/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 43The address format required by a particular socket object is automatically 44selected based on the address family specified when the socket object was 45created. Socket addresses are represented as follows: 46 47- The address of an :const:`AF_UNIX` socket bound to a file system node 48 is represented as a string, using the file system encoding and the 49 ``'surrogateescape'`` error handler (see :pep:`383`). An address in 50 Linux's abstract namespace is returned as a :class:`bytes` object with 51 an initial null byte; note that sockets in this namespace can 52 communicate with normal file system sockets, so programs intended to 53 run on Linux may need to deal with both types of address. A string or 54 :class:`bytes` object can be used for either type of address when 55 passing it as an argument. 56 57 .. versionchanged:: 3.3 58 Previously, :const:`AF_UNIX` socket paths were assumed to use UTF-8 59 encoding. 60 61- A pair ``(host, port)`` is used for the :const:`AF_INET` address family, 62 where *host* is a string representing either a hostname in Internet domain 63 notation like ``'daring.cwi.nl'`` or an IPv4 address like ``'100.50.200.5'``, 64 and *port* is an integer. 65 66- For :const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo, 67 scopeid)`` is used, where *flowinfo* and *scopeid* represent the ``sin6_flowinfo`` 68 and ``sin6_scope_id`` members in :const:`struct sockaddr_in6` in C. For 69 :mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for 70 backward compatibility. Note, however, omission of *scopeid* can cause problems 71 in manipulating scoped IPv6 addresses. 72 73- :const:`AF_NETLINK` sockets are represented as pairs ``(pid, groups)``. 74 75- Linux-only support for TIPC is available using the :const:`AF_TIPC` 76 address family. TIPC is an open, non-IP based networked protocol designed 77 for use in clustered computer environments. Addresses are represented by a 78 tuple, and the fields depend on the address type. The general tuple form is 79 ``(addr_type, v1, v2, v3 [, scope])``, where: 80 81 - *addr_type* is one of :const:`TIPC_ADDR_NAMESEQ`, :const:`TIPC_ADDR_NAME`, 82 or :const:`TIPC_ADDR_ID`. 83 - *scope* is one of :const:`TIPC_ZONE_SCOPE`, :const:`TIPC_CLUSTER_SCOPE`, and 84 :const:`TIPC_NODE_SCOPE`. 85 - If *addr_type* is :const:`TIPC_ADDR_NAME`, then *v1* is the server type, *v2* is 86 the port identifier, and *v3* should be 0. 87 88 If *addr_type* is :const:`TIPC_ADDR_NAMESEQ`, then *v1* is the server type, *v2* 89 is the lower port number, and *v3* is the upper port number. 90 91 If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the 92 reference, and *v3* should be set to 0. 93 94 If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the 95 reference, and *v3* should be set to 0. 96 97- A tuple ``(interface, )`` is used for the :const:`AF_CAN` address family, 98 where *interface* is a string representing a network interface name like 99 ``'can0'``. The network interface name ``''`` can be used to receive packets 100 from all network interfaces of this family. 101 102- A string or a tuple ``(id, unit)`` is used for the :const:`SYSPROTO_CONTROL` 103 protocol of the :const:`PF_SYSTEM` family. The string is the name of a 104 kernel control using a dynamically-assigned ID. The tuple can be used if ID 105 and unit number of the kernel control are known or if a registered ID is 106 used. 107 108 .. versionadded:: 3.3 109 110- Certain other address families (:const:`AF_BLUETOOTH`, :const:`AF_PACKET`) 111 support specific representations. 112 113 .. XXX document them! 114 115For IPv4 addresses, two special forms are accepted instead of a host address: 116the empty string represents :const:`INADDR_ANY`, and the string 117``'<broadcast>'`` represents :const:`INADDR_BROADCAST`. This behavior is not 118compatible with IPv6, therefore, you may want to avoid these if you intend 119to support IPv6 with your Python programs. 120 121If you use a hostname in the *host* portion of IPv4/v6 socket address, the 122program may show a nondeterministic behavior, as Python uses the first address 123returned from the DNS resolution. The socket address will be resolved 124differently into an actual IPv4/v6 address, depending on the results from DNS 125resolution and/or the host configuration. For deterministic behavior use a 126numeric address in *host* portion. 127 128All errors raise exceptions. The normal exceptions for invalid argument types 129and out-of-memory conditions can be raised; starting from Python 3.3, errors 130related to socket or address semantics raise :exc:`OSError` or one of its 131subclasses (they used to raise :exc:`socket.error`). 132 133Non-blocking mode is supported through :meth:`~socket.setblocking`. A 134generalization of this based on timeouts is supported through 135:meth:`~socket.settimeout`. 136 137 138Module contents 139--------------- 140 141The module :mod:`socket` exports the following constants and functions: 142 143 144.. exception:: error 145 146 A deprecated alias of :exc:`OSError`. 147 148 .. versionchanged:: 3.3 149 Following :pep:`3151`, this class was made an alias of :exc:`OSError`. 150 151 152.. exception:: herror 153 154 A subclass of :exc:`OSError`, this exception is raised for 155 address-related errors, i.e. for functions that use *h_errno* in the POSIX 156 C API, including :func:`gethostbyname_ex` and :func:`gethostbyaddr`. 157 The accompanying value is a pair ``(h_errno, string)`` representing an 158 error returned by a library call. *h_errno* is a numeric value, while 159 *string* represents the description of *h_errno*, as returned by the 160 :c:func:`hstrerror` C function. 161 162 .. versionchanged:: 3.3 163 This class was made a subclass of :exc:`OSError`. 164 165.. exception:: gaierror 166 167 A subclass of :exc:`OSError`, this exception is raised for 168 address-related errors by :func:`getaddrinfo` and :func:`getnameinfo`. 169 The accompanying value is a pair ``(error, string)`` representing an error 170 returned by a library call. *string* represents the description of 171 *error*, as returned by the :c:func:`gai_strerror` C function. The 172 numeric *error* value will match one of the :const:`EAI_\*` constants 173 defined in this module. 