. The file descriptor is returned, and can 678 be reused for other purposes. 679 680 .. versionadded:: 3.2 681 682 683.. method:: socket.fileno() 684 685 Return the socket's file descriptor (a small integer). This is useful with 686 :func:`select.select`. 687 688 Under Windows the small integer returned by this method cannot be used where a 689 file descriptor can be used (such as :func:`os.fdopen`). Unix does not have 690 this limitation. 691 692 693.. method:: socket.getpeername() 694 695 Return the remote address to which the socket is connected. This is useful to 696 find out the port number of a remote IPv4/v6 socket, for instance. (The format 697 of the address returned depends on the address family --- see above.) On some 698 systems this function is not supported. 699 700 701.. method:: socket.getsockname() 702 703 Return the socket's own address. This is useful to find out the port number of 704 an IPv4/v6 socket, for instance. (The format of the address returned depends on 705 the address family --- see above.) 706 707 708.. method:: socket.getsockopt(level, optname[, buflen]) 709 710 Return the value of the given socket option (see the Unix man page 711 :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.) 712 are defined in this module. If *buflen* is absent, an integer option is assumed 713 and its integer value is returned by the function. If *buflen* is present, it 714 specifies the maximum length of the buffer used to receive the option in, and 715 this buffer is returned as a bytes object. It is up to the caller to decode the 716 contents of the buffer (see the optional built-in module :mod:`struct` for a way 717 to decode C structures encoded as byte strings). 718 719 720.. method:: socket.gettimeout() 721 722 Return the timeout in seconds (float) associated with socket operations, 723 or ``None`` if no timeout is set. This reflects the last call to 724 :meth:`setblocking` or :meth:`settimeout`. 725 726 727.. method:: socket.ioctl(control, option) 728 729 :platform: Windows 730 731 The :meth:`ioctl` method is a limited interface to the WSAIoctl system 732 interface. Please refer to the `Win32 documentation 733 <http://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more 734 information. 735 736 On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl` 737 functions may be used; they accept a socket object as their first argument. 738 739.. method:: socket.listen(backlog) 740 741 Listen for connections made to the socket. The *backlog* argument specifies the 742 maximum number of queued connections and should be at least 0; the maximum value 743 is system-dependent (usually 5), the minimum value is forced to 0. 744 745 746.. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \ 747 errors=None, newline=None) 748 749 .. index:: single: I/O control; buffering 750 751 Return a :term:`file object` associated with the socket. The exact returned 752 type depends on the arguments given to :meth:`makefile`. These arguments are 753 interpreted the same way as by the built-in :func:`open` function. 754 755 Closing the file object won't close the socket unless there are no remaining 756 references to the socket. The socket must be in blocking mode; it can have 757 a timeout, but the file object's internal buffer may end up in a inconsistent 758 state if a timeout occurs. 759 760 .. note:: 761 762 On Windows, the file-like object created by :meth:`makefile` cannot be 763 used where a file object with a file descriptor is expected, such as the 764 stream arguments of :meth:`subprocess.Popen`. 765 766 767.. method:: socket.recv(bufsize[, flags]) 768 769 Receive data from the socket. The return value is a bytes object representing the 770 data received. The maximum amount of data to be received at once is specified 771 by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of 772 the optional argument *flags*; it defaults to zero. 773 774 .. note:: 775 776 For best match with hardware and network realities, the value of *bufsize* 777 should be a relatively small power of 2, for example, 4096. 778 779 780.. method:: socket.recvfrom(bufsize[, flags]) 781 782 Receive data from the socket. The return value is a pair ``(bytes, address)`` 783 where *bytes* is a bytes object representing the data received and *address* is the 784 address of the socket sending the data. See the Unix manual page 785 :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults 786 to zero. (The format of *address* depends on the address family --- see above.) 