/Doc/library/socket.rst
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1:mod:`socket` --- Low-level networking interface 2================================================ 3 4.. module:: socket 5 :synopsis: Low-level networking interface. 6 7 8This module provides access to the BSD *socket* interface. It is available on 9all modern Unix systems, Windows, MacOS, OS/2, and probably additional 10platforms. 11 12.. note:: 13 14 Some behavior may be platform dependent, since calls are made to the operating 15 system socket APIs. 16 17.. index:: object: socket 18 19The Python interface is a straightforward transliteration of the Unix system 20call and library interface for sockets to Python's object-oriented style: the 21:func:`socket` function returns a :dfn:`socket object` whose methods implement 22the various socket system calls. Parameter types are somewhat higher-level than 23in the C interface: as with :meth:`read` and :meth:`write` operations on Python 24files, buffer allocation on receive operations is automatic, and buffer length 25is implicit on send operations. 26 27 28.. seealso:: 29 30 Module :mod:`socketserver` 31 Classes that simplify writing network servers. 32 33 Module :mod:`ssl` 34 A TLS/SSL wrapper for socket objects. 35 36 37Socket families 38--------------- 39 40Depending on the system and the build options, various socket families 41are supported by this module. 42 43The address format required by a particular socket object is automatically 44selected based on the address family specified when the socket object was 45created. Socket addresses are represented as follows: 46 47- The address of an :const:`AF_UNIX` socket bound to a file system node 48 is represented as a string, using the file system encoding and the 49 ``'surrogateescape'`` error handler (see :pep:`383`). An address in 50 Linux's abstract namespace is returned as a :class:`bytes` object with 51 an initial null byte; note that sockets in this namespace can 52 communicate with normal file system sockets, so programs intended to 53 run on Linux may need to deal with both types of address. A string or 54 :class:`bytes` object can be used for either type of address when 55 passing it as an argument. 56 57 .. versionchanged:: 3.3 58 Previously, :const:`AF_UNIX` socket paths were assumed to use UTF-8 59 encoding. 60 61- A pair ``(host, port)`` is used for the :const:`AF_INET` address family, 62 where *host* is a string representing either a hostname in Internet domain 63 notation like ``'daring.cwi.nl'`` or an IPv4 address like ``'100.50.200.5'``, 64 and *port* is an integer. 65 66- For :const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo, 67 scopeid)`` is used, where *flowinfo* and *scopeid* represent the ``sin6_flowinfo`` 68 and ``sin6_scope_id`` members in :const:`struct sockaddr_in6` in C. For 69 :mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for 70 backward compatibility. Note, however, omission of *scopeid* can cause problems 71 in manipulating scoped IPv6 addresses. 72 73- :const:`AF_NETLINK` sockets are represented as pairs ``(pid, groups)``. 74 75- Linux-only support for TIPC is available using the :const:`AF_TIPC` 76 address family. TIPC is an open, non-IP based networked protocol designed 77 for use in clustered computer environments. Addresses are represented by a 78 tuple, and the fields depend on the address type. The general tuple form is 79 ``(addr_type, v1, v2, v3 [, scope])``, where: 80 81 - *addr_type* is one of :const:`TIPC_ADDR_NAMESEQ`, :const:`TIPC_ADDR_NAME`, 82 or :const:`TIPC_ADDR_ID`. 83 - *scope* is one of :const:`TIPC_ZONE_SCOPE`, :const:`TIPC_CLUSTER_SCOPE`, and 84 :const:`TIPC_NODE_SCOPE`. 85 - If *addr_type* is :const:`TIPC_ADDR_NAME`, then *v1* is the server type, *v2* is 86 the port identifier, and *v3* should be 0. 87 88 If *addr_type* is :const:`TIPC_ADDR_NAMESEQ`, then *v1* is the server type, *v2* 89 is the lower port number, and *v3* is the upper port number. 90 91 If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the 92 reference, and *v3* should be set to 0. 93 94 If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the 95 reference, and *v3* should be set to 0. 96 97- A tuple ``(interface, )`` is used for the :const:`AF_CAN` address family, 98 where *interface* is a string representing a network interface name like 99 ``'can0'``. The network interface name ``''`` can be used to receive packets 100 from all network interfaces of this family. 101 102- A string or a tuple ``(id, unit)`` is used for the :const:`SYSPROTO_CONTROL` 103 protocol of the :const:`PF_SYSTEM` family. The string is the name of a 104 kernel control using a dynamically-assigned ID. The tuple can be used if ID 105 and unit number of the kernel control are known or if a registered ID is 106 used. 107 108 .. versionadded:: 3.3 109 110- Certain other address families (:const:`AF_BLUETOOTH`, :const:`AF_PACKET`) 111 support specific representations. 112 113 .. XXX document them! 114 115For IPv4 addresses, two special forms are accepted instead of a host address: 116the empty string represents :const:`INADDR_ANY`, and the string 117``'<broadcast>'`` represents :const:`INADDR_BROADCAST`. This behavior is not 118compatible with IPv6, therefore, you may want to avoid these if you intend 119to support IPv6 with your Python programs. 120 121If you use a hostname in the *host* portion of IPv4/v6 socket address, the 122program may show a nondeterministic behavior, as Python uses the first address 123returned from the DNS resolution. The socket address will be resolved 124differently into an actual IPv4/v6 address, depending on the results from DNS 125resolution and/or the host configuration. For deterministic behavior use a 126numeric address in *host* portion. 