diff --git a/Doc/library/socket.rst b/Doc/library/socket.rst index 1eb183ee381..40e6d197f86 100644 --- a/Doc/library/socket.rst +++ b/Doc/library/socket.rst @@ -1,906 +1,906 @@ - -:mod:`socket` --- Low-level networking interface -================================================ - -.. module:: socket - :synopsis: Low-level networking interface. - - -This module provides access to the BSD *socket* interface. It is available on -all modern Unix systems, Windows, Mac OS X, BeOS, OS/2, and probably additional -platforms. - -.. note:: - - Some behavior may be platform dependent, since calls are made to the operating - system socket APIs. - -For an introduction to socket programming (in C), see the following papers: An -Introductory 4.3BSD Interprocess Communication Tutorial, by Stuart Sechrest and -An Advanced 4.3BSD Interprocess Communication Tutorial, by Samuel J. Leffler et -al, both in the UNIX Programmer's Manual, Supplementary Documents 1 (sections -PS1:7 and PS1:8). The platform-specific reference material for the various -socket-related system calls are also a valuable source of information on the -details of socket semantics. For Unix, refer to the manual pages; for Windows, -see the WinSock (or Winsock 2) specification. For IPv6-ready APIs, readers may -want to refer to :rfc:`2553` titled Basic Socket Interface Extensions for IPv6. - -.. index:: object: socket - -The Python interface is a straightforward transliteration of the Unix system -call and library interface for sockets to Python's object-oriented style: the -:func:`socket` function returns a :dfn:`socket object` whose methods implement -the various socket system calls. Parameter types are somewhat higher-level than -in the C interface: as with :meth:`read` and :meth:`write` operations on Python -files, buffer allocation on receive operations is automatic, and buffer length -is implicit on send operations. - -Socket addresses are represented as follows: A single string is used for the -:const:`AF_UNIX` address family. A pair ``(host, port)`` is used for the -:const:`AF_INET` address family, where *host* is a string representing either a -hostname in Internet domain notation like ``'daring.cwi.nl'`` or an IPv4 address -like ``'100.50.200.5'``, and *port* is an integral port number. For -:const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo, -scopeid)`` is used, where *flowinfo* and *scopeid* represents ``sin6_flowinfo`` -and ``sin6_scope_id`` member in :const:`struct sockaddr_in6` in C. For -:mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for -backward compatibility. Note, however, omission of *scopeid* can cause problems -in manipulating scoped IPv6 addresses. Other address families are currently not -supported. The address format required by a particular socket object is -automatically selected based on the address family specified when the socket -object was created. - -For IPv4 addresses, two special forms are accepted instead of a host address: -the empty string represents :const:`INADDR_ANY`, and the string -``''`` represents :const:`INADDR_BROADCAST`. The behavior is not -available for IPv6 for backward compatibility, therefore, you may want to avoid -these if you intend to support IPv6 with your Python programs. - -If you use a hostname in the *host* portion of IPv4/v6 socket address, the -program may show a nondeterministic behavior, as Python uses the first address -returned from the DNS resolution. The socket address will be resolved -differently into an actual IPv4/v6 address, depending on the results from DNS -resolution and/or the host configuration. For deterministic behavior use a -numeric address in *host* portion. - -.. versionadded:: 2.5 - AF_NETLINK sockets are represented as pairs ``pid, groups``. - -All errors raise exceptions. The normal exceptions for invalid argument types -and out-of-memory conditions can be raised; errors related to socket or address -semantics raise the error :exc:`socket.error`. - -Non-blocking mode is supported through :meth:`setblocking`. A generalization of -this based on timeouts is supported through :meth:`settimeout`. - -The module :mod:`socket` exports the following constants and functions: - - -.. exception:: error - - .. index:: module: errno - - This exception is raised for socket-related errors. The accompanying value is - either a string telling what went wrong or a pair ``(errno, string)`` - representing an error returned by a system call, similar to the value - accompanying :exc:`os.error`. See the module :mod:`errno`, which contains names - for the error codes defined by the underlying