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/library/socket.rst

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  1. :mod:`socket` --- Low-level networking interface
  2. ================================================
  3. .. module:: socket
  4. :synopsis: Low-level networking interface.
  5. This module provides access to the BSD *socket* interface. It is available on
  6. all modern Unix systems, Windows, MacOS, OS/2, and probably additional
  7. platforms.
  8. .. note::
  9. Some behavior may be platform dependent, since calls are made to the operating
  10. system socket APIs.
  11. .. index:: object: socket
  12. The Python interface is a straightforward transliteration of the Unix system
  13. call and library interface for sockets to Python's object-oriented style: the
  14. :func:`.socket` function returns a :dfn:`socket object` whose methods implement
  15. the various socket system calls. Parameter types are somewhat higher-level than
  16. in the C interface: as with :meth:`read` and :meth:`write` operations on Python
  17. files, buffer allocation on receive operations is automatic, and buffer length
  18. is implicit on send operations.
  19. .. seealso::
  20. Module :mod:`socketserver`
  21. Classes that simplify writing network servers.
  22. Module :mod:`ssl`
  23. A TLS/SSL wrapper for socket objects.
  24. Socket families
  25. ---------------
  26. Depending on the system and the build options, various socket families
  27. are supported by this module.
  28. The address format required by a particular socket object is automatically
  29. selected based on the address family specified when the socket object was
  30. created. Socket addresses are represented as follows:
  31. - The address of an :const:`AF_UNIX` socket bound to a file system node
  32. is represented as a string, using the file system encoding and the
  33. ``'surrogateescape'`` error handler (see :pep:`383`). An address in
  34. Linux's abstract namespace is returned as a :class:`bytes` object with
  35. an initial null byte; note that sockets in this namespace can
  36. communicate with normal file system sockets, so programs intended to
  37. run on Linux may need to deal with both types of address. A string or
  38. :class:`bytes` object can be used for either type of address when
  39. passing it as an argument.
  40. .. versionchanged:: 3.3
  41. Previously, :const:`AF_UNIX` socket paths were assumed to use UTF-8
  42. encoding.
  43. - A pair ``(host, port)`` is used for the :const:`AF_INET` address family,
  44. where *host* is a string representing either a hostname in Internet domain
  45. notation like ``'daring.cwi.nl'`` or an IPv4 address like ``'100.50.200.5'``,
  46. and *port* is an integer.
  47. - For :const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo,
  48. scopeid)`` is used, where *flowinfo* and *scopeid* represent the ``sin6_flowinfo``
  49. and ``sin6_scope_id`` members in :const:`struct sockaddr_in6` in C. For
  50. :mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for
  51. backward compatibility. Note, however, omission of *scopeid* can cause problems
  52. in manipulating scoped IPv6 addresses.
  53. - :const:`AF_NETLINK` sockets are represented as pairs ``(pid, groups)``.
  54. - Linux-only support for TIPC is available using the :const:`AF_TIPC`
  55. address family. TIPC is an open, non-IP based networked protocol designed
  56. for use in clustered computer environments. Addresses are represented by a
  57. tuple, and the fields depend on the address type. The general tuple form is
  58. ``(addr_type, v1, v2, v3 [, scope])``, where:
  59. - *addr_type* is one of :const:`TIPC_ADDR_NAMESEQ`, :const:`TIPC_ADDR_NAME`,
  60. or :const:`TIPC_ADDR_ID`.
  61. - *scope* is one of :const:`TIPC_ZONE_SCOPE`, :const:`TIPC_CLUSTER_SCOPE`, and
  62. :const:`TIPC_NODE_SCOPE`.
  63. - If *addr_type* is :const:`TIPC_ADDR_NAME`, then *v1* is the server type, *v2* is
  64. the port identifier, and *v3* should be 0.
  65. If *addr_type* is :const:`TIPC_ADDR_NAMESEQ`, then *v1* is the server type, *v2*
  66. is the lower port number, and *v3* is the upper port number.
  67. If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the
  68. reference, and *v3* should be set to 0.
  69. If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the
  70. reference, and *v3* should be set to 0.
  71. - A tuple ``(interface, )`` is used for the :const:`AF_CAN` address family,
  72. where *interface* is a string representing a network interface name like
  73. ``'can0'``. The network interface name ``''`` can be used to receive packets
  74. from all network interfaces of this family.
  75. - A string or a tuple ``(id, unit)`` is used for the :const:`SYSPROTO_CONTROL`
  76. protocol of the :const:`PF_SYSTEM` family. The string is the name of a
  77. kernel control using a dynamically-assigned ID. The tuple can be used if ID
  78. and unit number of the kernel control are known or if a registered ID is
  79. used.
  80. .. versionadded:: 3.3
  81. - Certain other address families (:const:`AF_BLUETOOTH`, :const:`AF_PACKET`)
  82. support specific representations.
  83. .. XXX document them!
  84. For IPv4 addresses, two special forms are accepted instead of a host address:
  85. the empty string represents :const:`INADDR_ANY`, and the string
  86. ``'<broadcast>'`` represents :const:`INADDR_BROADCAST`. This behavior is not
  87. compatible with IPv6, therefore, you may want to avoid these if you intend
  88. to support IPv6 with your Python programs.
  89. If you use a hostname in the *host* portion of IPv4/v6 socket address, the
  90. program may show a nondeterministic behavior, as Python uses the first address
  91. returned from the DNS resolution. The socket address will be resolved
  92. differently into an actual IPv4/v6 address, depending on the results from DNS
  93. resolution and/or the host configuration. For deterministic behavior use a
  94. numeric address in *host* portion.
  95. All errors raise exceptions. The normal exceptions for invalid argument types
  96. and out-of-memory conditions can be raised; starting from Python 3.3, errors
  97. related to socket or address semantics raise :exc:`OSError` or one of its
  98. subclasses (they used to raise :exc:`socket.error`).
  99. Non-blocking mode is supported through :meth:`~socket.setblocking`. A
  100. generalization of this based on timeouts is supported through
  101. :meth:`~socket.settimeout`.
  102. Module contents
  103. ---------------
  104. The module :mod:`socket` exports the following elements.
  105. Exceptions
  106. ^^^^^^^^^^
  107. .. exception:: error
  108. A deprecated alias of :exc:`OSError`.
  109. .. versionchanged:: 3.3
  110. Following :pep:`3151`, this class was made an alias of :exc:`OSError`.
  111. .. exception:: herror
  112. A subclass of :exc:`OSError`, this exception is raised for
  113. address-related errors, i.e. for functions that use *h_errno* in the POSIX
  114. C API, including :func:`gethostbyname_ex` and :func:`gethostbyaddr`.
  115. The accompanying value is a pair ``(h_errno, string)`` representing an
  116. error returned by a library call. *h_errno* is a numeric value, while
  117. *string* represents the description of *h_errno*, as returned by the
  118. :c:func:`hstrerror` C function.