787 788 789.. method:: socket.recvmsg(bufsize[, ancbufsize[, flags]]) 790 791 Receive normal data (up to *bufsize* bytes) and ancillary data from 792 the socket. The *ancbufsize* argument sets the size in bytes of 793 the internal buffer used to receive the ancillary data; it defaults 794 to 0, meaning that no ancillary data will be received. Appropriate 795 buffer sizes for ancillary data can be calculated using 796 :func:`CMSG_SPACE` or :func:`CMSG_LEN`, and items which do not fit 797 into the buffer might be truncated or discarded. The *flags* 798 argument defaults to 0 and has the same meaning as for 799 :meth:`recv`. 800 801 The return value is a 4-tuple: ``(data, ancdata, msg_flags, 802 address)``. The *data* item is a :class:`bytes` object holding the 803 non-ancillary data received. The *ancdata* item is a list of zero 804 or more tuples ``(cmsg_level, cmsg_type, cmsg_data)`` representing 805 the ancillary data (control messages) received: *cmsg_level* and 806 *cmsg_type* are integers specifying the protocol level and 807 protocol-specific type respectively, and *cmsg_data* is a 808 :class:`bytes` object holding the associated data. The *msg_flags* 809 item is the bitwise OR of various flags indicating conditions on 810 the received message; see your system documentation for details. 811 If the receiving socket is unconnected, *address* is the address of 812 the sending socket, if available; otherwise, its value is 813 unspecified. 814 815 On some systems, :meth:`sendmsg` and :meth:`recvmsg` can be used to 816 pass file descriptors between processes over an :const:`AF_UNIX` 817 socket. When this facility is used (it is often restricted to 818 :const:`SOCK_STREAM` sockets), :meth:`recvmsg` will return, in its 819 ancillary data, items of the form ``(socket.SOL_SOCKET, 820 socket.SCM_RIGHTS, fds)``, where *fds* is a :class:`bytes` object 821 representing the new file descriptors as a binary array of the 822 native C :c:type:`int` type. If :meth:`recvmsg` raises an 823 exception after the system call returns, it will first attempt to 824 close any file descriptors received via this mechanism. 825 826 Some systems do not indicate the truncated length of ancillary data 827 items which have been only partially received. If an item appears 828 to extend beyond the end of the buffer, :meth:`recvmsg` will issue 829 a :exc:`RuntimeWarning`, and will return the part of it which is 830 inside the buffer provided it has not been truncated before the 831 start of its associated data. 832 833 On systems which support the :const:`SCM_RIGHTS` mechanism, the 834 following function will receive up to *maxfds* file descriptors, 835 returning the message data and a list containing the descriptors 836 (while ignoring unexpected conditions such as unrelated control 837 messages being received). See also :meth:`sendmsg`. :: 838 839 import socket, array 840 841 def recv_fds(sock, msglen, maxfds): 842 fds = array.array("i") # Array of ints 843 msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize)) 844 for cmsg_level, cmsg_type, cmsg_data in ancdata: 845 if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS): 846 # Append data, ignoring any truncated integers at the end. 847 fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)]) 848 return msg, list(fds) 849 850 Availability: most Unix platforms, possibly others. 851 852 .. versionadded:: 3.3 853 854 855.. method:: socket.recvmsg_into(buffers[, ancbufsize[, flags]]) 856 857 Receive normal data and ancillary data from the socket, behaving as 858 :meth:`recvmsg` would, but scatter the non-ancillary data into a 859 series of buffers instead of returning a new bytes object. The 860 *buffers* argument must be an iterable of objects that export 861 writable buffers (e.g. :class:`bytearray` objects); these will be 862 filled with successive chunks of the non-ancillary data until it 863 has all been written or there are no more buffers. The operating 864 system may set a limit (:func:`~os.sysconf` value ``SC_IOV_MAX``) 865 on the number of buffers that can be used. The *ancbufsize* and 866 *flags* arguments have the same meaning as for :meth:`recvmsg`. 867 868 The return value is a 4-tuple: ``(nbytes, ancdata, msg_flags, 869 address)``, where *nbytes* is the total number of bytes of 870 non-ancillary data written into the buffers, and *ancdata*, 871 *msg_flags* and *address* are the same as for :meth:`recvmsg`. 872 873 Example:: 874 875 >>> import socket 876 >>> s1, s2 = socket.socketpair() 877 >>> b1 = bytearray(b'----') 878 >>> b2 = bytearray(b'0123456789') 879 >>> b3 = bytearray(b'--------------') 880 >>> s1.send(b'Mary had a little lamb') 881 22 882 >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3]) 883 (22, [], 0, None) 884 >>> [b1, b2, b3] 885 [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')] 886 887 Availability: most Unix platforms, possibly others. 