/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 integral port number. 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]]]) 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 .. versionchanged:: 3.3 459 The AF_CAN family was added. 460 The AF_RDS family was added. 461 462 463.. function:: socketpair([family[, type[, proto]]]) 464 465 Build a pair of connected socket objects using the given address family, socket 466 type, and protocol number. Address family, socket type, and protocol number are 467 as for the :func:`socket` function above. The default family is :const:`AF_UNIX` 468 if defined on the platform; otherwise, the default is :const:`AF_INET`. 469 Availability: Unix. 470 471 .. versionchanged:: 3.2 472 The returned socket objects now support the whole socket API, rather 473 than a subset. 474 475 476.. function:: fromfd(fd, family, type[, proto]) 477 478 Duplicate the file descriptor *fd* (an integer as returned by a file object's 479 :meth:`fileno` method) and build a socket object from the result. Address 480 family, socket type and protocol number are as for the :func:`socket` function 481 above. The file descriptor should refer to a socket, but this is not checked --- 482 subsequent operations on the object may fail if the file descriptor is invalid. 483 This function is rarely needed, but can be used to get or set socket options on 484 a socket passed to a program as standard input or output (such as a server 485 started by the Unix inet daemon). The socket is assumed to be in blocking mode. 486 487 488.. function:: ntohl(x) 489 490 Convert 32-bit positive integers from network to host byte order. On machines 491 where the host byte order is the same as network byte order, this is a no-op; 492 otherwise, it performs a 4-byte swap operation. 493 494 495.. function:: ntohs(x) 496 497 Convert 16-bit positive integers from network to host byte order. On machines 498 where the host byte order is the same as network byte order, this is a no-op; 499 otherwise, it performs a 2-byte swap operation. 500 501 502.. function:: htonl(x) 503 504 Convert 32-bit positive integers from host to network byte order. On machines 505 where the host byte order is the same as network byte order, this is a no-op; 506 otherwise, it performs a 4-byte swap operation. 507 508 509.. function:: htons(x) 510 511 Convert 16-bit positive integers from host to network byte order. On machines 512 where the host byte order is the same as network byte order, this is a no-op; 513 otherwise, it performs a 2-byte swap operation. 514 515 516.. function:: inet_aton(ip_string) 517 518 Convert an IPv4 address from dotted-quad string format (for example, 519 '123.45.67.89') to 32-bit packed binary format, as a bytes object four characters in 520 length. This is useful when conversing with a program that uses the standard C 521 library and needs objects of type :c:type:`struct in_addr`, which is the C type 522 for the 32-bit packed binary this function returns. 523 524 :func:`inet_aton` also accepts strings with less than three dots; see the 525 Unix manual page :manpage:`inet(3)` for details. 526 527 If the IPv4 address string passed to this function is invalid, 528 :exc:`OSError` will be raised. Note that exactly what is valid depends on 529 the underlying C implementation of :c:func:`inet_aton`. 530 531 :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used 532 instead for IPv4/v6 dual stack support. 533 534 535.. function:: inet_ntoa(packed_ip) 536 537 Convert a 32-bit packed IPv4 address (a bytes object four characters in 538 length) to its standard dotted-quad string representation (for example, 539 '123.45.67.89'). This is useful when conversing with a program that uses the 540 standard C library and needs objects of type :c:type:`struct in_addr`, which 541 is the C type for the 32-bit packed binary data this function takes as an 542 argument. 543 544 If the byte sequence passed to this function is not exactly 4 bytes in 545 length, :exc:`OSError` will be raised. :func:`inet_ntoa` does not 546 support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual 547 stack support. 548 549 550.. function:: inet_pton(address_family, ip_string) 551 552 Convert an IP address from its family-specific string format to a packed, 553 binary format. :func:`inet_pton` is useful when a library or network protocol 554 calls for an object of type :c:type:`struct in_addr` (similar to 555 :func:`inet_aton`) or :c:type:`struct in6_addr`. 556 557 Supported values for *address_family* are currently :const:`AF_INET` and 558 :const:`AF_INET6`. If the IP address string *ip_string* is invalid, 559 :exc:`OSError` will be raised. Note that exactly what is valid depends on 560 both the value of *address_family* and the underlying implementation of 561 :c:func:`inet_pton`. 