174 175 .. versionchanged:: 3.3 176 This class was made a subclass of :exc:`OSError`. 177 178.. exception:: timeout 179 180 A subclass of :exc:`OSError`, this exception is raised when a timeout 181 occurs on a socket which has had timeouts enabled via a prior call to 182 :meth:`~socket.settimeout` (or implicitly through 183 :func:`~socket.setdefaulttimeout`). The accompanying value is a string 184 whose value is currently always "timed out". 185 186 .. versionchanged:: 3.3 187 This class was made a subclass of :exc:`OSError`. 188 189.. data:: AF_UNIX 190 AF_INET 191 AF_INET6 192 193 These constants represent the address (and protocol) families, used for the 194 first argument to :func:`socket`. If the :const:`AF_UNIX` constant is not 195 defined then this protocol is unsupported. More constants may be available 196 depending on the system. 197 198 199.. data:: SOCK_STREAM 200 SOCK_DGRAM 201 SOCK_RAW 202 SOCK_RDM 203 SOCK_SEQPACKET 204 205 These constants represent the socket types, used for the second argument to 206 :func:`socket`. More constants may be available depending on the system. 207 (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be generally 208 useful.) 209 210.. data:: SOCK_CLOEXEC 211 SOCK_NONBLOCK 212 213 These two constants, if defined, can be combined with the socket types and 214 allow you to set some flags atomically (thus avoiding possible race 215 conditions and the need for separate calls). 216 217 .. seealso:: 218 219 `Secure File Descriptor Handling <http://udrepper.livejournal.com/20407.html>`_ 220 for a more thorough explanation. 221 222 Availability: Linux >= 2.6.27. 223 224 .. versionadded:: 3.2 225 226.. data:: SO_* 227 SOMAXCONN 228 MSG_* 229 SOL_* 230 SCM_* 231 IPPROTO_* 232 IPPORT_* 233 INADDR_* 234 IP_* 235 IPV6_* 236 EAI_* 237 AI_* 238 NI_* 239 TCP_* 240 241 Many constants of these forms, documented in the Unix documentation on sockets 242 and/or the IP protocol, are also defined in the socket module. They are 243 generally used in arguments to the :meth:`setsockopt` and :meth:`getsockopt` 244 methods of socket objects. In most cases, only those symbols that are defined 245 in the Unix header files are defined; for a few symbols, default values are 246 provided. 247 248.. data:: AF_CAN 249 PF_CAN 250 SOL_CAN_* 251 CAN_* 252 253 Many constants of these forms, documented in the Linux documentation, are 254 also defined in the socket module. 255 256 Availability: Linux >= 2.6.25. 257 258 .. versionadded:: 3.3 259 260 261.. data:: AF_RDS 262 PF_RDS 263 SOL_RDS 264 RDS_* 265 266 Many constants of these forms, documented in the Linux documentation, are 267 also defined in the socket module. 268 269 Availability: Linux >= 2.6.30. 270 271 .. versionadded:: 3.3 272 273 274.. data:: SIO_* 275 RCVALL_* 276 277 Constants for Windows' WSAIoctl(). The constants are used as arguments to the 278 :meth:`ioctl` method of socket objects. 279 280 281.. data:: TIPC_* 282 283 TIPC related constants, matching the ones exported by the C socket API. See 284 the TIPC documentation for more information. 285 286 287.. data:: has_ipv6 288 289 This constant contains a boolean value which indicates if IPv6 is supported on 290 this platform. 291 292 293.. function:: create_connection(address[, timeout[, source_address]]) 294 295 Connect to a TCP service listening on the Internet *address* (a 2-tuple 296 ``(host, port)``), and return the socket object. This is a higher-level 297 function than :meth:`socket.connect`: if *host* is a non-numeric hostname, 298 it will try to resolve it for both :data:`AF_INET` and :data:`AF_INET6`, 299 and then try to connect to all possible addresses in turn until a 300 connection succeeds. This makes it easy to write clients that are 301 compatible to both IPv4 and IPv6. 302 303 Passing the optional *timeout* parameter will set the timeout on the 304 socket instance before attempting to connect. If no *timeout* is 305 supplied, the global default timeout setting returned by 306 :func:`getdefaulttimeout` is used. 307 308 If supplied, *source_address* must be a 2-tuple ``(host, port)`` for the 309 socket to bind to as its source address before connecting. If host or port 310 are '' or 0 respectively the OS default behavior will be used. 311 312 .. versionchanged:: 3.2 313 *source_address* was added. 314 315 .. versionchanged:: 3.2 316 support for the :keyword:`with` statement was added. 317 318 319.. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0) 320 321 Translate the *host*/*port* argument into a sequence of 5-tuples that contain 322 all the necessary arguments for creating a socket connected to that service. 323 *host* is a domain name, a string representation of an IPv4/v6 address 324 or ``None``. *port* is a string service name such as ``'http'``, a numeric 325 port number or ``None``. By passing ``None`` as the value of *host* 326 and *port*, you can pass ``NULL`` to the underlying C API. 327 328 The *family*, *type* and *proto* arguments can be optionally specified 329 in order to narrow the list of addresses returned. Passing zero as a 330 value for each of these arguments selects the full range of results. 331 The *flags* argument can be one or several of the ``AI_*`` constants, 332 and will influence how results are computed and returned. 333 For example, :const:`AI_NUMERICHOST` will disable domain name resolution 334 and will raise an error if *host* is a domain name. 335 336 The function returns a list of 5-tuples with the following structure: 337 338 ``(family, type, proto, canonname, sockaddr)`` 339 340 In these tuples, *family*, *type*, *proto* are all integers and are 341 meant to be passed to the :func:`socket` function. *canonname* will be 342 a string representing the canonical name of the *host* if 343 :const:`AI_CANONNAME` is part of the *flags* argument; else *canonname* 344 will be empty. *sockaddr* is a tuple describing a socket address, whose 345 format depends on the returned *family* (a ``(address, port)`` 2-tuple for 346 :const:`AF_INET`, a ``(address, port, flow info, scope id)`` 4-tuple for 347 :const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect` 348 method. 