888 889 .. versionadded:: 3.3 890 891 892.. method:: socket.recvfrom_into(buffer[, nbytes[, flags]]) 893 894 Receive data from the socket, writing it into *buffer* instead of creating a 895 new bytestring. The return value is a pair ``(nbytes, address)`` where *nbytes* is 896 the number of bytes received and *address* is the address of the socket sending 897 the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the 898 optional argument *flags*; it defaults to zero. (The format of *address* 899 depends on the address family --- see above.) 900 901 902.. method:: socket.recv_into(buffer[, nbytes[, flags]]) 903 904 Receive up to *nbytes* bytes from the socket, storing the data into a buffer 905 rather than creating a new bytestring. If *nbytes* is not specified (or 0), 906 receive up to the size available in the given buffer. Returns the number of 907 bytes received. See the Unix manual page :manpage:`recv(2)` for the meaning 908 of the optional argument *flags*; it defaults to zero. 909 910 911.. method:: socket.send(bytes[, flags]) 912 913 Send data to the socket. The socket must be connected to a remote socket. The 914 optional *flags* argument has the same meaning as for :meth:`recv` above. 915 Returns the number of bytes sent. Applications are responsible for checking that 916 all data has been sent; if only some of the data was transmitted, the 917 application needs to attempt delivery of the remaining data. 918 919 920.. method:: socket.sendall(bytes[, flags]) 921 922 Send data to the socket. The socket must be connected to a remote socket. The 923 optional *flags* argument has the same meaning as for :meth:`recv` above. 924 Unlike :meth:`send`, this method continues to send data from *bytes* until 925 either all data has been sent or an error occurs. ``None`` is returned on 926 success. On error, an exception is raised, and there is no way to determine how 927 much data, if any, was successfully sent. 928 929 930.. method:: socket.sendto(bytes[, flags], address) 931 932 Send data to the socket. The socket should not be connected to a remote socket, 933 since the destination socket is specified by *address*. The optional *flags* 934 argument has the same meaning as for :meth:`recv` above. Return the number of 935 bytes sent. (The format of *address* depends on the address family --- see 936 above.) 937 938 939.. method:: socket.sendmsg(buffers[, ancdata[, flags[, address]]]) 940 941 Send normal and ancillary data to the socket, gathering the 942 non-ancillary data from a series of buffers and concatenating it 943 into a single message. The *buffers* argument specifies the 944 non-ancillary data as an iterable of buffer-compatible objects 945 (e.g. :class:`bytes` objects); the operating system may set a limit 946 (:func:`~os.sysconf` value ``SC_IOV_MAX``) on the number of buffers 947 that can be used. The *ancdata* argument specifies the ancillary 948 data (control messages) as an iterable of zero or more tuples 949 ``(cmsg_level, cmsg_type, cmsg_data)``, where *cmsg_level* and 950 *cmsg_type* are integers specifying the protocol level and 951 protocol-specific type respectively, and *cmsg_data* is a 952 buffer-compatible object holding the associated data. Note that 953 some systems (in particular, systems without :func:`CMSG_SPACE`) 954 might support sending only one control message per call. The 955 *flags* argument defaults to 0 and has the same meaning as for 956 :meth:`send`. If *address* is supplied and not ``None``, it sets a 957 destination address for the message. The return value is the 958 number of bytes of non-ancillary data sent. 959 960 The following function sends the list of file descriptors *fds* 961 over an :const:`AF_UNIX` socket, on systems which support the 962 :const:`SCM_RIGHTS` mechanism. See also :meth:`recvmsg`. :: 963 964 import socket, array 965 966 def send_fds(sock, msg, fds): 967 return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))]) 968 969 Availability: most Unix platforms, possibly others. 970 971 .. versionadded:: 3.3 972 973 974.. method:: socket.setblocking(flag) 975 976 Set blocking or non-blocking mode of the socket: if *flag* is false, the 977 socket is set to non-blocking, else to blocking mode. 978 979 This method is a shorthand for certain :meth:`~socket.settimeout` calls: 980 981 * ``sock.setblocking(True)`` is equivalent to ``sock.settimeout(None)`` 982 983 * ``sock.setblocking(False)`` is equivalent to ``sock.settimeout(0.0)`` 984 985 986.. method:: socket.settimeout(value) 987 988 Set a timeout on blocking socket operations. The *value* argument can be a 989 nonnegative floating point number expressing seconds, or ``None``. 990 If a non-zero value is given, subsequent socket operations will raise a 991 :exc:`timeout` exception if the timeout period *value* has elapsed before 992 the operation has completed. If zero is given, the socket is put in 993 non-blocking mode. If ``None`` is given, the socket is put in blocking mode. 994 995 For further information, please consult the :ref:`notes on socket timeouts <socket-timeouts>`. 