/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 :const:`AF_CAN`) 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.. data:: CAN_BCM 261 CAN_BCM_* 262 263 CAN_BCM, in the CAN protocol family, is the broadcast manager (BCM) protocol. 264 Broadcast manager constants, documented in the Linux documentation, are also 265 defined in the socket module. 266 267 Availability: Linux >= 2.6.25. 268 269 .. versionadded:: 3.4 270 271.. data:: AF_RDS 272 PF_RDS 273 SOL_RDS 274 RDS_* 275 276 Many constants of these forms, documented in the Linux documentation, are 277 also defined in the socket module. 278 279 Availability: Linux >= 2.6.30. 280 281 .. versionadded:: 3.3 282 283 284.. data:: SIO_* 285 RCVALL_* 286 287 Constants for Windows' WSAIoctl(). The constants are used as arguments to the 288 :meth:`ioctl` method of socket objects. 289 290 291.. data:: TIPC_* 292 293 TIPC related constants, matching the ones exported by the C socket API. See 294 the TIPC documentation for more information. 295 296.. data:: AF_LINK 297 298 Availability: BSD, OSX. 299 300 .. versionadded:: 3.4 301 302.. data:: has_ipv6 303 304 This constant contains a boolean value which indicates if IPv6 is supported on 305 this platform. 306 307 308.. function:: create_connection(address[, timeout[, source_address]]) 309 310 Connect to a TCP service listening on the Internet *address* (a 2-tuple 311 ``(host, port)``), and return the socket object. This is a higher-level 312 function than :meth:`socket.connect`: if *host* is a non-numeric hostname, 313 it will try to resolve it for both :data:`AF_INET` and :data:`AF_INET6`, 314 and then try to connect to all possible addresses in turn until a 315 connection succeeds. This makes it easy to write clients that are 316 compatible to both IPv4 and IPv6. 317 318 Passing the optional *timeout* parameter will set the timeout on the 319 socket instance before attempting to connect. If no *timeout* is 320 supplied, the global default timeout setting returned by 321 :func:`getdefaulttimeout` is used. 322 323 If supplied, *source_address* must be a 2-tuple ``(host, port)`` for the 324 socket to bind to as its source address before connecting. If host or port 325 are '' or 0 respectively the OS default behavior will be used. 326 327 .. versionchanged:: 3.2 328 *source_address* was added. 329 330 .. versionchanged:: 3.2 331 support for the :keyword:`with` statement was added. 332 333 334.. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0) 335 336 Translate the *host*/*port* argument into a sequence of 5-tuples that contain 337 all the necessary arguments for creating a socket connected to that service. 338 *host* is a domain name, a string representation of an IPv4/v6 address 339 or ``None``. *port* is a string service name such as ``'http'``, a numeric 340 port number or ``None``. By passing ``None`` as the value of *host* 341 and *port*, you can pass ``NULL`` to the underlying C API. 342 343 The *family*, *type* and *proto* arguments can be optionally specified 344 in order to narrow the list of addresses returned. Passing zero as a 345 value for each of these arguments selects the full range of results. 346 The *flags* argument can be one or several of the ``AI_*`` constants, 347 and will influence how results are computed and returned. 348 For example, :const:`AI_NUMERICHOST` will disable domain name resolution 349 and will raise an error if *host* is a domain name. 350 351 The function returns a list of 5-tuples with the following structure: 352 353 ``(family, type, proto, canonname, sockaddr)`` 354 355 In these tuples, *family*, *type*, *proto* are all integers and are 356 meant to be passed to the :func:`.socket` function. *canonname* will be 357 a string representing the canonical name of the *host* if 358 :const:`AI_CANONNAME` is part of the *flags* argument; else *canonname* 359 will be empty. *sockaddr* is a tuple describing a socket address, whose 360 format depends on the returned *family* (a ``(address, port)`` 2-tuple for 361 :const:`AF_INET`, a ``(address, port, flow info, scope id)`` 4-tuple for 362 :const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect` 363 method. 364 365 The following example fetches address information for a hypothetical TCP 366 connection to ``www.python.org`` on port 80 (results may differ on your 367 system if IPv6 isn't enabled):: 368 369 >>> socket.getaddrinfo("www.python.org", 80, proto=socket.SOL_TCP) 370 [(2, 1, 6, '', ('82.94.164.162', 80)), 371 (10, 1, 6, '', ('2001:888:2000:d::a2', 80, 0, 0))] 372 373 .. versionchanged:: 3.2 374 parameters can now be passed as single keyword arguments. 375 376.. function:: getfqdn([name]) 377 378 Return a fully qualified domain name for *name*. If *name* is omitted or empty, 379 it is interpreted as the local host. To find the fully qualified name, the 380 hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the 381 host, if available. The first name which includes a period is selected. In 382 case no fully qualified domain name is available, the hostname as returned by 383 :func:`gethostname` is returned. 