127 128All errors raise exceptions. The normal exceptions for invalid argument types 129and out-of-memory conditions can be raised; starting from Python 3.3, errors 130related to socket or address semantics raise :exc:`OSError` or one of its 131subclasses (they used to raise :exc:`socket.error`). 132 133Non-blocking mode is supported through :meth:`~socket.setblocking`. A 134generalization of this based on timeouts is supported through 135:meth:`~socket.settimeout`. 136 137 138Module contents 139--------------- 140 141The module :mod:`socket` exports the following constants and functions: 142 143 144.. exception:: error 145 146 A deprecated alias of :exc:`OSError`. 147 148 .. versionchanged:: 3.3 149 Following :pep:`3151`, this class was made an alias of :exc:`OSError`. 150 151 152.. exception:: herror 153 154 A subclass of :exc:`OSError`, this exception is raised for 155 address-related errors, i.e. for functions that use *h_errno* in the POSIX 156 C API, including :func:`gethostbyname_ex` and :func:`gethostbyaddr`. 157 The accompanying value is a pair ``(h_errno, string)`` representing an 158 error returned by a library call. *h_errno* is a numeric value, while 159 *string* represents the description of *h_errno*, as returned by the 160 :c:func:`hstrerror` C function. 161 162 .. versionchanged:: 3.3 163 This class was made a subclass of :exc:`OSError`. 164 165.. exception:: gaierror 166 167 A subclass of :exc:`OSError`, this exception is raised for 168 address-related errors by :func:`getaddrinfo` and :func:`getnameinfo`. 169 The accompanying value is a pair ``(error, string)`` representing an error 170 returned by a library call. *string* represents the description of 171 *error*, as returned by the :c:func:`gai_strerror` C function. The 172 numeric *error* value will match one of the :const:`EAI_\*` constants 173 defined in this module. 174 175 .. versionchanged:: 3.3 176 This class was made a subclass of :exc:`OSError`. 177 178.. exception:: timeout 179 180 A subclass of :exc:`OSError`, this exception is raised when a timeout 181 occurs on a socket which has had timeouts enabled via a prior call to 182 :meth:`~socket.settimeout` (or implicitly through 183 :func:`~socket.setdefaulttimeout`). The accompanying value is a string 184 whose value is currently always "timed out". 185 186 .. versionchanged:: 3.3 187 This class was made a subclass of :exc:`OSError`. 188 189.. data:: AF_UNIX 190 AF_INET 191 AF_INET6 192 193 These constants represent the address (and protocol) families, used for the 194 first argument to :func:`socket`. If the :const:`AF_UNIX` constant is not 195 defined then this protocol is unsupported. More constants may be available 196 depending on the system. 197 198 199.. data:: SOCK_STREAM 200 SOCK_DGRAM 201 SOCK_RAW 202 SOCK_RDM 203 SOCK_SEQPACKET 204 205 These constants represent the socket types, used for the second argument to 206 :func:`socket`. More constants may be available depending on the system. 207 (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be generally 208 useful.) 209 210.. data:: SOCK_CLOEXEC 211 SOCK_NONBLOCK 212 213 These two constants, if defined, can be combined with the socket types and 214 allow you to set some flags atomically (thus avoiding possible race 215 conditions and the need for separate calls). 216 217 .. seealso:: 218 219 `Secure File Descriptor Handling <http://udrepper.livejournal.com/20407.html>`_ 220 for a more thorough explanation. 221 222 Availability: Linux >= 2.6.27. 223 224 .. versionadded:: 3.2 225 226.. data:: SO_* 227 SOMAXCONN 228 MSG_* 229 SOL_* 230 SCM_* 231 IPPROTO_* 232 IPPORT_* 233 INADDR_* 234 IP_* 235 IPV6_* 236 EAI_* 237 AI_* 238 NI_* 239 TCP_* 240 241 Many constants of these forms, documented in the Unix documentation on sockets 242 and/or the IP protocol, are also defined in the socket module. They are 243 generally used in arguments to the :meth:`setsockopt` and :meth:`getsockopt` 244 methods of socket objects. In most cases, only those symbols that are defined 245 in the Unix header files are defined; for a few symbols, default values are 246 provided. 247 248.. data:: AF_CAN 249 PF_CAN 250 SOL_CAN_* 251 CAN_* 252 253 Many constants of these forms, documented in the Linux documentation, are 254 also defined in the socket module. 255 256 Availability: Linux >= 2.6.25. 257 258 .. versionadded:: 3.3 259 260 261.. data:: AF_RDS 262 PF_RDS 263 SOL_RDS 264 RDS_* 265 266 Many constants of these forms, documented in the Linux documentation, are 267 also defined in the socket module. 268 269 Availability: Linux >= 2.6.30. 270 271 .. versionadded:: 3.3 272 273 274.. data:: SIO_* 275 RCVALL_* 276 277 Constants for Windows' WSAIoctl(). The constants are used as arguments to the 278 :meth:`ioctl` method of socket objects. 279 280 281.. data:: TIPC_* 282 283 TIPC related constants, matching the ones exported by the C socket API. See 284 the TIPC documentation for more information. 285 286 287.. data:: has_ipv6 288 289 This constant contains a boolean value which indicates if IPv6 is supported on 290 this platform. 291 292 293.. function:: create_connection(address[, timeout[, source_address]]) 294 295 Connect to a TCP service listening on the Internet *address* (a 2-tuple 296 ``(host, port)``), and return the socket object. This is a higher-level 297 function than :meth:`socket.connect`: if *host* is a non-numeric hostname, 298 it will try to resolve it for both :data:`AF_INET` and :data:`AF_INET6`, 299 and then try to connect to all possible addresses in turn until a 300 connection succeeds. This makes it easy to write clients that are 301 compatible to both IPv4 and IPv6. 302 303 Passing the optional *timeout* parameter will set the timeout on the 304 socket instance before attempting to connect. If no *timeout* is 305 supplied, the global default timeout setting returned by 306 :func:`getdefaulttimeout` is used. 307 308 If supplied, *source_address* must be a 2-tuple ``(host, port)`` for the 309 socket to bind to as its source address before connecting. If host or port 310 are '' or 0 respectively the OS default behavior will be used. 311 312 .. versionchanged:: 3.2 313 *source_address* was added. 