996 997 998.. method:: socket.setsockopt(level, optname, value) 999 1000 .. index:: module: struct 1001 1002 Set the value of the given socket option (see the Unix manual page 1003 :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the 1004 :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a 1005 bytes object representing a buffer. In the latter case it is up to the caller to 1006 ensure that the bytestring contains the proper bits (see the optional built-in 1007 module :mod:`struct` for a way to encode C structures as bytestrings). 1008 1009 1010.. method:: socket.shutdown(how) 1011 1012 Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`, 1013 further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends 1014 are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are 1015 disallowed. Depending on the platform, shutting down one half of the connection 1016 can also close the opposite half (e.g. on Mac OS X, ``shutdown(SHUT_WR)`` does 1017 not allow further reads on the other end of the connection). 1018 1019Note that there are no methods :meth:`read` or :meth:`write`; use 1020:meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead. 1021 1022Socket objects also have these (read-only) attributes that correspond to the 1023values given to the :class:`socket` constructor. 1024 1025 1026.. attribute:: socket.family 1027 1028 The socket family. 1029 1030 1031.. attribute:: socket.type 1032 1033 The socket type. 1034 1035 1036.. attribute:: socket.proto 1037 1038 The socket protocol. 1039 1040 1041 1042.. _socket-timeouts: 1043 1044Notes on socket timeouts 1045------------------------ 1046 1047A socket object can be in one of three modes: blocking, non-blocking, or 1048timeout. Sockets are by default always created in blocking mode, but this 1049can be changed by calling :func:`setdefaulttimeout`. 1050 1051* In *blocking mode*, operations block until complete or the system returns 1052 an error (such as connection timed out). 1053 1054* In *non-blocking mode*, operations fail (with an error that is unfortunately 1055 system-dependent) if they cannot be completed immediately: functions from the 1056 :mod:`select` can be used to know when and whether a socket is available for 1057 reading or writing. 1058 1059* In *timeout mode*, operations fail if they cannot be completed within the 1060 timeout specified for the socket (they raise a :exc:`timeout` exception) 1061 or if the system returns an error. 1062 1063.. note:: 1064 At the operating system level, sockets in *timeout mode* are internally set 1065 in non-blocking mode. Also, the blocking and timeout modes are shared between 1066 file descriptors and socket objects that refer to the same network endpoint. 1067 This implementation detail can have visible consequences if e.g. you decide 1068 to use the :meth:`~socket.fileno()` of a socket. 1069 1070Timeouts and the ``connect`` method 1071^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1072 1073The :meth:`~socket.connect` operation is also subject to the timeout 1074setting, and in general it is recommended to call :meth:`~socket.settimeout` 1075before calling :meth:`~socket.connect` or pass a timeout parameter to 1076:meth:`create_connection`. However, the system network stack may also 1077return a connection timeout error of its own regardless of any Python socket 1078timeout setting. 1079 1080Timeouts and the ``accept`` method 1081^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1082 1083If :func:`getdefaulttimeout` is not :const:`None`, sockets returned by 1084the :meth:`~socket.accept` method inherit that timeout. Otherwise, the 1085behaviour depends on settings of the listening socket: 1086 1087* if the listening socket is in *blocking mode* or in *timeout mode*, 1088 the socket returned by :meth:`~socket.accept` is in *blocking mode*; 1089 1090* if the listening socket is in *non-blocking mode*, whether the socket 1091 returned by :meth:`~socket.accept` is in blocking or non-blocking mode 1092 is operating system-dependent. If you want to ensure cross-platform 1093 behaviour, it is recommended you manually override this setting. 1094 1095 1096.. _socket-example: 1097 1098Example 1099------- 1100 1101Here are four minimal example programs using the TCP/IP protocol: a server that 1102echoes all data that it receives back (servicing only one client), and a client 1103using it. Note that a server must perform the sequence :func:`socket`, 1104:meth:`~socket.bind`, :meth:`~socket.listen`, :meth:`~socket.accept` (possibly 1105repeating the :meth:`~socket.accept` to service more than one client), while a 1106client only needs the sequence :func:`socket`, :meth:`~socket.connect`. Also 1107note that the server does not :meth:`~socket.send`/:meth:`~socket.recv` on the 1108socket it is listening on but on the new socket returned by 1109:meth:`~socket.accept`. 