349 350 The following example fetches address information for a hypothetical TCP 351 connection to ``www.python.org`` on port 80 (results may differ on your 352 system if IPv6 isn't enabled):: 353 354 >>> socket.getaddrinfo("www.python.org", 80, proto=socket.SOL_TCP) 355 [(2, 1, 6, '', ('82.94.164.162', 80)), 356 (10, 1, 6, '', ('2001:888:2000:d::a2', 80, 0, 0))] 357 358 .. versionchanged:: 3.2 359 parameters can now be passed as single keyword arguments. 360 361.. function:: getfqdn([name]) 362 363 Return a fully qualified domain name for *name*. If *name* is omitted or empty, 364 it is interpreted as the local host. To find the fully qualified name, the 365 hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the 366 host, if available. The first name which includes a period is selected. In 367 case no fully qualified domain name is available, the hostname as returned by 368 :func:`gethostname` is returned. 369 370 371.. function:: gethostbyname(hostname) 372 373 Translate a host name to IPv4 address format. The IPv4 address is returned as a 374 string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself 375 it is returned unchanged. See :func:`gethostbyname_ex` for a more complete 376 interface. :func:`gethostbyname` does not support IPv6 name resolution, and 377 :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support. 378 379 380.. function:: gethostbyname_ex(hostname) 381 382 Translate a host name to IPv4 address format, extended interface. Return a 383 triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary 384 host name responding to the given *ip_address*, *aliaslist* is a (possibly 385 empty) list of alternative host names for the same address, and *ipaddrlist* is 386 a list of IPv4 addresses for the same interface on the same host (often but not 387 always a single address). :func:`gethostbyname_ex` does not support IPv6 name 388 resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual 389 stack support. 390 391 392.. function:: gethostname() 393 394 Return a string containing the hostname of the machine where the Python 395 interpreter is currently executing. 396 397 If you want to know the current machine's IP address, you may want to use 398 ``gethostbyname(gethostname())``. This operation assumes that there is a 399 valid address-to-host mapping for the host, and the assumption does not 400 always hold. 401 402 Note: :func:`gethostname` doesn't always return the fully qualified domain 403 name; use ``getfqdn()`` (see above). 404 405 406.. function:: gethostbyaddr(ip_address) 407 408 Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the 409 primary host name responding to the given *ip_address*, *aliaslist* is a 410 (possibly empty) list of alternative host names for the same address, and 411 *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same 412 host (most likely containing only a single address). To find the fully qualified 413 domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports 414 both IPv4 and IPv6. 415 416 417.. function:: getnameinfo(sockaddr, flags) 418 419 Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending 420 on the settings of *flags*, the result can contain a fully-qualified domain name 421 or numeric address representation in *host*. Similarly, *port* can contain a 422 string port name or a numeric port number. 423 424 425.. function:: getprotobyname(protocolname) 426 427 Translate an Internet protocol name (for example, ``'icmp'``) to a constant 428 suitable for passing as the (optional) third argument to the :func:`socket` 429 function. This is usually only needed for sockets opened in "raw" mode 430 (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen 431 automatically if the protocol is omitted or zero. 432 433 434.. function:: getservbyname(servicename[, protocolname]) 435 436 Translate an Internet service name and protocol name to a port number for that 437 service. The optional protocol name, if given, should be ``'tcp'`` or 438 ``'udp'``, otherwise any protocol will match. 439 440 441.. function:: getservbyport(port[, protocolname]) 442 443 Translate an Internet port number and protocol name to a service name for that 444 service. The optional protocol name, if given, should be ``'tcp'`` or 445 ``'udp'``, otherwise any protocol will match. 446 447 448.. function:: socket([family[, type[, proto]]], cloexec=True) 449 450 Create a new socket using the given address family, socket type and protocol 451 number. The address family should be :const:`AF_INET` (the default), 452 :const:`AF_INET6`, :const:`AF_UNIX`, :const:`AF_CAN` or :const:`AF_RDS`. The 453 socket type should be :const:`SOCK_STREAM` (the default), 454 :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other ``SOCK_`` 455 constants. The protocol number is usually zero and may be omitted in that 456 case or :const:`CAN_RAW` in case the address family is :const:`AF_CAN`. 457 458 If *cloexec* is ``True``, set :ref:`close-on-exec flag <cloexec>`. 459 460 .. versionchanged:: 3.3 461 The AF_CAN family was added. 462 The AF_RDS family was added. 463 464 .. versionchanged:: 3.4 465 *cloexec* parameter was added. 466 467 468.. function:: socketpair([family[, type[, proto]]], cloexec=True) 469 470 Build a pair of connected socket objects using the given address family, socket 471 type, and protocol number. Address family, socket type, and protocol number are 472 as for the :func:`socket` function above. The default family is :const:`AF_UNIX` 473 if defined on the platform; otherwise, the default is :const:`AF_INET`. 474 475 If *cloexec* is ``True``, set :ref:`close-on-exec flag <cloexec>`. 476 477 Availability: Unix. 478 479 .. versionchanged:: 3.2 480 The returned socket objects now support the whole socket API, rather 481 than a subset. 482 483 .. versionchanged:: 3.4 484 *cloexec* parameter was added. 485 486 487.. function:: fromfd(fd, family, type[, proto]) 488 489 Duplicate the file descriptor *fd* (an integer as returned by a file object's 490 :meth:`fileno` method) and build a socket object from the result. Address 491 family, socket type and protocol number are as for the :func:`socket` function 492 above. The file descriptor should refer to a socket, but this is not checked --- 493 subsequent operations on the object may fail if the file descriptor is invalid. 