PageRenderTime 31ms CodeModel.GetById 19ms RepoModel.GetById 0ms app.codeStats 0ms

/Doc/library/socket.rst

https://bitbucket.org/bluehorn/sampling_prof
ReStructuredText | 1730 lines | 1213 code | 517 blank | 0 comment | 0 complexity | fb5f837d76bc1bd35ba87978817b0238 MD5 | raw file
Possible License(s): BSD-3-Clause, Unlicense, CC-BY-SA-3.0, 0BSD
  1. :mod:`socket` --- Low-level networking interface
  2. ================================================
  3. .. module:: socket
  4. :synopsis: Low-level networking interface.
  5. **Source code:** :source:`Lib/socket.py`
  6. --------------
  7. This module provides access to the BSD *socket* interface. It is available on
  8. all modern Unix systems, Windows, MacOS, and probably additional platforms.
  9. .. note::
  10. Some behavior may be platform dependent, since calls are made to the operating
  11. system socket APIs.
  12. .. index:: object: socket
  13. The Python interface is a straightforward transliteration of the Unix system
  14. call and library interface for sockets to Python's object-oriented style: the
  15. :func:`.socket` function returns a :dfn:`socket object` whose methods implement
  16. the various socket system calls. Parameter types are somewhat higher-level than
  17. in the C interface: as with :meth:`read` and :meth:`write` operations on Python
  18. files, buffer allocation on receive operations is automatic, and buffer length
  19. is implicit on send operations.
  20. .. seealso::
  21. Module :mod:`socketserver`
  22. Classes that simplify writing network servers.
  23. Module :mod:`ssl`
  24. A TLS/SSL wrapper for socket objects.
  25. Socket families
  26. ---------------
  27. Depending on the system and the build options, various socket families
  28. are supported by this module.
  29. The address format required by a particular socket object is automatically
  30. selected based on the address family specified when the socket object was
  31. created. Socket addresses are represented as follows:
  32. - The address of an :const:`AF_UNIX` socket bound to a file system node
  33. is represented as a string, using the file system encoding and the
  34. ``'surrogateescape'`` error handler (see :pep:`383`). An address in
  35. Linux's abstract namespace is returned as a :term:`bytes-like object` with
  36. an initial null byte; note that sockets in this namespace can
  37. communicate with normal file system sockets, so programs intended to
  38. run on Linux may need to deal with both types of address. A string or
  39. bytes-like object can be used for either type of address when
  40. passing it as an argument.
  41. .. versionchanged:: 3.3
  42. Previously, :const:`AF_UNIX` socket paths were assumed to use UTF-8
  43. encoding.
  44. .. versionchanged:: 3.5
  45. Writable :term:`bytes-like object` is now accepted.
  46. - A pair ``(host, port)`` is used for the :const:`AF_INET` address family,
  47. where *host* is a string representing either a hostname in Internet domain
  48. notation like ``'daring.cwi.nl'`` or an IPv4 address like ``'100.50.200.5'``,
  49. and *port* is an integer.
  50. - For :const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo,
  51. scopeid)`` is used, where *flowinfo* and *scopeid* represent the ``sin6_flowinfo``
  52. and ``sin6_scope_id`` members in :const:`struct sockaddr_in6` in C. For
  53. :mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for
  54. backward compatibility. Note, however, omission of *scopeid* can cause problems
  55. in manipulating scoped IPv6 addresses.
  56. - :const:`AF_NETLINK` sockets are represented as pairs ``(pid, groups)``.
  57. - Linux-only support for TIPC is available using the :const:`AF_TIPC`
  58. address family. TIPC is an open, non-IP based networked protocol designed
  59. for use in clustered computer environments. Addresses are represented by a
  60. tuple, and the fields depend on the address type. The general tuple form is
  61. ``(addr_type, v1, v2, v3 [, scope])``, where:
  62. - *addr_type* is one of :const:`TIPC_ADDR_NAMESEQ`, :const:`TIPC_ADDR_NAME`,
  63. or :const:`TIPC_ADDR_ID`.
  64. - *scope* is one of :const:`TIPC_ZONE_SCOPE`, :const:`TIPC_CLUSTER_SCOPE`, and
  65. :const:`TIPC_NODE_SCOPE`.
  66. - If *addr_type* is :const:`TIPC_ADDR_NAME`, then *v1* is the server type, *v2* is
  67. the port identifier, and *v3* should be 0.
  68. If *addr_type* is :const:`TIPC_ADDR_NAMESEQ`, then *v1* is the server type, *v2*
  69. is the lower port number, and *v3* is the upper port number.
  70. If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the
  71. reference, and *v3* should be set to 0.
  72. - A tuple ``(interface, )`` is used for the :const:`AF_CAN` address family,
  73. where *interface* is a string representing a network interface name like
  74. ``'can0'``. The network interface name ``''`` can be used to receive packets
  75. from all network interfaces of this family.
  76. - A string or a tuple ``(id, unit)`` is used for the :const:`SYSPROTO_CONTROL`
  77. protocol of the :const:`PF_SYSTEM` family. The string is the name of a
  78. kernel control using a dynamically-assigned ID. The tuple can be used if ID
  79. and unit number of the kernel control are known or if a registered ID is
  80. used.
  81. .. versionadded:: 3.3
  82. - :const:`AF_BLUETOOTH` supports the following protocols and address
  83. formats:
  84. - :const:`BTPROTO_L2CAP` accepts ``(bdaddr, psm)`` where ``bdaddr`` is
  85. the Bluetooth address as a string and ``psm`` is an integer.
  86. - :const:`BTPROTO_RFCOMM` accepts ``(bdaddr, channel)`` where ``bdaddr``
  87. is the Bluetooth address as a string and ``channel`` is an integer.
  88. - :const:`BTPROTO_HCI` accepts ``(device_id,)`` where ``device_id`` is
  89. either an integer or a string with the Bluetooth address of the
  90. interface. (This depends on your OS; NetBSD and DragonFlyBSD expect
  91. a Bluetooth address while everything else expects an integer.)
  92. .. versionchanged:: 3.2
  93. NetBSD and DragonFlyBSD support added.
  94. - :const:`BTPROTO_SCO` accepts ``bdaddr`` where ``bdaddr`` is a
  95. :class:`bytes` object containing the Bluetooth address in a
  96. string format. (ex. ``b'12:23:34:45:56:67'``) This protocol is not
  97. supported under FreeBSD.
  98. - :const:`AF_ALG` is a Linux-only socket based interface to Kernel
  99. cryptography. An algorithm socket is configured with a tuple of two to four
  100. elements ``(type, name [, feat [, mask]])``, where:
  101. - *type* is the algorithm type as string, e.g. ``aead``, ``hash``,
  102. ``skcipher`` or ``rng``.
  103. - *name* is the algorithm name and operation mode as string, e.g.
  104. ``sha256``, ``hmac(sha256)``, ``cbc(aes)`` or ``drbg_nopr_ctr_aes256``.
  105. - *feat* and *mask* are unsigned 32bit integers.
  106. Availability Linux 2.6.38, some algorithm types require more recent Kernels.
  107. .. versionadded:: 3.6
  108. - Certain other address families (:const:`AF_PACKET`, :const:`AF_CAN`)
  109. support specific representations.
  110. .. XXX document them!
  111. For IPv4 addresses, two special forms are accepted instead of a host address:
  112. the empty string represents :const:`INADDR_ANY`, and the string
  113. ``'<broadcast>'`` represents :const:`INADDR_BROADCAST`. This behavior is not
  114. compatible with IPv6, therefore, you may want to avoid these if you intend
  115. to support IPv6 with your Python programs.
  116. If you use a hostname in the *host* portion of IPv4/v6 socket address, the
  117. program may show a nondeterministic behavior, as Python uses the first address
  118. returned from the DNS resolution. The socket address will be resolved
  119. differently into an actual IPv4/v6 address, depending on the results from DNS
  120. resolution and/or the host configuration. For deterministic behavior use a
  121. numeric address in *host* portion.
  122. All errors raise exceptions. The normal exceptions for invalid argument types
  123. and out-of-memory conditions can be raised; starting from Python 3.3, errors
  124. related to socket or address semantics raise :exc:`OSError` or one of its
  125. subclasses (they used to raise :exc:`socket.error`).