operating system. - - .. versionchanged:: 2.6 - :exc:`socket.error` is now a child class of :exc:`IOError`. - - -.. exception:: herror - - This exception is raised for address-related errors, i.e. for functions that use - *h_errno* in the C API, including :func:`gethostbyname_ex` and - :func:`gethostbyaddr`. - - The accompanying value is a pair ``(h_errno, string)`` representing an error - returned by a library call. *string* represents the description of *h_errno*, as - returned by the :cfunc:`hstrerror` C function. - - -.. exception:: gaierror - - This exception is raised for address-related errors, for :func:`getaddrinfo` and - :func:`getnameinfo`. The accompanying value is a pair ``(error, string)`` - representing an error returned by a library call. *string* represents the - description of *error*, as returned by the :cfunc:`gai_strerror` C function. The - *error* value will match one of the :const:`EAI_\*` constants defined in this - module. - - -.. exception:: timeout - - This exception is raised when a timeout occurs on a socket which has had - timeouts enabled via a prior call to :meth:`settimeout`. The accompanying value - is a string whose value is currently always "timed out". - - .. versionadded:: 2.3 - - -.. data:: AF_UNIX - AF_INET - AF_INET6 - - These constants represent the address (and protocol) families, used for the - first argument to :func:`socket`. If the :const:`AF_UNIX` constant is not - defined then this protocol is unsupported. - - -.. data:: SOCK_STREAM - SOCK_DGRAM - SOCK_RAW - SOCK_RDM - SOCK_SEQPACKET - - These constants represent the socket types, used for the second argument to - :func:`socket`. (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be - generally useful.) - - -.. data:: SO_* - SOMAXCONN - MSG_* - SOL_* - IPPROTO_* - IPPORT_* - INADDR_* - IP_* - IPV6_* - EAI_* - AI_* - NI_* - TCP_* - - Many constants of these forms, documented in the Unix documentation on sockets - and/or the IP protocol, are also defined in the socket module. They are - generally used in arguments to the :meth:`setsockopt` and :meth:`getsockopt` - methods of socket objects. In most cases, only those symbols that are defined - in the Unix header files are defined; for a few symbols, default values are - provided. - -.. data:: SIO_* - RCVALL_* - - Constants for Windows' WSAIoctl(). The constants are used as arguments to the - :meth:`ioctl` method of socket objects. - - .. versionadded:: 2.6 - - -.. data:: has_ipv6 - - This constant contains a boolean value which indicates if IPv6 is supported on - this platform. - - .. versionadded:: 2.3 - - -.. function:: create_connection(address[, timeout]) - - Connects to the *address* received (as usual, a ``(host, port)`` pair), with an - optional timeout for the connection. Especially useful for higher-level - protocols, it is not normally used directly from application-level code. - Passing the optional *timeout* parameter will set the timeout on the socket - instance (if it is not given or ``None``, the global default timeout setting is - used). - - .. versionadded:: 2.6 - - -.. function:: getaddrinfo(host, port[, family[, socktype[, proto[, flags]]]]) - - Resolves the *host*/*port* argument, into a sequence of 5-tuples that contain - all the necessary argument for the sockets manipulation. *host* is a domain - name, a string representation of IPv4/v6 address or ``None``. *port* is a string - service name (like ``'http'``), a numeric port number or ``None``. - - The rest of the arguments are optional and must be numeric if specified. For - *host* and *port*, by passing either an empty string or ``None``, you can pass - ``NULL`` to the C API. The :func:`getaddrinfo` function returns a list of - 5-tuples with the following structure: - - ``(family, socktype, proto, canonname, sockaddr)`` - - *family*, *socktype*, *proto* are all integer and are meant to be passed to the - :func:`socket` function. *canonname* is a string representing the canonical name - of the *host*. It can be a numeric IPv4/v6 address when :const:`AI_CANONNAME` is - specified for a numeric *host*. *sockaddr* is a tuple describing a socket - address, as described above. See the source for :mod:`socket` and other - library modules for a typical usage of the function. - - .. versionadded:: 2.2 - - -.. function:: getfqdn([name]) - - Return a fully qualified domain name for *name*. If *name* is omitted or empty, - it is interpreted as the local host. To find the fully qualified name, the - hostname returned by :func:`gethostbyaddr` is checked, then aliases for the - host, if available. The first name