/library/socket.rst
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1:mod:`socket` --- Low-level networking interface 2================================================ 3 4.. module:: socket 5 :synopsis: Low-level networking interface. 6 7 8This module provides access to the BSD *socket* interface. It is available on 9all modern Unix systems, Windows, MacOS, OS/2, and probably additional 10platforms. 11 12.. note:: 13 14 Some behavior may be platform dependent, since calls are made to the operating 15 system socket APIs. 16 17.. index:: object: socket 18 19The Python interface is a straightforward transliteration of the Unix system 20call and library interface for sockets to Python's object-oriented style: the 21:func:`socket` function returns a :dfn:`socket object` whose methods implement 22the various socket system calls. Parameter types are somewhat higher-level than 23in the C interface: as with :meth:`read` and :meth:`write` operations on Python 24files, buffer allocation on receive operations is automatic, and buffer length 25is implicit on send operations. 26 27 28.. seealso:: 29 30 Module :mod:`socketserver` 31 Classes that simplify writing network servers. 32 33 Module :mod:`ssl` 34 A TLS/SSL wrapper for socket objects. 35 36 37Socket families 38--------------- 39 40Depending on the system and the build options, various socket families 41are supported by this module. 42 43Socket addresses are represented as follows: 44 45- A single string is used for the :const:`AF_UNIX` address family. 46 47- A pair ``(host, port)`` is used for the :const:`AF_INET` address family, 48 where *host* is a string representing either a hostname in Internet domain 49 notation like ``'daring.cwi.nl'`` or an IPv4 address like ``'100.50.200.5'``, 50 and *port* is an integral port number. 51 52- For :const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo, 53 scopeid)`` is used, where *flowinfo* and *scopeid* represent the ``sin6_flowinfo`` 54 and ``sin6_scope_id`` members in :const:`struct sockaddr_in6` in C. For 55 :mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for 56 backward compatibility. Note, however, omission of *scopeid* can cause problems 57 in manipulating scoped IPv6 addresses. 58 59- :const:`AF_NETLINK` sockets are represented as pairs ``(pid, groups)``. 60 61- Linux-only support for TIPC is available using the :const:`AF_TIPC` 62 address family. TIPC is an open, non-IP based networked protocol designed 63 for use in clustered computer environments. Addresses are represented by a 64 tuple, and the fields depend on the address type. The general tuple form is 65 ``(addr_type, v1, v2, v3 [, scope])``, where: 66 67 - *addr_type* is one of TIPC_ADDR_NAMESEQ, TIPC_ADDR_NAME, or 68 TIPC_ADDR_ID. 69 - *scope* is one of TIPC_ZONE_SCOPE, TIPC_CLUSTER_SCOPE, and 70 TIPC_NODE_SCOPE. 71 - If *addr_type* is TIPC_ADDR_NAME, then *v1* is the server type, *v2* is 72 the port identifier, and *v3* should be 0. 73 74 If *addr_type* is TIPC_ADDR_NAMESEQ, then *v1* is the server type, *v2* 75 is the lower port number, and *v3* is the upper port number. 76 77 If *addr_type* is TIPC_ADDR_ID, then *v1* is the node, *v2* is the 78 reference, and *v3* should be set to 0. 79 80 If *addr_type* is TIPC_ADDR_ID, then *v1* is the node, *v2* is the 81 reference, and *v3* should be set to 0. 82 83- Certain other address families (:const:`AF_BLUETOOTH`, :const:`AF_PACKET`) 84 support specific representations. 85 86 .. XXX document them! 87 88For IPv4 addresses, two special forms are accepted instead of a host address: 89the empty string represents :const:`INADDR_ANY`, and the string 90``'<broadcast>'`` represents :const:`INADDR_BROADCAST`. This behavior is not 91compatible with IPv6, therefore, you may want to avoid these if you intend 92to support IPv6 with your Python programs. 93 94If you use a hostname in the *host* portion of IPv4/v6 socket address, the 95program may show a nondeterministic behavior, as Python uses the first address 96returned from the DNS resolution. The socket address will be resolved 97differently into an actual IPv4/v6 address, depending on the results from DNS 98resolution and/or the host configuration. For deterministic behavior use a 99numeric address in *host* portion. 100 101All errors raise exceptions. The normal exceptions for invalid argument types 102and out-of-memory conditions can be raised; errors related to socket or address 103semantics raise :exc:`socket.error` or one of its subclasses. 104 105Non-blocking mode is supported through :meth:`~socket.setblocking`. A 106generalization of this based on timeouts is supported through 107:meth:`~socket.settimeout`. 108 109 110Module contents 111--------------- 112 113The module :mod:`socket` exports the following constants and functions: 114 115 116.. exception:: error 117 118 .. index:: module: errno 119 120 A subclass of :exc:`IOError`, this exception is raised for socket-related 121 errors. It is recommended that you inspect its ``errno`` attribute to 122 discriminate between different kinds of errors. 123 124 .. seealso:: 125 The :mod:`errno` module contains symbolic names for the error codes 126 defined by the underlying operating system. 