384 385 386.. function:: gethostbyname(hostname) 387 388 Translate a host name to IPv4 address format. The IPv4 address is returned as a 389 string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself 390 it is returned unchanged. See :func:`gethostbyname_ex` for a more complete 391 interface. :func:`gethostbyname` does not support IPv6 name resolution, and 392 :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support. 393 394 395.. function:: gethostbyname_ex(hostname) 396 397 Translate a host name to IPv4 address format, extended interface. Return a 398 triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary 399 host name responding to the given *ip_address*, *aliaslist* is a (possibly 400 empty) list of alternative host names for the same address, and *ipaddrlist* is 401 a list of IPv4 addresses for the same interface on the same host (often but not 402 always a single address). :func:`gethostbyname_ex` does not support IPv6 name 403 resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual 404 stack support. 405 406 407.. function:: gethostname() 408 409 Return a string containing the hostname of the machine where the Python 410 interpreter is currently executing. 411 412 If you want to know the current machine's IP address, you may want to use 413 ``gethostbyname(gethostname())``. This operation assumes that there is a 414 valid address-to-host mapping for the host, and the assumption does not 415 always hold. 416 417 Note: :func:`gethostname` doesn't always return the fully qualified domain 418 name; use ``getfqdn()`` (see above). 419 420 421.. function:: gethostbyaddr(ip_address) 422 423 Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the 424 primary host name responding to the given *ip_address*, *aliaslist* is a 425 (possibly empty) list of alternative host names for the same address, and 426 *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same 427 host (most likely containing only a single address). To find the fully qualified 428 domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports 429 both IPv4 and IPv6. 430 431 432.. function:: getnameinfo(sockaddr, flags) 433 434 Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending 435 on the settings of *flags*, the result can contain a fully-qualified domain name 436 or numeric address representation in *host*. Similarly, *port* can contain a 437 string port name or a numeric port number. 438 439 440.. function:: getprotobyname(protocolname) 441 442 Translate an Internet protocol name (for example, ``'icmp'``) to a constant 443 suitable for passing as the (optional) third argument to the :func:`.socket` 444 function. This is usually only needed for sockets opened in "raw" mode 445 (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen 446 automatically if the protocol is omitted or zero. 447 448 449.. function:: getservbyname(servicename[, protocolname]) 450 451 Translate an Internet service name and protocol name to a port number for that 452 service. The optional protocol name, if given, should be ``'tcp'`` or 453 ``'udp'``, otherwise any protocol will match. 454 455 456.. function:: getservbyport(port[, protocolname]) 457 458 Translate an Internet port number and protocol name to a service name for that 459 service. The optional protocol name, if given, should be ``'tcp'`` or 460 ``'udp'``, otherwise any protocol will match. 461 462 463.. function:: socket([family[, type[, proto]]]) 464 465 Create a new socket using the given address family, socket type and protocol 466 number. The address family should be :const:`AF_INET` (the default), 467 :const:`AF_INET6`, :const:`AF_UNIX`, :const:`AF_CAN` or :const:`AF_RDS`. The 468 socket type should be :const:`SOCK_STREAM` (the default), 469 :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other ``SOCK_`` 470 constants. The protocol number is usually zero and may be omitted or in the 471 case where the address family is :const:`AF_CAN` the protocol should be one 472 of :const:`CAN_RAW` or :const:`CAN_BCM`. 473 474 .. versionchanged:: 3.3 475 The AF_CAN family was added. 476 The AF_RDS family was added. 477 478 .. versionchanged:: 3.4 479 The CAN_BCM protocol was added. 480 481.. function:: socketpair([family[, type[, proto]]]) 482 483 Build a pair of connected socket objects using the given address family, socket 484 type, and protocol number. Address family, socket type, and protocol number are 485 as for the :func:`.socket` function above. The default family is :const:`AF_UNIX` 486 if defined on the platform; otherwise, the default is :const:`AF_INET`. 487 Availability: Unix. 488 489 .. versionchanged:: 3.2 490 The returned socket objects now support the whole socket API, rather 491 than a subset. 492 493 494.. function:: fromfd(fd, family, type[, proto]) 495 496 Duplicate the file descriptor *fd* (an integer as returned by a file object's 497 :meth:`fileno` method) and build a socket object from the result. Address 498 family, socket type and protocol number are as for the :func:`.socket` function 499 above. The file descriptor should refer to a socket, but this is not checked --- 500 subsequent operations on the object may fail if the file descriptor is invalid. 