which includes a period is selected. In - case no fully qualified domain name is available, the hostname as returned by - :func:`gethostname` is returned. - - .. versionadded:: 2.0 - - -.. function:: gethostbyname(hostname) - - Translate a host name to IPv4 address format. The IPv4 address is returned as a - string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself - it is returned unchanged. See :func:`gethostbyname_ex` for a more complete - interface. :func:`gethostbyname` does not support IPv6 name resolution, and - :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support. - - -.. function:: gethostbyname_ex(hostname) - - Translate a host name to IPv4 address format, extended interface. Return a - triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary - host name responding to the given *ip_address*, *aliaslist* is a (possibly - empty) list of alternative host names for the same address, and *ipaddrlist* is - a list of IPv4 addresses for the same interface on the same host (often but not - always a single address). :func:`gethostbyname_ex` does not support IPv6 name - resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual - stack support. - - -.. function:: gethostname() - - Return a string containing the hostname of the machine where the Python - interpreter is currently executing. If you want to know the current machine's IP - address, you may want to use ``gethostbyname(gethostname())``. This operation - assumes that there is a valid address-to-host mapping for the host, and the - assumption does not always hold. Note: :func:`gethostname` doesn't always return - the fully qualified domain name; use ``getfqdn()`` (see above). - - -.. function:: gethostbyaddr(ip_address) - - Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the - primary host name responding to the given *ip_address*, *aliaslist* is a - (possibly empty) list of alternative host names for the same address, and - *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same - host (most likely containing only a single address). To find the fully qualified - domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports - both IPv4 and IPv6. - - -.. function:: getnameinfo(sockaddr, flags) - - Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending - on the settings of *flags*, the result can contain a fully-qualified domain name - or numeric address representation in *host*. Similarly, *port* can contain a - string port name or a numeric port number. - - .. versionadded:: 2.2 - - -.. function:: getprotobyname(protocolname) - - Translate an Internet protocol name (for example, ``'icmp'``) to a constant - suitable for passing as the (optional) third argument to the :func:`socket` - function. This is usually only needed for sockets opened in "raw" mode - (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen - automatically if the protocol is omitted or zero. - - -.. function:: getservbyname(servicename[, protocolname]) - - Translate an Internet service name and protocol name to a port number for that - service. The optional protocol name, if given, should be ``'tcp'`` or - ``'udp'``, otherwise any protocol will match. - - -.. function:: getservbyport(port[, protocolname]) - - Translate an Internet port number and protocol name to a service name for that - service. The optional protocol name, if given, should be ``'tcp'`` or - ``'udp'``, otherwise any protocol will match. - - -.. function:: socket([family[, type[, proto]]]) - - Create a new socket using the given address family, socket type and protocol - number. The address family should be :const:`AF_INET` (the default), - :const:`AF_INET6` or :const:`AF_UNIX`. The socket type should be - :const:`SOCK_STREAM` (the default), :const:`SOCK_DGRAM` or perhaps one of the - other ``SOCK_`` constants. The protocol number is usually zero and may be - omitted in that case. - - -.. function:: socketpair([family[, type[, proto]]]) - - Build a pair of connected socket objects using the given address family, socket - type, and protocol number. Address family, socket type, and protocol number are - as for the :func:`socket` function above. The default family is :const:`AF_UNIX` - if defined on the platform; otherwise, the default is :const:`AF_INET`. - Availability: Unix. - - .. versionadded:: 2.4 - - -.. function:: fromfd(fd, family, type[, proto]) - - Duplicate the file descriptor *fd* (an integer as returned by a file object's - :meth:`fileno` method) and build a socket object from the result. Address - family, socket type and protocol number are as for the :func:`socket` function - above. The