127 128 129.. exception:: herror 130 131 A subclass of :exc:`socket.error`, this exception is raised for 132 address-related errors, i.e. for functions that use *h_errno* in the POSIX 133 C API, including :func:`gethostbyname_ex` and :func:`gethostbyaddr`. 134 The accompanying value is a pair ``(h_errno, string)`` representing an 135 error returned by a library call. *h_errno* is a numeric value, while 136 *string* represents the description of *h_errno*, as returned by the 137 :c:func:`hstrerror` C function. 138 139 140.. exception:: gaierror 141 142 A subclass of :exc:`socket.error`, this exception is raised for 143 address-related errors by :func:`getaddrinfo` and :func:`getnameinfo`. 144 The accompanying value is a pair ``(error, string)`` representing an error 145 returned by a library call. *string* represents the description of 146 *error*, as returned by the :c:func:`gai_strerror` C function. The 147 numeric *error* value will match one of the :const:`EAI_\*` constants 148 defined in this module. 149 150 151.. exception:: timeout 152 153 A subclass of :exc:`socket.error`, this exception is raised when a timeout 154 occurs on a socket which has had timeouts enabled via a prior call to 155 :meth:`~socket.settimeout` (or implicitly through 156 :func:`~socket.setdefaulttimeout`). The accompanying value is a string 157 whose value is currently always "timed out". 158 159 160.. data:: AF_UNIX 161 AF_INET 162 AF_INET6 163 164 These constants represent the address (and protocol) families, used for the 165 first argument to :func:`socket`. If the :const:`AF_UNIX` constant is not 166 defined then this protocol is unsupported. More constants may be available 167 depending on the system. 168 169 170.. data:: SOCK_STREAM 171 SOCK_DGRAM 172 SOCK_RAW 173 SOCK_RDM 174 SOCK_SEQPACKET 175 176 These constants represent the socket types, used for the second argument to 177 :func:`socket`. More constants may be available depending on the system. 178 (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be generally 179 useful.) 180 181.. data:: SOCK_CLOEXEC 182 SOCK_NONBLOCK 183 184 These two constants, if defined, can be combined with the socket types and 185 allow you to set some flags atomically (thus avoiding possible race 186 conditions and the need for separate calls). 187 188 .. seealso:: 189 190 `Secure File Descriptor Handling <http://udrepper.livejournal.com/20407.html>`_ 191 for a more thorough explanation. 192 193 Availability: Linux >= 2.6.27. 194 195 .. versionadded:: 3.2 196 197.. data:: SO_* 198 SOMAXCONN 199 MSG_* 200 SOL_* 201 IPPROTO_* 202 IPPORT_* 203 INADDR_* 204 IP_* 205 IPV6_* 206 EAI_* 207 AI_* 208 NI_* 209 TCP_* 210 211 Many constants of these forms, documented in the Unix documentation on sockets 212 and/or the IP protocol, are also defined in the socket module. They are 213 generally used in arguments to the :meth:`setsockopt` and :meth:`getsockopt` 214 methods of socket objects. In most cases, only those symbols that are defined 215 in the Unix header files are defined; for a few symbols, default values are 216 provided. 217 218.. data:: SIO_* 219 RCVALL_* 220 221 Constants for Windows' WSAIoctl(). The constants are used as arguments to the 222 :meth:`ioctl` method of socket objects. 223 224 225.. data:: TIPC_* 226 227 TIPC related constants, matching the ones exported by the C socket API. See 228 the TIPC documentation for more information. 229 230 231.. data:: has_ipv6 232 233 This constant contains a boolean value which indicates if IPv6 is supported on 234 this platform. 235 236 237.. function:: create_connection(address[, timeout[, source_address]]) 238 239 Convenience function. Connect to *address* (a 2-tuple ``(host, port)``), 240 and return the socket object. Passing the optional *timeout* parameter will 241 set the timeout on the socket instance before attempting to connect. If no 242 *timeout* is supplied, the global default timeout setting returned by 243 :func:`getdefaulttimeout` is used. 244 245 If supplied, *source_address* must be a 2-tuple ``(host, port)`` for the 246 socket to bind to as its source address before connecting. If host or port 247 are '' or 0 respectively the OS default behavior will be used. 248 249 .. versionchanged:: 3.2 250 *source_address* was added. 251 252 .. versionchanged:: 3.2 253 support for the :keyword:`with` statement was added. 254 255 256.. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0) 257 258 Translate the *host*/*port* argument into a sequence of 5-tuples that contain 259 all the necessary arguments for creating a socket connected to that service. 260 *host* is a domain name, a string representation of an IPv4/v6 address 261 or ``None``. *port* is a string service name such as ``'http'``, a numeric 262 port number or ``None``. By passing ``None`` as the value of *host* 263 and *port*, you can pass ``NULL`` to the underlying C API. 264 265 The *family*, *type* and *proto* arguments can be optionally specified 266 in order to narrow the list of addresses returned. Passing zero as a 267 value for each of these arguments selects the full range of results. 268 The *flags* argument can be one or several of the ``AI_*`` constants, 269 and will influence how results are computed and returned. 