501 This function is rarely needed, but can be used to get or set socket options on 502 a socket passed to a program as standard input or output (such as a server 503 started by the Unix inet daemon). The socket is assumed to be in blocking mode. 504 505 506.. function:: ntohl(x) 507 508 Convert 32-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 4-byte swap operation. 511 512 513.. function:: ntohs(x) 514 515 Convert 16-bit positive integers from network to host 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 2-byte swap operation. 518 519 520.. function:: htonl(x) 521 522 Convert 32-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 4-byte swap operation. 525 526 527.. function:: htons(x) 528 529 Convert 16-bit positive integers from host to network byte order. On machines 530 where the host byte order is the same as network byte order, this is a no-op; 531 otherwise, it performs a 2-byte swap operation. 532 533 534.. function:: inet_aton(ip_string) 535 536 Convert an IPv4 address from dotted-quad string format (for example, 537 '123.45.67.89') to 32-bit packed binary format, as a bytes object four characters in 538 length. This is useful when conversing with a program that uses the standard C 539 library and needs objects of type :c:type:`struct in_addr`, which is the C type 540 for the 32-bit packed binary this function returns. 541 542 :func:`inet_aton` also accepts strings with less than three dots; see the 543 Unix manual page :manpage:`inet(3)` for details. 544 545 If the IPv4 address string passed to this function is invalid, 546 :exc:`OSError` will be raised. Note that exactly what is valid depends on 547 the underlying C implementation of :c:func:`inet_aton`. 548 549 :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used 550 instead for IPv4/v6 dual stack support. 551 552 553.. function:: inet_ntoa(packed_ip) 554 555 Convert a 32-bit packed IPv4 address (a bytes object four characters in 556 length) to its standard dotted-quad string representation (for example, 557 '123.45.67.89'). This is useful when conversing with a program that uses the 558 standard C library and needs objects of type :c:type:`struct in_addr`, which 559 is the C type for the 32-bit packed binary data this function takes as an 560 argument. 561 562 If the byte sequence passed to this function is not exactly 4 bytes in 563 length, :exc:`OSError` will be raised. :func:`inet_ntoa` does not 564 support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual 565 stack support. 566 567 568.. function:: inet_pton(address_family, ip_string) 569 570 Convert an IP address from its family-specific string format to a packed, 571 binary format. :func:`inet_pton` is useful when a library or network protocol 572 calls for an object of type :c:type:`struct in_addr` (similar to 573 :func:`inet_aton`) or :c:type:`struct in6_addr`. 574 575 Supported values for *address_family* are currently :const:`AF_INET` and 576 :const:`AF_INET6`. If the IP address string *ip_string* is invalid, 577 :exc:`OSError` will be raised. Note that exactly what is valid depends on 578 both the value of *address_family* and the underlying implementation of 579 :c:func:`inet_pton`. 580 581 Availability: Unix (maybe not all platforms). 582 583 584.. function:: inet_ntop(address_family, packed_ip) 585 586 Convert a packed IP address (a bytes object of some number of characters) to its 587 standard, family-specific string representation (for example, ``'7.10.0.5'`` or 588 ``'5aef:2b::8'``). :func:`inet_ntop` is useful when a library or network protocol 589 returns an object of type :c:type:`struct in_addr` (similar to :func:`inet_ntoa`) 590 or :c:type:`struct in6_addr`. 591 592 Supported values for *address_family* are currently :const:`AF_INET` and 593 :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the 594 specified address family, :exc:`ValueError` will be raised. A 595 :exc:`OSError` is raised for errors from the call to :func:`inet_ntop`. 596 597 Availability: Unix (maybe not all platforms). 598 599 600.. 601 XXX: Are sendmsg(), recvmsg() and CMSG_*() available on any 602 non-Unix platforms? The old (obsolete?) 4.2BSD form of the 603 interface, in which struct msghdr has no msg_control or 604 msg_controllen members, is not currently supported. 605 606.. function:: CMSG_LEN(length) 607 608 Return the total length, without trailing padding, of an ancillary 609 data item with associated data of the given *length*. This value 610 can often be used as the buffer size for :meth:`~socket.recvmsg` to 611 receive a single item of ancillary data, but :rfc:`3542` requires 612 portable applications to use :func:`CMSG_SPACE` and thus include 613 space for padding, even when the item will be the last in the 614 buffer. Raises :exc:`OverflowError` if *length* is outside the 615 permissible range of values. 616 617 Availability: most Unix platforms, possibly others. 