494 This function is rarely needed, but can be used to get or set socket options on 495 a socket passed to a program as standard input or output (such as a server 496 started by the Unix inet daemon). The socket is assumed to be in blocking mode. 497 498 499.. function:: ntohl(x) 500 501 Convert 32-bit positive integers from network to host byte order. On machines 502 where the host byte order is the same as network byte order, this is a no-op; 503 otherwise, it performs a 4-byte swap operation. 504 505 506.. function:: ntohs(x) 507 508 Convert 16-bit positive integers from network to host byte order. On machines 509 where the host byte order is the same as network byte order, this is a no-op; 510 otherwise, it performs a 2-byte swap operation. 511 512 513.. function:: htonl(x) 514 515 Convert 32-bit positive integers from host to network byte order. On machines 516 where the host byte order is the same as network byte order, this is a no-op; 517 otherwise, it performs a 4-byte swap operation. 518 519 520.. function:: htons(x) 521 522 Convert 16-bit positive integers from host to network byte order. On machines 523 where the host byte order is the same as network byte order, this is a no-op; 524 otherwise, it performs a 2-byte swap operation. 525 526 527.. function:: inet_aton(ip_string) 528 529 Convert an IPv4 address from dotted-quad string format (for example, 530 '123.45.67.89') to 32-bit packed binary format, as a bytes object four characters in 531 length. This is useful when conversing with a program that uses the standard C 532 library and needs objects of type :c:type:`struct in_addr`, which is the C type 533 for the 32-bit packed binary this function returns. 534 535 :func:`inet_aton` also accepts strings with less than three dots; see the 536 Unix manual page :manpage:`inet(3)` for details. 537 538 If the IPv4 address string passed to this function is invalid, 539 :exc:`OSError` will be raised. Note that exactly what is valid depends on 540 the underlying C implementation of :c:func:`inet_aton`. 541 542 :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used 543 instead for IPv4/v6 dual stack support. 544 545 546.. function:: inet_ntoa(packed_ip) 547 548 Convert a 32-bit packed IPv4 address (a bytes object four characters in 549 length) to its standard dotted-quad string representation (for example, 550 '123.45.67.89'). This is useful when conversing with a program that uses the 551 standard C library and needs objects of type :c:type:`struct in_addr`, which 552 is the C type for the 32-bit packed binary data this function takes as an 553 argument. 554 555 If the byte sequence passed to this function is not exactly 4 bytes in 556 length, :exc:`OSError` will be raised. :func:`inet_ntoa` does not 557 support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual 558 stack support. 559 560 561.. function:: inet_pton(address_family, ip_string) 562 563 Convert an IP address from its family-specific string format to a packed, 564 binary format. :func:`inet_pton` is useful when a library or network protocol 565 calls for an object of type :c:type:`struct in_addr` (similar to 566 :func:`inet_aton`) or :c:type:`struct in6_addr`. 567 568 Supported values for *address_family* are currently :const:`AF_INET` and 569 :const:`AF_INET6`. If the IP address string *ip_string* is invalid, 570 :exc:`OSError` will be raised. Note that exactly what is valid depends on 571 both the value of *address_family* and the underlying implementation of 572 :c:func:`inet_pton`. 573 574 Availability: Unix (maybe not all platforms). 575 576 577.. function:: inet_ntop(address_family, packed_ip) 578 579 Convert a packed IP address (a bytes object of some number of characters) to its 580 standard, family-specific string representation (for example, ``'7.10.0.5'`` or 581 ``'5aef:2b::8'``). :func:`inet_ntop` is useful when a library or network protocol 582 returns an object of type :c:type:`struct in_addr` (similar to :func:`inet_ntoa`) 583 or :c:type:`struct in6_addr`. 584 585 Supported values for *address_family* are currently :const:`AF_INET` and 586 :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the 587 specified address family, :exc:`ValueError` will be raised. A 588 :exc:`OSError` is raised for errors from the call to :func:`inet_ntop`. 589 590 Availability: Unix (maybe not all platforms). 591 592 593.. 594 XXX: Are sendmsg(), recvmsg() and CMSG_*() available on any 595 non-Unix platforms? The old (obsolete?) 4.2BSD form of the 596 interface, in which struct msghdr has no msg_control or 597 msg_controllen members, is not currently supported. 598 599.. function:: CMSG_LEN(length) 600 601 Return the total length, without trailing padding, of an ancillary 602 data item with associated data of the given *length*. This value 603 can often be used as the buffer size for :meth:`~socket.recvmsg` to 604 receive a single item of ancillary data, but :rfc:`3542` requires 605 portable applications to use :func:`CMSG_SPACE` and thus include 606 space for padding, even when the item will be the last in the 607 buffer. Raises :exc:`OverflowError` if *length* is outside the 608 permissible range of values. 609 610 Availability: most Unix platforms, possibly others. 611 612 .. versionadded:: 3.3 613 614 615.. function:: CMSG_SPACE(length) 616 617 Return the buffer size needed for :meth:`~socket.recvmsg` to 618 receive an ancillary data item with associated data of the given 619 *length*, along with any trailing padding. The buffer space needed 620 to receive multiple items is the sum of the :func:`CMSG_SPACE` 621 values for their associated data lengths. Raises 622 :exc:`OverflowError` if *length* is outside the permissible range 623 of values. 624 625 Note that some systems might support ancillary data without 626 providing this function. Also note that setting the buffer size 627 using the results of this function may not precisely limit the 628 amount of ancillary data that can be received, since additional 629 data may be able to fit into the padding area. 630 631 Availability: most Unix platforms, possibly others. 