314 315 .. versionchanged:: 3.2 316 support for the :keyword:`with` statement was added. 317 318 319.. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0) 320 321 Translate the *host*/*port* argument into a sequence of 5-tuples that contain 322 all the necessary arguments for creating a socket connected to that service. 323 *host* is a domain name, a string representation of an IPv4/v6 address 324 or ``None``. *port* is a string service name such as ``'http'``, a numeric 325 port number or ``None``. By passing ``None`` as the value of *host* 326 and *port*, you can pass ``NULL`` to the underlying C API. 327 328 The *family*, *type* and *proto* arguments can be optionally specified 329 in order to narrow the list of addresses returned. Passing zero as a 330 value for each of these arguments selects the full range of results. 331 The *flags* argument can be one or several of the ``AI_*`` constants, 332 and will influence how results are computed and returned. 333 For example, :const:`AI_NUMERICHOST` will disable domain name resolution 334 and will raise an error if *host* is a domain name. 335 336 The function returns a list of 5-tuples with the following structure: 337 338 ``(family, type, proto, canonname, sockaddr)`` 339 340 In these tuples, *family*, *type*, *proto* are all integers and are 341 meant to be passed to the :func:`socket` function. *canonname* will be 342 a string representing the canonical name of the *host* if 343 :const:`AI_CANONNAME` is part of the *flags* argument; else *canonname* 344 will be empty. *sockaddr* is a tuple describing a socket address, whose 345 format depends on the returned *family* (a ``(address, port)`` 2-tuple for 346 :const:`AF_INET`, a ``(address, port, flow info, scope id)`` 4-tuple for 347 :const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect` 348 method. 349 350 The following example fetches address information for a hypothetical TCP 351 connection to ``www.python.org`` on port 80 (results may differ on your 352 system if IPv6 isn't enabled):: 353 354 >>> socket.getaddrinfo("www.python.org", 80, proto=socket.SOL_TCP) 355 [(2, 1, 6, '', ('82.94.164.162', 80)), 356 (10, 1, 6, '', ('2001:888:2000:d::a2', 80, 0, 0))] 357 358 .. versionchanged:: 3.2 359 parameters can now be passed as single keyword arguments. 360 361.. function:: getfqdn([name]) 362 363 Return a fully qualified domain name for *name*. If *name* is omitted or empty, 364 it is interpreted as the local host. To find the fully qualified name, the 365 hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the 366 host, if available. The first name which includes a period is selected. In 367 case no fully qualified domain name is available, the hostname as returned by 368 :func:`gethostname` is returned. 369 370 371.. function:: gethostbyname(hostname) 372 373 Translate a host name to IPv4 address format. The IPv4 address is returned as a 374 string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself 375 it is returned unchanged. See :func:`gethostbyname_ex` for a more complete 376 interface. :func:`gethostbyname` does not support IPv6 name resolution, and 377 :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support. 378 379 380.. function:: gethostbyname_ex(hostname) 381 382 Translate a host name to IPv4 address format, extended interface. Return a 383 triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary 384 host name responding to the given *ip_address*, *aliaslist* is a (possibly 385 empty) list of alternative host names for the same address, and *ipaddrlist* is 386 a list of IPv4 addresses for the same interface on the same host (often but not 387 always a single address). :func:`gethostbyname_ex` does not support IPv6 name 388 resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual 389 stack support. 390 391 392.. function:: gethostname() 393 394 Return a string containing the hostname of the machine where the Python 395 interpreter is currently executing. 396 397 If you want to know the current machine's IP address, you may want to use 398 ``gethostbyname(gethostname())``. This operation assumes that there is a 399 valid address-to-host mapping for the host, and the assumption does not 400 always hold. 401 402 Note: :func:`gethostname` doesn't always return the fully qualified domain 403 name; use ``getfqdn()`` (see above). 404 405 406.. function:: gethostbyaddr(ip_address) 407 408 Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the 409 primary host name responding to the given *ip_address*, *aliaslist* is a 410 (possibly empty) list of alternative host names for the same address, and 411 *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same 412 host (most likely containing only a single address). To find the fully qualified 413 domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports 414 both IPv4 and IPv6. 415 416 417.. function:: getnameinfo(sockaddr, flags) 418 419 Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending 420 on the settings of *flags*, the result can contain a fully-qualified domain name 421 or numeric address representation in *host*. Similarly, *port* can contain a 422 string port name or a numeric port number. 423 424 425.. function:: getprotobyname(protocolname) 426 427 Translate an Internet protocol name (for example, ``'icmp'``) to a constant 428 suitable for passing as the (optional) third argument to the :func:`socket` 429 function. This is usually only needed for sockets opened in "raw" mode 430 (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen 431 automatically if the protocol is omitted or zero. 432 433 434.. function:: getservbyname(servicename[, protocolname]) 435 436 Translate an Internet service name and protocol name to a port number for that 437 service. The optional protocol name, if given, should be ``'tcp'`` or 438 ``'udp'``, otherwise any protocol will match. 