  119. .. versionchanged:: 3.3
  120. This class was made a subclass of :exc:`OSError`.
  121. .. exception:: gaierror
  122. A subclass of :exc:`OSError`, this exception is raised for
  123. address-related errors by :func:`getaddrinfo` and :func:`getnameinfo`.
  124. The accompanying value is a pair ``(error, string)`` representing an error
  125. returned by a library call. *string* represents the description of
  126. *error*, as returned by the :c:func:`gai_strerror` C function. The
  127. numeric *error* value will match one of the :const:`EAI_\*` constants
  128. defined in this module.
  129. .. versionchanged:: 3.3
  130. This class was made a subclass of :exc:`OSError`.
  131. .. exception:: timeout
  132. A subclass of :exc:`OSError`, this exception is raised when a timeout
  133. occurs on a socket which has had timeouts enabled via a prior call to
  134. :meth:`~socket.settimeout` (or implicitly through
  135. :func:`~socket.setdefaulttimeout`). The accompanying value is a string
  136. whose value is currently always "timed out".
  137. .. versionchanged:: 3.3
  138. This class was made a subclass of :exc:`OSError`.
  139. Constants
  140. ^^^^^^^^^
  141. .. data:: AF_UNIX
  142. AF_INET
  143. AF_INET6
  144. These constants represent the address (and protocol) families, used for the
  145. first argument to :func:`.socket`. If the :const:`AF_UNIX` constant is not
  146. defined then this protocol is unsupported. More constants may be available
  147. depending on the system.
  148. .. data:: SOCK_STREAM
  149. SOCK_DGRAM
  150. SOCK_RAW
  151. SOCK_RDM
  152. SOCK_SEQPACKET
  153. These constants represent the socket types, used for the second argument to
  154. :func:`.socket`. More constants may be available depending on the system.
  155. (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be generally
  156. useful.)
  157. .. data:: SOCK_CLOEXEC
  158. SOCK_NONBLOCK
  159. These two constants, if defined, can be combined with the socket types and
  160. allow you to set some flags atomically (thus avoiding possible race
  161. conditions and the need for separate calls).
  162. .. seealso::
  163. `Secure File Descriptor Handling <http://udrepper.livejournal.com/20407.html>`_
  164. for a more thorough explanation.
  165. Availability: Linux >= 2.6.27.
  166. .. versionadded:: 3.2
  167. .. data:: SO_*
  168. SOMAXCONN
  169. MSG_*
  170. SOL_*
  171. SCM_*
  172. IPPROTO_*
  173. IPPORT_*
  174. INADDR_*
  175. IP_*
  176. IPV6_*
  177. EAI_*
  178. AI_*
  179. NI_*
  180. TCP_*
  181. Many constants of these forms, documented in the Unix documentation on sockets
  182. and/or the IP protocol, are also defined in the socket module. They are
  183. generally used in arguments to the :meth:`setsockopt` and :meth:`getsockopt`
  184. methods of socket objects. In most cases, only those symbols that are defined
  185. in the Unix header files are defined; for a few symbols, default values are
  186. provided.
  187. .. data:: AF_CAN
  188. PF_CAN
  189. SOL_CAN_*
  190. CAN_*
  191. Many constants of these forms, documented in the Linux documentation, are
  192. also defined in the socket module.
  193. Availability: Linux >= 2.6.25.
  194. .. versionadded:: 3.3
  195. .. data:: AF_RDS
  196. PF_RDS
  197. SOL_RDS
  198. RDS_*
  199. Many constants of these forms, documented in the Linux documentation, are
  200. also defined in the socket module.
  201. Availability: Linux >= 2.6.30.
  202. .. versionadded:: 3.3
  203. .. data:: SIO_*
  204. RCVALL_*
  205. Constants for Windows' WSAIoctl(). The constants are used as arguments to the
  206. :meth:`~socket.socket.ioctl` method of socket objects.
  207. .. data:: TIPC_*
  208. TIPC related constants, matching the ones exported by the C socket API. See
  209. the TIPC documentation for more information.
  210. .. data:: has_ipv6
  211. This constant contains a boolean value which indicates if IPv6 is supported on
  212. this platform.
  213. Functions
  214. ^^^^^^^^^
  215. Creating sockets
  216. ''''''''''''''''
  217. The following functions all create :ref:`socket objects <socket-objects>`.
  218. .. function:: socket([family[, type[, proto]]])
  219. Create a new socket using the given address family, socket type and protocol
  220. number. The address family should be :const:`AF_INET` (the default),
  221. :const:`AF_INET6`, :const:`AF_UNIX`, :const:`AF_CAN` or :const:`AF_RDS`. The
  222. socket type should be :const:`SOCK_STREAM` (the default),
  223. :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other ``SOCK_``
  224. constants. The protocol number is usually zero and may be omitted in that
  225. case or :const:`CAN_RAW` in case the address family is :const:`AF_CAN`.
  226. .. versionchanged:: 3.3
  227. The AF_CAN family was added.
  228. The AF_RDS family was added.
  229. .. function:: socketpair([family[, type[, proto]]])
  230. Build a pair of connected socket objects using the given address family, socket
  231. type, and protocol number. Address family, socket type, and protocol number are
  232. as for the :func:`.socket` function above. The default family is :const:`AF_UNIX`
  233. if defined on the platform; otherwise, the default is :const:`AF_INET`.
  234. Availability: Unix.
  235. .. versionchanged:: 3.2
  236. The returned socket objects now support the whole socket API, rather
  237. than a subset.
  238. .. function:: create_connection(address[, timeout[, source_address]])
  239. Connect to a TCP service listening on the Internet *address* (a 2-tuple
  240. ``(host, port)``), and return the socket object. This is a higher-level
  241. function than :meth:`socket.connect`: if *host* is a non-numeric hostname,
  242. it will try to resolve it for both :data:`AF_INET` and :data:`AF_INET6`,
  243. and then try to connect to all possible addresses in turn until a
  244. connection succeeds. This makes it easy to write clients that are
  245. compatible to both IPv4 and IPv6.
  246. Passing the optional *timeout* parameter will set the timeout on the
  247. socket instance before attempting to connect. If no *timeout* is
  248. supplied, the global default timeout setting returned by
  249. :func:`getdefaulttimeout` is used.