270 For example, :const:`AI_NUMERICHOST` will disable domain name resolution 271 and will raise an error if *host* is a domain name. 272 273 The function returns a list of 5-tuples with the following structure: 274 275 ``(family, type, proto, canonname, sockaddr)`` 276 277 In these tuples, *family*, *type*, *proto* are all integers and are 278 meant to be passed to the :func:`socket` function. *canonname* will be 279 a string representing the canonical name of the *host* if 280 :const:`AI_CANONNAME` is part of the *flags* argument; else *canonname* 281 will be empty. *sockaddr* is a tuple describing a socket address, whose 282 format depends on the returned *family* (a ``(address, port)`` 2-tuple for 283 :const:`AF_INET`, a ``(address, port, flow info, scope id)`` 4-tuple for 284 :const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect` 285 method. 286 287 The following example fetches address information for a hypothetical TCP 288 connection to ``www.python.org`` on port 80 (results may differ on your 289 system if IPv6 isn't enabled):: 290 291 >>> socket.getaddrinfo("www.python.org", 80, proto=socket.SOL_TCP) 292 [(2, 1, 6, '', ('82.94.164.162', 80)), 293 (10, 1, 6, '', ('2001:888:2000:d::a2', 80, 0, 0))] 294 295 .. versionchanged:: 3.2 296 parameters can now be passed as single keyword arguments. 297 298.. function:: getfqdn([name]) 299 300 Return a fully qualified domain name for *name*. If *name* is omitted or empty, 301 it is interpreted as the local host. To find the fully qualified name, the 302 hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the 303 host, if available. The first name which includes a period is selected. In 304 case no fully qualified domain name is available, the hostname as returned by 305 :func:`gethostname` is returned. 306 307 308.. function:: gethostbyname(hostname) 309 310 Translate a host name to IPv4 address format. The IPv4 address is returned as a 311 string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself 312 it is returned unchanged. See :func:`gethostbyname_ex` for a more complete 313 interface. :func:`gethostbyname` does not support IPv6 name resolution, and 314 :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support. 315 316 317.. function:: gethostbyname_ex(hostname) 318 319 Translate a host name to IPv4 address format, extended interface. Return a 320 triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary 321 host name responding to the given *ip_address*, *aliaslist* is a (possibly 322 empty) list of alternative host names for the same address, and *ipaddrlist* is 323 a list of IPv4 addresses for the same interface on the same host (often but not 324 always a single address). :func:`gethostbyname_ex` does not support IPv6 name 325 resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual 326 stack support. 327 328 329.. function:: gethostname() 330 331 Return a string containing the hostname of the machine where the Python 332 interpreter is currently executing. 333 334 If you want to know the current machine's IP address, you may want to use 335 ``gethostbyname(gethostname())``. This operation assumes that there is a 336 valid address-to-host mapping for the host, and the assumption does not 337 always hold. 338 339 Note: :func:`gethostname` doesn't always return the fully qualified domain 340 name; use ``getfqdn()`` (see above). 341 342 343.. function:: gethostbyaddr(ip_address) 344 345 Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the 346 primary host name responding to the given *ip_address*, *aliaslist* is a 347 (possibly empty) list of alternative host names for the same address, and 348 *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same 349 host (most likely containing only a single address). To find the fully qualified 350 domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports 351 both IPv4 and IPv6. 352 353 354.. function:: getnameinfo(sockaddr, flags) 355 356 Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending 357 on the settings of *flags*, the result can contain a fully-qualified domain name 358 or numeric address representation in *host*. Similarly, *port* can contain a 359 string port name or a numeric port number. 360 361 362.. function:: getprotobyname(protocolname) 363 364 Translate an Internet protocol name (for example, ``'icmp'``) to a constant 365 suitable for passing as the (optional) third argument to the :func:`socket` 366 function. This is usually only needed for sockets opened in "raw" mode 367 (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen 368 automatically if the protocol is omitted or zero. 369 370 371.. function:: getservbyname(servicename[, protocolname]) 372 373 Translate an Internet service name and protocol name to a port number for that 374 service. The optional protocol name, if given, should be ``'tcp'`` or 375 ``'udp'``, otherwise any protocol will match. 376 377 378.. function:: getservbyport(port[, protocolname]) 379 380 Translate an Internet port number and protocol name to a service name for that 381 service. The optional protocol name, if given, should be ``'tcp'`` or 382 ``'udp'``, otherwise any protocol will match. 