1110 1111The first two examples support IPv4 only. :: 1112 1113 # Echo server program 1114 import socket 1115 1116 HOST = '' # Symbolic name meaning all available interfaces 1117 PORT = 50007 # Arbitrary non-privileged port 1118 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1119 s.bind((HOST, PORT)) 1120 s.listen(1) 1121 conn, addr = s.accept() 1122 print('Connected by', addr) 1123 while True: 1124 data = conn.recv(1024) 1125 if not data: break 1126 conn.send(data) 1127 conn.close() 1128 1129:: 1130 1131 # Echo client program 1132 import socket 1133 1134 HOST = 'daring.cwi.nl' # The remote host 1135 PORT = 50007 # The same port as used by the server 1136 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1137 s.connect((HOST, PORT)) 1138 s.send(b'Hello, world') 1139 data = s.recv(1024) 1140 s.close() 1141 print('Received', repr(data)) 1142 1143The next two examples are identical to the above two, but support both IPv4 and 1144IPv6. The server side will listen to the first address family available (it 1145should listen to both instead). On most of IPv6-ready systems, IPv6 will take 1146precedence and the server may not accept IPv4 traffic. The client side will try 1147to connect to the all addresses returned as a result of the name resolution, and 1148sends traffic to the first one connected successfully. :: 1149 1150 # Echo server program 1151 import socket 1152 import sys 1153 1154 HOST = None # Symbolic name meaning all available interfaces 1155 PORT = 50007 # Arbitrary non-privileged port 1156 s = None 1157 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, 1158 socket.SOCK_STREAM, 0, socket.AI_PASSIVE): 1159 af, socktype, proto, canonname, sa = res 1160 try: 1161 s = socket.socket(af, socktype, proto) 1162 except socket.error as msg: 1163 s = None 1164 continue 1165 try: 1166 s.bind(sa) 1167 s.listen(1) 1168 except socket.error as msg: 1169 s.close() 1170 s = None 1171 continue 1172 break 1173 if s is None: 1174 print('could not open socket') 1175 sys.exit(1) 1176 conn, addr = s.accept() 1177 print('Connected by', addr) 1178 while True: 1179 data = conn.recv(1024) 1180 if not data: break 1181 conn.send(data) 1182 conn.close() 1183 1184:: 1185 1186 # Echo client program 1187 import socket 1188 import sys 1189 1190 HOST = 'daring.cwi.nl' # The remote host 1191 PORT = 50007 # The same port as used by the server 1192 s = None 1193 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM): 1194 af, socktype, proto, canonname, sa = res 1195 try: 1196 s = socket.socket(af, socktype, proto) 1197 except socket.error as msg: 1198 s = None 1199 continue 1200 try: 1201 s.connect(sa) 1202 except socket.error as msg: 1203 s.close() 1204 s = None 1205 continue 1206 break 1207 if s is None: 1208 print('could not open socket') 1209 sys.exit(1) 1210 s.send(b'Hello, world') 1211 data = s.recv(1024) 1212 s.close() 1213 print('Received', repr(data)) 1214 1215 1216The last example shows how to write a very simple network sniffer with raw 1217sockets on Windows. The example requires administrator privileges to modify 1218the interface:: 1219 1220 import socket 1221 1222 # the public network interface 1223 HOST = socket.gethostbyname(socket.gethostname()) 1224 1225 # create a raw socket and bind it to the public interface 1226 s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP) 1227 s.bind((HOST, 0)) 1228 1229 # Include IP headers 1230 s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1) 1231 1232 # receive all packages 1233 s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON) 1234 1235 # receive a package 1236 print(s.recvfrom(65565)) 1237 1238 # disabled promiscuous mode 1239 s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF) 1240 1241 1242Running an example several times with too small delay between executions, could 1243lead to this error:: 1244 1245 socket.error: [Errno 98] Address already in use 1246 1247This is because the previous execution has left the socket in a ``TIME_WAIT`` 1248state, and can't be immediately reused. 1249 1250There is a :mod:`socket` flag to set, in order to prevent this, 1251:data:`socket.SO_REUSEADDR`:: 1252 1253 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1254 s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) 1255 s.bind((HOST, PORT)) 1256 1257the :data:`SO_REUSEADDR` flag tells the kernel to reuse a local socket in 1258``TIME_WAIT`` state, without waiting for its natural timeout to expire. 1259 1260 1261.. seealso:: 1262 1263 For an introduction to socket programming (in C), see the following papers: 1264 1265 - *An Introductory 4.3BSD Interprocess Communication Tutorial*, by Stuart Sechrest 1266 1267 - *An Advanced 4.3BSD Interprocess Communication Tutorial*, by Samuel J. Leffler et 1268 al, 1269 1270 bo…
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