  126. Non-blocking mode is supported through :meth:`~socket.setblocking`. A
  127. generalization of this based on timeouts is supported through
  128. :meth:`~socket.settimeout`.
  129. Module contents
  130. ---------------
  131. The module :mod:`socket` exports the following elements.
  132. Exceptions
  133. ^^^^^^^^^^
  134. .. exception:: error
  135. A deprecated alias of :exc:`OSError`.
  136. .. versionchanged:: 3.3
  137. Following :pep:`3151`, this class was made an alias of :exc:`OSError`.
  138. .. exception:: herror
  139. A subclass of :exc:`OSError`, this exception is raised for
  140. address-related errors, i.e. for functions that use *h_errno* in the POSIX
  141. C API, including :func:`gethostbyname_ex` and :func:`gethostbyaddr`.
  142. The accompanying value is a pair ``(h_errno, string)`` representing an
  143. error returned by a library call. *h_errno* is a numeric value, while
  144. *string* represents the description of *h_errno*, as returned by the
  145. :c:func:`hstrerror` C function.
  146. .. versionchanged:: 3.3
  147. This class was made a subclass of :exc:`OSError`.
  148. .. exception:: gaierror
  149. A subclass of :exc:`OSError`, this exception is raised for
  150. address-related errors by :func:`getaddrinfo` and :func:`getnameinfo`.
  151. The accompanying value is a pair ``(error, string)`` representing an error
  152. returned by a library call. *string* represents the description of
  153. *error*, as returned by the :c:func:`gai_strerror` C function. The
  154. numeric *error* value will match one of the :const:`EAI_\*` constants
  155. defined in this module.
  156. .. versionchanged:: 3.3
  157. This class was made a subclass of :exc:`OSError`.
  158. .. exception:: timeout
  159. A subclass of :exc:`OSError`, this exception is raised when a timeout
  160. occurs on a socket which has had timeouts enabled via a prior call to
  161. :meth:`~socket.settimeout` (or implicitly through
  162. :func:`~socket.setdefaulttimeout`). The accompanying value is a string
  163. whose value is currently always "timed out".
  164. .. versionchanged:: 3.3
  165. This class was made a subclass of :exc:`OSError`.
  166. Constants
  167. ^^^^^^^^^
  168. The AF_* and SOCK_* constants are now :class:`AddressFamily` and
  169. :class:`SocketKind` :class:`.IntEnum` collections.
  170. .. versionadded:: 3.4
  171. .. data:: AF_UNIX
  172. AF_INET
  173. AF_INET6
  174. These constants represent the address (and protocol) families, used for the
  175. first argument to :func:`.socket`. If the :const:`AF_UNIX` constant is not
  176. defined then this protocol is unsupported. More constants may be available
  177. depending on the system.
  178. .. data:: SOCK_STREAM
  179. SOCK_DGRAM
  180. SOCK_RAW
  181. SOCK_RDM
  182. SOCK_SEQPACKET
  183. These constants represent the socket types, used for the second argument to
  184. :func:`.socket`. More constants may be available depending on the system.
  185. (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be generally
  186. useful.)
  187. .. data:: SOCK_CLOEXEC
  188. SOCK_NONBLOCK
  189. These two constants, if defined, can be combined with the socket types and
  190. allow you to set some flags atomically (thus avoiding possible race
  191. conditions and the need for separate calls).
  192. .. seealso::
  193. `Secure File Descriptor Handling <http://udrepper.livejournal.com/20407.html>`_
  194. for a more thorough explanation.
  195. Availability: Linux >= 2.6.27.
  196. .. versionadded:: 3.2
  197. .. data:: SO_*
  198. SOMAXCONN
  199. MSG_*
  200. SOL_*
  201. SCM_*
  202. IPPROTO_*
  203. IPPORT_*
  204. INADDR_*
  205. IP_*
  206. IPV6_*
  207. EAI_*
  208. AI_*
  209. NI_*
  210. TCP_*
  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. .. versionchanged:: 3.6
  218. ``SO_DOMAIN``, ``SO_PROTOCOL``, ``SO_PEERSEC``, ``SO_PASSSEC``
  219. were added.
  220. .. data:: AF_CAN
  221. PF_CAN
  222. SOL_CAN_*
  223. CAN_*
  224. Many constants of these forms, documented in the Linux documentation, are
  225. also defined in the socket module.
  226. Availability: Linux >= 2.6.25.
  227. .. versionadded:: 3.3
  228. .. data:: CAN_BCM
  229. CAN_BCM_*
  230. CAN_BCM, in the CAN protocol family, is the broadcast manager (BCM) protocol.
  231. Broadcast manager constants, documented in the Linux documentation, are also
  232. defined in the socket module.
  233. Availability: Linux >= 2.6.25.
  234. .. versionadded:: 3.4
  235. .. data:: CAN_RAW_FD_FRAMES
  236. Enables CAN FD support in a CAN_RAW socket. This is disabled by default.
  237. This allows your application to send both CAN and CAN FD frames; however,
  238. you one must accept both CAN and CAN FD frames when reading from the socket.
  239. This constant is documented in the Linux documentation.
  240. Availability: Linux >= 3.6.
  241. .. versionadded:: 3.5
  242. .. data:: AF_RDS
  243. PF_RDS
  244. SOL_RDS
  245. RDS_*
  246. Many constants of these forms, documented in the Linux documentation, are
  247. also defined in the socket module.
  248. Availability: Linux >= 2.6.30.
  249. .. versionadded:: 3.3
  250. .. data:: SIO_RCVALL
  251. SIO_KEEPALIVE_VALS
  252. SIO_LOOPBACK_FAST_PATH
  253. RCVALL_*
  254. Constants for Windows' WSAIoctl(). The constants are used as arguments to the
  255. :meth:`~socket.socket.ioctl` method of socket objects.
  256. .. versionchanged:: 3.6
  257. ``SIO_LOOPBACK_FAST_PATH`` was added.
  258. .. data:: TIPC_*
  259. TIPC related constants, matching the ones exported by the C socket API. See
  260. the TIPC documentation for more information.
  261. .. data:: AF_ALG
  262. SOL_ALG
  263. ALG_*
  264. Constants for Linux Kernel cryptography.
  265. Availability: Linux >= 2.6.38.
  266. .. versionadded:: 3.6
  267. .. data:: AF_LINK
  268. Availability: BSD, OSX.
  269. .. versionadded:: 3.4
  270. .. data:: has_ipv6
  271. This constant contains a boolean value which indicates if IPv6 is supported on
  272. this platform.
  273. .. data:: BDADDR_ANY
  274. BDADDR_LOCAL
  275. These are string constants containing Bluetooth addresses with special
  276. meanings. For example, :const:`BDADDR_ANY` can be used to indicate
  277. any address when specifying the binding socket with
  278. :const:`BTPROTO_RFCOMM`.
  279. .. data:: HCI_FILTER
  280. HCI_TIME_STAMP
  281. HCI_DATA_DIR
  282. For use with :const:`BTPROTO_HCI`. :const:`HCI_FILTER` is not
  283. available for NetBSD or DragonFlyBSD. :const:`HCI_TIME_STAMP` and
  284. :const:`HCI_DATA_DIR` are not available for FreeBSD, NetBSD, or
  285. DragonFlyBSD.
  286. Functions
  287. ^^^^^^^^^
  288. Creating sockets
  289. ''''''''''''''''
  290. The following functions all create :ref:`socket objects <socket-objects>`.
  291. .. function:: socket(family=AF_INET, type=SOCK_STREAM, proto=0, fileno=None)
  292. Create a new socket using the given address family, socket type and protocol
  293. number. The address family should be :const:`AF_INET` (the default),
  294. :const:`AF_INET6`, :const:`AF_UNIX`, :const:`AF_CAN` or :const:`AF_RDS`. The
  295. socket type should be :const:`SOCK_STREAM` (the default),
  296. :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other ``SOCK_``
  297. constants. The protocol number is usually zero and may be omitted or in the
  298. case where the address family is :const:`AF_CAN` the protocol should be one
  299. of :const:`CAN_RAW` or :const:`CAN_BCM`. If *fileno* is specified, the other
  300. arguments are ignored, causing the socket with the specified file descriptor
  301. to return. Unlike :func:`socket.fromfd`, *fileno* will return the same
  302. socket and not a duplicate. This may help close a detached socket using
  303. :meth:`socket.close()`.