618 619 .. versionadded:: 3.3 620 621 622.. function:: CMSG_SPACE(length) 623 624 Return the buffer size needed for :meth:`~socket.recvmsg` to 625 receive an ancillary data item with associated data of the given 626 *length*, along with any trailing padding. The buffer space needed 627 to receive multiple items is the sum of the :func:`CMSG_SPACE` 628 values for their associated data lengths. Raises 629 :exc:`OverflowError` if *length* is outside the permissible range 630 of values. 631 632 Note that some systems might support ancillary data without 633 providing this function. Also note that setting the buffer size 634 using the results of this function may not precisely limit the 635 amount of ancillary data that can be received, since additional 636 data may be able to fit into the padding area. 637 638 Availability: most Unix platforms, possibly others. 639 640 .. versionadded:: 3.3 641 642 643.. function:: getdefaulttimeout() 644 645 Return the default timeout in seconds (float) for new socket objects. A value 646 of ``None`` indicates that new socket objects have no timeout. When the socket 647 module is first imported, the default is ``None``. 648 649 650.. function:: setdefaulttimeout(timeout) 651 652 Set the default timeout in seconds (float) for new socket objects. When 653 the socket module is first imported, the default is ``None``. See 654 :meth:`~socket.settimeout` for possible values and their respective 655 meanings. 656 657 658.. function:: sethostname(name) 659 660 Set the machine's hostname to *name*. This will raise a 661 :exc:`OSError` if you don't have enough rights. 662 663 Availability: Unix. 664 665 .. versionadded:: 3.3 666 667 668.. function:: if_nameindex() 669 670 Return a list of network interface information 671 (index int, name string) tuples. 672 :exc:`OSError` if the system call fails. 673 674 Availability: Unix. 675 676 .. versionadded:: 3.3 677 678 679.. function:: if_nametoindex(if_name) 680 681 Return a network interface index number corresponding to an 682 interface name. 683 :exc:`OSError` if no interface with the given name exists. 684 685 Availability: Unix. 686 687 .. versionadded:: 3.3 688 689 690.. function:: if_indextoname(if_index) 691 692 Return a network interface name corresponding to a 693 interface index number. 694 :exc:`OSError` if no interface with the given index exists. 695 696 Availability: Unix. 697 698 .. versionadded:: 3.3 699 700 701.. function:: fromshare(data) 702 703 Instantiate a socket from data obtained from :meth:`~socket.share`. 704 The socket is assumed to be in blocking mode. 705 706 Availability: Windows. 707 708 .. versionadded:: 3.3 709 710 711.. data:: SocketType 712 713 This is a Python type object that represents the socket object type. It is the 714 same as ``type(socket(...))``. 715 716 717.. _socket-objects: 718 719Socket Objects 720-------------- 721 722Socket objects have the following methods. Except for :meth:`makefile` these 723correspond to Unix system calls applicable to sockets. 724 725 726.. method:: socket.accept() 727 728 Accept a connection. The socket must be bound to an address and listening for 729 connections. The return value is a pair ``(conn, address)`` where *conn* is a 730 *new* socket object usable to send and receive data on the connection, and 731 *address* is the address bound to the socket on the other end of the connection. 732 733 734.. method:: socket.bind(address) 735 736 Bind the socket to *address*. The socket must not already be bound. (The format 737 of *address* depends on the address family --- see above.) 738 739 740.. method:: socket.close() 741 742 Close the socket. All future operations on the socket object will fail. The 743 remote end will receive no more data (after queued data is flushed). Sockets are 744 automatically closed when they are garbage-collected. 745 746 .. note:: 747 :meth:`close()` releases the resource associated with a connection but 748 does not necessarily close the connection immediately. If you want 749 to close the connection in a timely fashion, call :meth:`shutdown()` 750 before :meth:`close()`. 751 752 753.. method:: socket.connect(address) 754 755 Connect to a remote socket at *address*. (The format of *address* depends on the 756 address family --- see above.) 757 758 759.. method:: socket.connect_ex(address) 760 761 Like ``connect(address)``, but return an error indicator instead of raising an 762 exception for errors returned by the C-level :c:func:`connect` call (other 763 problems, such as "host not found," can still raise exceptions). The error 764 indicator is ``0`` if the operation succeeded, otherwise the value of the 765 :c:data:`errno` variable. This is useful to support, for example, asynchronous 766 connects. 767 768 769.. method:: socket.detach() 770 771 Put the socket object into closed state without actually closing the 772 underlying file descriptor. The file descriptor is returned, and can 773 be reused for other purposes. 774 775 .. versionadded:: 3.2 776 777 778.. method:: socket.fileno() 779 780 Return the socket's file descriptor (a small integer). This is useful with 781 :func:`select.select`. 782 783 Under Windows the small integer returned by this method cannot be used where a 784 file descriptor can be used (such as :func:`os.fdopen`). Unix does not have 785 this limitation. 