439 440 441.. function:: getservbyport(port[, protocolname]) 442 443 Translate an Internet port number and protocol name to a service name for that 444 service. The optional protocol name, if given, should be ``'tcp'`` or 445 ``'udp'``, otherwise any protocol will match. 446 447 448.. function:: socket([family[, type[, proto]]]) 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.. function:: fromshare(data) 684 685 Instantiate a socket from data obtained from :meth:`~socket.share`. 686 The socket is assumed to be in blocking mode. 687 688 Availability: Windows. 689 690 .. versionadded:: 3.3 691 692 693.. data:: SocketType 694 695 This is a Python type object that represents the socket object type. It is the 696 same as ``type(socket(...))``. 697 698 699.. _socket-objects: 700 701Socket Objects 702-------------- 703 704Socket objects have the following methods. Except for :meth:`makefile` these 705correspond to Unix system calls applicable to sockets. 706 707 708.. method:: socket.accept() 709 710 Accept a connection. The socket must be bound to an address and listening for 711 connections. The return value is a pair ``(conn, address)`` where *conn* is a 712 *new* socket object usable to send and receive data on the connection, and 713 *address* is the address bound to the socket on the other end of the connection. 714 715 716.. method:: socket.bind(address) 717 718 Bind the socket to *address*. The socket must not already be bound. (The format 719 of *address* depends on the address family --- see above.) 720 721 722.. method:: socket.close() 723 724 Close the socket. All future operations on the socket object will fail. The 725 remote end will receive no more data (after queued data is flushed). Sockets are 726 automatically closed when they are garbage-collected. 727 728 .. note:: 729 :meth:`close()` releases the resource associated with a connection but 730 does not necessarily close the connection immediately. If you want 731 to close the connection in a timely fashion, call :meth:`shutdown()` 732 before :meth:`close()`. 733 734 735.. method:: socket.connect(address) 736 737 Connect to a remote socket at *address*. (The format of *address* depends on the 738 address family --- see above.) 739 740 741.. method:: socket.connect_ex(address) 742 743 Like ``connect(address)``, but return an error indicator instead of raising an 744 exception for errors returned by the C-level :c:func:`connect` call (other 745 problems, such as "host not found," can still raise exceptions). The error 746 indicator is ``0`` if the operation succeeded, otherwise the value of the 747 :c:data:`errno` variable. This is useful to support, for example, asynchronous 748 connects. 749 750 751.. method:: socket.detach() 752 753 Put the socket object into closed state without actually closing the 754 underlying file descriptor. The file descriptor is returned, and can 755 be reused for other purposes. 756 757 .. versionadded:: 3.2 758 759 760.. method:: socket.fileno() 761 762 Return the socket's file descriptor (a small integer). This is useful with 763 :func:`select.select`. 764 765 Under Windows the small integer returned by this method cannot be used where a 766 file descriptor can be used (such as :func:`os.fdopen`). Unix does not have 767 this limitation. 768 769 770.. method:: socket.getpeername() 771 772 Return the remote address to which the socket is connected. This is useful to 773 find out the port number of a remote IPv4/v6 socket, for instance. (The format 774 of the address returned depends on the address family --- see above.) On some 775 systems this function is not supported. 776 777 778.. method:: socket.getsockname() 779 780 Return the socket's own address. This is useful to find out the port number of 781 an IPv4/v6 socket, for instance. (The format of the address returned depends on 782 the address family --- see above.) 783 784 785.. method:: socket.getsockopt(level, optname[, buflen]) 786 787 Return the value of the given socket option (see the Unix man page 788 :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.) 789 are defined in this module. If *buflen* is absent, an integer option is assumed 790 and its integer value is returned by the function. If *buflen* is present, it 791 specifies the maximum length of the buffer used to receive the option in, and 792 this buffer is returned as a bytes object. It is up to the caller to decode the 793 contents of the buffer (see the optional built-in module :mod:`struct` for a way 794 to decode C structures encoded as byte strings). 795 796 797.. method:: socket.gettimeout() 798 799 Return the timeout in seconds (float) associated with socket operations, 800 or ``None`` if no timeout is set. This reflects the last call to 801 :meth:`setblocking` or :meth:`settimeout`. 802 803 804.. method:: socket.ioctl(control, option) 805 806 :platform: Windows 807 808 The :meth:`ioctl` method is a limited interface to the WSAIoctl system 809 interface. Please refer to the `Win32 documentation 810 <http://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more 811 information. 812 813 On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl` 814 functions may be used; they accept a socket object as their first argument. 815 816.. method:: socket.listen(backlog) 817 818 Listen for connections made to the socket. The *backlog* argument specifies the 819 maximum number of queued connections and should be at least 0; the maximum value 820 is system-dependent (usually 5), the minimum value is forced to 0. 821 822 823.. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \ 824 errors=None, newline=None) 825 826 .. index:: single: I/O control; buffering 827 828 Return a :term:`file object` associated with the socket. The exact returned 829 type depends on the arguments given to :meth:`makefile`. These arguments are 830 interpreted the same way as by the built-in :func:`open` function. 831 832 Closing the file object won't close the socket unless there are no remaining 833 references to the socket. The socket must be in blocking mode; it can have 834 a timeout, but the file object's internal buffer may end up in a inconsistent 835 state if a timeout occurs. 836 837 .. note:: 838 839 On Windows, the file-like object created by :meth:`makefile` cannot be 840 used where a file object with a file descriptor is expected, such as the 841 stream arguments of :meth:`subprocess.Popen`. 842 843 844.. method:: socket.recv(bufsize[, flags]) 845 846 Receive data from the socket. The return value is a bytes object representing the 847 data received. The maximum amount of data to be received at once is specified 848 by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of 849 the optional argument *flags*; it defaults to zero. 850 851 .. note:: 852 853 For best match with hardware and network realities, the value of *bufsize* 854 should be a relatively small power of 2, for example, 4096. 855 856 857.. method:: socket.recvfrom(bufsize[, flags]) 858 859 Receive data from the socket. The return value is a pair ``(bytes, address)`` 860 where *bytes* is a bytes object representing the data received and *address* is the 861 address of the socket sending the data. See the Unix manual page 862 :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults 863 to zero. (The format of *address* depends on the address family --- see above.) 864 865 866.. method:: socket.recvmsg(bufsize[, ancbufsize[, flags]]) 867 868 Receive normal data (up to *bufsize* bytes) and ancillary data from 869 the socket. The *ancbufsize* argument sets the size in bytes of 870 the internal buffer used to receive the ancillary data; it defaults 871 to 0, meaning that no ancillary data will be received. Appropriate 872 buffer sizes for ancillary data can be calculated using 873 :func:`CMSG_SPACE` or :func:`CMSG_LEN`, and items which do not fit 874 into the buffer might be truncated or discarded. The *flags* 875 argument defaults to 0 and has the same meaning as for 876 :meth:`recv`. 877 878 The return value is a 4-tuple: ``(data, ancdata, msg_flags, 879 address)``. The *data* item is a :class:`bytes` object holding the 880 non-ancillary data received. The *ancdata* item is a list of zero 881 or more tuples ``(cmsg_level, cmsg_type, cmsg_data)`` representing 882 the ancillary data (control messages) received: *cmsg_level* and 883 *cmsg_type* are integers specifying the protocol level and 884 protocol-specific type respectively, and *cmsg_data* is a 885 :class:`bytes` object holding the associated data. The *msg_flags* 886 item is the bitwise OR of various flags indicating conditions on 887 the received message; see your system documentation for details. 888 If the receiving socket is unconnected, *address* is the address of 889 the sending socket, if available; otherwise, its value is 890 unspecified. 891 892 On some systems, :meth:`sendmsg` and :meth:`recvmsg` can be used to 893 pass file descriptors between processes over an :const:`AF_UNIX` 894 socket. When this facility is used (it is often restricted to 895 :const:`SOCK_STREAM` sockets), :meth:`recvmsg` will return, in its 896 ancillary data, items of the form ``(socket.SOL_SOCKET, 897 socket.SCM_RIGHTS, fds)``, where *fds* is a :class:`bytes` object 898 representing the new file descriptors as a binary array of the 899 native C :c:type:`int` type. If :meth:`recvmsg` raises an 900 exception after the system call returns, it will first attempt to 901 close any file descriptors received via this mechanism. 902 903 Some systems do not indicate the truncated length of ancillary data 904 items which have been only partially received. If an item appears 905 to extend beyond the end of the buffer, :meth:`recvmsg` will issue 906 a :exc:`RuntimeWarning`, and will return the part of it which is 907 inside the buffer provided it has not been truncated before the 908 start of its associated data. 909 910 On systems which support the :const:`SCM_RIGHTS` mechanism, the 911 following function will receive up to *maxfds* file descriptors, 912 returning the message data and a list containing the descriptors 913 (while ignoring unexpected conditions such as unrelated control 914 messages being received). See also :meth:`sendmsg`. :: 915 916 import socket, array 917 918 def recv_fds(sock, msglen, maxfds): 919 fds = array.array("i") # Array of ints 920 msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize)) 921 for cmsg_level, cmsg_type, cmsg_data in ancdata: 922 if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS): 923 # Append data, ignoring any truncated integers at the end. 924 fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)]) 925 return msg, list(fds) 926 927 Availability: most Unix platforms, possibly others. 928 929 .. versionadded:: 3.3 930 931 932.. method:: socket.recvmsg_into(buffers[, ancbufsize[, flags]]) 933 934 Receive normal data and ancillary data from the socket, behaving as 935 :meth:`recvmsg` would, but scatter the non-ancillary data into a 936 series of buffers instead of returning a new bytes object. The 937 *buffers* argument must be an iterable of objects that export 938 writable buffers (e.g. :class:`bytearray` objects); these will be 939 filled with successive chunks of the non-ancillary data until it 940 has all been written or there are no more buffers. The operating 941 system may set a limit (:func:`~os.sysconf` value ``SC_IOV_MAX``) 942 on the number of buffers that can be used. The *ancbufsize* and 943 *flags* arguments have the same meaning as for :meth:`recvmsg`. 