  250. If supplied, *source_address* must be a 2-tuple ``(host, port)`` for the
  251. socket to bind to as its source address before connecting. If host or port
  252. are '' or 0 respectively the OS default behavior will be used.
  253. .. versionchanged:: 3.2
  254. *source_address* was added.
  255. .. versionchanged:: 3.2
  256. support for the :keyword:`with` statement was added.
  257. .. function:: fromfd(fd, family, type[, proto])
  258. Duplicate the file descriptor *fd* (an integer as returned by a file object's
  259. :meth:`fileno` method) and build a socket object from the result. Address
  260. family, socket type and protocol number are as for the :func:`.socket` function
  261. above. The file descriptor should refer to a socket, but this is not checked ---
  262. subsequent operations on the object may fail if the file descriptor is invalid.
  263. This function is rarely needed, but can be used to get or set socket options on
  264. a socket passed to a program as standard input or output (such as a server
  265. started by the Unix inet daemon). The socket is assumed to be in blocking mode.
  266. .. function:: fromshare(data)
  267. Instantiate a socket from data obtained from the :meth:`socket.share`
  268. method. The socket is assumed to be in blocking mode.
  269. Availability: Windows.
  270. .. versionadded:: 3.3
  271. .. data:: SocketType
  272. This is a Python type object that represents the socket object type. It is the
  273. same as ``type(socket(...))``.
  274. Other functions
  275. '''''''''''''''
  276. The :mod:`socket` module also offers various network-related services:
  277. .. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0)
  278. Translate the *host*/*port* argument into a sequence of 5-tuples that contain
  279. all the necessary arguments for creating a socket connected to that service.
  280. *host* is a domain name, a string representation of an IPv4/v6 address
  281. or ``None``. *port* is a string service name such as ``'http'``, a numeric
  282. port number or ``None``. By passing ``None`` as the value of *host*
  283. and *port*, you can pass ``NULL`` to the underlying C API.
  284. The *family*, *type* and *proto* arguments can be optionally specified
  285. in order to narrow the list of addresses returned. Passing zero as a
  286. value for each of these arguments selects the full range of results.
  287. The *flags* argument can be one or several of the ``AI_*`` constants,
  288. and will influence how results are computed and returned.
  289. For example, :const:`AI_NUMERICHOST` will disable domain name resolution
  290. and will raise an error if *host* is a domain name.
  291. The function returns a list of 5-tuples with the following structure:
  292. ``(family, type, proto, canonname, sockaddr)``
  293. In these tuples, *family*, *type*, *proto* are all integers and are
  294. meant to be passed to the :func:`.socket` function. *canonname* will be
  295. a string representing the canonical name of the *host* if
  296. :const:`AI_CANONNAME` is part of the *flags* argument; else *canonname*
  297. will be empty. *sockaddr* is a tuple describing a socket address, whose
  298. format depends on the returned *family* (a ``(address, port)`` 2-tuple for
  299. :const:`AF_INET`, a ``(address, port, flow info, scope id)`` 4-tuple for
  300. :const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect`
  301. method.
  302. The following example fetches address information for a hypothetical TCP
  303. connection to ``www.python.org`` on port 80 (results may differ on your
  304. system if IPv6 isn't enabled)::
  305. >>> socket.getaddrinfo("www.python.org", 80, proto=socket.SOL_TCP)
  306. [(2, 1, 6, '', ('82.94.164.162', 80)),
  307. (10, 1, 6, '', ('2001:888:2000:d::a2', 80, 0, 0))]
  308. .. versionchanged:: 3.2
  309. parameters can now be passed as single keyword arguments.
  310. .. function:: getfqdn([name])
  311. Return a fully qualified domain name for *name*. If *name* is omitted or empty,
  312. it is interpreted as the local host. To find the fully qualified name, the
  313. hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the
  314. host, if available. The first name which includes a period is selected. In
  315. case no fully qualified domain name is available, the hostname as returned by
  316. :func:`gethostname` is returned.
  317. .. function:: gethostbyname(hostname)
  318. Translate a host name to IPv4 address format. The IPv4 address is returned as a
  319. string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself
  320. it is returned unchanged. See :func:`gethostbyname_ex` for a more complete
  321. interface. :func:`gethostbyname` does not support IPv6 name resolution, and
  322. :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support.
  323. .. function:: gethostbyname_ex(hostname)
  324. Translate a host name to IPv4 address format, extended interface. Return a
  325. triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary
  326. host name responding to the given *ip_address*, *aliaslist* is a (possibly
  327. empty) list of alternative host names for the same address, and *ipaddrlist* is
  328. a list of IPv4 addresses for the same interface on the same host (often but not
  329. always a single address). :func:`gethostbyname_ex` does not support IPv6 name
  330. resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual
  331. stack support.
  332. .. function:: gethostname()
  333. Return a string containing the hostname of the machine where the Python
  334. interpreter is currently executing.
  335. If you want to know the current machine's IP address, you may want to use
  336. ``gethostbyname(gethostname())``. This operation assumes that there is a
  337. valid address-to-host mapping for the host, and the assumption does not
  338. always hold.
  339. Note: :func:`gethostname` doesn't always return the fully qualified domain
  340. name; use ``getfqdn()`` (see above).
  341. .. function:: gethostbyaddr(ip_address)
  342. Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the
  343. primary host name responding to the given *ip_address*, *aliaslist* is a
  344. (possibly empty) list of alternative host names for the same address, and
  345. *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same
  346. host (most likely containing only a single address). To find the fully qualified
  347. domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports
  348. both IPv4 and IPv6.
  349. .. function:: getnameinfo(sockaddr, flags)
  350. Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending
  351. on the settings of *flags*, the result can contain a fully-qualified domain name
  352. or numeric address representation in *host*. Similarly, *port* can contain a
  353. string port name or a numeric port number.
  354. .. function:: getprotobyname(protocolname)
  355. Translate an Internet protocol name (for example, ``'icmp'``) to a constant
  356. suitable for passing as the (optional) third argument to the :func:`.socket`
  357. function. This is usually only needed for sockets opened in "raw" mode
  358. (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen
  359. automatically if the protocol is omitted or zero.
  360. .. function:: getservbyname(servicename[, protocolname])
  361. Translate an Internet service name and protocol name to a port number for that
  362. service. The optional protocol name, if given, should be ``'tcp'`` or
  363. ``'udp'``, otherwise any protocol will match.
  364. .. function:: getservbyport(port[, protocolname])
  365. Translate an Internet port number and protocol name to a service name for that
  366. service. The optional protocol name, if given, should be ``'tcp'`` or
  367. ``'udp'``, otherwise any protocol will match.