786 787 788.. method:: socket.getpeername() 789 790 Return the remote address to which the socket is connected. This is useful to 791 find out the port number of a remote IPv4/v6 socket, for instance. (The format 792 of the address returned depends on the address family --- see above.) On some 793 systems this function is not supported. 794 795 796.. method:: socket.getsockname() 797 798 Return the socket's own address. This is useful to find out the port number of 799 an IPv4/v6 socket, for instance. (The format of the address returned depends on 800 the address family --- see above.) 801 802 803.. method:: socket.getsockopt(level, optname[, buflen]) 804 805 Return the value of the given socket option (see the Unix man page 806 :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.) 807 are defined in this module. If *buflen* is absent, an integer option is assumed 808 and its integer value is returned by the function. If *buflen* is present, it 809 specifies the maximum length of the buffer used to receive the option in, and 810 this buffer is returned as a bytes object. It is up to the caller to decode the 811 contents of the buffer (see the optional built-in module :mod:`struct` for a way 812 to decode C structures encoded as byte strings). 813 814 815.. method:: socket.gettimeout() 816 817 Return the timeout in seconds (float) associated with socket operations, 818 or ``None`` if no timeout is set. This reflects the last call to 819 :meth:`setblocking` or :meth:`settimeout`. 820 821 822.. method:: socket.ioctl(control, option) 823 824 :platform: Windows 825 826 The :meth:`ioctl` method is a limited interface to the WSAIoctl system 827 interface. Please refer to the `Win32 documentation 828 <http://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more 829 information. 830 831 On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl` 832 functions may be used; they accept a socket object as their first argument. 833 834.. method:: socket.listen(backlog) 835 836 Listen for connections made to the socket. The *backlog* argument specifies the 837 maximum number of queued connections and should be at least 0; the maximum value 838 is system-dependent (usually 5), the minimum value is forced to 0. 839 840 841.. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \ 842 errors=None, newline=None) 843 844 .. index:: single: I/O control; buffering 845 846 Return a :term:`file object` associated with the socket. The exact returned 847 type depends on the arguments given to :meth:`makefile`. These arguments are 848 interpreted the same way as by the built-in :func:`open` function. 849 850 Closing the file object won't close the socket unless there are no remaining 851 references to the socket. The socket must be in blocking mode; it can have 852 a timeout, but the file object's internal buffer may end up in a inconsistent 853 state if a timeout occurs. 854 855 .. note:: 856 857 On Windows, the file-like object created by :meth:`makefile` cannot be 858 used where a file object with a file descriptor is expected, such as the 859 stream arguments of :meth:`subprocess.Popen`. 860 861 862.. method:: socket.recv(bufsize[, flags]) 863 864 Receive data from the socket. The return value is a bytes object representing the 865 data received. The maximum amount of data to be received at once is specified 866 by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of 867 the optional argument *flags*; it defaults to zero. 868 869 .. note:: 870 871 For best match with hardware and network realities, the value of *bufsize* 872 should be a relatively small power of 2, for example, 4096. 873 874 875.. method:: socket.recvfrom(bufsize[, flags]) 876 877 Receive data from the socket. The return value is a pair ``(bytes, address)`` 878 where *bytes* is a bytes object representing the data received and *address* is the 879 address of the socket sending the data. See the Unix manual page 880 :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults 881 to zero. (The format of *address* depends on the address family --- see above.) 882 883 884.. method:: socket.recvmsg(bufsize[, ancbufsize[, flags]]) 885 886 Receive normal data (up to *bufsize* bytes) and ancillary data from 887 the socket. The *ancbufsize* argument sets the size in bytes of 888 the internal buffer used to receive the ancillary data; it defaults 889 to 0, meaning that no ancillary data will be received. Appropriate 890 buffer sizes for ancillary data can be calculated using 891 :func:`CMSG_SPACE` or :func:`CMSG_LEN`, and items which do not fit 892 into the buffer might be truncated or discarded. The *flags* 893 argument defaults to 0 and has the same meaning as for 894 :meth:`recv`. 895 896 The return value is a 4-tuple: ``(data, ancdata, msg_flags, 897 address)``. The *data* item is a :class:`bytes` object holding the 898 non-ancillary data received. The *ancdata* item is a list of zero 899 or more tuples ``(cmsg_level, cmsg_type, cmsg_data)`` representing 900 the ancillary data (control messages) received: *cmsg_level* and 901 *cmsg_type* are integers specifying the protocol level and 902 protocol-specific type respectively, and *cmsg_data* is a 903 :class:`bytes` object holding the associated data. The *msg_flags* 904 item is the bitwise OR of various flags indicating conditions on 905 the received message; see your system documentation for details. 