file descriptor should refer to a socket, but this is not checked --- - subsequent operations on the object may fail if the file descriptor is invalid. - This function is rarely needed, but can be used to get or set socket options on - a socket passed to a program as standard input or output (such as a server - started by the Unix inet daemon). The socket is assumed to be in blocking mode. - Availability: Unix. - - -.. function:: ntohl(x) - - Convert 32-bit positive integers from network to host byte order. On machines - where the host byte order is the same as network byte order, this is a no-op; - otherwise, it performs a 4-byte swap operation. - - -.. function:: ntohs(x) - - Convert 16-bit positive integers from network to host byte order. On machines - where the host byte order is the same as network byte order, this is a no-op; - otherwise, it performs a 2-byte swap operation. - - -.. function:: htonl(x) - - Convert 32-bit positive integers from host to network byte order. On machines - where the host byte order is the same as network byte order, this is a no-op; - otherwise, it performs a 4-byte swap operation. - - -.. function:: htons(x) - - Convert 16-bit positive integers from host to network byte order. On machines - where the host byte order is the same as network byte order, this is a no-op; - otherwise, it performs a 2-byte swap operation. - - -.. function:: inet_aton(ip_string) - - Convert an IPv4 address from dotted-quad string format (for example, - '123.45.67.89') to 32-bit packed binary format, as a string four characters in - length. This is useful when conversing with a program that uses the standard C - library and needs objects of type :ctype:`struct in_addr`, which is the C type - for the 32-bit packed binary this function returns. - - If the IPv4 address string passed to this function is invalid, - :exc:`socket.error` will be raised. Note that exactly what is valid depends on - the underlying C implementation of :cfunc:`inet_aton`. - - :func:`inet_aton` does not support IPv6, and :func:`getnameinfo` should be used - instead for IPv4/v6 dual stack support. - - -.. function:: inet_ntoa(packed_ip) - - Convert a 32-bit packed IPv4 address (a string four characters in length) to its - standard dotted-quad string representation (for example, '123.45.67.89'). This - is useful when conversing with a program that uses the standard C library and - needs objects of type :ctype:`struct in_addr`, which is the C type for the - 32-bit packed binary data this function takes as an argument. - - If the string passed to this function is not exactly 4 bytes in length, - :exc:`socket.error` will be raised. :func:`inet_ntoa` does not support IPv6, and - :func:`getnameinfo` should be used instead for IPv4/v6 dual stack support. - - -.. function:: inet_pton(address_family, ip_string) - - Convert an IP address from its family-specific string format to a packed, binary - format. :func:`inet_pton` is useful when a library or network protocol calls for - an object of type :ctype:`struct in_addr` (similar to :func:`inet_aton`) or - :ctype:`struct in6_addr`. - - Supported values for *address_family* are currently :const:`AF_INET` and - :const:`AF_INET6`. If the IP address string *ip_string* is invalid, - :exc:`socket.error` will be raised. Note that exactly what is valid depends on - both the value of *address_family* and the underlying implementation of - :cfunc:`inet_pton`. - - Availability: Unix (maybe not all platforms). - - .. versionadded:: 2.3 - - -.. function:: inet_ntop(address_family, packed_ip) - - Convert a packed IP address (a string of some number of characters) to its - standard, family-specific string representation (for example, ``'7.10.0.5'`` or - ``'5aef:2b::8'``) :func:`inet_ntop` is useful when a library or network protocol - returns an object of type :ctype:`struct in_addr` (similar to :func:`inet_ntoa`) - or :ctype:`struct in6_addr`. - - Supported values for *address_family* are currently :const:`AF_INET` and - :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the - specified address family, :exc:`ValueError` will be raised. A - :exc:`socket.error` is raised for errors from the call to :func:`inet_ntop`. - - Availability: Unix (maybe not all platforms). - - .. versionadded:: 2.3 - - -.. function:: getdefaulttimeout() - - Return the default timeout in floating seconds for new socket objects. A value - of ``None`` indicates that new socket objects have no timeout. When the socket - module is first imported, the default is ``None``. - - .. versionadded:: 2.3 - - -.. function:: setdefaulttimeout(timeout) - - Set the default timeout in floating seconds for new socket objects. A value of - ``None`` indicates that new socket objects have no timeout. When the socket - module is first imported, the default is ``None``. - - .. versionadded:: 2.3 - - -.. data:: SocketType - - This is a Python type object that represents the socket object type. It is the - same as ``type(socket(...))