383 384 385.. function:: socket([family[, type[, proto]]]) 386 387 Create a new socket using the given address family, socket type and protocol 388 number. The address family should be :const:`AF_INET` (the default), 389 :const:`AF_INET6` or :const:`AF_UNIX`. The socket type should be 390 :const:`SOCK_STREAM` (the default), :const:`SOCK_DGRAM` or perhaps one of the 391 other ``SOCK_`` constants. The protocol number is usually zero and may be 392 omitted in that case. 393 394 395.. function:: socketpair([family[, type[, proto]]]) 396 397 Build a pair of connected socket objects using the given address family, socket 398 type, and protocol number. Address family, socket type, and protocol number are 399 as for the :func:`socket` function above. The default family is :const:`AF_UNIX` 400 if defined on the platform; otherwise, the default is :const:`AF_INET`. 401 Availability: Unix. 402 403 .. versionchanged:: 3.2 404 The returned socket objects now support the whole socket API, rather 405 than a subset. 406 407 408.. function:: fromfd(fd, family, type[, proto]) 409 410 Duplicate the file descriptor *fd* (an integer as returned by a file object's 411 :meth:`fileno` method) and build a socket object from the result. Address 412 family, socket type and protocol number are as for the :func:`socket` function 413 above. The file descriptor should refer to a socket, but this is not checked --- 414 subsequent operations on the object may fail if the file descriptor is invalid. 415 This function is rarely needed, but can be used to get or set socket options on 416 a socket passed to a program as standard input or output (such as a server 417 started by the Unix inet daemon). The socket is assumed to be in blocking mode. 418 419 420.. function:: ntohl(x) 421 422 Convert 32-bit positive integers from network to host byte order. On machines 423 where the host byte order is the same as network byte order, this is a no-op; 424 otherwise, it performs a 4-byte swap operation. 425 426 427.. function:: ntohs(x) 428 429 Convert 16-bit positive integers from network to host byte order. On machines 430 where the host byte order is the same as network byte order, this is a no-op; 431 otherwise, it performs a 2-byte swap operation. 432 433 434.. function:: htonl(x) 435 436 Convert 32-bit positive integers from host to network byte order. On machines 437 where the host byte order is the same as network byte order, this is a no-op; 438 otherwise, it performs a 4-byte swap operation. 439 440 441.. function:: htons(x) 442 443 Convert 16-bit positive integers from host to network byte order. On machines 444 where the host byte order is the same as network byte order, this is a no-op; 445 otherwise, it performs a 2-byte swap operation. 446 447 448.. function:: inet_aton(ip_string) 449 450 Convert an IPv4 address from dotted-quad string format (for example, 451 '123.45.67.89') to 32-bit packed binary format, as a bytes object four characters in 452 length. This is useful when conversing with a program that uses the standard C 453 library and needs objects of type :c:type:`struct in_addr`, which is the C type 454 for the 32-bit packed binary this function returns. 455 456 :func:`inet_aton` also accepts strings with less than three dots; see the 457 Unix manual page :manpage:`inet(3)` for details. 458 459 If the IPv4 address string passed to this function is invalid, 460 :exc:`socket.error` will be raised. Note that exactly what is valid depends on 461 the underlying C implementation of :c:func:`inet_aton`. 462 463 :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used 464 instead for IPv4/v6 dual stack support. 465 466 467.. function:: inet_ntoa(packed_ip) 468 469 Convert a 32-bit packed IPv4 address (a bytes object four characters in 470 length) to its standard dotted-quad string representation (for example, 471 '123.45.67.89'). This is useful when conversing with a program that uses the 472 standard C library and needs objects of type :c:type:`struct in_addr`, which 473 is the C type for the 32-bit packed binary data this function takes as an 474 argument. 475 476 If the byte sequence passed to this function is not exactly 4 bytes in 477 length, :exc:`socket.error` will be raised. :func:`inet_ntoa` does not 478 support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual 479 stack support. 480 481 482.. function:: inet_pton(address_family, ip_string) 483 484 Convert an IP address from its family-specific string format to a packed, 485 binary format. :func:`inet_pton` is useful when a library or network protocol 486 calls for an object of type :c:type:`struct in_addr` (similar to 487 :func:`inet_aton`) or :c:type:`struct in6_addr`. 488 489 Supported values for *address_family* are currently :const:`AF_INET` and 490 :const:`AF_INET6`. If the IP address string *ip_string* is invalid, 491 :exc:`socket.error` will be raised. Note that exactly what is valid depends on 492 both the value of *address_family* and the underlying implementation of 493 :c:func:`inet_pton`. 494 495 Availability: Unix (maybe not all platforms). 496 497 498.. function:: inet_ntop(address_family, packed_ip) 499 500 Convert a packed IP address (a bytes object of some number of characters) to its 501 standard, family-specific string representation (for example, ``'7.10.0.5'`` or 502 ``'5aef:2b::8'``). :func:`inet_ntop` is useful when a library or network protocol 503 returns an object of type :c:type:`struct in_addr` (similar to :func:`inet_ntoa`) 504 or :c:type:`struct in6_addr`. 