  368. .. function:: ntohl(x)
  369. Convert 32-bit positive integers from network to host byte order. On machines
  370. where the host byte order is the same as network byte order, this is a no-op;
  371. otherwise, it performs a 4-byte swap operation.
  372. .. function:: ntohs(x)
  373. Convert 16-bit positive integers from network to host byte order. On machines
  374. where the host byte order is the same as network byte order, this is a no-op;
  375. otherwise, it performs a 2-byte swap operation.
  376. .. function:: htonl(x)
  377. Convert 32-bit positive integers from host to network byte order. On machines
  378. where the host byte order is the same as network byte order, this is a no-op;
  379. otherwise, it performs a 4-byte swap operation.
  380. .. function:: htons(x)
  381. Convert 16-bit positive integers from host to network byte order. On machines
  382. where the host byte order is the same as network byte order, this is a no-op;
  383. otherwise, it performs a 2-byte swap operation.
  384. .. function:: inet_aton(ip_string)
  385. Convert an IPv4 address from dotted-quad string format (for example,
  386. '123.45.67.89') to 32-bit packed binary format, as a bytes object four characters in
  387. length. This is useful when conversing with a program that uses the standard C
  388. library and needs objects of type :c:type:`struct in_addr`, which is the C type
  389. for the 32-bit packed binary this function returns.
  390. :func:`inet_aton` also accepts strings with less than three dots; see the
  391. Unix manual page :manpage:`inet(3)` for details.
  392. If the IPv4 address string passed to this function is invalid,
  393. :exc:`OSError` will be raised. Note that exactly what is valid depends on
  394. the underlying C implementation of :c:func:`inet_aton`.
  395. :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used
  396. instead for IPv4/v6 dual stack support.
  397. .. function:: inet_ntoa(packed_ip)
  398. Convert a 32-bit packed IPv4 address (a bytes object four characters in
  399. length) to its standard dotted-quad string representation (for example,
  400. '123.45.67.89'). This is useful when conversing with a program that uses the
  401. standard C library and needs objects of type :c:type:`struct in_addr`, which
  402. is the C type for the 32-bit packed binary data this function takes as an
  403. argument.
  404. If the byte sequence passed to this function is not exactly 4 bytes in
  405. length, :exc:`OSError` will be raised. :func:`inet_ntoa` does not
  406. support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual
  407. stack support.
  408. .. function:: inet_pton(address_family, ip_string)
  409. Convert an IP address from its family-specific string format to a packed,
  410. binary format. :func:`inet_pton` is useful when a library or network protocol
  411. calls for an object of type :c:type:`struct in_addr` (similar to
  412. :func:`inet_aton`) or :c:type:`struct in6_addr`.
  413. Supported values for *address_family* are currently :const:`AF_INET` and
  414. :const:`AF_INET6`. If the IP address string *ip_string* is invalid,
  415. :exc:`OSError` will be raised. Note that exactly what is valid depends on
  416. both the value of *address_family* and the underlying implementation of
  417. :c:func:`inet_pton`.
  418. Availability: Unix (maybe not all platforms).
  419. .. function:: inet_ntop(address_family, packed_ip)
  420. Convert a packed IP address (a bytes object of some number of characters) to its
  421. standard, family-specific string representation (for example, ``'7.10.0.5'`` or
  422. ``'5aef:2b::8'``). :func:`inet_ntop` is useful when a library or network protocol
  423. returns an object of type :c:type:`struct in_addr` (similar to :func:`inet_ntoa`)
  424. or :c:type:`struct in6_addr`.
  425. Supported values for *address_family* are currently :const:`AF_INET` and
  426. :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the
  427. specified address family, :exc:`ValueError` will be raised. A
  428. :exc:`OSError` is raised for errors from the call to :func:`inet_ntop`.
  429. Availability: Unix (maybe not all platforms).
  430. ..
  431. XXX: Are sendmsg(), recvmsg() and CMSG_*() available on any
  432. non-Unix platforms? The old (obsolete?) 4.2BSD form of the
  433. interface, in which struct msghdr has no msg_control or
  434. msg_controllen members, is not currently supported.
  435. .. function:: CMSG_LEN(length)
  436. Return the total length, without trailing padding, of an ancillary
  437. data item with associated data of the given *length*. This value
  438. can often be used as the buffer size for :meth:`~socket.recvmsg` to
  439. receive a single item of ancillary data, but :rfc:`3542` requires
  440. portable applications to use :func:`CMSG_SPACE` and thus include
  441. space for padding, even when the item will be the last in the
  442. buffer. Raises :exc:`OverflowError` if *length* is outside the
  443. permissible range of values.
  444. Availability: most Unix platforms, possibly others.
  445. .. versionadded:: 3.3
  446. .. function:: CMSG_SPACE(length)
  447. Return the buffer size needed for :meth:`~socket.recvmsg` to
  448. receive an ancillary data item with associated data of the given
  449. *length*, along with any trailing padding. The buffer space needed
  450. to receive multiple items is the sum of the :func:`CMSG_SPACE`
  451. values for their associated data lengths. Raises
  452. :exc:`OverflowError` if *length* is outside the permissible range
  453. of values.
  454. Note that some systems might support ancillary data without
  455. providing this function. Also note that setting the buffer size
  456. using the results of this function may not precisely limit the
  457. amount of ancillary data that can be received, since additional
  458. data may be able to fit into the padding area.
  459. Availability: most Unix platforms, possibly others.
  460. .. versionadded:: 3.3
  461. .. function:: getdefaulttimeout()
  462. Return the default timeout in seconds (float) for new socket objects. A value
  463. of ``None`` indicates that new socket objects have no timeout. When the socket
  464. module is first imported, the default is ``None``.
  465. .. function:: setdefaulttimeout(timeout)
  466. Set the default timeout in seconds (float) for new socket objects. When
  467. the socket module is first imported, the default is ``None``. See
  468. :meth:`~socket.settimeout` for possible values and their respective
  469. meanings.
  470. .. function:: sethostname(name)
  471. Set the machine's hostname to *name*. This will raise a
  472. :exc:`OSError` if you don't have enough rights.
  473. Availability: Unix.
  474. .. versionadded:: 3.3
  475. .. function:: if_nameindex()
  476. Return a list of network interface information
  477. (index int, name string) tuples.
  478. :exc:`OSError` if the system call fails.
  479. Availability: Unix.
  480. .. versionadded:: 3.3
  481. .. function:: if_nametoindex(if_name)
  482. Return a network interface index number corresponding to an
  483. interface name.
  484. :exc:`OSError` if no interface with the given name exists.
  485. Availability: Unix.
  486. .. versionadded:: 3.3
  487. .. function:: if_indextoname(if_index)
  488. Return a network interface name corresponding to a
  489. interface index number.