``. - - -.. seealso:: - - Module :mod:`SocketServer` - Classes that simplify writing network servers. - - -.. _socket-objects: - -Socket Objects --------------- - -Socket objects have the following methods. Except for :meth:`makefile` these -correspond to Unix system calls applicable to sockets. - - -.. method:: socket.accept() - - Accept a connection. The socket must be bound to an address and listening for - connections. The return value is a pair ``(conn, address)`` where *conn* is a - *new* socket object usable to send and receive data on the connection, and - *address* is the address bound to the socket on the other end of the connection. - - -.. method:: socket.bind(address) - - Bind the socket to *address*. The socket must not already be bound. (The format - of *address* depends on the address family --- see above.) - - .. note:: - - This method has historically accepted a pair of parameters for :const:`AF_INET` - addresses instead of only a tuple. This was never intentional and is no longer - available in Python 2.0 and later. - - -.. method:: socket.close() - - Close the socket. All future operations on the socket object will fail. The - remote end will receive no more data (after queued data is flushed). Sockets are - automatically closed when they are garbage-collected. - - -.. method:: socket.connect(address) - - Connect to a remote socket at *address*. (The format of *address* depends on the - address family --- see above.) - - .. note:: - - This method has historically accepted a pair of parameters for :const:`AF_INET` - addresses instead of only a tuple. This was never intentional and is no longer - available in Python 2.0 and later. - - -.. method:: socket.connect_ex(address) - - Like ``connect(address)``, but return an error indicator instead of raising an - exception for errors returned by the C-level :cfunc:`connect` call (other - problems, such as "host not found," can still raise exceptions). The error - indicator is ``0`` if the operation succeeded, otherwise the value of the - :cdata:`errno` variable. This is useful to support, for example, asynchronous - connects. - - .. note:: - - This method has historically accepted a pair of parameters for :const:`AF_INET` - addresses instead of only a tuple. This was never intentional and is no longer - available in Python 2.0 and later. - - -.. method:: socket.fileno() - - Return the socket's file descriptor (a small integer). This is useful with - :func:`select.select`. - - Under Windows the small integer returned by this method cannot be used where a - file descriptor can be used (such as :func:`os.fdopen`). Unix does not have - this limitation. - - -.. method:: socket.getpeername() - - Return the remote address to which the socket is connected. This is useful to - find out the port number of a remote IPv4/v6 socket, for instance. (The format - of the address returned depends on the address family --- see above.) On some - systems this function is not supported. - - -.. method:: socket.getsockname() - - Return the socket's own address. This is useful to find out the port number of - an IPv4/v6 socket, for instance. (The format of the address returned depends on - the address family --- see above.) - - -.. method:: socket.getsockopt(level, optname[, buflen]) - - Return the value of the given socket option (see the Unix man page - :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.) - are defined in this module. If *buflen* is absent, an integer option is assumed - and its integer value is returned by the function. If *buflen* is present, it - specifies the maximum length of the buffer used to receive the option in, and - this buffer is returned as a string. It is up to the caller to decode the - contents of the buffer (see the optional built-in module :mod:`struct` for a way - to decode C structures encoded as strings). - - -.. method:: socket.ioctl(control, option) - - :platform: Windows - - The `meth:ioctl` method is a limited interface to the WSAIoctl system - interface. Please refer to the MSDN documentation for more information. - - .. versionadded:: 2.6 - - -.. method:: socket.listen(backlog) - - Listen for connections made to the socket. The *backlog* argument specifies