944 945 The return value is a 4-tuple: ``(nbytes, ancdata, msg_flags, 946 address)``, where *nbytes* is the total number of bytes of 947 non-ancillary data written into the buffers, and *ancdata*, 948 *msg_flags* and *address* are the same as for :meth:`recvmsg`. 949 950 Example:: 951 952 >>> import socket 953 >>> s1, s2 = socket.socketpair() 954 >>> b1 = bytearray(b'----') 955 >>> b2 = bytearray(b'0123456789') 956 >>> b3 = bytearray(b'--------------') 957 >>> s1.send(b'Mary had a little lamb') 958 22 959 >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3]) 960 (22, [], 0, None) 961 >>> [b1, b2, b3] 962 [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')] 963 964 Availability: most Unix platforms, possibly others. 965 966 .. versionadded:: 3.3 967 968 969.. method:: socket.recvfrom_into(buffer[, nbytes[, flags]]) 970 971 Receive data from the socket, writing it into *buffer* instead of creating a 972 new bytestring. The return value is a pair ``(nbytes, address)`` where *nbytes* is 973 the number of bytes received and *address* is the address of the socket sending 974 the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the 975 optional argument *flags*; it defaults to zero. (The format of *address* 976 depends on the address family --- see above.) 977 978 979.. method:: socket.recv_into(buffer[, nbytes[, flags]]) 980 981 Receive up to *nbytes* bytes from the socket, storing the data into a buffer 982 rather than creating a new bytestring. If *nbytes* is not specified (or 0), 983 receive up to the size available in the given buffer. Returns the number of 984 bytes received. See the Unix manual page :manpage:`recv(2)` for the meaning 985 of the optional argument *flags*; it defaults to zero. 986 987 988.. method:: socket.send(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 Returns the number of bytes sent. Applications are responsible for checking that 993 all data has been sent; if only some of the data was transmitted, the 994 application needs to attempt delivery of the remaining data. For further 995 information on this topic, consult the :ref:`socket-howto`. 996 997 998.. method:: socket.sendall(bytes[, flags]) 999 1000 Send data to the socket. The socket must be connected to a remote socket. The 1001 optional *flags* argument has the same meaning as for :meth:`recv` above. 1002 Unlike :meth:`send`, this method continues to send data from *bytes* until 1003 either all data has been sent or an error occurs. ``None`` is returned on 1004 success. On error, an exception is raised, and there is no way to determine how 1005 much data, if any, was successfully sent. 1006 1007 1008.. method:: socket.sendto(bytes[, flags], address) 1009 1010 Send data to the socket. The socket should not be connected to a remote socket, 1011 since the destination socket is specified by *address*. The optional *flags* 1012 argument has the same meaning as for :meth:`recv` above. Return the number of 1013 bytes sent. (The format of *address* depends on the address family --- see 1014 above.) 1015 1016 1017.. method:: socket.sendmsg(buffers[, ancdata[, flags[, address]]]) 1018 1019 Send normal and ancillary data to the socket, gathering the 1020 non-ancillary data from a series of buffers and concatenating it 1021 into a single message. The *buffers* argument specifies the 1022 non-ancillary data as an iterable of buffer-compatible objects 1023 (e.g. :class:`bytes` objects); the operating system may set a limit 1024 (:func:`~os.sysconf` value ``SC_IOV_MAX``) on the number of buffers 1025 that can be used. The *ancdata* argument specifies the ancillary 1026 data (control messages) as an iterable of zero or more tuples 1027 ``(cmsg_level, cmsg_type, cmsg_data)``, where *cmsg_level* and 1028 *cmsg_type* are integers specifying the protocol level and 1029 protocol-specific type respectively, and *cmsg_data* is a 1030 buffer-compatible object holding the associated data. Note that 1031 some systems (in particular, systems without :func:`CMSG_SPACE`) 1032 might support sending only one control message per call. The 1033 *flags* argument defaults to 0 and has the same meaning as for 1034 :meth:`send`. If *address* is supplied and not ``None``, it sets a 1035 destination address for the message. The return value is the 1036 number of bytes of non-ancillary data sent. 1037 1038 The following function sends the list of file descriptors *fds* 1039 over an :const:`AF_UNIX` socket, on systems which support the 1040 :const:`SCM_RIGHTS` mechanism. See also :meth:`recvmsg`. :: 1041 1042 import socket, array 1043 1044 def send_fds(sock, msg, fds): 1045 return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))]) 1046 1047 Availability: most Unix platforms, possibly others. 1048 1049 .. versionadded:: 3.3 1050 1051 1052.. method:: socket.setblocking(flag) 1053 1054 Set blocking or non-blocking mode of the socket: if *flag* is false, the 1055 socket is set to non-blocking, else to blocking mode. 1056 1057 This method is a shorthand for certain :meth:`~socket.settimeout` calls: 1058 1059 * ``sock.setblocking(True)`` is equivalent to ``sock.settimeout(None)`` 1060 1061 * ``sock.setblocking(False)`` is equivalent to ``sock.settimeout(0.0)`` 1062 1063 1064.. method:: socket.settimeout(value) 1065 1066 Set a timeout on blocking socket operations. The *value* argument can be a 1067 nonnegative floating point number expressing seconds, or ``None``. 1068 If a non-zero value is given, subsequent socket operations will raise a 1069 :exc:`timeout` exception if the timeout period *value* has elapsed before 1070 the operation has completed. If zero is given, the socket is put in 1071 non-blocking mode. If ``None`` is given, the socket is put in blocking mode. 1072 1073 For further information, please consult the :ref:`notes on socket timeouts <socket-timeouts>`. 