  490. :exc:`OSError` if no interface with the given index exists.
  491. Availability: Unix.
  492. .. versionadded:: 3.3
  493. .. _socket-objects:
  494. Socket Objects
  495. --------------
  496. Socket objects have the following methods. Except for
  497. :meth:`~socket.makefile`, these correspond to Unix system calls applicable
  498. to sockets.
  499. .. method:: socket.accept()
  500. Accept a connection. The socket must be bound to an address and listening for
  501. connections. The return value is a pair ``(conn, address)`` where *conn* is a
  502. *new* socket object usable to send and receive data on the connection, and
  503. *address* is the address bound to the socket on the other end of the connection.
  504. .. method:: socket.bind(address)
  505. Bind the socket to *address*. The socket must not already be bound. (The format
  506. of *address* depends on the address family --- see above.)
  507. .. method:: socket.close()
  508. Mark the socket closed. The underlying system resource (e.g. a file
  509. descriptor) is also closed when all file objects from :meth:`makefile()`
  510. are closed. Once that happens, all future operations on the socket
  511. object will fail. The remote end will receive no more data (after
  512. queued data is flushed).
  513. Sockets are automatically closed when they are garbage-collected, but
  514. it is recommended to :meth:`close` them explicitly, or to use a
  515. :keyword:`with` statement around them.
  516. .. note::
  517. :meth:`close()` releases the resource associated with a connection but
  518. does not necessarily close the connection immediately. If you want
  519. to close the connection in a timely fashion, call :meth:`shutdown()`
  520. before :meth:`close()`.
  521. .. method:: socket.connect(address)
  522. Connect to a remote socket at *address*. (The format of *address* depends on the
  523. address family --- see above.)
  524. .. method:: socket.connect_ex(address)
  525. Like ``connect(address)``, but return an error indicator instead of raising an
  526. exception for errors returned by the C-level :c:func:`connect` call (other
  527. problems, such as "host not found," can still raise exceptions). The error
  528. indicator is ``0`` if the operation succeeded, otherwise the value of the
  529. :c:data:`errno` variable. This is useful to support, for example, asynchronous
  530. connects.
  531. .. method:: socket.detach()
  532. Put the socket object into closed state without actually closing the
  533. underlying file descriptor. The file descriptor is returned, and can
  534. be reused for other purposes.
  535. .. versionadded:: 3.2
  536. .. method:: socket.fileno()
  537. Return the socket's file descriptor (a small integer). This is useful with
  538. :func:`select.select`.
  539. Under Windows the small integer returned by this method cannot be used where a
  540. file descriptor can be used (such as :func:`os.fdopen`). Unix does not have
  541. this limitation.
  542. .. method:: socket.getpeername()
  543. Return the remote address to which the socket is connected. This is useful to
  544. find out the port number of a remote IPv4/v6 socket, for instance. (The format
  545. of the address returned depends on the address family --- see above.) On some
  546. systems this function is not supported.
  547. .. method:: socket.getsockname()
  548. Return the socket's own address. This is useful to find out the port number of
  549. an IPv4/v6 socket, for instance. (The format of the address returned depends on
  550. the address family --- see above.)
  551. .. method:: socket.getsockopt(level, optname[, buflen])
  552. Return the value of the given socket option (see the Unix man page
  553. :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.)
  554. are defined in this module. If *buflen* is absent, an integer option is assumed
  555. and its integer value is returned by the function. If *buflen* is present, it
  556. specifies the maximum length of the buffer used to receive the option in, and
  557. this buffer is returned as a bytes object. It is up to the caller to decode the
  558. contents of the buffer (see the optional built-in module :mod:`struct` for a way
  559. to decode C structures encoded as byte strings).
  560. .. method:: socket.gettimeout()
  561. Return the timeout in seconds (float) associated with socket operations,
  562. or ``None`` if no timeout is set. This reflects the last call to
  563. :meth:`setblocking` or :meth:`settimeout`.
  564. .. method:: socket.ioctl(control, option)
  565. :platform: Windows
  566. The :meth:`ioctl` method is a limited interface to the WSAIoctl system
  567. interface. Please refer to the `Win32 documentation
  568. <http://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more
  569. information.
  570. On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl`
  571. functions may be used; they accept a socket object as their first argument.
  572. .. method:: socket.listen(backlog)
  573. Listen for connections made to the socket. The *backlog* argument specifies the
  574. maximum number of queued connections and should be at least 0; the maximum value
  575. is system-dependent (usually 5), the minimum value is forced to 0.
  576. .. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \
  577. errors=None, newline=None)
  578. .. index:: single: I/O control; buffering
  579. Return a :term:`file object` associated with the socket. The exact returned
  580. type depends on the arguments given to :meth:`makefile`. These arguments are
  581. interpreted the same way as by the built-in :func:`open` function.
  582. The socket must be in blocking mode; it can have a timeout, but the file
  583. object's internal buffer may end up in a inconsistent state if a timeout
  584. occurs.
  585. Closing the file object returned by :meth:`makefile` won't close the
  586. original socket unless all other file objects have been closed and
  587. :meth:`socket.close` has been called on the socket object.
  588. .. note::
  589. On Windows, the file-like object created by :meth:`makefile` cannot be
  590. used where a file object with a file descriptor is expected, such as the
  591. stream arguments of :meth:`subprocess.Popen`.
  592. .. method:: socket.recv(bufsize[, flags])
  593. Receive data from the socket. The return value is a bytes object representing the
  594. data received. The maximum amount of data to be received at once is specified
  595. by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of
  596. the optional argument *flags*; it defaults to zero.
  597. .. note::
  598. For best match with hardware and network realities, the value of *bufsize*
  599. should be a relatively small power of 2, for example, 4096.
  600. .. method:: socket.recvfrom(bufsize[, flags])
  601. Receive data from the socket. The return value is a pair ``(bytes, address)``
  602. where *bytes* is a bytes object representing the data received and *address* is the
  603. address of the socket sending the data. See the Unix manual page
  604. :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults
  605. to zero. (The format of *address* depends on the address family --- see above.)
  606. .. method:: socket.recvmsg(bufsize[, ancbufsize[, flags]])
  607. Receive normal data (up to *bufsize* bytes) and ancillary data from
  608. the socket. The *ancbufsize* argument sets the size in bytes of
  609. the internal buffer used to receive the ancillary data; it defaults
  610. to 0, meaning that no ancillary data will be received. Appropriate
  611. buffer sizes for ancillary data can be calculated using
  612. :func:`CMSG_SPACE` or :func:`CMSG_LEN`, and items which do not fit
  613. into the buffer might be truncated or discarded. The *flags*
  614. argument defaults to 0 and has the same meaning as for
  615. :meth:`recv`.