562 563 Availability: Unix (maybe not all platforms). 564 565 566.. function:: inet_ntop(address_family, packed_ip) 567 568 Convert a packed IP address (a bytes object of some number of characters) to its 569 standard, family-specific string representation (for example, ``'7.10.0.5'`` or 570 ``'5aef:2b::8'``). :func:`inet_ntop` is useful when a library or network protocol 571 returns an object of type :c:type:`struct in_addr` (similar to :func:`inet_ntoa`) 572 or :c:type:`struct in6_addr`. 573 574 Supported values for *address_family* are currently :const:`AF_INET` and 575 :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the 576 specified address family, :exc:`ValueError` will be raised. A 577 :exc:`OSError` is raised for errors from the call to :func:`inet_ntop`. 578 579 Availability: Unix (maybe not all platforms). 580 581 582.. 583 XXX: Are sendmsg(), recvmsg() and CMSG_*() available on any 584 non-Unix platforms? The old (obsolete?) 4.2BSD form of the 585 interface, in which struct msghdr has no msg_control or 586 msg_controllen members, is not currently supported. 587 588.. function:: CMSG_LEN(length) 589 590 Return the total length, without trailing padding, of an ancillary 591 data item with associated data of the given *length*. This value 592 can often be used as the buffer size for :meth:`~socket.recvmsg` to 593 receive a single item of ancillary data, but :rfc:`3542` requires 594 portable applications to use :func:`CMSG_SPACE` and thus include 595 space for padding, even when the item will be the last in the 596 buffer. Raises :exc:`OverflowError` if *length* is outside the 597 permissible range of values. 598 599 Availability: most Unix platforms, possibly others. 600 601 .. versionadded:: 3.3 602 603 604.. function:: CMSG_SPACE(length) 605 606 Return the buffer size needed for :meth:`~socket.recvmsg` to 607 receive an ancillary data item with associated data of the given 608 *length*, along with any trailing padding. The buffer space needed 609 to receive multiple items is the sum of the :func:`CMSG_SPACE` 610 values for their associated data lengths. Raises 611 :exc:`OverflowError` if *length* is outside the permissible range 612 of values. 613 614 Note that some systems might support ancillary data without 615 providing this function. Also note that setting the buffer size 616 using the results of this function may not precisely limit the 617 amount of ancillary data that can be received, since additional 618 data may be able to fit into the padding area. 619 620 Availability: most Unix platforms, possibly others. 621 622 .. versionadded:: 3.3 623 624 625.. function:: getdefaulttimeout() 626 627 Return the default timeout in seconds (float) for new socket objects. A value 628 of ``None`` indicates that new socket objects have no timeout. When the socket 629 module is first imported, the default is ``None``. 630 631 632.. function:: setdefaulttimeout(timeout) 633 634 Set the default timeout in seconds (float) for new socket objects. When 635 the socket module is first imported, the default is ``None``. See 636 :meth:`~socket.settimeout` for possible values and their respective 637 meanings. 638 639 640.. function:: sethostname(name) 641 642 Set the machine's hostname to *name*. This will raise a 643 :exc:`OSError` if you don't have enough rights. 644 645 Availability: Unix. 646 647 .. versionadded:: 3.3 648 649 650.. function:: if_nameindex() 651 652 Return a list of network interface information 653 (index int, name string) tuples. 654 :exc:`OSError` if the system call fails. 655 656 Availability: Unix. 657 658 .. versionadded:: 3.3 659 660 661.. function:: if_nametoindex(if_name) 662 663 Return a network interface index number corresponding to an 664 interface name. 665 :exc:`OSError` if no interface with the given name exists. 666 667 Availability: Unix. 668 669 .. versionadded:: 3.3 670 671 672.. function:: if_indextoname(if_index) 673 674 Return a network interface name corresponding to a 675 interface index number. 676 :exc:`OSError` if no interface with the given index exists. 677 678 Availability: Unix. 679 680 .. versionadded:: 3.3 681 682 683.. data:: SocketType 684 685 This is a Python type object that represents the socket object type. It is the 686 same as ``type(socket(...))``. 687 688 689.. _socket-objects: 690 691Socket Objects 692-------------- 693 694Socket objects have the following methods. Except for :meth:`makefile` these 695correspond to Unix system calls applicable to sockets. 