  304. The newly created socket is :ref:`non-inheritable <fd_inheritance>`.
  305. .. versionchanged:: 3.3
  306. The AF_CAN family was added.
  307. The AF_RDS family was added.
  308. .. versionchanged:: 3.4
  309. The CAN_BCM protocol was added.
  310. .. versionchanged:: 3.4
  311. The returned socket is now non-inheritable.
  312. .. function:: socketpair([family[, type[, proto]]])
  313. Build a pair of connected socket objects using the given address family, socket
  314. type, and protocol number. Address family, socket type, and protocol number are
  315. as for the :func:`.socket` function above. The default family is :const:`AF_UNIX`
  316. if defined on the platform; otherwise, the default is :const:`AF_INET`.
  317. The newly created sockets are :ref:`non-inheritable <fd_inheritance>`.
  318. .. versionchanged:: 3.2
  319. The returned socket objects now support the whole socket API, rather
  320. than a subset.
  321. .. versionchanged:: 3.4
  322. The returned sockets are now non-inheritable.
  323. .. versionchanged:: 3.5
  324. Windows support added.
  325. .. function:: create_connection(address[, timeout[, source_address]])
  326. Connect to a TCP service listening on the Internet *address* (a 2-tuple
  327. ``(host, port)``), and return the socket object. This is a higher-level
  328. function than :meth:`socket.connect`: if *host* is a non-numeric hostname,
  329. it will try to resolve it for both :data:`AF_INET` and :data:`AF_INET6`,
  330. and then try to connect to all possible addresses in turn until a
  331. connection succeeds. This makes it easy to write clients that are
  332. compatible to both IPv4 and IPv6.
  333. Passing the optional *timeout* parameter will set the timeout on the
  334. socket instance before attempting to connect. If no *timeout* is
  335. supplied, the global default timeout setting returned by
  336. :func:`getdefaulttimeout` is used.
  337. If supplied, *source_address* must be a 2-tuple ``(host, port)`` for the
  338. socket to bind to as its source address before connecting. If host or port
  339. are '' or 0 respectively the OS default behavior will be used.
  340. .. versionchanged:: 3.2
  341. *source_address* was added.
  342. .. function:: fromfd(fd, family, type, proto=0)
  343. Duplicate the file descriptor *fd* (an integer as returned by a file object's
  344. :meth:`fileno` method) and build a socket object from the result. Address
  345. family, socket type and protocol number are as for the :func:`.socket` function
  346. above. The file descriptor should refer to a socket, but this is not checked ---
  347. subsequent operations on the object may fail if the file descriptor is invalid.
  348. This function is rarely needed, but can be used to get or set socket options on
  349. a socket passed to a program as standard input or output (such as a server
  350. started by the Unix inet daemon). The socket is assumed to be in blocking mode.
  351. The newly created socket is :ref:`non-inheritable <fd_inheritance>`.
  352. .. versionchanged:: 3.4
  353. The returned socket is now non-inheritable.
  354. .. function:: fromshare(data)
  355. Instantiate a socket from data obtained from the :meth:`socket.share`
  356. method. The socket is assumed to be in blocking mode.
  357. Availability: Windows.
  358. .. versionadded:: 3.3
  359. .. data:: SocketType
  360. This is a Python type object that represents the socket object type. It is the
  361. same as ``type(socket(...))``.
  362. Other functions
  363. '''''''''''''''
  364. The :mod:`socket` module also offers various network-related services:
  365. .. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0)
  366. Translate the *host*/*port* argument into a sequence of 5-tuples that contain
  367. all the necessary arguments for creating a socket connected to that service.
  368. *host* is a domain name, a string representation of an IPv4/v6 address
  369. or ``None``. *port* is a string service name such as ``'http'``, a numeric
  370. port number or ``None``. By passing ``None`` as the value of *host*
  371. and *port*, you can pass ``NULL`` to the underlying C API.
  372. The *family*, *type* and *proto* arguments can be optionally specified
  373. in order to narrow the list of addresses returned. Passing zero as a
  374. value for each of these arguments selects the full range of results.
  375. The *flags* argument can be one or several of the ``AI_*`` constants,
  376. and will influence how results are computed and returned.
  377. For example, :const:`AI_NUMERICHOST` will disable domain name resolution
  378. and will raise an error if *host* is a domain name.
  379. The function returns a list of 5-tuples with the following structure:
  380. ``(family, type, proto, canonname, sockaddr)``
  381. In these tuples, *family*, *type*, *proto* are all integers and are
  382. meant to be passed to the :func:`.socket` function. *canonname* will be
  383. a string representing the canonical name of the *host* if
  384. :const:`AI_CANONNAME` is part of the *flags* argument; else *canonname*
  385. will be empty. *sockaddr* is a tuple describing a socket address, whose
  386. format depends on the returned *family* (a ``(address, port)`` 2-tuple for
  387. :const:`AF_INET`, a ``(address, port, flow info, scope id)`` 4-tuple for
  388. :const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect`
  389. method.
  390. The following example fetches address information for a hypothetical TCP
  391. connection to ``example.org`` on port 80 (results may differ on your
  392. system if IPv6 isn't enabled)::
  393. >>> socket.getaddrinfo("example.org", 80, proto=socket.IPPROTO_TCP)
  394. [(<AddressFamily.AF_INET6: 10>, <SocketType.SOCK_STREAM: 1>,
  395. 6, '', ('2606:2800:220:1:248:1893:25c8:1946', 80, 0, 0)),
  396. (<AddressFamily.AF_INET: 2>, <SocketType.SOCK_STREAM: 1>,
  397. 6, '', ('93.184.216.34', 80))]
  398. .. versionchanged:: 3.2
  399. parameters can now be passed using keyword arguments.
  400. .. function:: getfqdn([name])
  401. Return a fully qualified domain name for *name*. If *name* is omitted or empty,
  402. it is interpreted as the local host. To find the fully qualified name, the
  403. hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the
  404. host, if available. The first name which includes a period is selected. In
  405. case no fully qualified domain name is available, the hostname as returned by
  406. :func:`gethostname` is returned.
  407. .. function:: gethostbyname(hostname)
  408. Translate a host name to IPv4 address format. The IPv4 address is returned as a
  409. string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself
  410. it is returned unchanged. See :func:`gethostbyname_ex` for a more complete
  411. interface. :func:`gethostbyname` does not support IPv6 name resolution, and
  412. :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support.
  413. .. function:: gethostbyname_ex(hostname)
  414. Translate a host name to IPv4 address format, extended interface. Return a
  415. triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary
  416. host name responding to the given *ip_address*, *aliaslist* is a (possibly
  417. empty) list of alternative host names for the same address, and *ipaddrlist* is
  418. a list of IPv4 addresses for the same interface on the same host (often but not
  419. always a single address). :func:`gethostbyname_ex` does not support IPv6 name
  420. resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual
  421. stack support.
  422. .. function:: gethostname()
  423. Return a string containing the hostname of the machine where the Python
  424. interpreter is currently executing.
  425. Note: :func:`gethostname` doesn't always return the fully qualified domain
  426. name; use :func:`getfqdn` for that.
  427. .. function:: gethostbyaddr(ip_address)
  428. Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the
  429. primary host name responding to the given *ip_address*, *aliaslist* is a
  430. (possibly empty) list of alternative host names for the same address, and
  431. *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same
  432. host (most likely containing only a single address). To find the fully qualified
  433. domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports
  434. both IPv4 and IPv6.
  435. .. function:: getnameinfo(sockaddr, flags)
  436. Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending
  437. on the settings of *flags*, the result can contain a fully-qualified domain name
  438. or numeric address representation in *host*. Similarly, *port* can contain a
  439. string port name or a numeric port number.
  440. .. function:: getprotobyname(protocolname)
  441. Translate an Internet protocol name (for example, ``'icmp'``) to a constant
  442. suitable for passing as the (optional) third argument to the :func:`.socket`
  443. function. This is usually only needed for sockets opened in "raw" mode
  444. (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen
  445. automatically if the protocol is omitted or zero.