  616. The return value is a 4-tuple: ``(data, ancdata, msg_flags,
  617. address)``. The *data* item is a :class:`bytes` object holding the
  618. non-ancillary data received. The *ancdata* item is a list of zero
  619. or more tuples ``(cmsg_level, cmsg_type, cmsg_data)`` representing
  620. the ancillary data (control messages) received: *cmsg_level* and
  621. *cmsg_type* are integers specifying the protocol level and
  622. protocol-specific type respectively, and *cmsg_data* is a
  623. :class:`bytes` object holding the associated data. The *msg_flags*
  624. item is the bitwise OR of various flags indicating conditions on
  625. the received message; see your system documentation for details.
  626. If the receiving socket is unconnected, *address* is the address of
  627. the sending socket, if available; otherwise, its value is
  628. unspecified.
  629. On some systems, :meth:`sendmsg` and :meth:`recvmsg` can be used to
  630. pass file descriptors between processes over an :const:`AF_UNIX`
  631. socket. When this facility is used (it is often restricted to
  632. :const:`SOCK_STREAM` sockets), :meth:`recvmsg` will return, in its
  633. ancillary data, items of the form ``(socket.SOL_SOCKET,
  634. socket.SCM_RIGHTS, fds)``, where *fds* is a :class:`bytes` object
  635. representing the new file descriptors as a binary array of the
  636. native C :c:type:`int` type. If :meth:`recvmsg` raises an
  637. exception after the system call returns, it will first attempt to
  638. close any file descriptors received via this mechanism.
  639. Some systems do not indicate the truncated length of ancillary data
  640. items which have been only partially received. If an item appears
  641. to extend beyond the end of the buffer, :meth:`recvmsg` will issue
  642. a :exc:`RuntimeWarning`, and will return the part of it which is
  643. inside the buffer provided it has not been truncated before the
  644. start of its associated data.
  645. On systems which support the :const:`SCM_RIGHTS` mechanism, the
  646. following function will receive up to *maxfds* file descriptors,
  647. returning the message data and a list containing the descriptors
  648. (while ignoring unexpected conditions such as unrelated control
  649. messages being received). See also :meth:`sendmsg`. ::
  650. import socket, array
  651. def recv_fds(sock, msglen, maxfds):
  652. fds = array.array("i") # Array of ints
  653. msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize))
  654. for cmsg_level, cmsg_type, cmsg_data in ancdata:
  655. if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS):
  656. # Append data, ignoring any truncated integers at the end.
  657. fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])
  658. return msg, list(fds)
  659. Availability: most Unix platforms, possibly others.
  660. .. versionadded:: 3.3
  661. .. method:: socket.recvmsg_into(buffers[, ancbufsize[, flags]])
  662. Receive normal data and ancillary data from the socket, behaving as
  663. :meth:`recvmsg` would, but scatter the non-ancillary data into a
  664. series of buffers instead of returning a new bytes object. The
  665. *buffers* argument must be an iterable of objects that export
  666. writable buffers (e.g. :class:`bytearray` objects); these will be
  667. filled with successive chunks of the non-ancillary data until it
  668. has all been written or there are no more buffers. The operating
  669. system may set a limit (:func:`~os.sysconf` value ``SC_IOV_MAX``)
  670. on the number of buffers that can be used. The *ancbufsize* and
  671. *flags* arguments have the same meaning as for :meth:`recvmsg`.
  672. The return value is a 4-tuple: ``(nbytes, ancdata, msg_flags,
  673. address)``, where *nbytes* is the total number of bytes of
  674. non-ancillary data written into the buffers, and *ancdata*,
  675. *msg_flags* and *address* are the same as for :meth:`recvmsg`.
  676. Example::
  677. >>> import socket
  678. >>> s1, s2 = socket.socketpair()
  679. >>> b1 = bytearray(b'----')
  680. >>> b2 = bytearray(b'0123456789')
  681. >>> b3 = bytearray(b'--------------')
  682. >>> s1.send(b'Mary had a little lamb')
  683. 22
  684. >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3])
  685. (22, [], 0, None)
  686. >>> [b1, b2, b3]
  687. [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')]
  688. Availability: most Unix platforms, possibly others.
  689. .. versionadded:: 3.3
  690. .. method:: socket.recvfrom_into(buffer[, nbytes[, flags]])
  691. Receive data from the socket, writing it into *buffer* instead of creating a
  692. new bytestring. The return value is a pair ``(nbytes, address)`` where *nbytes* is
  693. the number of bytes received and *address* is the address of the socket sending
  694. the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the
  695. optional argument *flags*; it defaults to zero. (The format of *address*
  696. depends on the address family --- see above.)
  697. .. method:: socket.recv_into(buffer[, nbytes[, flags]])
  698. Receive up to *nbytes* bytes from the socket, storing the data into a buffer
  699. rather than creating a new bytestring. If *nbytes* is not specified (or 0),
  700. receive up to the size available in the given buffer. Returns the number of
  701. bytes received. See the Unix manual page :manpage:`recv(2)` for the meaning
  702. of the optional argument *flags*; it defaults to zero.
  703. .. method:: socket.send(bytes[, flags])
  704. Send data to the socket. The socket must be connected to a remote socket. The
  705. optional *flags* argument has the same meaning as for :meth:`recv` above.
  706. Returns the number of bytes sent. Applications are responsible for checking that
  707. all data has been sent; if only some of the data was transmitted, the
  708. application needs to attempt delivery of the remaining data. For further
  709. information on this topic, consult the :ref:`socket-howto`.
  710. .. method:: socket.sendall(bytes[, flags])
  711. Send data to the socket. The socket must be connected to a remote socket. The
  712. optional *flags* argument has the same meaning as for :meth:`recv` above.
  713. Unlike :meth:`send`, this method continues to send data from *bytes* until
  714. either all data has been sent or an error occurs. ``None`` is returned on
  715. success. On error, an exception is raised, and there is no way to determine how
  716. much data, if any, was successfully sent.
  717. .. method:: socket.sendto(bytes, address)
  718. socket.sendto(bytes, flags, address)
  719. Send data to the socket. The socket should not be connected to a remote socket,
  720. since the destination socket is specified by *address*. The optional *flags*
  721. argument has the same meaning as for :meth:`recv` above. Return the number of
  722. bytes sent. (The format of *address* depends on the address family --- see
  723. above.)