906 If the receiving socket is unconnected, *address* is the address of 907 the sending socket, if available; otherwise, its value is 908 unspecified. 909 910 On some systems, :meth:`sendmsg` and :meth:`recvmsg` can be used to 911 pass file descriptors between processes over an :const:`AF_UNIX` 912 socket. When this facility is used (it is often restricted to 913 :const:`SOCK_STREAM` sockets), :meth:`recvmsg` will return, in its 914 ancillary data, items of the form ``(socket.SOL_SOCKET, 915 socket.SCM_RIGHTS, fds)``, where *fds* is a :class:`bytes` object 916 representing the new file descriptors as a binary array of the 917 native C :c:type:`int` type. If :meth:`recvmsg` raises an 918 exception after the system call returns, it will first attempt to 919 close any file descriptors received via this mechanism. 920 921 Some systems do not indicate the truncated length of ancillary data 922 items which have been only partially received. If an item appears 923 to extend beyond the end of the buffer, :meth:`recvmsg` will issue 924 a :exc:`RuntimeWarning`, and will return the part of it which is 925 inside the buffer provided it has not been truncated before the 926 start of its associated data. 927 928 On systems which support the :const:`SCM_RIGHTS` mechanism, the 929 following function will receive up to *maxfds* file descriptors, 930 returning the message data and a list containing the descriptors 931 (while ignoring unexpected conditions such as unrelated control 932 messages being received). See also :meth:`sendmsg`. :: 933 934 import socket, array 935 936 def recv_fds(sock, msglen, maxfds): 937 fds = array.array("i") # Array of ints 938 msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize)) 939 for cmsg_level, cmsg_type, cmsg_data in ancdata: 940 if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS): 941 # Append data, ignoring any truncated integers at the end. 942 fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)]) 943 return msg, list(fds) 944 945 Availability: most Unix platforms, possibly others. 946 947 .. versionadded:: 3.3 948 949 950.. method:: socket.recvmsg_into(buffers[, ancbufsize[, flags]]) 951 952 Receive normal data and ancillary data from the socket, behaving as 953 :meth:`recvmsg` would, but scatter the non-ancillary data into a 954 series of buffers instead of returning a new bytes object. The 955 *buffers* argument must be an iterable of objects that export 956 writable buffers (e.g. :class:`bytearray` objects); these will be 957 filled with successive chunks of the non-ancillary data until it 958 has all been written or there are no more buffers. The operating 959 system may set a limit (:func:`~os.sysconf` value ``SC_IOV_MAX``) 960 on the number of buffers that can be used. The *ancbufsize* and 961 *flags* arguments have the same meaning as for :meth:`recvmsg`. 962 963 The return value is a 4-tuple: ``(nbytes, ancdata, msg_flags, 964 address)``, where *nbytes* is the total number of bytes of 965 non-ancillary data written into the buffers, and *ancdata*, 966 *msg_flags* and *address* are the same as for :meth:`recvmsg`. 967 968 Example:: 969 970 >>> import socket 971 >>> s1, s2 = socket.socketpair() 972 >>> b1 = bytearray(b'----') 973 >>> b2 = bytearray(b'0123456789') 974 >>> b3 = bytearray(b'--------------') 975 >>> s1.send(b'Mary had a little lamb') 976 22 977 >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3]) 978 (22, [], 0, None) 979 >>> [b1, b2, b3] 980 [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')] 981 982 Availability: most Unix platforms, possibly others. 983 984 .. versionadded:: 3.3 985 986 987.. method:: socket.recvfrom_into(buffer[, nbytes[, flags]]) 988 989 Receive data from the socket, writing it into *buffer* instead of creating a 990 new bytestring. The return value is a pair ``(nbytes, address)`` where *nbytes* is 991 the number of bytes received and *address* is the address of the socket sending 992 the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the 993 optional argument *flags*; it defaults to zero. (The format of *address* 994 depends on the address family --- see above.) 995 996 997.. method:: socket.recv_into(buffer[, nbytes[, flags]]) 998 999 Receive up to *nbytes* bytes from the socket, storing the data into a buffer 1000 rather than creating a new bytestring. If *nbytes* is not specified (or 0), 1001 receive up to the size available in the given buffer. Returns the number of 1002 bytes received. See the Unix manual page :manpage:`recv(2)` for the meaning 1003 of the optional argument *flags*; it defaults to zero. 1004 1005 1006.. method:: socket.send(bytes[, flags]) 1007 1008 Send data to the socket. The socket must be connected to a remote socket. The 1009 optional *flags* argument has the same meaning as for :meth:`recv` above. 