505 506 Supported values for *address_family* are currently :const:`AF_INET` and 507 :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the 508 specified address family, :exc:`ValueError` will be raised. A 509 :exc:`socket.error` is raised for errors from the call to :func:`inet_ntop`. 510 511 Availability: Unix (maybe not all platforms). 512 513 514.. function:: getdefaulttimeout() 515 516 Return the default timeout in floating seconds for new socket objects. A value 517 of ``None`` indicates that new socket objects have no timeout. When the socket 518 module is first imported, the default is ``None``. 519 520 521.. function:: setdefaulttimeout(timeout) 522 523 Set the default timeout in floating seconds for new socket objects. When 524 the socket module is first imported, the default is ``None``. See 525 :meth:`~socket.settimeout` for possible values and their respective 526 meanings. 527 528 529.. function:: sethostname(name) 530 531 Set the machine's hostname to *name*. This will raise a 532 :exc:`socket.error` if you don't have enough rights. 533 534 Availability: Unix. 535 536 .. versionadded:: 3.3 537 538 539.. function:: if_nameindex() 540 541 Return a list of network interface information 542 (index int, name string) tuples. 543 :exc:`socket.error` if the system call fails. 544 545 Availability: Unix. 546 547 .. versionadded:: 3.3 548 549 550.. function:: if_nametoindex(if_name) 551 552 Return a network interface index number corresponding to an 553 interface name. 554 :exc:`socket.error` if no interface with the given name exists. 555 556 Availability: Unix. 557 558 .. versionadded:: 3.3 559 560 561.. function:: if_indextoname(if_index) 562 563 Return a network interface name corresponding to a 564 interface index number. 565 :exc:`socket.error` if no interface with the given index exists. 566 567 Availability: Unix. 568 569 .. versionadded:: 3.3 570 571 572.. data:: SocketType 573 574 This is a Python type object that represents the socket object type. It is the 575 same as ``type(socket(...))``. 576 577 578.. _socket-objects: 579 580Socket Objects 581-------------- 582 583Socket objects have the following methods. Except for :meth:`makefile` these 584correspond to Unix system calls applicable to sockets. 585 586 587.. method:: socket.accept() 588 589 Accept a connection. The socket must be bound to an address and listening for 590 connections. The return value is a pair ``(conn, address)`` where *conn* is a 591 *new* socket object usable to send and receive data on the connection, and 592 *address* is the address bound to the socket on the other end of the connection. 593 594 595.. method:: socket.bind(address) 596 597 Bind the socket to *address*. The socket must not already be bound. (The format 598 of *address* depends on the address family --- see above.) 599 600 601.. method:: socket.close() 602 603 Close the socket. All future operations on the socket object will fail. The 604 remote end will receive no more data (after queued data is flushed). Sockets are 605 automatically closed when they are garbage-collected. 606 607 .. note:: 608 609 :meth:`close()` releases the resource associated with a connection but 610 does not necessarily close the connection immediately. If you want 611 to close the connection in a timely fashion, call :meth:`shutdown()` 612 before :meth:`close()`. 613 614 615.. method:: socket.connect(address) 616 617 Connect to a remote socket at *address*. (The format of *address* depends on the 618 address family --- see above.) 619 620 621.. method:: socket.connect_ex(address) 622 623 Like ``connect(address)``, but return an error indicator instead of raising an 624 exception for errors returned by the C-level :c:func:`connect` call (other 625 problems, such as "host not found," can still raise exceptions). The error 626 indicator is ``0`` if the operation succeeded, otherwise the value of the 627 :c:data:`errno` variable. This is useful to support, for example, asynchronous 628 connects. 629 630 631.. method:: socket.detach() 632 633 Put the socket object into closed state without actually closing the 634 underlying file descriptor. The file descriptor is returned, and can 635 be reused for other purposes. 636 637 .. versionadded:: 3.2 638 639 640.. method:: socket.fileno() 641 642 Return the socket's file descriptor (a small integer). This is useful with 643 :func:`select.select`. 644 645 Under Windows the small integer returned by this method cannot be used where a 646 file descriptor can be used (such as :func:`os.fdopen`). Unix does not have 647 this limitation. 648 649 650.. method:: socket.getpeername() 651 652 Return the remote address to which the socket is connected. This is useful to 653 find out the port number of a remote IPv4/v6 socket, for instance. (The format 654 of the address returned depends on the address family --- see above.) On some 655 systems this function is not supported. 656 657 658.. method:: socket.getsockname() 659 660 Return the socket's own address. This is useful to find out the port number of 661 an IPv4/v6 socket, for instance. (The format of the address returned depends on 662 the address family --- see above.) 663 664 665.. method:: socket.getsockopt(level, optname[, buflen]) 666 667 Return the value of the given socket option (see the Unix man page 668 :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.) 