  446. .. function:: getservbyname(servicename[, protocolname])
  447. Translate an Internet service name and protocol name to a port number for that
  448. service. The optional protocol name, if given, should be ``'tcp'`` or
  449. ``'udp'``, otherwise any protocol will match.
  450. .. function:: getservbyport(port[, protocolname])
  451. Translate an Internet port number and protocol name to a service name for that
  452. service. The optional protocol name, if given, should be ``'tcp'`` or
  453. ``'udp'``, otherwise any protocol will match.
  454. .. function:: ntohl(x)
  455. Convert 32-bit positive integers from network to host byte order. On machines
  456. where the host byte order is the same as network byte order, this is a no-op;
  457. otherwise, it performs a 4-byte swap operation.
  458. .. function:: ntohs(x)
  459. Convert 16-bit positive integers from network to host byte order. On machines
  460. where the host byte order is the same as network byte order, this is a no-op;
  461. otherwise, it performs a 2-byte swap operation.
  462. .. function:: htonl(x)
  463. Convert 32-bit positive integers from host to network byte order. On machines
  464. where the host byte order is the same as network byte order, this is a no-op;
  465. otherwise, it performs a 4-byte swap operation.
  466. .. function:: htons(x)
  467. Convert 16-bit positive integers from host to network byte order. On machines
  468. where the host byte order is the same as network byte order, this is a no-op;
  469. otherwise, it performs a 2-byte swap operation.
  470. .. function:: inet_aton(ip_string)
  471. Convert an IPv4 address from dotted-quad string format (for example,
  472. '123.45.67.89') to 32-bit packed binary format, as a bytes object four characters in
  473. length. This is useful when conversing with a program that uses the standard C
  474. library and needs objects of type :c:type:`struct in_addr`, which is the C type
  475. for the 32-bit packed binary this function returns.
  476. :func:`inet_aton` also accepts strings with less than three dots; see the
  477. Unix manual page :manpage:`inet(3)` for details.
  478. If the IPv4 address string passed to this function is invalid,
  479. :exc:`OSError` will be raised. Note that exactly what is valid depends on
  480. the underlying C implementation of :c:func:`inet_aton`.
  481. :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used
  482. instead for IPv4/v6 dual stack support.
  483. .. function:: inet_ntoa(packed_ip)
  484. Convert a 32-bit packed IPv4 address (a :term:`bytes-like object` four
  485. bytes in length) to its standard dotted-quad string representation (for example,
  486. '123.45.67.89'). This is useful when conversing with a program that uses the
  487. standard C library and needs objects of type :c:type:`struct in_addr`, which
  488. is the C type for the 32-bit packed binary data this function takes as an
  489. argument.
  490. If the byte sequence passed to this function is not exactly 4 bytes in
  491. length, :exc:`OSError` will be raised. :func:`inet_ntoa` does not
  492. support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual
  493. stack support.
  494. .. versionchanged:: 3.5
  495. Writable :term:`bytes-like object` is now accepted.
  496. .. function:: inet_pton(address_family, ip_string)
  497. Convert an IP address from its family-specific string format to a packed,
  498. binary format. :func:`inet_pton` is useful when a library or network protocol
  499. calls for an object of type :c:type:`struct in_addr` (similar to
  500. :func:`inet_aton`) or :c:type:`struct in6_addr`.
  501. Supported values for *address_family* are currently :const:`AF_INET` and
  502. :const:`AF_INET6`. If the IP address string *ip_string* is invalid,
  503. :exc:`OSError` will be raised. Note that exactly what is valid depends on
  504. both the value of *address_family* and the underlying implementation of
  505. :c:func:`inet_pton`.
  506. Availability: Unix (maybe not all platforms), Windows.
  507. .. versionchanged:: 3.4
  508. Windows support added
  509. .. function:: inet_ntop(address_family, packed_ip)
  510. Convert a packed IP address (a :term:`bytes-like object` of some number of
  511. bytes) to its standard, family-specific string representation (for
  512. example, ``'7.10.0.5'`` or ``'5aef:2b::8'``).
  513. :func:`inet_ntop` is useful when a library or network protocol returns an
  514. object of type :c:type:`struct in_addr` (similar to :func:`inet_ntoa`) or
  515. :c:type:`struct in6_addr`.
  516. Supported values for *address_family* are currently :const:`AF_INET` and
  517. :const:`AF_INET6`. If the bytes object *packed_ip* is not the correct
  518. length for the specified address family, :exc:`ValueError` will be raised.
  519. :exc:`OSError` is raised for errors from the call to :func:`inet_ntop`.
  520. Availability: Unix (maybe not all platforms), Windows.
  521. .. versionchanged:: 3.4
  522. Windows support added
  523. .. versionchanged:: 3.5
  524. Writable :term:`bytes-like object` is now accepted.
  525. ..
  526. XXX: Are sendmsg(), recvmsg() and CMSG_*() available on any
  527. non-Unix platforms? The old (obsolete?) 4.2BSD form of the
  528. interface, in which struct msghdr has no msg_control or
  529. msg_controllen members, is not currently supported.
  530. .. function:: CMSG_LEN(length)
  531. Return the total length, without trailing padding, of an ancillary
  532. data item with associated data of the given *length*. This value
  533. can often be used as the buffer size for :meth:`~socket.recvmsg` to
  534. receive a single item of ancillary data, but :rfc:`3542` requires
  535. portable applications to use :func:`CMSG_SPACE` and thus include
  536. space for padding, even when the item will be the last in the
  537. buffer. Raises :exc:`OverflowError` if *length* is outside the
  538. permissible range of values.
  539. Availability: most Unix platforms, possibly others.
  540. .. versionadded:: 3.3
  541. .. function:: CMSG_SPACE(length)
  542. Return the buffer size needed for :meth:`~socket.recvmsg` to
  543. receive an ancillary data item with associated data of the given
  544. *length*, along with any trailing padding. The buffer space needed
  545. to receive multiple items is the sum of the :func:`CMSG_SPACE`
  546. values for their associated data lengths. Raises
  547. :exc:`OverflowError` if *length* is outside the permissible range
  548. of values.
  549. Note that some systems might support ancillary data without
  550. providing this function. Also note that setting the buffer size
  551. using the results of this function may not precisely limit the
  552. amount of ancillary data that can be received, since additional
  553. data may be able to fit into the padding area.
  554. Availability: most Unix platforms, possibly others.
  555. .. versionadded:: 3.3
  556. .. function:: getdefaulttimeout()
  557. Return the default timeout in seconds (float) for new socket objects. A value
  558. of ``None`` indicates that new socket objects have no timeout. When the socket
  559. module is first imported, the default is ``None``.
  560. .. function:: setdefaulttimeout(timeout)
  561. Set the default timeout in seconds (float) for new socket objects. When
  562. the socket module is first imported, the default is ``None``. See
  563. :meth:`~socket.settimeout` for possible values and their respective
  564. meanings.
  565. .. function:: sethostname(name)
  566. Set the machine's hostname to *name*. This will raise an
  567. :exc:`OSError` if you don't have enough rights.
  568. Availability: Unix.
  569. .. versionadded:: 3.3
  570. .. function:: if_nameindex()
  571. Return a list of network interface information
  572. (index int, name string) tuples.
  573. :exc:`OSError` if the system call fails.
  574. Availability: Unix.
  575. .. versionadded:: 3.3
  576. .. function:: if_nametoindex(if_name)
  577. Return a network interface index number corresponding to an
  578. interface name.
  579. :exc:`OSError` if no interface with the given name exists.
  580. Availability: Unix.
  581. .. versionadded:: 3.3
  582. .. function:: if_indextoname(if_index)
  583. Return a network interface name corresponding to an
  584. interface index number.
  585. :exc:`OSError` if no interface with the given index exists.
  586. Availability: Unix.
  587. .. versionadded:: 3.3
  588. .. _socket-objects:
  589. Socket Objects
  590. --------------
  591. Socket objects have the following methods. Except for
  592. :meth:`~socket.makefile`, these correspond to Unix system calls applicable
  593. to sockets.
  594. .. versionchanged:: 3.2
  595. Support for the :term:`context manager` protocol was added. Exiting the
  596. context manager is equivalent to calling :meth:`~socket.close`.