632 633 .. versionadded:: 3.3 634 635 636.. function:: getdefaulttimeout() 637 638 Return the default timeout in seconds (float) for new socket objects. A value 639 of ``None`` indicates that new socket objects have no timeout. When the socket 640 module is first imported, the default is ``None``. 641 642 643.. function:: setdefaulttimeout(timeout) 644 645 Set the default timeout in seconds (float) for new socket objects. When 646 the socket module is first imported, the default is ``None``. See 647 :meth:`~socket.settimeout` for possible values and their respective 648 meanings. 649 650 651.. function:: sethostname(name) 652 653 Set the machine's hostname to *name*. This will raise a 654 :exc:`OSError` if you don't have enough rights. 655 656 Availability: Unix. 657 658 .. versionadded:: 3.3 659 660 661.. function:: if_nameindex() 662 663 Return a list of network interface information 664 (index int, name string) tuples. 665 :exc:`OSError` if the system call fails. 666 667 Availability: Unix. 668 669 .. versionadded:: 3.3 670 671 672.. function:: if_nametoindex(if_name) 673 674 Return a network interface index number corresponding to an 675 interface name. 676 :exc:`OSError` if no interface with the given name exists. 677 678 Availability: Unix. 679 680 .. versionadded:: 3.3 681 682 683.. function:: if_indextoname(if_index) 684 685 Return a network interface name corresponding to a 686 interface index number. 687 :exc:`OSError` if no interface with the given index exists. 688 689 Availability: Unix. 690 691 .. versionadded:: 3.3 692 693 694.. function:: fromshare(data) 695 696 Instantiate a socket from data obtained from :meth:`~socket.share`. 697 The socket is assumed to be in blocking mode. 698 699 Availability: Windows. 700 701 .. versionadded:: 3.3 702 703 704.. data:: SocketType 705 706 This is a Python type object that represents the socket object type. It is the 707 same as ``type(socket(...))``. 708 709 710.. _socket-objects: 711 712Socket Objects 713-------------- 714 715Socket objects have the following methods. Except for :meth:`makefile` these 716correspond to Unix system calls applicable to sockets. 717 718 719.. method:: socket.accept(cloexec=True) 720 721 Accept a connection. The socket must be bound to an address and listening for 722 connections. The return value is a pair ``(conn, address)`` where *conn* is a 723 *new* socket object usable to send and receive data on the connection, and 724 *address* is the address bound to the socket on the other end of the connection. 725 726 If *cloexec* is ``True``, set :ref:`close-on-exec flag <cloexec>`. 727 728 .. versionchanged:: 3.4 729 *cloexec* parameter was added. 730 731 732.. method:: socket.bind(address) 733 734 Bind the socket to *address*. The socket must not already be bound. (The format 735 of *address* depends on the address family --- see above.) 736 737 738.. method:: socket.close() 739 740 Close the socket. All future operations on the socket object will fail. The 741 remote end will receive no more data (after queued data is flushed). Sockets are 742 automatically closed when they are garbage-collected. 743 744 .. note:: 745 :meth:`close()` releases the resource associated with a connection but 746 does not necessarily close the connection immediately. If you want 747 to close the connection in a timely fashion, call :meth:`shutdown()` 748 before :meth:`close()`. 749 750 751.. method:: socket.connect(address) 752 753 Connect to a remote socket at *address*. (The format of *address* depends on the 754 address family --- see above.) 755 756 757.. method:: socket.connect_ex(address) 758 759 Like ``connect(address)``, but return an error indicator instead of raising an 760 exception for errors returned by the C-level :c:func:`connect` call (other 761 problems, such as "host not found," can still raise exceptions). The error 762 indicator is ``0`` if the operation succeeded, otherwise the value of the 763 :c:data:`errno` variable. This is useful to support, for example, asynchronous 764 connects. 765 766 767.. method:: socket.detach() 768 769 Put the socket object into closed state without actually closing the 770 underlying file descriptor. The file descriptor is returned, and can 771 be reused for other purposes. 772 773 .. versionadded:: 3.2 774 775 776.. method:: socket.fileno() 777 778 Return the socket's file descriptor (a small integer). This is useful with 779 :func:`select.select`. 780 781 Under Windows the small integer returned by this method cannot be used where a 782 file descriptor can be used (such as :func:`os.fdopen`). Unix does not have 783 this limitation. 784 785 786.. method:: socket.getpeername() 787 788 Return the remote address to which the socket is connected. This is useful to 789 find out the port number of a remote IPv4/v6 socket, for instance. (The format 790 of the address returned depends on the address family --- see above.) On some 791 systems this function is not supported. 792 793 794.. method:: socket.getsockname() 795 796 Return the socket's own address. This is useful to find out the port number of 797 an IPv4/v6 socket, for instance. (The format of the address returned depends on 798 the address family --- see above.) 799 800 801.. method:: socket.getsockopt(level, optname[, buflen]) 802 803 Return the value of the given socket option (see the Unix man page 804 :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.) 805 are defined in this module. If *buflen* is absent, an integer option is assumed 806 and its integer value is returned by the function. If *buflen* is present, it 807 specifies the maximum length of the buffer used to receive the option in, and 808 this buffer is returned as a bytes object. It is up to the caller to decode the 809 contents of the buffer (see the optional built-in module :mod:`struct` for a way 810 to decode C structures encoded as byte strings). 811 812 813.. method:: socket.gettimeout() 814 815 Return the timeout in seconds (float) associated with socket operations, 816 or ``None`` if no timeout is set. This reflects the last call to 817 :meth:`setblocking` or :meth:`settimeout`. 818 819 820.. method:: socket.ioctl(control, option) 821 822 :platform: Windows 823 824 The :meth:`ioctl` method is a limited interface to the WSAIoctl system 825 interface. Please refer to the `Win32 documentation 826 <http://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more 827 information. 