1074 1075 1076.. method:: socket.setsockopt(level, optname, value) 1077 1078 .. index:: module: struct 1079 1080 Set the value of the given socket option (see the Unix manual page 1081 :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the 1082 :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a 1083 bytes object representing a buffer. In the latter case it is up to the caller to 1084 ensure that the bytestring contains the proper bits (see the optional built-in 1085 module :mod:`struct` for a way to encode C structures as bytestrings). 1086 1087 1088.. method:: socket.shutdown(how) 1089 1090 Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`, 1091 further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends 1092 are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are 1093 disallowed. 1094 1095 1096.. method:: socket.share(process_id) 1097 1098 :platform: Windows 1099 1100 Duplacet a socket and prepare it for sharing with a target process. The 1101 target process must be provided with *process_id*. The resulting bytes object 1102 can then be passed to the target process using some form of interprocess 1103 communication and the socket can be recreated there using :func:`fromshare`. 1104 Once this method has been called, it is safe to close the socket since 1105 the operating system has already duplicated it for the target process. 1106 1107 .. versionadded:: 3.3 1108 1109 1110Note that there are no methods :meth:`read` or :meth:`write`; use 1111:meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead. 1112 1113Socket objects also have these (read-only) attributes that correspond to the 1114values given to the :class:`socket` constructor. 1115 1116 1117.. attribute:: socket.family 1118 1119 The socket family. 1120 1121 1122.. attribute:: socket.type 1123 1124 The socket type. 1125 1126 1127.. attribute:: socket.proto 1128 1129 The socket protocol. 1130 1131 1132 1133.. _socket-timeouts: 1134 1135Notes on socket timeouts 1136------------------------ 1137 1138A socket object can be in one of three modes: blocking, non-blocking, or 1139timeout. Sockets are by default always created in blocking mode, but this 1140can be changed by calling :func:`setdefaulttimeout`. 1141 1142* In *blocking mode*, operations block until complete or the system returns 1143 an error (such as connection timed out). 1144 1145* In *non-blocking mode*, operations fail (with an error that is unfortunately 1146 system-dependent) if they cannot be completed immediately: functions from the 1147 :mod:`select` can be used to know when and whether a socket is available for 1148 reading or writing. 1149 1150* In *timeout mode*, operations fail if they cannot be completed within the 1151 timeout specified for the socket (they raise a :exc:`timeout` exception) 1152 or if the system returns an error. 1153 1154.. note:: 1155 At the operating system level, sockets in *timeout mode* are internally set 1156 in non-blocking mode. Also, the blocking and timeout modes are shared between 1157 file descriptors and socket objects that refer to the same network endpoint. 1158 This implementation detail can have visible consequences if e.g. you decide 1159 to use the :meth:`~socket.fileno()` of a socket. 1160 1161Timeouts and the ``connect`` method 1162^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1163 1164The :meth:`~socket.connect` operation is also subject to the timeout 1165setting, and in general it is recommended to call :meth:`~socket.settimeout` 1166before calling :meth:`~socket.connect` or pass a timeout parameter to 1167:meth:`create_connection`. However, the system network stack may also 1168return a connection timeout error of its own regardless of any Python socket 1169timeout setting. 1170 1171Timeouts and the ``accept`` method 1172^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1173 1174If :func:`getdefaulttimeout` is not :const:`None`, sockets returned by 1175the :meth:`~socket.accept` method inherit that timeout. Otherwise, the 1176behaviour depends on settings of the listening socket: 1177 1178* if the listening socket is in *blocking mode* or in *timeout mode*, 1179 the socket returned by :meth:`~socket.accept` is in *blocking mode*; 1180 1181* if the listening socket is in *non-blocking mode*, whether the socket 1182 returned by :meth:`~socket.accept` is in blocking or non-blocking mode 1183 is operating system-dependent. If you want to ensure cross-platform 1184 behaviour, it is recommended you manually override this setting. 1185 1186 1187.. _socket-example: 1188 1189Example 1190------- 1191 1192Here are four minimal example programs using the TCP/IP protocol: a server that 1193echoes all data that it receives back (servicing only one client), and a client 1194using it. Note that a server must perform the sequence :func:`socket`, 1195:meth:`~socket.bind`, :meth:`~socket.listen`, :meth:`~socket.accept` (possibly 1196repeating the :meth:`~socket.accept` to service more than one client), while a 1197client only needs the sequence :func:`socket`, :meth:`~socket.connect`. Also 1198note that the server does not :meth:`~socket.sendall`/:meth:`~socket.recv` on 1199the socket it is listening on but on the new socket returned by 1200:meth:`~socket.accept`. 