696 697 698.. method:: socket.accept() 699 700 Accept a connection. The socket must be bound to an address and listening for 701 connections. The return value is a pair ``(conn, address)`` where *conn* is a 702 *new* socket object usable to send and receive data on the connection, and 703 *address* is the address bound to the socket on the other end of the connection. 704 705 706.. method:: socket.bind(address) 707 708 Bind the socket to *address*. The socket must not already be bound. (The format 709 of *address* depends on the address family --- see above.) 710 711 712.. method:: socket.close() 713 714 Close the socket. All future operations on the socket object will fail. The 715 remote end will receive no more data (after queued data is flushed). Sockets are 716 automatically closed when they are garbage-collected. 717 718 .. note:: 719 :meth:`close()` releases the resource associated with a connection but 720 does not necessarily close the connection immediately. If you want 721 to close the connection in a timely fashion, call :meth:`shutdown()` 722 before :meth:`close()`. 723 724 725.. method:: socket.connect(address) 726 727 Connect to a remote socket at *address*. (The format of *address* depends on the 728 address family --- see above.) 729 730 731.. method:: socket.connect_ex(address) 732 733 Like ``connect(address)``, but return an error indicator instead of raising an 734 exception for errors returned by the C-level :c:func:`connect` call (other 735 problems, such as "host not found," can still raise exceptions). The error 736 indicator is ``0`` if the operation succeeded, otherwise the value of the 737 :c:data:`errno` variable. This is useful to support, for example, asynchronous 738 connects. 739 740 741.. method:: socket.detach() 742 743 Put the socket object into closed state without actually closing the 744 underlying file descriptor. The file descriptor is returned, and can 745 be reused for other purposes. 746 747 .. versionadded:: 3.2 748 749 750.. method:: socket.fileno() 751 752 Return the socket's file descriptor (a small integer). This is useful with 753 :func:`select.select`. 754 755 Under Windows the small integer returned by this method cannot be used where a 756 file descriptor can be used (such as :func:`os.fdopen`). Unix does not have 757 this limitation. 758 759 760.. method:: socket.getpeername() 761 762 Return the remote address to which the socket is connected. This is useful to 763 find out the port number of a remote IPv4/v6 socket, for instance. (The format 764 of the address returned depends on the address family --- see above.) On some 765 systems this function is not supported. 766 767 768.. method:: socket.getsockname() 769 770 Return the socket's own address. This is useful to find out the port number of 771 an IPv4/v6 socket, for instance. (The format of the address returned depends on 772 the address family --- see above.) 773 774 775.. method:: socket.getsockopt(level, optname[, buflen]) 776 777 Return the value of the given socket option (see the Unix man page 778 :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.) 779 are defined in this module. If *buflen* is absent, an integer option is assumed 780 and its integer value is returned by the function. If *buflen* is present, it 781 specifies the maximum length of the buffer used to receive the option in, and 782 this buffer is returned as a bytes object. It is up to the caller to decode the 783 contents of the buffer (see the optional built-in module :mod:`struct` for a way 784 to decode C structures encoded as byte strings). 785 786 787.. method:: socket.gettimeout() 788 789 Return the timeout in seconds (float) associated with socket operations, 790 or ``None`` if no timeout is set. This reflects the last call to 791 :meth:`setblocking` or :meth:`settimeout`. 792 793 794.. method:: socket.ioctl(control, option) 795 796 :platform: Windows 797 798 The :meth:`ioctl` method is a limited interface to the WSAIoctl system 799 interface. Please refer to the `Win32 documentation 800 <http://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more 801 information. 802 803 On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl` 804 functions may be used; they accept a socket object as their first argument. 805 806.. method:: socket.listen(backlog) 807 808 Listen for connections made to the socket. The *backlog* argument specifies the 809 maximum number of queued connections and should be at least 0; the maximum value 810 is system-dependent (usually 5), the minimum value is forced to 0. 811 812 813.. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \ 814 errors=None, newline=None) 815 816 .. index:: single: I/O control; buffering 817 818 Return a :term:`file object` associated with the socket. The exact returned 819 type depends on the arguments given to :meth:`makefile`. These arguments are 820 interpreted the same way as by the built-in :func:`open` function. 821 822 Closing the file object won't close the socket unless there are no remaining 823 references to the socket. The socket must be in blocking mode; it can have 824 a timeout, but the file object's internal buffer may end up in a inconsistent 825 state if a timeout occurs. 826 827 .. note:: 828 829 On Windows, the file-like object created by :meth:`makefile` cannot be 830 used where a file object with a file descriptor is expected, such as the 831 stream arguments of :meth:`subprocess.Popen`. 832 833 834.. method:: socket.recv(bufsize[, flags]) 835 836 Receive data from the socket. The return value is a bytes object representing the 837 data received. The maximum amount of data to be received at once is specified 838 by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of 839 the optional argument *flags*; it defaults to zero. 840 841 .. note:: 842 843 For best match with hardware and network realities, the value of *bufsize* 844 should be a relatively small power of 2, for example, 4096. 845 846 847.. method:: socket.recvfrom(bufsize[, flags]) 848 849 Receive data from the socket. The return value is a pair ``(bytes, address)`` 850 where *bytes* is a bytes object representing the data received and *address* is the 851 address of the socket sending the data. See the Unix manual page 852 :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults 853 to zero. (The format of *address* depends on the address family --- see above.) 854 855 856.. method:: socket.recvmsg(bufsize[, ancbufsize[, flags]]) 857 858 Receive normal data (up to *bufsize* bytes) and ancillary data from 859 the socket. The *ancbufsize* argument sets the size in bytes of 860 the internal buffer used to receive the ancillary data; it defaults 861 to 0, meaning that no ancillary data will be received. Appropriate 862 buffer sizes for ancillary data can be calculated using 863 :func:`CMSG_SPACE` or :func:`CMSG_LEN`, and items which do not fit 864 into the buffer might be truncated or discarded. The *flags* 865 argument defaults to 0 and has the same meaning as for 866 :meth:`recv`. 867 868 The return value is a 4-tuple: ``(data, ancdata, msg_flags, 869 address)``. The *data* item is a :class:`bytes` object holding the 870 non-ancillary data received. The *ancdata* item is a list of zero 871 or more tuples ``(cmsg_level, cmsg_type, cmsg_data)`` representing 872 the ancillary data (control messages) received: *cmsg_level* and 873 *cmsg_type* are integers specifying the protocol level and 874 protocol-specific type respectively, and *cmsg_data* is a 875 :class:`bytes` object holding the associated data. The *msg_flags* 876 item is the bitwise OR of various flags indicating conditions on 877 the received message; see your system documentation for details. 878 If the receiving socket is unconnected, *address* is the address of 879 the sending socket, if available; otherwise, its value is 880 unspecified. 881 882 On some systems, :meth:`sendmsg` and :meth:`recvmsg` can be used to 883 pass file descriptors between processes over an :const:`AF_UNIX` 884 socket. When this facility is used (it is often restricted to 885 :const:`SOCK_STREAM` sockets), :meth:`recvmsg` will return, in its 886 ancillary data, items of the form ``(socket.SOL_SOCKET, 887 socket.SCM_RIGHTS, fds)``, where *fds* is a :class:`bytes` object 888 representing the new file descriptors as a binary array of the 889 native C :c:type:`int` type. If :meth:`recvmsg` raises an 890 exception after the system call returns, it will first attempt to 891 close any file descriptors received via this mechanism. 892 893 Some systems do not indicate the truncated length of ancillary data 894 items which have been only partially received. If an item appears 895 to extend beyond the end of the buffer, :meth:`recvmsg` will issue 896 a :exc:`RuntimeWarning`, and will return the part of it which is 897 inside the buffer provided it has not been truncated before the 898 start of its associated data. 899 900 On systems which support the :const:`SCM_RIGHTS` mechanism, the 901 following function will receive up to *maxfds* file descriptors, 902 returning the message data and a list containing the descriptors 903 (while ignoring unexpected conditions such as unrelated control 904 messages being received). See also :meth:`sendmsg`. :: 905 906 import socket, array 907 908 def recv_fds(sock, msglen, maxfds): 909 fds = array.array("i") # Array of ints 910 msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize)) 911 for cmsg_level, cmsg_type, cmsg_data in ancdata: 912 if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS): 913 # Append data, ignoring any truncated integers at the end. 914 fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)]) 915 return msg, list(fds) 916 917 Availability: most Unix platforms, possibly others. 