  724. .. method:: socket.sendmsg(buffers[, ancdata[, flags[, address]]])
  725. Send normal and ancillary data to the socket, gathering the
  726. non-ancillary data from a series of buffers and concatenating it
  727. into a single message. The *buffers* argument specifies the
  728. non-ancillary data as an iterable of buffer-compatible objects
  729. (e.g. :class:`bytes` objects); the operating system may set a limit
  730. (:func:`~os.sysconf` value ``SC_IOV_MAX``) on the number of buffers
  731. that can be used. The *ancdata* argument specifies the ancillary
  732. data (control messages) as an iterable of zero or more tuples
  733. ``(cmsg_level, cmsg_type, cmsg_data)``, where *cmsg_level* and
  734. *cmsg_type* are integers specifying the protocol level and
  735. protocol-specific type respectively, and *cmsg_data* is a
  736. buffer-compatible object holding the associated data. Note that
  737. some systems (in particular, systems without :func:`CMSG_SPACE`)
  738. might support sending only one control message per call. The
  739. *flags* argument defaults to 0 and has the same meaning as for
  740. :meth:`send`. If *address* is supplied and not ``None``, it sets a
  741. destination address for the message. The return value is the
  742. number of bytes of non-ancillary data sent.
  743. The following function sends the list of file descriptors *fds*
  744. over an :const:`AF_UNIX` socket, on systems which support the
  745. :const:`SCM_RIGHTS` mechanism. See also :meth:`recvmsg`. ::
  746. import socket, array
  747. def send_fds(sock, msg, fds):
  748. return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))])
  749. Availability: most Unix platforms, possibly others.
  750. .. versionadded:: 3.3
  751. .. method:: socket.setblocking(flag)
  752. Set blocking or non-blocking mode of the socket: if *flag* is false, the
  753. socket is set to non-blocking, else to blocking mode.
  754. This method is a shorthand for certain :meth:`~socket.settimeout` calls:
  755. * ``sock.setblocking(True)`` is equivalent to ``sock.settimeout(None)``
  756. * ``sock.setblocking(False)`` is equivalent to ``sock.settimeout(0.0)``
  757. .. method:: socket.settimeout(value)
  758. Set a timeout on blocking socket operations. The *value* argument can be a
  759. nonnegative floating point number expressing seconds, or ``None``.
  760. If a non-zero value is given, subsequent socket operations will raise a
  761. :exc:`timeout` exception if the timeout period *value* has elapsed before
  762. the operation has completed. If zero is given, the socket is put in
  763. non-blocking mode. If ``None`` is given, the socket is put in blocking mode.
  764. For further information, please consult the :ref:`notes on socket timeouts <socket-timeouts>`.
  765. .. method:: socket.setsockopt(level, optname, value)
  766. .. index:: module: struct
  767. Set the value of the given socket option (see the Unix manual page
  768. :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the
  769. :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a
  770. bytes object representing a buffer. In the latter case it is up to the caller to
  771. ensure that the bytestring contains the proper bits (see the optional built-in
  772. module :mod:`struct` for a way to encode C structures as bytestrings).
  773. .. method:: socket.shutdown(how)
  774. Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`,
  775. further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends
  776. are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are
  777. disallowed.
  778. .. method:: socket.share(process_id)
  779. Duplicate a socket and prepare it for sharing with a target process. The
  780. target process must be provided with *process_id*. The resulting bytes object
  781. can then be passed to the target process using some form of interprocess
  782. communication and the socket can be recreated there using :func:`fromshare`.
  783. Once this method has been called, it is safe to close the socket since
  784. the operating system has already duplicated it for the target process.
  785. Availability: Windows.
  786. .. versionadded:: 3.3
  787. Note that there are no methods :meth:`read` or :meth:`write`; use
  788. :meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead.
  789. Socket objects also have these (read-only) attributes that correspond to the
  790. values given to the :class:`socket` constructor.
  791. .. attribute:: socket.family
  792. The socket family.
  793. .. attribute:: socket.type
  794. The socket type.
  795. .. attribute:: socket.proto
  796. The socket protocol.
  797. .. _socket-timeouts:
  798. Notes on socket timeouts
  799. ------------------------
  800. A socket object can be in one of three modes: blocking, non-blocking, or
  801. timeout. Sockets are by default always created in blocking mode, but this
  802. can be changed by calling :func:`setdefaulttimeout`.
  803. * In *blocking mode*, operations block until complete or the system returns
  804. an error (such as connection timed out).
  805. * In *non-blocking mode*, operations fail (with an error that is unfortunately
  806. system-dependent) if they cannot be completed immediately: functions from the
  807. :mod:`select` can be used to know when and whether a socket is available for
  808. reading or writing.
  809. * In *timeout mode*, operations fail if they cannot be completed within the
  810. timeout specified for the socket (they raise a :exc:`timeout` exception)
  811. or if the system returns an error.
  812. .. note::
  813. At the operating system level, sockets in *timeout mode* are internally set
  814. in non-blocking mode. Also, the blocking and timeout modes are shared between
  815. file descriptors and socket objects that refer to the same network endpoint.
  816. This implementation detail can have visible consequences if e.g. you decide
  817. to use the :meth:`~socket.fileno()` of a socket.
  818. Timeouts and the ``connect`` method
  819. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  820. The :meth:`~socket.connect` operation is also subject to the timeout
  821. setting, and in general it is recommended to call :meth:`~socket.settimeout`
  822. before calling :meth:`~socket.connect` or pass a timeout parameter to
  823. :meth:`create_connection`. However, the system network stack may also
  824. return a connection timeout error of its own regardless of any Python socket
  825. timeout setting.
  826. Timeouts and the ``accept`` method
  827. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  828. If :func:`getdefaulttimeout` is not :const:`None`, sockets returned by
  829. the :meth:`~socket.accept` method inherit that timeout. Otherwise, the
  830. behaviour depends on settings of the listening socket:
  831. * if the listening socket is in *blocking mode* or in *timeout mode*,
  832. the socket returned by :meth:`~socket.accept` is in *blocking mode*;
  833. * if the listening socket is in *non-blocking mode*, whether the socket
  834. returned by :meth:`~socket.accept` is in blocking or non-blocking mode
  835. is operating system-dependent. If you want to ensure cross-platform
  836. behaviour, it is recommended you manually override this setting.
  837. .. _socket-example:
  838. Example
  839. -------
  840. Here are four minimal example programs using the TCP/IP protocol: a server that
  841. echoes all data that it receives back (servicing only one client), and a client
  842. using it. Note that a server must perform the sequence :func:`.socket`,
  843. :meth:`~socket.bind`, :meth:`~socket.listen`, :meth:`~socket.accept` (possibly
  844. repeating the :meth:`~socket.accept` to service more than one client), while a
  845. client only needs the sequence :func:`.socket`, :meth:`~socket.connect`. Also
  846. note that the server does not :meth:`~socket.sendall`/:meth:`~socket.recv` on
  847. the socket it is listening on but on the new socket returned by
  848. :meth:`~socket.accept`.