828 829 On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl` 830 functions may be used; they accept a socket object as their first argument. 831 832.. method:: socket.listen(backlog) 833 834 Listen for connections made to the socket. The *backlog* argument specifies the 835 maximum number of queued connections and should be at least 0; the maximum value 836 is system-dependent (usually 5), the minimum value is forced to 0. 837 838 839.. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \ 840 errors=None, newline=None) 841 842 .. index:: single: I/O control; buffering 843 844 Return a :term:`file object` associated with the socket. The exact returned 845 type depends on the arguments given to :meth:`makefile`. These arguments are 846 interpreted the same way as by the built-in :func:`open` function. 847 848 Closing the file object won't close the socket unless there are no remaining 849 references to the socket. The socket must be in blocking mode; it can have 850 a timeout, but the file object's internal buffer may end up in a inconsistent 851 state if a timeout occurs. 852 853 .. note:: 854 855 On Windows, the file-like object created by :meth:`makefile` cannot be 856 used where a file object with a file descriptor is expected, such as the 857 stream arguments of :meth:`subprocess.Popen`. 858 859 860.. method:: socket.recv(bufsize[, flags]) 861 862 Receive data from the socket. The return value is a bytes object representing the 863 data received. The maximum amount of data to be received at once is specified 864 by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of 865 the optional argument *flags*; it defaults to zero. 866 867 .. note:: 868 869 For best match with hardware and network realities, the value of *bufsize* 870 should be a relatively small power of 2, for example, 4096. 871 872 873.. method:: socket.recvfrom(bufsize[, flags]) 874 875 Receive data from the socket. The return value is a pair ``(bytes, address)`` 876 where *bytes* is a bytes object representing the data received and *address* is the 877 address of the socket sending the data. See the Unix manual page 878 :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults 879 to zero. (The format of *address* depends on the address family --- see above.) 880 881 882.. method:: socket.recvmsg(bufsize[, ancbufsize[, flags]]) 883 884 Receive normal data (up to *bufsize* bytes) and ancillary data from 885 the socket. The *ancbufsize* argument sets the size in bytes of 886 the internal buffer used to receive the ancillary data; it defaults 887 to 0, meaning that no ancillary data will be received. Appropriate 888 buffer sizes for ancillary data can be calculated using 889 :func:`CMSG_SPACE` or :func:`CMSG_LEN`, and items which do not fit 890 into the buffer might be truncated or discarded. The *flags* 891 argument defaults to 0 and has the same meaning as for 892 :meth:`recv`. 893 894 The return value is a 4-tuple: ``(data, ancdata, msg_flags, 895 address)``. The *data* item is a :class:`bytes` object holding the 896 non-ancillary data received. The *ancdata* item is a list of zero 897 or more tuples ``(cmsg_level, cmsg_type, cmsg_data)`` representing 898 the ancillary data (control messages) received: *cmsg_level* and 899 *cmsg_type* are integers specifying the protocol level and 900 protocol-specific type respectively, and *cmsg_data* is a 901 :class:`bytes` object holding the associated data. The *msg_flags* 902 item is the bitwise OR of various flags indicating conditions on 903 the received message; see your system documentation for details. 904 If the receiving socket is unconnected, *address* is the address of 905 the sending socket, if available; otherwise, its value is 906 unspecified. 907 908 On some systems, :meth:`sendmsg` and :meth:`recvmsg` can be used to 909 pass file descriptors between processes over an :const:`AF_UNIX` 910 socket. When this facility is used (it is often restricted to 911 :const:`SOCK_STREAM` sockets), :meth:`recvmsg` will return, in its 912 ancillary data, items of the form ``(socket.SOL_SOCKET, 913 socket.SCM_RIGHTS, fds)``, where *fds* is a :class:`bytes` object 914 representing the new file descriptors as a binary array of the 915 native C :c:type:`int` type. If :meth:`recvmsg` raises an 916 exception after the system call returns, it will first attempt to 917 close any file descriptors received via this mechanism. 918 919 Some systems do not indicate the truncated length of ancillary data 920 items which have been only partially received. If an item appears 921 to extend beyond the end of the buffer, :meth:`recvmsg` will issue 922 a :exc:`RuntimeWarning`, and will return the part of it which is 923 inside the buffer provided it has not been truncated before the 924 start of its associated data. 925 926 On systems which support the :const:`SCM_RIGHTS` mechanism, the 927 following function will receive up to *maxfds* file descriptors, 928 returning the message data and a list containing the descriptors 929 (while ignoring unexpected conditions such as unrelated control 930 messages being received). See also :meth:`sendmsg`. :: 931 932 import socket, array 933 934 def recv_fds(sock, msglen, maxfds): 935 fds = array.array("i") # Array of ints 936 msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize)) 937 for cmsg_level, cmsg_type, cmsg_data in ancdata: 938 if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS): 939 # Append data, ignoring any truncated integers at the end. 940 fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)]) 941 return msg, list(fds) 942 943 Availability: most Unix platforms, possibly others. 944 945 .. versionadded:: 3.3 946 947 948.. method:: socket.recvmsg_into(buffers[, ancbufsize[, flags]]) 949 950 Receive normal data and ancillary data from the socket, behaving as 951 :meth:`recvmsg` would, but scatter the non-ancillary data into a 952 series of buffers instead of returning a new bytes object. The 953 *buffers* argument must be an iterable of objects that export 954 writable buffers (e.g. :class:`bytearray` objects); these will be 955 filled with successive chunks of the non-ancillary data until it 956 has all been written or there are no more buffers. The operating 957 system may set a limit (:func:`~os.sysconf` value ``SC_IOV_MAX``) 958 on the number of buffers that can be used. The *ancbufsize* and 959 *flags* arguments have the same meaning as for :meth:`recvmsg`. 