  597. .. method:: socket.accept()
  598. Accept a connection. The socket must be bound to an address and listening for
  599. connections. The return value is a pair ``(conn, address)`` where *conn* is a
  600. *new* socket object usable to send and receive data on the connection, and
  601. *address* is the address bound to the socket on the other end of the connection.
  602. The newly created socket is :ref:`non-inheritable <fd_inheritance>`.
  603. .. versionchanged:: 3.4
  604. The socket is now non-inheritable.
  605. .. versionchanged:: 3.5
  606. If the system call is interrupted and the signal handler does not raise
  607. an exception, the method now retries the system call instead of raising
  608. an :exc:`InterruptedError` exception (see :pep:`475` for the rationale).
  609. .. method:: socket.bind(address)
  610. Bind the socket to *address*. The socket must not already be bound. (The format
  611. of *address* depends on the address family --- see above.)
  612. .. method:: socket.close()
  613. Mark the socket closed. The underlying system resource (e.g. a file
  614. descriptor) is also closed when all file objects from :meth:`makefile()`
  615. are closed. Once that happens, all future operations on the socket
  616. object will fail. The remote end will receive no more data (after
  617. queued data is flushed).
  618. Sockets are automatically closed when they are garbage-collected, but
  619. it is recommended to :meth:`close` them explicitly, or to use a
  620. :keyword:`with` statement around them.
  621. .. versionchanged:: 3.6
  622. :exc:`OSError` is now raised if an error occurs when the underlying
  623. :c:func:`close` call is made.
  624. .. note::
  625. :meth:`close()` releases the resource associated with a connection but
  626. does not necessarily close the connection immediately. If you want
  627. to close the connection in a timely fashion, call :meth:`shutdown()`
  628. before :meth:`close()`.
  629. .. method:: socket.connect(address)
  630. Connect to a remote socket at *address*. (The format of *address* depends on the
  631. address family --- see above.)
  632. If the connection is interrupted by a signal, the method waits until the
  633. connection completes, or raise a :exc:`socket.timeout` on timeout, if the
  634. signal handler doesn't raise an exception and the socket is blocking or has
  635. a timeout. For non-blocking sockets, the method raises an
  636. :exc:`InterruptedError` exception if the connection is interrupted by a
  637. signal (or the exception raised by the signal handler).
  638. .. versionchanged:: 3.5
  639. The method now waits until the connection completes instead of raising an
  640. :exc:`InterruptedError` exception if the connection is interrupted by a
  641. signal, the signal handler doesn't raise an exception and the socket is
  642. blocking or has a timeout (see the :pep:`475` for the rationale).
  643. .. method:: socket.connect_ex(address)
  644. Like ``connect(address)``, but return an error indicator instead of raising an
  645. exception for errors returned by the C-level :c:func:`connect` call (other
  646. problems, such as "host not found," can still raise exceptions). The error
  647. indicator is ``0`` if the operation succeeded, otherwise the value of the
  648. :c:data:`errno` variable. This is useful to support, for example, asynchronous
  649. connects.
  650. .. method:: socket.detach()
  651. Put the socket object into closed state without actually closing the
  652. underlying file descriptor. The file descriptor is returned, and can
  653. be reused for other purposes.
  654. .. versionadded:: 3.2
  655. .. method:: socket.dup()
  656. Duplicate the socket.
  657. The newly created socket is :ref:`non-inheritable <fd_inheritance>`.
  658. .. versionchanged:: 3.4
  659. The socket is now non-inheritable.
  660. .. method:: socket.fileno()
  661. Return the socket's file descriptor (a small integer), or -1 on failure. This
  662. is useful with :func:`select.select`.
  663. Under Windows the small integer returned by this method cannot be used where a
  664. file descriptor can be used (such as :func:`os.fdopen`). Unix does not have
  665. this limitation.
  666. .. method:: socket.get_inheritable()
  667. Get the :ref:`inheritable flag <fd_inheritance>` of the socket's file
  668. descriptor or socket's handle: ``True`` if the socket can be inherited in
  669. child processes, ``False`` if it cannot.
  670. .. versionadded:: 3.4
  671. .. method:: socket.getpeername()
  672. Return the remote address to which the socket is connected. This is useful to
  673. find out the port number of a remote IPv4/v6 socket, for instance. (The format
  674. of the address returned depends on the address family --- see above.) On some
  675. systems this function is not supported.
  676. .. method:: socket.getsockname()
  677. Return the socket's own address. This is useful to find out the port number of
  678. an IPv4/v6 socket, for instance. (The format of the address returned depends on
  679. the address family --- see above.)
  680. .. method:: socket.getsockopt(level, optname[, buflen])
  681. Return the value of the given socket option (see the Unix man page
  682. :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.)
  683. are defined in this module. If *buflen* is absent, an integer option is assumed
  684. and its integer value is returned by the function. If *buflen* is present, it
  685. specifies the maximum length of the buffer used to receive the option in, and
  686. this buffer is returned as a bytes object. It is up to the caller to decode the
  687. contents of the buffer (see the optional built-in module :mod:`struct` for a way
  688. to decode C structures encoded as byte strings).
  689. .. method:: socket.gettimeout()
  690. Return the timeout in seconds (float) associated with socket operations,
  691. or ``None`` if no timeout is set. This reflects the last call to
  692. :meth:`setblocking` or :meth:`settimeout`.
  693. .. method:: socket.ioctl(control, option)
  694. :platform: Windows
  695. The :meth:`ioctl` method is a limited interface to the WSAIoctl system
  696. interface. Please refer to the `Win32 documentation
  697. <https://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more
  698. information.
  699. On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl`
  700. functions may be used; they accept a socket object as their first argument.
  701. Currently only the following control codes are supported:
  702. ``SIO_RCVALL``, ``SIO_KEEPALIVE_VALS``, and ``SIO_LOOPBACK_FAST_PATH``.
  703. .. versionchanged:: 3.6
  704. ``SIO_LOOPBACK_FAST_PATH`` was added.
  705. .. method:: socket.listen([backlog])
  706. Enable a server to accept connections. If *backlog* is specified, it must
  707. be at least 0 (if it is lower, it is set to 0); it specifies the number of
  708. unaccepted connections that the system will allow before refusing new
  709. connections. If not specified, a default reasonable value is chosen.
  710. .. versionchanged:: 3.5
  711. The *backlog* parameter is now optional.
  712. .. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \
  713. errors=None, newline=None)
  714. .. index:: single: I/O control; buffering
  715. Return a :term:`file object` associated with the socket. The exact returned
  716. type depends on the arguments given to :meth:`makefile`. These arguments are
  717. interpreted the same way as by the built-in :func:`open` function, except
  718. the only supported *mode* values are ``'r'`` (default), ``'w'`` and ``'b'``.
  719. The socket must be in blocking mode; it can have a timeout, but the file
  720. object's internal buffer may end up in an inconsistent state if a timeout
  721. occurs.
  722. Closing the file object returned by :meth:`makefile` won't close the
  723. original socket unless all other file objects have been closed and
  724. :meth:`socket.close` has been called on the socket object.
  725. .. note::
  726. On Windows, the file-like object created by :meth:`makefile` cannot be
  727. used where a file object with a file descriptor is expected, such as the
  728. stream arguments of :meth:`subprocess.Popen`.
  729. .. method:: socket.recv(bufsize[, flags])
  730. Receive data from the socket. The return value is a bytes object representing the
  731. data received. The maximum amount of data to be received at once is specified
  732. by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of
  733. the optional argument *flags*; it defaults to zero.
  734. .. note::
  735. For best match with hardware and network realities, the value of *bufsize*
  736. should be a relatively small power of 2, for example, 4096.
  737. .. versionchanged:: 3.5
  738. If the system call is interrupted and the signal handler does not raise
  739. an exception, the method now retries the system call instead of raising
  740. an :exc:`InterruptedError` exception (see :pep:`475` for the rationale).
  741. .. method:: socket.recvfrom(bufsize[, flags])
  742. Receive data from the socket. The return value is a pair ``(bytes, address)``
  743. where *bytes* is a bytes object representing the data received and *address* is the
  744. address of the socket sending the data. See the Unix manual page
  745. :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults
  746. to zero. (The format of *address* depends on the address family --- see above.)