1010 Returns the number of bytes sent. Applications are responsible for checking that 1011 all data has been sent; if only some of the data was transmitted, the 1012 application needs to attempt delivery of the remaining data. For further 1013 information on this topic, consult the :ref:`socket-howto`. 1014 1015 1016.. method:: socket.sendall(bytes[, flags]) 1017 1018 Send data to the socket. The socket must be connected to a remote socket. The 1019 optional *flags* argument has the same meaning as for :meth:`recv` above. 1020 Unlike :meth:`send`, this method continues to send data from *bytes* until 1021 either all data has been sent or an error occurs. ``None`` is returned on 1022 success. On error, an exception is raised, and there is no way to determine how 1023 much data, if any, was successfully sent. 1024 1025 1026.. method:: socket.sendto(bytes, address) 1027 socket.sendto(bytes, flags, address) 1028 1029 Send data to the socket. The socket should not be connected to a remote socket, 1030 since the destination socket is specified by *address*. The optional *flags* 1031 argument has the same meaning as for :meth:`recv` above. Return the number of 1032 bytes sent. (The format of *address* depends on the address family --- see 1033 above.) 1034 1035 1036.. method:: socket.sendmsg(buffers[, ancdata[, flags[, address]]]) 1037 1038 Send normal and ancillary data to the socket, gathering the 1039 non-ancillary data from a series of buffers and concatenating it 1040 into a single message. The *buffers* argument specifies the 1041 non-ancillary data as an iterable of buffer-compatible objects 1042 (e.g. :class:`bytes` objects); the operating system may set a limit 1043 (:func:`~os.sysconf` value ``SC_IOV_MAX``) on the number of buffers 1044 that can be used. The *ancdata* argument specifies the ancillary 1045 data (control messages) as an iterable of zero or more tuples 1046 ``(cmsg_level, cmsg_type, cmsg_data)``, where *cmsg_level* and 1047 *cmsg_type* are integers specifying the protocol level and 1048 protocol-specific type respectively, and *cmsg_data* is a 1049 buffer-compatible object holding the associated data. Note that 1050 some systems (in particular, systems without :func:`CMSG_SPACE`) 1051 might support sending only one control message per call. The 1052 *flags* argument defaults to 0 and has the same meaning as for 1053 :meth:`send`. If *address* is supplied and not ``None``, it sets a 1054 destination address for the message. The return value is the 1055 number of bytes of non-ancillary data sent. 1056 1057 The following function sends the list of file descriptors *fds* 1058 over an :const:`AF_UNIX` socket, on systems which support the 1059 :const:`SCM_RIGHTS` mechanism. See also :meth:`recvmsg`. :: 1060 1061 import socket, array 1062 1063 def send_fds(sock, msg, fds): 1064 return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))]) 1065 1066 Availability: most Unix platforms, possibly others. 1067 1068 .. versionadded:: 3.3 1069 1070 1071.. method:: socket.setblocking(flag) 1072 1073 Set blocking or non-blocking mode of the socket: if *flag* is false, the 1074 socket is set to non-blocking, else to blocking mode. 1075 1076 This method is a shorthand for certain :meth:`~socket.settimeout` calls: 1077 1078 * ``sock.setblocking(True)`` is equivalent to ``sock.settimeout(None)`` 1079 1080 * ``sock.setblocking(False)`` is equivalent to ``sock.settimeout(0.0)`` 1081 1082 1083.. method:: socket.settimeout(value) 1084 1085 Set a timeout on blocking socket operations. The *value* argument can be a 1086 nonnegative floating point number expressing seconds, or ``None``. 1087 If a non-zero value is given, subsequent socket operations will raise a 1088 :exc:`timeout` exception if the timeout period *value* has elapsed before 1089 the operation has completed. If zero is given, the socket is put in 1090 non-blocking mode. If ``None`` is given, the socket is put in blocking mode. 1091 1092 For further information, please consult the :ref:`notes on socket timeouts <socket-timeouts>`. 1093 1094 1095.. method:: socket.setsockopt(level, optname, value) 1096 1097 .. index:: module: struct 1098 1099 Set the value of the given socket option (see the Unix manual page 1100 :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the 1101 :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a 1102 bytes object representing a buffer. In the latter case it is up to the caller to 1103 ensure that the bytestring contains the proper bits (see the optional built-in 1104 module :mod:`struct` for a way to encode C structures as bytestrings). 1105 1106 1107.. method:: socket.shutdown(how) 1108 1109 Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`, 1110 further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends 1111 are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are 1112 disallowed. 1113 1114 1115.. method:: socket.share(process_id) 1116 1117 :platform: Windows 1118 1119 Duplacet a socket and prepare it for sharing with a target process. The 1120 target process must be provided with *process_id*. The resulting bytes object 1121 can then be passed to the target process using some form of interprocess 1122 communication and the socket can be recreated there using :func:`fromshare`. 