918 919 .. versionadded:: 3.3 920 921 922.. method:: socket.recvmsg_into(buffers[, ancbufsize[, flags]]) 923 924 Receive normal data and ancillary data from the socket, behaving as 925 :meth:`recvmsg` would, but scatter the non-ancillary data into a 926 series of buffers instead of returning a new bytes object. The 927 *buffers* argument must be an iterable of objects that export 928 writable buffers (e.g. :class:`bytearray` objects); these will be 929 filled with successive chunks of the non-ancillary data until it 930 has all been written or there are no more buffers. The operating 931 system may set a limit (:func:`~os.sysconf` value ``SC_IOV_MAX``) 932 on the number of buffers that can be used. The *ancbufsize* and 933 *flags* arguments have the same meaning as for :meth:`recvmsg`. 934 935 The return value is a 4-tuple: ``(nbytes, ancdata, msg_flags, 936 address)``, where *nbytes* is the total number of bytes of 937 non-ancillary data written into the buffers, and *ancdata*, 938 *msg_flags* and *address* are the same as for :meth:`recvmsg`. 939 940 Example:: 941 942 >>> import socket 943 >>> s1, s2 = socket.socketpair() 944 >>> b1 = bytearray(b'----') 945 >>> b2 = bytearray(b'0123456789') 946 >>> b3 = bytearray(b'--------------') 947 >>> s1.send(b'Mary had a little lamb') 948 22 949 >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3]) 950 (22, [], 0, None) 951 >>> [b1, b2, b3] 952 [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')] 953 954 Availability: most Unix platforms, possibly others. 955 956 .. versionadded:: 3.3 957 958 959.. method:: socket.recvfrom_into(buffer[, nbytes[, flags]]) 960 961 Receive data from the socket, writing it into *buffer* instead of creating a 962 new bytestring. The return value is a pair ``(nbytes, address)`` where *nbytes* is 963 the number of bytes received and *address* is the address of the socket sending 964 the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the 965 optional argument *flags*; it defaults to zero. (The format of *address* 966 depends on the address family --- see above.) 967 968 969.. method:: socket.recv_into(buffer[, nbytes[, flags]]) 970 971 Receive up to *nbytes* bytes from the socket, storing the data into a buffer 972 rather than creating a new bytestring. If *nbytes* is not specified (or 0), 973 receive up to the size available in the given buffer. Returns the number of 974 bytes received. See the Unix manual page :manpage:`recv(2)` for the meaning 975 of the optional argument *flags*; it defaults to zero. 976 977 978.. method:: socket.send(bytes[, flags]) 979 980 Send data to the socket. The socket must be connected to a remote socket. The 981 optional *flags* argument has the same meaning as for :meth:`recv` above. 982 Returns the number of bytes sent. Applications are responsible for checking that 983 all data has been sent; if only some of the data was transmitted, the 984 application needs to attempt delivery of the remaining data. For further 985 information on this topic, consult the :ref:`socket-howto`. 986 987 988.. method:: socket.sendall(bytes[, flags]) 989 990 Send data to the socket. The socket must be connected to a remote socket. The 991 optional *flags* argument has the same meaning as for :meth:`recv` above. 992 Unlike :meth:`send`, this method continues to send data from *bytes* until 993 either all data has been sent or an error occurs. ``None`` is returned on 994 success. On error, an exception is raised, and there is no way to determine how 995 much data, if any, was successfully sent. 996 997 998.. method:: socket.sendto(bytes[, flags], address) 999 1000 Send data to the socket. The socket should not be connected to a remote socket, 1001 since the destination socket is specified by *address*. The optional *flags* 1002 argument has the same meaning as for :meth:`recv` above. Return the number of 1003 bytes sent. (The format of *address* depends on the address family --- see 1004 above.) 