  747. .. versionchanged:: 3.5
  748. If the system call is interrupted and the signal handler does not raise
  749. an exception, the method now retries the system call instead of raising
  750. an :exc:`InterruptedError` exception (see :pep:`475` for the rationale).
  751. .. method:: socket.recvmsg(bufsize[, ancbufsize[, flags]])
  752. Receive normal data (up to *bufsize* bytes) and ancillary data from
  753. the socket. The *ancbufsize* argument sets the size in bytes of
  754. the internal buffer used to receive the ancillary data; it defaults
  755. to 0, meaning that no ancillary data will be received. Appropriate
  756. buffer sizes for ancillary data can be calculated using
  757. :func:`CMSG_SPACE` or :func:`CMSG_LEN`, and items which do not fit
  758. into the buffer might be truncated or discarded. The *flags*
  759. argument defaults to 0 and has the same meaning as for
  760. :meth:`recv`.
  761. The return value is a 4-tuple: ``(data, ancdata, msg_flags,
  762. address)``. The *data* item is a :class:`bytes` object holding the
  763. non-ancillary data received. The *ancdata* item is a list of zero
  764. or more tuples ``(cmsg_level, cmsg_type, cmsg_data)`` representing
  765. the ancillary data (control messages) received: *cmsg_level* and
  766. *cmsg_type* are integers specifying the protocol level and
  767. protocol-specific type respectively, and *cmsg_data* is a
  768. :class:`bytes` object holding the associated data. The *msg_flags*
  769. item is the bitwise OR of various flags indicating conditions on
  770. the received message; see your system documentation for details.
  771. If the receiving socket is unconnected, *address* is the address of
  772. the sending socket, if available; otherwise, its value is
  773. unspecified.
  774. On some systems, :meth:`sendmsg` and :meth:`recvmsg` can be used to
  775. pass file descriptors between processes over an :const:`AF_UNIX`
  776. socket. When this facility is used (it is often restricted to
  777. :const:`SOCK_STREAM` sockets), :meth:`recvmsg` will return, in its
  778. ancillary data, items of the form ``(socket.SOL_SOCKET,
  779. socket.SCM_RIGHTS, fds)``, where *fds* is a :class:`bytes` object
  780. representing the new file descriptors as a binary array of the
  781. native C :c:type:`int` type. If :meth:`recvmsg` raises an
  782. exception after the system call returns, it will first attempt to
  783. close any file descriptors received via this mechanism.
  784. Some systems do not indicate the truncated length of ancillary data
  785. items which have been only partially received. If an item appears
  786. to extend beyond the end of the buffer, :meth:`recvmsg` will issue
  787. a :exc:`RuntimeWarning`, and will return the part of it which is
  788. inside the buffer provided it has not been truncated before the
  789. start of its associated data.
  790. On systems which support the :const:`SCM_RIGHTS` mechanism, the
  791. following function will receive up to *maxfds* file descriptors,
  792. returning the message data and a list containing the descriptors
  793. (while ignoring unexpected conditions such as unrelated control
  794. messages being received). See also :meth:`sendmsg`. ::
  795. import socket, array
  796. def recv_fds(sock, msglen, maxfds):
  797. fds = array.array("i") # Array of ints
  798. msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize))
  799. for cmsg_level, cmsg_type, cmsg_data in ancdata:
  800. if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS):
  801. # Append data, ignoring any truncated integers at the end.
  802. fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])
  803. return msg, list(fds)
  804. Availability: most Unix platforms, possibly others.
  805. .. versionadded:: 3.3
  806. .. versionchanged:: 3.5
  807. If the system call is interrupted and the signal handler does not raise
  808. an exception, the method now retries the system call instead of raising
  809. an :exc:`InterruptedError` exception (see :pep:`475` for the rationale).
  810. .. method:: socket.recvmsg_into(buffers[, ancbufsize[, flags]])
  811. Receive normal data and ancillary data from the socket, behaving as
  812. :meth:`recvmsg` would, but scatter the non-ancillary data into a
  813. series of buffers instead of returning a new bytes object. The
  814. *buffers* argument must be an iterable of objects that export
  815. writable buffers (e.g. :class:`bytearray` objects); these will be
  816. filled with successive chunks of the non-ancillary data until it
  817. has all been written or there are no more buffers. The operating
  818. system may set a limit (:func:`~os.sysconf` value ``SC_IOV_MAX``)
  819. on the number of buffers that can be used. The *ancbufsize* and
  820. *flags* arguments have the same meaning as for :meth:`recvmsg`.
  821. The return value is a 4-tuple: ``(nbytes, ancdata, msg_flags,
  822. address)``, where *nbytes* is the total number of bytes of
  823. non-ancillary data written into the buffers, and *ancdata*,
  824. *msg_flags* and *address* are the same as for :meth:`recvmsg`.
  825. Example::
  826. >>> import socket
  827. >>> s1, s2 = socket.socketpair()
  828. >>> b1 = bytearray(b'----')
  829. >>> b2 = bytearray(b'0123456789')
  830. >>> b3 = bytearray(b'--------------')
  831. >>> s1.send(b'Mary had a little lamb')
  832. 22
  833. >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3])
  834. (22, [], 0, None)
  835. >>> [b1, b2, b3]
  836. [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')]
  837. Availability: most Unix platforms, possibly others.
  838. .. versionadded:: 3.3
  839. .. method:: socket.recvfrom_into(buffer[, nbytes[, flags]])
  840. Receive data from the socket, writing it into *buffer* instead of creating a
  841. new bytestring. The return value is a pair ``(nbytes, address)`` where *nbytes* is
  842. the number of bytes received and *address* is the address of the socket sending
  843. the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the
  844. optional argument *flags*; it defaults to zero. (The format of *address*
  845. depends on the address family --- see above.)
  846. .. method:: socket.recv_into(buffer[, nbytes[, flags]])
  847. Receive up to *nbytes* bytes from the socket, storing the data into a buffer
  848. rather than creating a new bytestring. If *nbytes* is not specified (or 0),
  849. receive up to the size available in the given buffer. Returns the number of
  850. bytes received. See the Unix manual page :manpage:`recv(2)` for the meaning
  851. of the optional argument *flags*; it defaults to zero.
  852. .. method:: socket.send(bytes[, flags])
  853. Send data to the socket. The socket must be connected to a remote socket. The
  854. optional *flags* argument has the same meaning as for :meth:`recv` above.
  855. Returns the number of bytes sent. Applications are responsible for checking that
  856. all data has been sent; if only some of the data was transmitted, the
  857. application needs to attempt delivery of the remaining data. For further
  858. information on this topic, consult the :ref:`socket-howto`.
  859. .. versionchanged:: 3.5
  860. If the system call is interrupted and the signal handler does not raise
  861. an exception, the method now retries the system call instead of raising
  862. an :exc:`InterruptedError` exception (see :pep:`475` for the rationale).
  863. .. method:: socket.sendall(bytes[, flags])
  864. Send data to the socket. The socket must be connected to a remote socket. The
  865. optional *flags* argument has the same meaning as for :meth:`recv` above.
  866. Unlike :meth:`send`, this method continues to send data from *bytes* until
  867. either all data has been sent or an error occurs. ``None`` is returned on
  868. success. On error, an exception is raised, and there is no way to determine how
  869. much data, if any, was successfully sent.
  870. .. versionchanged:: 3.5
  871. The socket timeout is no more reset each time data is sent successfully.
  872. The socket timeout is now the maximum total duration to send all data.
  873. .. versionchanged:: 3.5
  874. If the system call is interrupted and the signal handler does not raise
  875. an exception, the method now retries the system call instead of raising
  876. an :exc:`InterruptedError` exception (see :pep:`475` for the rationale).
  877. .. method:: socket.sendto(bytes, address)
  878. socket.sendto(bytes, flags, address)
  879. Send data to the socket. The socket should not be connected to a remote socket,
  880. since the destination socket is specified by *address*. The optional *flags*
  881. argument has the same meaning as for :meth:`recv` above. Return the number of
  882. bytes sent. (The format of *address* depends on the address family --- see
  883. above.)
  884. .. versionchanged:: 3.5
  885. If the system call is interrupted and the signal handler does not raise
  886. an exception, the method now retries the system call instead of raising
  887. an :exc:`InterruptedError` exception (see :pep:`475` for the rationale).