960 961 The return value is a 4-tuple: ``(nbytes, ancdata, msg_flags, 962 address)``, where *nbytes* is the total number of bytes of 963 non-ancillary data written into the buffers, and *ancdata*, 964 *msg_flags* and *address* are the same as for :meth:`recvmsg`. 965 966 Example:: 967 968 >>> import socket 969 >>> s1, s2 = socket.socketpair() 970 >>> b1 = bytearray(b'----') 971 >>> b2 = bytearray(b'0123456789') 972 >>> b3 = bytearray(b'--------------') 973 >>> s1.send(b'Mary had a little lamb') 974 22 975 >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3]) 976 (22, [], 0, None) 977 >>> [b1, b2, b3] 978 [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')] 979 980 Availability: most Unix platforms, possibly others. 981 982 .. versionadded:: 3.3 983 984 985.. method:: socket.recvfrom_into(buffer[, nbytes[, flags]]) 986 987 Receive data from the socket, writing it into *buffer* instead of creating a 988 new bytestring. The return value is a pair ``(nbytes, address)`` where *nbytes* is 989 the number of bytes received and *address* is the address of the socket sending 990 the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the 991 optional argument *flags*; it defaults to zero. (The format of *address* 992 depends on the address family --- see above.) 993 994 995.. method:: socket.recv_into(buffer[, nbytes[, flags]]) 996 997 Receive up to *nbytes* bytes from the socket, storing the data into a buffer 998 rather than creating a new bytestring. If *nbytes* is not specified (or 0), 999 receive up to the size available in the given buffer. Returns the number of 1000 bytes received. See the Unix manual page :manpage:`recv(2)` for the meaning 1001 of the optional argument *flags*; it defaults to zero. 1002 1003 1004.. method:: socket.send(bytes[, flags]) 1005 1006 Send data to the socket. The socket must be connected to a remote socket. The 1007 optional *flags* argument has the same meaning as for :meth:`recv` above. 1008 Returns the number of bytes sent. Applications are responsible for checking that 1009 all data has been sent; if only some of the data was transmitted, the 1010 application needs to attempt delivery of the remaining data. For further 1011 information on this topic, consult the :ref:`socket-howto`. 1012 1013 1014.. method:: socket.sendall(bytes[, flags]) 1015 1016 Send data to the socket. The socket must be connected to a remote socket. The 1017 optional *flags* argument has the same meaning as for :meth:`recv` above. 1018 Unlike :meth:`send`, this method continues to send data from *bytes* until 1019 either all data has been sent or an error occurs. ``None`` is returned on 1020 success. On error, an exception is raised, and there is no way to determine how 1021 much data, if any, was successfully sent. 1022 1023 1024.. method:: socket.sendto(bytes, address) 1025 socket.sendto(bytes, flags, address) 1026 1027 Send data to the socket. The socket should not be connected to a remote socket, 1028 since the destination socket is specified by *address*. The optional *flags* 1029 argument has the same meaning as for :meth:`recv` above. Return the number of 1030 bytes sent. (The format of *address* depends on the address family --- see 1031 above.) 1032 1033 1034.. method:: socket.sendmsg(buffers[, ancdata[, flags[, address]]]) 1035 1036 Send normal and ancillary data to the socket, gathering the 1037 non-ancillary data from a series of buffers and concatenating it 1038 into a single message. The *buffers* argument specifies the 1039 non-ancillary data as an iterable of buffer-compatible objects 1040 (e.g. :class:`bytes` objects); the operating system may set a limit 1041 (:func:`~os.sysconf` value ``SC_IOV_MAX``) on the number of buffers 1042 that can be used. The *ancdata* argument specifies the ancillary 1043 data (control messages) as an iterable of zero or more tuples 1044 ``(cmsg_level, cmsg_type, cmsg_data)``, where *cmsg_level* and 1045 *cmsg_type* are integers specifying the protocol level and 1046 protocol-specific type respectively, and *cmsg_data* is a 1047 buffer-compatible object holding the associated data. Note that 1048 some systems (in particular, systems without :func:`CMSG_SPACE`) 1049 might support sending only one control message per call. The 1050 *flags* argument defaults to 0 and has the same meaning as for 1051 :meth:`send`. If *address* is supplied and not ``None``, it sets a 1052 destination address for the message. The return value is the 1053 number of bytes of non-ancillary data sent. 1054 1055 The following function sends the list of file descriptors *fds* 1056 over an :const:`AF_UNIX` socket, on systems which support the 1057 :const:`SCM_RIGHTS` mechanism. See also :meth:`recvmsg`. :: 1058 1059 import socket, array 1060 1061 def send_fds(sock, msg, fds): 1062 return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))]) 1063 1064 Availability: most Unix platforms, possibly others. 1065 1066 .. versionadded:: 3.3 1067 1068 1069.. method:: socket.setblocking(flag) 1070 1071 Set blocking or non-blocking mode of the socket: if *flag* is false, the 1072 socket is set to non-blocking, else to blocking mode. 1073 1074 This method is a shorthand for certain :meth:`~socket.settimeout` calls: 1075 1076 * ``sock.setblocking(True)`` is equivalent to ``sock.settimeout(None)`` 1077 1078 * ``sock.setblocking(False)`` is equivalent to ``sock.settimeout(0.0)`` 1079 1080 1081.. method:: socket.settimeout(value) 1082 1083 Set a timeout on blocking socket operations. The *value* argument can be a 1084 nonnegative floating point number expressing seconds, or ``None``. 1085 If a non-zero value is given, subsequent socket operations will raise a 1086 :exc:`timeout` exception if the timeout period *value* has elapsed before 1087 the operation has completed. If zero is given, the socket is put in 1088 non-blocking mode. If ``None`` is given, the socket is put in blocking mode. 1089 1090 For further information, please consult the :ref:`notes on socket timeouts <socket-timeouts>`. 