1005 1006 1007.. method:: socket.sendmsg(buffers[, ancdata[, flags[, address]]]) 1008 1009 Send normal and ancillary data to the socket, gathering the 1010 non-ancillary data from a series of buffers and concatenating it 1011 into a single message. The *buffers* argument specifies the 1012 non-ancillary data as an iterable of buffer-compatible objects 1013 (e.g. :class:`bytes` objects); the operating system may set a limit 1014 (:func:`~os.sysconf` value ``SC_IOV_MAX``) on the number of buffers 1015 that can be used. The *ancdata* argument specifies the ancillary 1016 data (control messages) as an iterable of zero or more tuples 1017 ``(cmsg_level, cmsg_type, cmsg_data)``, where *cmsg_level* and 1018 *cmsg_type* are integers specifying the protocol level and 1019 protocol-specific type respectively, and *cmsg_data* is a 1020 buffer-compatible object holding the associated data. Note that 1021 some systems (in particular, systems without :func:`CMSG_SPACE`) 1022 might support sending only one control message per call. The 1023 *flags* argument defaults to 0 and has the same meaning as for 1024 :meth:`send`. If *address* is supplied and not ``None``, it sets a 1025 destination address for the message. The return value is the 1026 number of bytes of non-ancillary data sent. 1027 1028 The following function sends the list of file descriptors *fds* 1029 over an :const:`AF_UNIX` socket, on systems which support the 1030 :const:`SCM_RIGHTS` mechanism. See also :meth:`recvmsg`. :: 1031 1032 import socket, array 1033 1034 def send_fds(sock, msg, fds): 1035 return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))]) 1036 1037 Availability: most Unix platforms, possibly others. 1038 1039 .. versionadded:: 3.3 1040 1041 1042.. method:: socket.setblocking(flag) 1043 1044 Set blocking or non-blocking mode of the socket: if *flag* is false, the 1045 socket is set to non-blocking, else to blocking mode. 1046 1047 This method is a shorthand for certain :meth:`~socket.settimeout` calls: 1048 1049 * ``sock.setblocking(True)`` is equivalent to ``sock.settimeout(None)`` 1050 1051 * ``sock.setblocking(False)`` is equivalent to ``sock.settimeout(0.0)`` 1052 1053 1054.. method:: socket.settimeout(value) 1055 1056 Set a timeout on blocking socket operations. The *value* argument can be a 1057 nonnegative floating point number expressing seconds, or ``None``. 1058 If a non-zero value is given, subsequent socket operations will raise a 1059 :exc:`timeout` exception if the timeout period *value* has elapsed before 1060 the operation has completed. If zero is given, the socket is put in 1061 non-blocking mode. If ``None`` is given, the socket is put in blocking mode. 1062 1063 For further information, please consult the :ref:`notes on socket timeouts <socket-timeouts>`. 1064 1065 1066.. method:: socket.setsockopt(level, optname, value) 1067 1068 .. index:: module: struct 1069 1070 Set the value of the given socket option (see the Unix manual page 1071 :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the 1072 :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a 1073 bytes object representing a buffer. In the latter case it is up to the caller to 1074 ensure that the bytestring contains the proper bits (see the optional built-in 1075 module :mod:`struct` for a way to encode C structures as bytestrings). 1076 1077 1078.. method:: socket.shutdown(how) 1079 1080 Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`, 1081 further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends 1082 are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are 1083 disallowed. 1084 1085Note that there are no methods :meth:`read` or :meth:`write`; use 1086:meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead. 1087 1088Socket objects also have these (read-only) attributes that correspond to the 1089values given to the :class:`socket` constructor. 1090 1091 1092.. attribute:: socket.family 1093 1094 The socket family. 1095 1096 1097.. attribute:: socket.type 1098 1099 The socket type. 1100 1101 1102.. attribute:: socket.proto 1103 1104 The socket protocol. 1105 1106 1107 1108.. _socket-timeouts: 1109 1110Notes on socket timeouts 1111------------------------ 1112 1113A socket object can be in one of three modes: blocking, non-blocking, or 1114timeout. Sockets are by default always created in blocking mode, but this 1115can be changed by calling :func:`setdefaulttimeout`. 1116 1117* In *blocking mode*, operations block until complete or the system returns 1118 an error (such as connection timed out). 1119 1120* In *non-blocking mode*, operations fail (with an error that is unfortunately 1121 system-dependent) if they cannot be completed immediately: functions from the 1122 :mod:`select` can be used to know when and whether a socket is available for 1123 reading or writing. 1124 1125* In *timeout mode*, operations fail if they cannot be completed within the 1126 timeout specified for the socket (they raise a :exc:`timeout` exception) 1127 or if the system returns an error. 