  888. .. method:: socket.sendmsg(buffers[, ancdata[, flags[, address]]])
  889. Send normal and ancillary data to the socket, gathering the
  890. non-ancillary data from a series of buffers and concatenating it
  891. into a single message. The *buffers* argument specifies the
  892. non-ancillary data as an iterable of
  893. :term:`bytes-like objects <bytes-like object>`
  894. (e.g. :class:`bytes` objects); the operating system may set a limit
  895. (:func:`~os.sysconf` value ``SC_IOV_MAX``) on the number of buffers
  896. that can be used. The *ancdata* argument specifies the ancillary
  897. data (control messages) as an iterable of zero or more tuples
  898. ``(cmsg_level, cmsg_type, cmsg_data)``, where *cmsg_level* and
  899. *cmsg_type* are integers specifying the protocol level and
  900. protocol-specific type respectively, and *cmsg_data* is a
  901. bytes-like object holding the associated data. Note that
  902. some systems (in particular, systems without :func:`CMSG_SPACE`)
  903. might support sending only one control message per call. The
  904. *flags* argument defaults to 0 and has the same meaning as for
  905. :meth:`send`. If *address* is supplied and not ``None``, it sets a
  906. destination address for the message. The return value is the
  907. number of bytes of non-ancillary data sent.
  908. The following function sends the list of file descriptors *fds*
  909. over an :const:`AF_UNIX` socket, on systems which support the
  910. :const:`SCM_RIGHTS` mechanism. See also :meth:`recvmsg`. ::
  911. import socket, array
  912. def send_fds(sock, msg, fds):
  913. return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))])
  914. Availability: most Unix platforms, possibly others.
  915. .. versionadded:: 3.3
  916. .. versionchanged:: 3.5
  917. If the system call is interrupted and the signal handler does not raise
  918. an exception, the method now retries the system call instead of raising
  919. an :exc:`InterruptedError` exception (see :pep:`475` for the rationale).
  920. .. method:: socket.sendmsg_afalg([msg], *, op[, iv[, assoclen[, flags]]])
  921. Specialized version of :meth:`~socket.sendmsg` for :const:`AF_ALG` socket.
  922. Set mode, IV, AEAD associated data length and flags for :const:`AF_ALG` socket.
  923. Availability: Linux >= 2.6.38
  924. .. versionadded:: 3.6
  925. .. method:: socket.sendfile(file, offset=0, count=None)
  926. Send a file until EOF is reached by using high-performance
  927. :mod:`os.sendfile` and return the total number of bytes which were sent.
  928. *file* must be a regular file object opened in binary mode. If
  929. :mod:`os.sendfile` is not available (e.g. Windows) or *file* is not a
  930. regular file :meth:`send` will be used instead. *offset* tells from where to
  931. start reading the file. If specified, *count* is the total number of bytes
  932. to transmit as opposed to sending the file until EOF is reached. File
  933. position is updated on return or also in case of error in which case
  934. :meth:`file.tell() <io.IOBase.tell>` can be used to figure out the number of
  935. bytes which were sent. The socket must be of :const:`SOCK_STREAM` type. Non-
  936. blocking sockets are not supported.
  937. .. versionadded:: 3.5
  938. .. method:: socket.set_inheritable(inheritable)
  939. Set the :ref:`inheritable flag <fd_inheritance>` of the socket's file
  940. descriptor or socket's handle.
  941. .. versionadded:: 3.4
  942. .. method:: socket.setblocking(flag)
  943. Set blocking or non-blocking mode of the socket: if *flag* is false, the
  944. socket is set to non-blocking, else to blocking mode.
  945. This method is a shorthand for certain :meth:`~socket.settimeout` calls:
  946. * ``sock.setblocking(True)`` is equivalent to ``sock.settimeout(None)``
  947. * ``sock.setblocking(False)`` is equivalent to ``sock.settimeout(0.0)``
  948. .. method:: socket.settimeout(value)
  949. Set a timeout on blocking socket operations. The *value* argument can be a
  950. nonnegative floating point number expressing seconds, or ``None``.
  951. If a non-zero value is given, subsequent socket operations will raise a
  952. :exc:`timeout` exception if the timeout period *value* has elapsed before
  953. the operation has completed. If zero is given, the socket is put in
  954. non-blocking mode. If ``None`` is given, the socket is put in blocking mode.
  955. For further information, please consult the :ref:`notes on socket timeouts <socket-timeouts>`.
  956. .. method:: socket.setsockopt(level, optname, value: int)
  957. .. method:: socket.setsockopt(level, optname, value: buffer)
  958. .. method:: socket.setsockopt(level, optname, None, optlen: int)
  959. .. index:: module: struct
  960. Set the value of the given socket option (see the Unix manual page
  961. :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the
  962. :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer,
  963. None or a :term:`bytes-like object` representing a buffer. In the later
  964. case it is up to the caller to ensure that the bytestring contains the
  965. proper bits (see the optional built-in module :mod:`struct` for a way to
  966. encode C structures as bytestrings). When value is set to None,
  967. optlen argument is required. It's equivalent to call setsockopt C
  968. function with optval=NULL and optlen=optlen.
  969. .. versionchanged:: 3.5
  970. Writable :term:`bytes-like object` is now accepted.
  971. .. versionchanged:: 3.6
  972. setsockopt(level, optname, None, optlen: int) form added.
  973. .. method:: socket.shutdown(how)
  974. Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`,
  975. further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends
  976. are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are
  977. disallowed.
  978. .. method:: socket.share(process_id)
  979. Duplicate a socket and prepare it for sharing with a target process. The
  980. target process must be provided with *process_id*. The resulting bytes object
  981. can then be passed to the target process using some form of interprocess
  982. communication and the socket can be recreated there using :func:`fromshare`.
  983. Once this method has been called, it is safe to close the socket since
  984. the operating system has already duplicated it for the target process.
  985. Availability: Windows.
  986. .. versionadded:: 3.3
  987. Note that there are no methods :meth:`read` or :meth:`write`; use
  988. :meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead.
  989. Socket objects also have these (read-only) attributes that correspond to the
  990. values given to the :class:`socket` constructor.
  991. .. attribute:: socket.family
  992. The socket family.
  993. .. attribute:: socket.type
  994. The socket type.
  995. .. attribute:: socket.proto
  996. The socket protocol.
  997. .. _socket-timeouts:
  998. Notes on socket timeouts
  999. ------------------------
  1000. A socket object can be in one of three modes: blocking, non-blocking, or
  1001. timeout. Sockets are by default always created in blocking mode, but this
  1002. can be changed by calling :func:`setdefaulttimeout`.
  1003. * In *blocking mode*, operations block until complete or the system returns
  1004. an error (such as connection timed out).
  1005. * In *non-blocking mode*, operations fail (with an error that is unfortunately
  1006. system-dependent) if they cannot be completed immediately: functions from the
  1007. :mod:`select` can be used to know when and whether a socket is available for
  1008. reading or writing.
  1009. * In *timeout mode*, operations fail if they cannot be completed within the
  1010. timeout specified for the socket (they raise a :exc:`timeout` exception)
  1011. or if the system returns an error.
  1012. .. note::
  1013. At the operating system level, sockets in *timeout mode* are internally set
  1014. in non-blocking mode. Also, the blocking and timeout modes are shared between
  1015. file descriptors and socket objects that refer to the same network endpoint.
  1016. This implementation detail can have visible consequences if e.g. you decide
  1017. to use the :meth:`~socket.fileno()` of a socket.
  1018. Timeouts and the ``connect`` method
  1019. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  1020. The :meth:`~socket.connect` operation is also subject to the timeout
  1021. setting, and in general it is recommended to call :meth:`~socket.settimeout`
  1022. before calling :meth:`~socket.connect` or pass a timeout parameter to
  1023. :meth:`create_connection`. However, the system network stack may also
  1024. return a connection timeout error of its own regardless of any Python socket
  1025. timeout setting.
  1026. Timeouts and the ``accept`` method
  1027. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  1028. If :func:`getdefaulttimeout` is not :const:`None`, sockets returned by
  1029. the :meth:`~socket.accept` method inherit that timeout. Otherwise, the
  1030. behaviour depends on settings of the listening socket:
  1031. * if the listening socket is in *blocking mode* or in *timeout mode*,
  1032. the socket returned by :meth:`~socket.accept` is in *blocking mode*;
  1033. * if the listening socket is in *non-blocking mode*, whether the socket
  1034. returned by :meth:`~socket.accept` is in blocking or non-blocking mode
  1035. is operating system-dependent. If you want to ensure cross-platform
  1036. behaviour, it is recommended you manually override this setting.