the - maximum number of queued connections and should be at least 1; the maximum value - is system-dependent (usually 5). - - -.. method:: socket.makefile([mode[, bufsize]]) - - .. index:: single: I/O control; buffering - - Return a :dfn:`file object` associated with the socket. (File objects are - described in :ref:`bltin-file-objects`.) The file object - references a :cfunc:`dup`\ ped version of the socket file descriptor, so the - file object and socket object may be closed or garbage-collected independently. - The socket must be in blocking mode (it can not have a timeout). The optional - *mode* and *bufsize* arguments are interpreted the same way as by the built-in - :func:`file` function. - - -.. method:: socket.recv(bufsize[, flags]) - - Receive data from the socket. The return value is a string representing the - data received. The maximum amount of data to be received at once is specified - by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of - the optional argument *flags*; it defaults to zero. - - .. note:: - - For best match with hardware and network realities, the value of *bufsize* - should be a relatively small power of 2, for example, 4096. - - -.. method:: socket.recvfrom(bufsize[, flags]) - - Receive data from the socket. The return value is a pair ``(string, address)`` - where *string* is a string representing the data received and *address* is the - address of the socket sending the data. See the Unix manual page - :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults - to zero. (The format of *address* depends on the address family --- see above.) - - -.. method:: socket.recvfrom_into(buffer[, nbytes[, flags]]) - - Receive data from the socket, writing it into *buffer* instead of creating a - new string. The return value is a pair ``(nbytes, address)`` where *nbytes* is - the number of bytes received and *address* is the address of the socket sending - the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the - optional argument *flags*; it defaults to zero. (The format of *address* - depends on the address family --- see above.) - - .. versionadded:: 2.5 - - -.. method:: socket.recv_into(buffer[, nbytes[, flags]]) - - Receive up to *nbytes* bytes from the socket, storing the data into a buffer - rather than creating a new string. If *nbytes* is not specified (or 0), - receive up to the size available in the given buffer. See the Unix manual page - :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults - to zero. - - .. versionadded:: 2.5 - - -.. method:: socket.send(string[, flags]) - - Send data to the socket. The socket must be connected to a remote socket. The - optional *flags* argument has the same meaning as for :meth:`recv` above. - Returns the number of bytes sent. Applications are responsible for checking that - all data has been sent; if only some of the data was transmitted, the - application needs to attempt delivery of the remaining data. - - -.. method:: socket.sendall(string[, flags]) - - Send data to the socket. The socket must be connected to a remote socket. The - optional *flags* argument has the same meaning as for :meth:`recv` above. - Unlike :meth:`send`, this method continues to send data from *string* until - either all data has been sent or an error occurs. ``None`` is returned on - success. On error, an exception is raised, and there is no way to determine how - much data, if any, was successfully sent. - - -.. method:: socket.sendto(string[, flags], address) - - Send data to the socket. The socket should not be connected to a remote socket, - since the destination socket is specified by *address*. The optional *flags* - argument has the same meaning as for :meth:`recv` above. Return the number of - bytes sent. (The format of *address* depends on the address family --- see - above.) - - -.. method:: socket.setblocking(flag) - - Set blocking or non-blocking mode of the socket: if *flag* is 0, the socket is - set to non-blocking, else to blocking mode. Initially all sockets are in - blocking mode. In non-blocking mode, if a :meth:`recv` call doesn't find any - data, or if a :meth:`send` call can't immediately dispose of the data, a - :exc:`error` exception is raised; in blocking mode, the calls block until they - can proceed. ``s.setblocking(0)`` is equivalent to ``s.settimeout(0)``; - ``s.setblocking(1)`` is equivalent to ``s.settimeout(None)``. - - -.. method:: socket.settimeout(value) - - Set a timeout on blocking socket operations. The *value* argument can be a - nonnegative float expressing seconds, or ``None``. If a float is given, - subsequent socket