1128 1129.. note:: 1130 At the operating system level, sockets in *timeout mode* are internally set 1131 in non-blocking mode. Also, the blocking and timeout modes are shared between 1132 file descriptors and socket objects that refer to the same network endpoint. 1133 This implementation detail can have visible consequences if e.g. you decide 1134 to use the :meth:`~socket.fileno()` of a socket. 1135 1136Timeouts and the ``connect`` method 1137^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1138 1139The :meth:`~socket.connect` operation is also subject to the timeout 1140setting, and in general it is recommended to call :meth:`~socket.settimeout` 1141before calling :meth:`~socket.connect` or pass a timeout parameter to 1142:meth:`create_connection`. However, the system network stack may also 1143return a connection timeout error of its own regardless of any Python socket 1144timeout setting. 1145 1146Timeouts and the ``accept`` method 1147^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1148 1149If :func:`getdefaulttimeout` is not :const:`None`, sockets returned by 1150the :meth:`~socket.accept` method inherit that timeout. Otherwise, the 1151behaviour depends on settings of the listening socket: 1152 1153* if the listening socket is in *blocking mode* or in *timeout mode*, 1154 the socket returned by :meth:`~socket.accept` is in *blocking mode*; 1155 1156* if the listening socket is in *non-blocking mode*, whether the socket 1157 returned by :meth:`~socket.accept` is in blocking or non-blocking mode 1158 is operating system-dependent. If you want to ensure cross-platform 1159 behaviour, it is recommended you manually override this setting. 1160 1161 1162.. _socket-example: 1163 1164Example 1165------- 1166 1167Here are four minimal example programs using the TCP/IP protocol: a server that 1168echoes all data that it receives back (servicing only one client), and a client 1169using it. Note that a server must perform the sequence :func:`socket`, 1170:meth:`~socket.bind`, :meth:`~socket.listen`, :meth:`~socket.accept` (possibly 1171repeating the :meth:`~socket.accept` to service more than one client), while a 1172client only needs the sequence :func:`socket`, :meth:`~socket.connect`. Also 1173note that the server does not :meth:`~socket.sendall`/:meth:`~socket.recv` on 1174the socket it is listening on but on the new socket returned by 1175:meth:`~socket.accept`. 1176 1177The first two examples support IPv4 only. :: 1178 1179 # Echo server program 1180 import socket 1181 1182 HOST = '' # Symbolic name meaning all available interfaces 1183 PORT = 50007 # Arbitrary non-privileged port 1184 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1185 s.bind((HOST, PORT)) 1186 s.listen(1) 1187 conn, addr = s.accept() 1188 print('Connected by', addr) 1189 while True: 1190 data = conn.recv(1024) 1191 if not data: break 1192 conn.sendall(data) 1193 conn.close() 1194 1195:: 1196 1197 # Echo client program 1198 import socket 1199 1200 HOST = 'daring.cwi.nl' # The remote host 1201 PORT = 50007 # The same port as used by the server 1202 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1203 s.connect((HOST, PORT)) 1204 s.sendall(b'Hello, world') 1205 data = s.recv(1024) 1206 s.close() 1207 print('Received', repr(data)) 1208 1209The next two examples are identical to the above two, but support both IPv4 and 1210IPv6. The server side will listen to the first address family available (it 1211should listen to both instead). On most of IPv6-ready systems, IPv6 will take 1212precedence and the server may not accept IPv4 traffic. The client side will try 1213to connect to the all addresses returned as a result of the name resolution, and 1214sends traffic to the first one connected successfully. :: 1215 1216 # Echo server program 1217 import socket 1218 import sys 1219 1220 HOST = None # Symbolic name meaning all available interfaces 1221 PORT = 50007 # Arbitrary non-privileged port 1222 s = None 1223 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, 1224 socket.SOCK_STREAM, 0, socket.AI_PASSIVE): 1225 af, socktype, proto, canonname, sa = res 1226 try: 1227 s = socket.socket(af, socktype, proto) 1228 except OSError as msg: 1229 s = None 1230 continue 1231 try: 1232 s.bind(sa) 1233 s.listen(1) 1234 except OSError as msg: 1235 s.close() 1236 s = None 1237 continue 1238 break 1239 if s is None: 1240 print('could not open socket') 1241 sys.exit(1) 1242 conn, addr = s.accept() 1243 print('Connected by', addr) 1244 while True: 1245 data = conn.recv(1024) 1246 if not data:…
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