669 are defined in this module. If *buflen* is absent, an integer option is assumed 670 and its integer value is returned by the function. If *buflen* is present, it 671 specifies the maximum length of the buffer used to receive the option in, and 672 this buffer is returned as a bytes object. It is up to the caller to decode the 673 contents of the buffer (see the optional built-in module :mod:`struct` for a way 674 to decode C structures encoded as byte strings). 675 676 677.. method:: socket.gettimeout() 678 679 Return the timeout in floating seconds associated with socket operations, 680 or ``None`` if no timeout is set. This reflects the last call to 681 :meth:`setblocking` or :meth:`settimeout`. 682 683 684.. method:: socket.ioctl(control, option) 685 686 :platform: Windows 687 688 The :meth:`ioctl` method is a limited interface to the WSAIoctl system 689 interface. Please refer to the `Win32 documentation 690 <http://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more 691 information. 692 693 On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl` 694 functions may be used; they accept a socket object as their first argument. 695 696.. method:: socket.listen(backlog) 697 698 Listen for connections made to the socket. The *backlog* argument specifies the 699 maximum number of queued connections and should be at least 0; the maximum value 700 is system-dependent (usually 5), the minimum value is forced to 0. 701 702 703.. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \ 704 errors=None, newline=None) 705 706 .. index:: single: I/O control; buffering 707 708 Return a :term:`file object` associated with the socket. The exact returned 709 type depends on the arguments given to :meth:`makefile`. These arguments are 710 interpreted the same way as by the built-in :func:`open` function. 711 712 Closing the file object won't close the socket unless there are no remaining 713 references to the socket. The socket must be in blocking mode; it can have 714 a timeout, but the file object's internal buffer may end up in a inconsistent 715 state if a timeout occurs. 716 717 .. note:: 718 719 On Windows, the file-like object created by :meth:`makefile` cannot be 720 used where a file object with a file descriptor is expected, such as the 721 stream arguments of :meth:`subprocess.Popen`. 722 723 724.. method:: socket.recv(bufsize[, flags]) 725 726 Receive data from the socket. The return value is a bytes object representing the 727 data received. The maximum amount of data to be received at once is specified 728 by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of 729 the optional argument *flags*; it defaults to zero. 730 731 .. note:: 732 733 For best match with hardware and network realities, the value of *bufsize* 734 should be a relatively small power of 2, for example, 4096. 735 736 737.. method:: socket.recvfrom(bufsize[, flags]) 738 739 Receive data from the socket. The return value is a pair ``(bytes, address)`` 740 where *bytes* is a bytes object representing the data received and *address* is the 741 address of the socket sending the data. See the Unix manual page 742 :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults 743 to zero. (The format of *address* depends on the address family --- see above.) 744 745 746.. method:: socket.recvfrom_into(buffer[, nbytes[, flags]]) 747 748 Receive data from the socket, writing it into *buffer* instead of creating a 749 new bytestring. The return value is a pair ``(nbytes, address)`` where *nbytes* is 750 the number of bytes received and *address* is the address of the socket sending 751 the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the 752 optional argument *flags*; it defaults to zero. (The format of *address* 753 depends on the address family --- see above.) 754 755 756.. method:: socket.recv_into(buffer[, nbytes[, flags]]) 757 758 Receive up to *nbytes* bytes from the socket, storing the data into a buffer 759 rather than creating a new bytestring. If *nbytes* is not specified (or 0), 760 receive up to the size available in the given buffer. Returns the number of 761 bytes received. See the Unix manual page :manpage:`recv(2)` for the meaning 762 of the optional argument *flags*; it defaults to zero. 763 764 765.. method:: socket.send(bytes[, flags]) 766 767 Send data to the socket. The socket must be connected to a remote socket. The 768 optional *flags* argument has the same meaning as for :meth:`recv` above. 769 Returns the number of bytes sent. Applications are responsible for checking that 770 all data has been sent; if only some of the data was transmitted, the 771 application needs to attempt delivery of the remaining data. 772 773 774.. method:: socket.sendall(bytes[, flags]) 775 776 Send data to the socket. The socket must be connected to a remote socket. The 777 optional *flags* argument has the same meaning as for :meth:`recv` above. 