1201 1202The first two examples support IPv4 only. :: 1203 1204 # Echo server program 1205 import socket 1206 1207 HOST = '' # Symbolic name meaning all available interfaces 1208 PORT = 50007 # Arbitrary non-privileged port 1209 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1210 s.bind((HOST, PORT)) 1211 s.listen(1) 1212 conn, addr = s.accept() 1213 print('Connected by', addr) 1214 while True: 1215 data = conn.recv(1024) 1216 if not data: break 1217 conn.sendall(data) 1218 conn.close() 1219 1220:: 1221 1222 # Echo client program 1223 import socket 1224 1225 HOST = 'daring.cwi.nl' # The remote host 1226 PORT = 50007 # The same port as used by the server 1227 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1228 s.connect((HOST, PORT)) 1229 s.sendall(b'Hello, world') 1230 data = s.recv(1024) 1231 s.close() 1232 print('Received', repr(data)) 1233 1234The next two examples are identical to the above two, but support both IPv4 and 1235IPv6. The server side will listen to the first address family available (it 1236should listen to both instead). On most of IPv6-ready systems, IPv6 will take 1237precedence and the server may not accept IPv4 traffic. The client side will try 1238to connect to the all addresses returned as a result of the name resolution, and 1239sends traffic to the first one connected successfully. :: 1240 1241 # Echo server program 1242 import socket 1243 import sys 1244 1245 HOST = None # Symbolic name meaning all available interfaces 1246 PORT = 50007 # Arbitrary non-privileged port 1247 s = None 1248 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, 1249 socket.SOCK_STREAM, 0, socket.AI_PASSIVE): 1250 af, socktype, proto, canonname, sa = res 1251 try: 1252 s = socket.socket(af, socktype, proto) 1253 except OSError as msg: 1254 s = None 1255 continue 1256 try: 1257 s.bind(sa) 1258 s.listen(1) 1259 except OSError as msg: 1260 s.close() 1261 s = None 1262 continue 1263 break 1264 if s is None: 1265 print('could not open socket') 1266 sys.exit(1) 1267 conn, addr = s.accept() 1268 print('Connected by', addr) 1269 while True: 1270 data = conn.recv(1024) 1271 if not data: break 1272 conn.send(data) 1273 conn.close() 1274 1275:: 1276 1277 # Echo client program 1278 import socket 1279 import sys 1280 1281 HOST = 'daring.cwi.nl' # The remote host 1282 PORT = 50007 # The same port as used by the server 1283 s = None 1284 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM): 1285 af, socktype, proto, canonname, sa = res 1286 try: 1287 s = socket.socket(af, socktype, proto) 1288 except OSError as msg: 1289 s = None 1290 continue 1291 try: 1292 s.connect(sa) 1293 except OSError as msg: 1294 s.close() 1295 s = None 1296 continue 1297 break 1298 if s is None: 1299 print('could not open socket') 1300 sys.exit(1) 1301 s.sendall(b'Hello, world') 1302 data = s.recv(1024) 1303 s.close() 1304 print('Received', repr(data)) 1305 1306 1307The next example shows how to write a very simple network sniffer with raw 1308sockets on Windows. The example requires administrator privileges to modify 1309the interface:: 1310 1311 import socket 1312 1313 # the public network interface 1314 HOST = socket.gethostbyname(socket.gethostname()) 1315 1316 # create a raw socket and bind it to the public interface 1317 s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP) 1318 s.bind((HOST, 0)) 1319 1320 # Include IP headers 1321 s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1) 1322 1323 # receive all packages 1324 s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON) 1325 1326 # receive a package 1327 print(s.recvfrom(65565)) 1328 1329 # disabled promiscuous mode 1330 s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF) 1331 1332The last example shows how to use the socket interface to communicate to a CAN 1333network. This example might require special priviledge:: 1334 1335 import socket 1336 import struct 1337 1338 1339 # CAN frame packing/unpacking (see 'struct can_frame' in <linux/can.h>) 1340 1341 can_frame_fmt = "=IB3x8s" 1342 can_frame_size = struct.calcsize(can_frame_fmt) 1343 1344 def build_can_frame(can_id, data): 1345 can_dlc = len(data) 1346 data = data.ljust(8, b'\x00') 1347 return struct.pack(can_frame_fmt, can_id, can_dlc, data) 1348 1349 def dissect_can_frame(frame): 1350 can_id, can_dlc, data = struct.unpack(can_frame_fmt, frame) 1351 return (can_id, can_dlc, data[:can_dlc]) 1352 1353 1354 # create a raw socket and bind it to the 'vcan0' interface 1355 s = socket.socket(socket.AF_CAN, socket.SOCK_RAW, socket.CAN_RAW) 1356 s.bind(('vcan0',)) 1357 1358 while True: 1359 cf, addr = s.recvfrom(can_frame_size) 1360 1361 print('Received: can_id=%x, can_dlc=%x, data=%s' % dissect_can_frame(cf)) 1362 1363 try: 1364 s.send(cf) 1365 except OSError: 1366 print('Error sending CAN frame') 1367 1368 try: 1369 s.send(build_can_frame(0x01, b'\x01\x02\x03')) 1370 except OSError: 1371 print('Error sending CAN frame') 1372 1373Running an example several times with too small delay between executions, could 1374lead to this error:: 1375 1376 OSError: [Errno 98] Address already in use 1377 1378This is because the previous execution has left the socket in a ``TIME_WAIT`` 1379state, and can't be immediately reused. 1380 1381There is a :mod:`socket` flag to set, in order to prevent this, 1382:data:`socket.SO_REUSEADDR`:: 1383 1384 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 1385 s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) 1386 s.bind((HOST, PORT)) 1387 1388the :data:`SO_REUSEADDR` flag tells the kernel to reuse a local socket in 1389``TIME_WAIT`` state, without waiting for its natural timeout to expire. 1390 1391 1392.. seealso:: 1393 1394 For an introduction to socket programming (in C), see the following papers: 1395 1396 - *An Introductory 4.3BSD Interprocess Communication Tutorial*, by Stuart Sechrest 1397 1398 - *An Advanced 4.3BSD Interprocess Communication Tutorial*, by Samuel J. Leffler et 1399 al, 1400 1401 both in the UNIX Programmer's Manual, Supplementary Documents 1 (sections 1402 PS1:7 and PS1:8). The platform-specific reference material for the various 1403 socket-related system calls are also a valuable source of information on the 1404 details of socket semantics. For Unix, refer to the manual pages; for Windows, 1405 see the WinSock (or Winsock 2) specification. For IPv6-ready APIs, readers may 1406 want to refer to :rfc:`3493` titled Basic Socket Interface Extensions for IPv6. 1407