  849. The first two examples support IPv4 only. ::
  850. # Echo server program
  851. import socket
  852. HOST = '' # Symbolic name meaning all available interfaces
  853. PORT = 50007 # Arbitrary non-privileged port
  854. s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  855. s.bind((HOST, PORT))
  856. s.listen(1)
  857. conn, addr = s.accept()
  858. print('Connected by', addr)
  859. while True:
  860. data = conn.recv(1024)
  861. if not data: break
  862. conn.sendall(data)
  863. conn.close()
  864. ::
  865. # Echo client program
  866. import socket
  867. HOST = 'daring.cwi.nl' # The remote host
  868. PORT = 50007 # The same port as used by the server
  869. s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  870. s.connect((HOST, PORT))
  871. s.sendall(b'Hello, world')
  872. data = s.recv(1024)
  873. s.close()
  874. print('Received', repr(data))
  875. The next two examples are identical to the above two, but support both IPv4 and
  876. IPv6. The server side will listen to the first address family available (it
  877. should listen to both instead). On most of IPv6-ready systems, IPv6 will take
  878. precedence and the server may not accept IPv4 traffic. The client side will try
  879. to connect to the all addresses returned as a result of the name resolution, and
  880. sends traffic to the first one connected successfully. ::
  881. # Echo server program
  882. import socket
  883. import sys
  884. HOST = None # Symbolic name meaning all available interfaces
  885. PORT = 50007 # Arbitrary non-privileged port
  886. s = None
  887. for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC,
  888. socket.SOCK_STREAM, 0, socket.AI_PASSIVE):
  889. af, socktype, proto, canonname, sa = res
  890. try:
  891. s = socket.socket(af, socktype, proto)
  892. except OSError as msg:
  893. s = None
  894. continue
  895. try:
  896. s.bind(sa)
  897. s.listen(1)
  898. except OSError as msg:
  899. s.close()
  900. s = None
  901. continue
  902. break
  903. if s is None:
  904. print('could not open socket')
  905. sys.exit(1)
  906. conn, addr = s.accept()
  907. print('Connected by', addr)
  908. while True:
  909. data = conn.recv(1024)
  910. if not data: break
  911. conn.send(data)
  912. conn.close()
  913. ::
  914. # Echo client program
  915. import socket
  916. import sys
  917. HOST = 'daring.cwi.nl' # The remote host
  918. PORT = 50007 # The same port as used by the server
  919. s = None
  920. for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM):
  921. af, socktype, proto, canonname, sa = res
  922. try:
  923. s = socket.socket(af, socktype, proto)
  924. except OSError as msg:
  925. s = None
  926. continue
  927. try:
  928. s.connect(sa)
  929. except OSError as msg:
  930. s.close()
  931. s = None
  932. continue
  933. break
  934. if s is None:
  935. print('could not open socket')
  936. sys.exit(1)
  937. s.sendall(b'Hello, world')
  938. data = s.recv(1024)
  939. s.close()
  940. print('Received', repr(data))
  941. The next example shows how to write a very simple network sniffer with raw
  942. sockets on Windows. The example requires administrator privileges to modify
  943. the interface::
  944. import socket
  945. # the public network interface
  946. HOST = socket.gethostbyname(socket.gethostname())
  947. # create a raw socket and bind it to the public interface
  948. s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP)
  949. s.bind((HOST, 0))
  950. # Include IP headers
  951. s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)
  952. # receive all packages
  953. s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)
  954. # receive a package
  955. print(s.recvfrom(65565))
  956. # disabled promiscuous mode
  957. s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)
  958. The last example shows how to use the socket interface to communicate to a CAN
  959. network. This example might require special priviledge::
  960. import socket
  961. import struct
  962. # CAN frame packing/unpacking (see 'struct can_frame' in <linux/can.h>)
  963. can_frame_fmt = "=IB3x8s"
  964. can_frame_size = struct.calcsize(can_frame_fmt)
  965. def build_can_frame(can_id, data):
  966. can_dlc = len(data)
  967. data = data.ljust(8, b'\x00')
  968. return struct.pack(can_frame_fmt, can_id, can_dlc, data)
  969. def dissect_can_frame(frame):
  970. can_id, can_dlc, data = struct.unpack(can_frame_fmt, frame)
  971. return (can_id, can_dlc, data[:can_dlc])
  972. # create a raw socket and bind it to the 'vcan0' interface
  973. s = socket.socket(socket.AF_CAN, socket.SOCK_RAW, socket.CAN_RAW)
  974. s.bind(('vcan0',))
  975. while True:
  976. cf, addr = s.recvfrom(can_frame_size)
  977. print('Received: can_id=%x, can_dlc=%x, data=%s' % dissect_can_frame(cf))
  978. try:
  979. s.send(cf)
  980. except OSError:
  981. print('Error sending CAN frame')
  982. try:
  983. s.send(build_can_frame(0x01, b'\x01\x02\x03'))
  984. except OSError:
  985. print('Error sending CAN frame')
  986. Running an example several times with too small delay between executions, could
  987. lead to this error::
  988. OSError: [Errno 98] Address already in use
  989. This is because the previous execution has left the socket in a ``TIME_WAIT``
  990. state, and can't be immediately reused.
  991. There is a :mod:`socket` flag to set, in order to prevent this,
  992. :data:`socket.SO_REUSEADDR`::
  993. s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  994. s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
  995. s.bind((HOST, PORT))
  996. the :data:`SO_REUSEADDR` flag tells the kernel to reuse a local socket in
  997. ``TIME_WAIT`` state, without waiting for its natural timeout to expire.
  998. .. seealso::
  999. For an introduction to socket programming (in C), see the following papers:
  1000. - *An Introductory 4.3BSD Interprocess Communication Tutorial*, by Stuart Sechrest
  1001. - *An Advanced 4.3BSD Interprocess Communication Tutorial*, by Samuel J. Leffler et
  1002. al,
  1003. both in the UNIX Programmer's Manual, Supplementary Documents 1 (sections
  1004. PS1:7 and PS1:8). The platform-specific reference material for the various
  1005. socket-related system calls are also a valuable source of information on the
  1006. details of socket semantics. For Unix, refer to the manual pages; for Windows,
  1007. see the WinSock (or Winsock 2) specification. For IPv6-ready APIs, readers may
  1008. want to refer to :rfc:`3493` titled Basic Socket Interface Extensions for IPv6.