778 Unlike :meth:`send`, this method continues to send data from *bytes* until 779 either all data has been sent or an error occurs. ``None`` is returned on 780 success. On error, an exception is raised, and there is no way to determine how 781 much data, if any, was successfully sent. 782 783 784.. method:: socket.sendto(bytes[, flags], address) 785 786 Send data to the socket. The socket should not be connected to a remote socket, 787 since the destination socket is specified by *address*. The optional *flags* 788 argument has the same meaning as for :meth:`recv` above. Return the number of 789 bytes sent. (The format of *address* depends on the address family --- see 790 above.) 791 792 793.. method:: socket.setblocking(flag) 794 795 Set blocking or non-blocking mode of the socket: if *flag* is false, the 796 socket is set to non-blocking, else to blocking mode. 797 798 This method is a shorthand for certain :meth:`~socket.settimeout` calls: 799 800 * ``sock.setblocking(True)`` is equivalent to ``sock.settimeout(None)`` 801 802 * ``sock.setblocking(False)`` is equivalent to ``sock.settimeout(0.0)`` 803 804 805.. method:: socket.settimeout(value) 806 807 Set a timeout on blocking socket operations. The *value* argument can be a 808 nonnegative floating point number expressing seconds, or ``None``. 809 If a non-zero value is given, subsequent socket operations will raise a 810 :exc:`timeout` exception if the timeout period *value* has elapsed before 811 the operation has completed. If zero is given, the socket is put in 812 non-blocking mode. If ``None`` is given, the socket is put in blocking mode. 813 814 For further information, please consult the :ref:`notes on socket timeouts <socket-timeouts>`. 815 816 817.. method:: socket.setsockopt(level, optname, value) 818 819 .. index:: module: struct 820 821 Set the value of the given socket option (see the Unix manual page 822 :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the 823 :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a 824 bytes object representing a buffer. In the latter case it is up to the caller to 825 ensure that the bytestring contains the proper bits (see the optional built-in 826 module :mod:`struct` for a way to encode C structures as bytestrings). 827 828 829.. method:: socket.shutdown(how) 830 831 Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`, 832 further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends 833 are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are 834 disallowed. Depending on the platform, shutting down one half of the connection 835 can also close the opposite half (e.g. on Mac OS X, ``shutdown(SHUT_WR)`` does 836 not allow further reads on the other end of the connection). 837 838Note that there are no methods :meth:`read` or :meth:`write`; use 839:meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead. 840 841Socket objects also have these (read-only) attributes that correspond to the 842values given to the :class:`socket` constructor. 843 844 845.. attribute:: socket.family 846 847 The socket family. 848 849 850.. attribute:: socket.type 851 852 The socket type. 853 854 855.. attribute:: socket.proto 856 857 The socket protocol. 858 859 860 861.. _socket-timeouts: 862 863Notes on socket timeouts 864------------------------ 865 866A socket object can be in one of three modes: blocking, non-blocking, or 867timeout. Sockets are by default always created in blocking mode, but this 868can be changed by calling :func:`setdefaulttimeout`. 869 870* In *blocking mode*, operations block until complete or the system returns 871 an error (such as connection timed out). 872 873* In *non-blocking mode*, operations fail (with an error that is unfortunately 874 system-dependent) if they cannot be completed immediately: functions from the 875 :mod:`select` can be used to know when and whether a socket is available for 876 reading or writing. 877 878* In *timeout mode*, operations fail if they cannot be completed within the 879 timeout specified for the socket (they raise a :exc:`timeout` exception) 880 or if the system returns an error. 881 882.. note:: 883 At the operating system level, sockets in *timeout mode* are internally set 884 in non-blocking mode. Also, the blocking and timeout modes are shared between 885 file descriptors and socket objects that refer to the same network endpoint. 886 This implementation detail can have visible consequences if e.g. you decide 887 to use the :meth:`~socket.fileno()` of a socket. 888 889Timeouts and the ``connect`` method 890^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 891 892The :meth:`~socket.connect` operation is also subject to the timeout 893setting, and in general it is recommended to call :meth:`~socket.settimeout` 894before calling :meth:`~socket.connect` or pass a timeout parameter to 895:meth:`create_connection`. However, the system network stack may also 896return a connection timeout error of its own regardless of any Python socket 897timeout setting. 898 899Timeouts and the ``accept`` method 900^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 901 902If :func:`getdefaulttimeout` is not :const:`None`, sockets returned by 903the :meth:`~socket.accept` method inherit that timeout. Otherwise, the 904behaviour depends on settings of the listening socket: 905 906* if the listening socket is in *blocking mode* or in *timeout mode*, 907 the socket returned by :meth:`~socket.accept` is in *blocking mode*; 908 909* if the listening socket is in *non-blocking mode*, whether the socket 910 returned by :meth:`~socket.accept` is in blocking or non-blocking mode 911 is operating system-dependent. If you want to ensure cross-platform 912 behaviour, it is recommended you manually override this setting. 