1091 1092 1093.. method:: socket.setsockopt(level, optname, value) 1094 1095 .. index:: module: struct 1096 1097 Set the value of the given socket option (see the Unix manual page 1098 :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the 1099 :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a 1100 bytes object representing a buffer. In the latter case it is up to the caller to 1101 ensure that the bytestring contains the proper bits (see the optional built-in 1102 module :mod:`struct` for a way to encode C structures as bytestrings). 1103 1104 1105.. method:: socket.shutdown(how) 1106 1107 Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`, 1108 further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends 1109 are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are 1110 disallowed. 1111 1112 1113.. method:: socket.share(process_id) 1114 1115 :platform: Windows 1116 1117 Duplacet a socket and prepare it for sharing with a target process. The 1118 target process must be provided with *process_id*. The resulting bytes object 1119 can then be passed to the target process using some form of interprocess 1120 communication and the socket can be recreated there using :func:`fromshare`. 1121 Once this method has been called, it is safe to close the socket since 1122 the operating system has already duplicated it for the target process. 1123 1124 .. versionadded:: 3.3 1125 1126 1127Note that there are no methods :meth:`read` or :meth:`write`; use 1128:meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead. 1129 1130Socket objects also have these (read-only) attributes that correspond to the 1131values given to the :class:`socket` constructor. 1132 1133 1134.. attribute:: socket.family 1135 1136 The socket family. 1137 1138 1139.. attribute:: socket.type 1140 1141 The socket type. 1142 1143 1144.. attribute:: socket.proto 1145 1146 The socket protocol. 1147 1148 1149 1150.. _socket-timeouts: 1151 1152Notes on socket timeouts 1153------------------------ 1154 1155A socket object can be in one of three modes: blocking, non-blocking, or 1156timeout. Sockets are by default always created in blocking mode, but this 1157can be changed by calling :func:`setdefaulttimeout`. 1158 1159* In *blocking mode*, operations block until complete or the system returns 1160 an error (such as connection timed out). 1161 1162* In *non-blocking mode*, operations fail (with an error that is unfortunately 1163 system-dependent) if they cannot be completed immediately: functions from the 1164 :mod:`select` can be used to know when and whether a socket is available for 1165 reading or writing. 1166 1167* In *timeout mode*, operations fail if they cannot be completed within the 1168 timeout specified for the socket (they raise a :exc:`timeout` exception) 1169 or if the system returns an error. 1170 1171.. note:: 1172 At the operating system level, sockets in *timeout mode* are internally set 1173 in non-blocking mode. Also, the blocking and timeout modes are shared between 1174 file descriptors and socket objects that refer to the same network endpoint. 1175 This implementation detail can have visible consequences if e.g. you decide 1176 to use the :meth:`~socket.fileno()` of a socket. 1177 1178Timeouts and the ``connect`` method 1179^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1180 1181The :meth:`~socket.connect` operation is also subject to the timeout 1182setting, and in general it is recommended to call :meth:`~socket.settimeout` 1183before calling :meth:`~socket.connect` or pass a timeout parameter to 1184:meth:`create_connection`. However, the system network stack may also 1185return a connection timeout error of its own regardless of any Python socket 1186timeout setting. 1187 1188Timeouts and the ``accept`` method 1189^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1190 1191If :func:`getdefaulttimeout` is not :const:`None`, sockets returned by 1192the :meth:`~socket.accept` method inherit that timeout. Otherwise, the 1193behaviour depends on settings of the listening socket: 1194 1195* if the listening socket is in *blocking mode* or in *timeout mode*, 1196 the socket returned by :meth:`~socket.accept` is in *blocking mode*; 1197 1198* if the listening socket is in *non-blocking mode*, whether the socket 1199 returned by :meth:`~socket.accept` is in blocking or non-blocking mode 1200 is operating system-dependent. If you want to ensure cross-platform 1201 behaviour, it is recommended you manually override this setting. 1202 1203 1204.. _socket-example: 1205 1206Example 1207------- 1208 1209Here are four minimal example programs using the TCP/IP protocol: a server that 1210echoes all data that it receives back (servicing only one client), and a client 1211using it. Note that a server must perform the sequence :func:`socket`, 1212:meth:`~socket.bind`, :meth:`~socket.listen`, :meth:`~socket.accept` (possibly 1213repeating the :meth:`~socket.accept` to service more than one client), while a 1214client only needs the sequence :func:`socket`, :meth:`~socket.connect`. Also 1215note that the server does not :meth:`~socket.sendall`/:meth:`~socket.recv` on 1216the socket it is listening on but on the new socket returned by 1217:meth:`~socket.accept`. 1218 1219The first two examples support IPv4 only. :: 1220 1221 # Echo server program 1222 import socket 1223 1224 HOST = '' # Symbolic name meaning all available interfaces 1225 PORT = 50007 # Arbitrary non-privileged port 1226 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1227 s.bind((HOST, PORT)) 1228 s.listen(1) 1229 conn, addr = s.accept() 1230 print('Connected by', addr) 1231 while True: 1232 data = conn.recv(1024) 1233 if not data: break 1234 conn.sendall(data) 1235 conn.close() 1236 1237:: 1238 1239 # Echo client program 1240 import socket 1241 1242 HOST = 'daring.cwi.nl' # The remote host 1243 PORT = 50007 # The same port as used by the server 1244 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1245 s.connect((HOST, PORT)) 1246 s.sendall(b'Hello, world') 1247 data = s.recv(1024) 1248 s.close() 1249 print('Received', repr(data)) 1250 1251The next two examples are identical to the above two, but support both IPv4 and 1252IPv6. The server …
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