1123 Once this method has been called, it is safe to close the socket since 1124 the operating system has already duplicated it for the target process. 1125 1126 .. versionadded:: 3.3 1127 1128 1129Note that there are no methods :meth:`read` or :meth:`write`; use 1130:meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead. 1131 1132Socket objects also have these (read-only) attributes that correspond to the 1133values given to the :class:`socket` constructor. 1134 1135 1136.. attribute:: socket.family 1137 1138 The socket family. 1139 1140 1141.. attribute:: socket.type 1142 1143 The socket type. 1144 1145 1146.. attribute:: socket.proto 1147 1148 The socket protocol. 1149 1150 1151 1152.. _socket-timeouts: 1153 1154Notes on socket timeouts 1155------------------------ 1156 1157A socket object can be in one of three modes: blocking, non-blocking, or 1158timeout. Sockets are by default always created in blocking mode, but this 1159can be changed by calling :func:`setdefaulttimeout`. 1160 1161* In *blocking mode*, operations block until complete or the system returns 1162 an error (such as connection timed out). 1163 1164* In *non-blocking mode*, operations fail (with an error that is unfortunately 1165 system-dependent) if they cannot be completed immediately: functions from the 1166 :mod:`select` can be used to know when and whether a socket is available for 1167 reading or writing. 1168 1169* In *timeout mode*, operations fail if they cannot be completed within the 1170 timeout specified for the socket (they raise a :exc:`timeout` exception) 1171 or if the system returns an error. 1172 1173.. note:: 1174 At the operating system level, sockets in *timeout mode* are internally set 1175 in non-blocking mode. Also, the blocking and timeout modes are shared between 1176 file descriptors and socket objects that refer to the same network endpoint. 1177 This implementation detail can have visible consequences if e.g. you decide 1178 to use the :meth:`~socket.fileno()` of a socket. 1179 1180Timeouts and the ``connect`` method 1181^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1182 1183The :meth:`~socket.connect` operation is also subject to the timeout 1184setting, and in general it is recommended to call :meth:`~socket.settimeout` 1185before calling :meth:`~socket.connect` or pass a timeout parameter to 1186:meth:`create_connection`. However, the system network stack may also 1187return a connection timeout error of its own regardless of any Python socket 1188timeout setting. 1189 1190Timeouts and the ``accept`` method 1191^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1192 1193If :func:`getdefaulttimeout` is not :const:`None`, sockets returned by 1194the :meth:`~socket.accept` method inherit that timeout. Otherwise, the 1195behaviour depends on settings of the listening socket: 1196 1197* if the listening socket is in *blocking mode* or in *timeout mode*, 1198 the socket returned by :meth:`~socket.accept` is in *blocking mode*; 1199 1200* if the listening socket is in *non-blocking mode*, whether the socket 1201 returned by :meth:`~socket.accept` is in blocking or non-blocking mode 1202 is operating system-dependent. If you want to ensure cross-platform 1203 behaviour, it is recommended you manually override this setting. 1204 1205 1206.. _socket-example: 1207 1208Example 1209------- 1210 1211Here are four minimal example programs using the TCP/IP protocol: a server that 1212echoes all data that it receives back (servicing only one client), and a client 1213using it. Note that a server must perform the sequence :func:`.socket`, 1214:meth:`~socket.bind`, :meth:`~socket.listen`, :meth:`~socket.accept` (possibly 1215repeating the :meth:`~socket.accept` to service more than one client), while a 1216client only needs the sequence :func:`.socket`, :meth:`~socket.connect`. Also 1217note that the server does not :meth:`~socket.sendall`/:meth:`~socket.recv` on 1218the socket it is listening on but on the new socket returned by 1219:meth:`~socket.accept`. 1220 1221The first two examples support IPv4 only. :: 1222 1223 # Echo server program 1224 import socket 1225 1226 HOST = '' # Symbolic name meaning all available interfaces 1227 PORT = 50007 # Arbitrary non-privileged port 1228 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1229 s.bind((HOST, PORT)) 1230 s.listen(1) 1231 conn, addr = s.accept() 1232 print('Connected by', addr) 1233 while True: 1234 data = conn.recv(1024) 1235 if not data: break 1236 conn.sendall(data) 1237 conn.close() 1238 1239:: 1240 1241 # Echo client program 1242 import socket 1243 1244 HOST = 'daring.cwi.nl' # The remote host 1245 PORT = 50007 # The same port as used by the server 1246 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1247 s.connect((HOST, PORT)) 1248 s.sendall(b'Hello, world') 1249 data = s.recv(1024) 1250 s.close() 1251 print('Received', repr(data)) 1252 1253The next two examples are identical to the…
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