  1037. .. _socket-example:
  1038. Example
  1039. -------
  1040. Here are four minimal example programs using the TCP/IP protocol: a server that
  1041. echoes all data that it receives back (servicing only one client), and a client
  1042. using it. Note that a server must perform the sequence :func:`.socket`,
  1043. :meth:`~socket.bind`, :meth:`~socket.listen`, :meth:`~socket.accept` (possibly
  1044. repeating the :meth:`~socket.accept` to service more than one client), while a
  1045. client only needs the sequence :func:`.socket`, :meth:`~socket.connect`. Also
  1046. note that the server does not :meth:`~socket.sendall`/:meth:`~socket.recv` on
  1047. the socket it is listening on but on the new socket returned by
  1048. :meth:`~socket.accept`.
  1049. The first two examples support IPv4 only. ::
  1050. # Echo server program
  1051. import socket
  1052. HOST = '' # Symbolic name meaning all available interfaces
  1053. PORT = 50007 # Arbitrary non-privileged port
  1054. with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
  1055. s.bind((HOST, PORT))
  1056. s.listen(1)
  1057. conn, addr = s.accept()
  1058. with conn:
  1059. print('Connected by', addr)
  1060. while True:
  1061. data = conn.recv(1024)
  1062. if not data: break
  1063. conn.sendall(data)
  1064. ::
  1065. # Echo client program
  1066. import socket
  1067. HOST = 'daring.cwi.nl' # The remote host
  1068. PORT = 50007 # The same port as used by the server
  1069. with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
  1070. s.connect((HOST, PORT))
  1071. s.sendall(b'Hello, world')
  1072. data = s.recv(1024)
  1073. print('Received', repr(data))
  1074. The next two examples are identical to the above two, but support both IPv4 and
  1075. IPv6. The server side will listen to the first address family available (it
  1076. should listen to both instead). On most of IPv6-ready systems, IPv6 will take
  1077. precedence and the server may not accept IPv4 traffic. The client side will try
  1078. to connect to the all addresses returned as a result of the name resolution, and
  1079. sends traffic to the first one connected successfully. ::
  1080. # Echo server program
  1081. import socket
  1082. import sys
  1083. HOST = None # Symbolic name meaning all available interfaces
  1084. PORT = 50007 # Arbitrary non-privileged port
  1085. s = None
  1086. for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC,
  1087. socket.SOCK_STREAM, 0, socket.AI_PASSIVE):
  1088. af, socktype, proto, canonname, sa = res
  1089. try:
  1090. s = socket.socket(af, socktype, proto)
  1091. except OSError as msg:
  1092. s = None
  1093. continue
  1094. try:
  1095. s.bind(sa)
  1096. s.listen(1)
  1097. except OSError as msg:
  1098. s.close()
  1099. s = None
  1100. continue
  1101. break
  1102. if s is None:
  1103. print('could not open socket')
  1104. sys.exit(1)
  1105. conn, addr = s.accept()
  1106. with conn:
  1107. print('Connected by', addr)
  1108. while True:
  1109. data = conn.recv(1024)
  1110. if not data: break
  1111. conn.send(data)
  1112. ::
  1113. # Echo client program
  1114. import socket
  1115. import sys
  1116. HOST = 'daring.cwi.nl' # The remote host
  1117. PORT = 50007 # The same port as used by the server
  1118. s = None
  1119. for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM):
  1120. af, socktype, proto, canonname, sa = res
  1121. try:
  1122. s = socket.socket(af, socktype, proto)
  1123. except OSError as msg:
  1124. s = None
  1125. continue
  1126. try:
  1127. s.connect(sa)
  1128. except OSError as msg:
  1129. s.close()
  1130. s = None
  1131. continue
  1132. break
  1133. if s is None:
  1134. print('could not open socket')
  1135. sys.exit(1)
  1136. with s:
  1137. s.sendall(b'Hello, world')
  1138. data = s.recv(1024)
  1139. print('Received', repr(data))
  1140. The next example shows how to write a very simple network sniffer with raw
  1141. sockets on Windows. The example requires administrator privileges to modify
  1142. the interface::
  1143. import socket
  1144. # the public network interface
  1145. HOST = socket.gethostbyname(socket.gethostname())
  1146. # create a raw socket and bind it to the public interface
  1147. s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP)
  1148. s.bind((HOST, 0))
  1149. # Include IP headers
  1150. s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)
  1151. # receive all packages
  1152. s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)
  1153. # receive a package
  1154. print(s.recvfrom(65565))
  1155. # disabled promiscuous mode
  1156. s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)
  1157. The last example shows how to use the socket interface to communicate to a CAN
  1158. network using the raw socket protocol. To use CAN with the broadcast
  1159. manager protocol instead, open a socket with::
  1160. socket.socket(socket.AF_CAN, socket.SOCK_DGRAM, socket.CAN_BCM)
  1161. After binding (:const:`CAN_RAW`) or connecting (:const:`CAN_BCM`) the socket, you
  1162. can use the :meth:`socket.send`, and the :meth:`socket.recv` operations (and
  1163. their counterparts) on the socket object as usual.
  1164. This example might require special privileges::
  1165. import socket
  1166. import struct
  1167. # CAN frame packing/unpacking (see 'struct can_frame' in <linux/can.h>)
  1168. can_frame_fmt = "=IB3x8s"
  1169. can_frame_size = struct.calcsize(can_frame_fmt)
  1170. def build_can_frame(can_id, data):
  1171. can_dlc = len(data)
  1172. data = data.ljust(8, b'\x00')
  1173. return struct.pack(can_frame_fmt, can_id, can_dlc, data)
  1174. def dissect_can_frame(frame):
  1175. can_id, can_dlc, data = struct.unpack(can_frame_fmt, frame)
  1176. return (can_id, can_dlc, data[:can_dlc])
  1177. # create a raw socket and bind it to the 'vcan0' interface
  1178. s = socket.socket(socket.AF_CAN, socket.SOCK_RAW, socket.CAN_RAW)
  1179. s.bind(('vcan0',))
  1180. while True:
  1181. cf, addr = s.recvfrom(can_frame_size)
  1182. print('Received: can_id=%x, can_dlc=%x, data=%s' % dissect_can_frame(cf))
  1183. try:
  1184. s.send(cf)
  1185. except OSError:
  1186. print('Error sending CAN frame')
  1187. try:
  1188. s.send(build_can_frame(0x01, b'\x01\x02\x03'))
  1189. except OSError:
  1190. print('Error sending CAN frame')
  1191. Running an example several times with too small delay between executions, could
  1192. lead to this error::
  1193. OSError: [Errno 98] Address already in use
  1194. This is because the previous execution has left the socket in a ``TIME_WAIT``
  1195. state, and can't be immediately reused.
  1196. There is a :mod:`socket` flag to set, in order to prevent this,
  1197. :data:`socket.SO_REUSEADDR`::
  1198. s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  1199. s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
  1200. s.bind((HOST, PORT))
  1201. the :data:`SO_REUSEADDR` flag tells the kernel to reuse a local socket in
  1202. ``TIME_WAIT`` state, without waiting for its natural timeout to expire.
  1203. .. seealso::
  1204. For an introduction to socket programming (in C), see the following papers:
  1205. - *An Introductory 4.3BSD Interprocess Communication Tutorial*, by Stuart Sechrest
  1206. - *An Advanced 4.3BSD Interprocess Communication Tutorial*, by Samuel J. Leffler et
  1207. al,
  1208. both in the UNIX Programmer's Manual, Supplementary Documents 1 (sections
  1209. PS1:7 and PS1:8). The platform-specific reference material for the various
  1210. socket-related system calls are also a valuable source of information on the
  1211. details of socket semantics. For Unix, refer to the manual pages; for Windows,
  1212. see the WinSock (or Winsock 2) specification. For IPv6-ready APIs, readers may
  1213. want to refer to :rfc:`3493` titled Basic Socket Interface Extensions for IPv6.