operations will raise an :exc:`timeout` exception if the - timeout period *value* has elapsed before the operation has completed. Setting - a timeout of ``None`` disables timeouts on socket operations. - ``s.settimeout(0.0)`` is equivalent to ``s.setblocking(0)``; - ``s.settimeout(None)`` is equivalent to ``s.setblocking(1)``. - - .. versionadded:: 2.3 - - -.. method:: socket.gettimeout() - - Return the timeout in floating seconds associated with socket operations, or - ``None`` if no timeout is set. This reflects the last call to - :meth:`setblocking` or :meth:`settimeout`. - - .. versionadded:: 2.3 - -Some notes on socket blocking and timeouts: A socket object can be in one of -three modes: blocking, non-blocking, or timeout. Sockets are always created in -blocking mode. In blocking mode, operations block until complete. In -non-blocking mode, operations fail (with an error that is unfortunately -system-dependent) if they cannot be completed immediately. In timeout mode, -operations fail if they cannot be completed within the timeout specified for the -socket. The :meth:`setblocking` method is simply a shorthand for certain -:meth:`settimeout` calls. - -Timeout mode internally sets the socket in non-blocking mode. The blocking and -timeout modes are shared between file descriptors and socket objects that refer -to the same network endpoint. A consequence of this is that file objects -returned by the :meth:`makefile` method must only be used when the socket is in -blocking mode; in timeout or non-blocking mode file operations that cannot be -completed immediately will fail. - -Note that the :meth:`connect` operation is subject to the timeout setting, and -in general it is recommended to call :meth:`settimeout` before calling -:meth:`connect`. - - -.. method:: socket.setsockopt(level, optname, value) - - .. index:: module: struct - - Set the value of the given socket option (see the Unix manual page - :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the - :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a - string representing a buffer. In the latter case it is up to the caller to - ensure that the string contains the proper bits (see the optional built-in - module :mod:`struct` for a way to encode C structures as strings). - - -.. method:: socket.shutdown(how) - - Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`, - further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends - are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are - disallowed. - -Note that there are no methods :meth:`read` or :meth:`write`; use :meth:`recv` -and :meth:`send` without *flags* argument instead. - -Socket objects also have these (read-only) attributes that correspond to the -values given to the :class:`socket` constructor. - - -.. attribute:: socket.family - - The socket family. - - .. versionadded:: 2.5 - - -.. attribute:: socket.type - - The socket type. - - .. versionadded:: 2.5 - - -.. attribute:: socket.proto - - The socket protocol. - - .. versionadded:: 2.5 - - -.. _socket-example: - -Example -------- - -Here are four minimal example programs using the TCP/IP protocol: a server that -echoes all data that it receives back (servicing only one client), and a client -using it. Note that a server must perform the sequence :func:`socket`, -:meth:`bind`, :meth:`listen`, :meth:`accept` (possibly repeating the -:meth:`accept` to service more than one client), while a client only needs the -sequence :func:`socket`, :meth:`connect`. Also note that the server does not -:meth:`send`/:meth:`recv` on the socket it is listening on but on the new -socket returned by :meth:`accept`. - -The first two examples support IPv4 only. :: - - # Echo server program - import socket - - HOST = '' # Symbolic name meaning the local host - PORT = 50007 # Arbitrary non-privileged port - s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) - s.bind((HOST, PORT)) - s.listen(1) - conn, addr = s.accept() - print 'Connected by', addr - while 1: - data = conn.recv(1024) - if not data: break - conn.send(data) - conn.close() - -:: - - # Echo client program - import socket - - HOST = 'daring.cwi.nl' # The remote host - PORT = 50007 # The same port as used by the server - s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) - s.connect((HOST, PORT)) - s.send('Hello, world') - data = s.recv(1024) - s.close() - print 'Received', repr(data) - -The next two examples are identical to the above two, but support both IPv4 and -IPv6. The server side will listen to the first address family available (it -should listen to both instead). On most of IPv6-ready