913 914 915.. _socket-example: 916 917Example 918------- 919 920Here are four minimal example programs using the TCP/IP protocol: a server that 921echoes all data that it receives back (servicing only one client), and a client 922using it. Note that a server must perform the sequence :func:`socket`, 923:meth:`~socket.bind`, :meth:`~socket.listen`, :meth:`~socket.accept` (possibly 924repeating the :meth:`~socket.accept` to service more than one client), while a 925client only needs the sequence :func:`socket`, :meth:`~socket.connect`. Also 926note that the server does not :meth:`~socket.send`/:meth:`~socket.recv` on the 927socket it is listening on but on the new socket returned by 928:meth:`~socket.accept`. 929 930The first two examples support IPv4 only. :: 931 932 # Echo server program 933 import socket 934 935 HOST = '' # Symbolic name meaning all available interfaces 936 PORT = 50007 # Arbitrary non-privileged port 937 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 938 s.bind((HOST, PORT)) 939 s.listen(1) 940 conn, addr = s.accept() 941 print('Connected by', addr) 942 while True: 943 data = conn.recv(1024) 944 if not data: break 945 conn.send(data) 946 conn.close() 947 948:: 949 950 # Echo client program 951 import socket 952 953 HOST = 'daring.cwi.nl' # The remote host 954 PORT = 50007 # The same port as used by the server 955 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 956 s.connect((HOST, PORT)) 957 s.send(b'Hello, world') 958 data = s.recv(1024) 959 s.close() 960 print('Received', repr(data)) 961 962The next two examples are identical to the above two, but support both IPv4 and 963IPv6. The server side will listen to the first address family available (it 964should listen to both instead). On most of IPv6-ready systems, IPv6 will take 965precedence and the server may not accept IPv4 traffic. The client side will try 966to connect to the all addresses returned as a result of the name resolution, and 967sends traffic to the first one connected successfully. :: 968 969 # Echo server program 970 import socket 971 import sys 972 973 HOST = None # Symbolic name meaning all available interfaces 974 PORT = 50007 # Arbitrary non-privileged port 975 s = None 976 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, 977 socket.SOCK_STREAM, 0, socket.AI_PASSIVE): 978 af, socktype, proto, canonname, sa = res 979 try: 980 s = socket.socket(af, socktype, proto) 981 except socket.error as msg: 982 s = None 983 continue 984 try: 985 s.bind(sa) 986 s.listen(1) 987 except socket.error as msg: 988 s.close() 989 s = None 990 continue 991 break 992 if s is None: 993 print('could not open socket') 994 sys.exit(1) 995 conn, addr = s.accept() 996 print('Connected by', addr) 997 while True: 998 data = conn.recv(1024) 999 if not data: break 1000 conn.send(data) 1001 conn.close() 1002 1003:: 1004 1005 # Echo client program 1006 import socket 1007 import sys 1008 1009 HOST = 'daring.cwi.nl' # The remote host 1010 PORT = 50007 # The same port as used by the server 1011 s = None 1012 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM): 1013 af, socktype, proto, canonname, sa = res 1014 try: 1015 s = socket.socket(af, socktype, proto) 1016 except socket.error as msg: 1017 s = None 1018 continue 1019 try: 1020 s.connect(sa) 1021 except socket.error as msg: 1022 s.close() 1023 s = None 1024 continue 1025 break 1026 if s is None: 1027 print('could not open socket') 1028 sys.exit(1) 1029 s.send(b'Hello, world') 1030 data = s.recv(1024) 1031 s.close() 1032 print('Received', repr(data)) 1033 1034 1035The last example shows how to write a very simple network sniffer with raw 1036sockets on Windows. The example requires administrator privileges to modify 1037the interface:: 1038 1039 import socket 1040 1041 # the public network interface 1042 HOST = socket.gethostbyname(socket.gethostname()) 1043 1044 # create a raw socket and bind it to the public interface 1045 s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP) 1046 s.bind((HOST, 0)) 1047 1048 # Include IP headers 1049 s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1) 1050 1051 # receive all packages 1052 s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON) 1053 1054 # receive a package 1055 print(s.recvfrom(65565)) 1056 1057 # disabled promiscuous mode 1058 s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF) 1059 1060 1061.. seealso:: 1062 1063 For an introduction to socket programming (in C), see the following papers: 1064 1065 - *An Introductory 4.3BSD Interprocess Communication Tutorial*, by Stuart Sechrest 1066 1067 - *An Advanced 4.3BSD Interprocess Communication Tutorial*, by Samuel J. Leffler et 1068 al, 1069 1070 both in the UNIX Programmer's Manual, Supplementary Documents 1 (sections 1071 PS1:7 and PS1:8). The platform-specific reference material for the various 1072 socket-related system calls are also a valuable source of information on the 1073 details of socket semantics. For Unix, refer to the manual pages; for Windows, 1074 see the WinSock (or Winsock 2) specification. For IPv6-ready APIs, readers may 1075 want to refer to :rfc:`3493` titled Basic Socket Interface Extensions for IPv6. 1076