systems, IPv6 will take -precedence and the server may not accept IPv4 traffic. The client side will try -to connect to the all addresses returned as a result of the name resolution, and -sends traffic to the first one connected successfully. :: - - # Echo server program - import socket - import sys - - HOST = '' # Symbolic name meaning the local host - PORT = 50007 # Arbitrary non-privileged port - s = None - for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM, 0, socket.AI_PASSIVE): - af, socktype, proto, canonname, sa = res - try: - s = socket.socket(af, socktype, proto) - except socket.error, msg: - s = None - continue - try: - s.bind(sa) - s.listen(1) - except socket.error, msg: - s.close() - s = None - continue - break - if s is None: - print 'could not open socket' - sys.exit(1) - conn, addr = s.accept() - print 'Connected by', addr - while 1: - data = conn.recv(1024) - if not data: break - conn.send(data) - conn.close() - -:: - - # Echo client program - import socket - import sys - - HOST = 'daring.cwi.nl' # The remote host - PORT = 50007 # The same port as used by the server - s = None - for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM): - af, socktype, proto, canonname, sa = res - try: - s = socket.socket(af, socktype, proto) - except socket.error, msg: - s = None - continue - try: - s.connect(sa) - except socket.error, msg: - s.close() - s = None - continue - break - if s is None: - print 'could not open socket' - sys.exit(1) - s.send('Hello, world') - data = s.recv(1024) - s.close() - print 'Received', repr(data) - - -The last example shows how to write a very simple network sniffer with raw -sockets on Windows. The example requires administrator priviliges to modify -the interface:: - - import socket - - # the public network interface - HOST = socket.gethostbyname(socket.gethostname()) - - # create a raw socket and bind it to the public interface - s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP) - s.bind((HOST, 0)) - - # Include IP headers - s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1) - - # receive all packages - s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON) - - # receive a package - print s.recvfrom(65565) - - # disabled promiscous mode - s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF) + +:mod:`socket` --- Low-level networking interface +================================================ + +.. module:: socket + :synopsis: Low-level networking interface. + + +This module provides access to the BSD *socket* interface. It is available on +all modern Unix systems, Windows, Mac OS X, BeOS, OS/2, and probably additional +platforms. + +.. note:: + + Some behavior may be platform dependent, since calls are made to the operating + system socket APIs. + +For an introduction to socket programming (in C), see the following papers: An +Introductory 4.3BSD Interprocess Communication Tutorial, by Stuart Sechrest and +An Advanced 4.3BSD Interprocess Communication Tutorial, by Samuel J. Leffler et +al, both in the UNIX Programmer's Manual, Supplementary Documents 1 (sections +PS1:7 and PS1:8). The platform-specific reference material for the various +socket-related system calls are also a valuable source of information on the +details of socket semantics. For Unix, refer to the manual pages; for Windows, +see the WinSock (or Winsock 2) specification. For IPv6-ready APIs, readers may +want to refer to :rfc:`2553` titled Basic Socket Interface Extensions for IPv6. + +.. index:: object: socket + +The Python interface is a straightforward transliteration of the Unix system +call and library interface for sockets to Python's object-oriented style: the +:func:`socket` function returns a :dfn:`socket object` whose methods implement +the various socket system calls. Parameter types are somewhat higher-level than +in the C interface: as with :meth:`read` and :meth:`write` operations on Python +files, buffer allocation on receive operations is automatic, and buffer length +is implicit on send operations. + +Socket addresses are represented as follows: A single string is used for the +:const:`AF_UNIX` address family. A pair ``(host, port)`` is used for the +:const:`AF_INET` address family, where *host* is a string representing either a +hostname in Internet domain notation like ``'daring.cwi.nl'`` or an IPv4 address +like ``'100.50.200.5'``, and *port* is an integral port number. For +:const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo, +scopeid)`` is used, where *flowinfo* and *scopeid* represents ``sin6_flowinfo`` +and ``sin6_scope_id`` member in :const:`struct sockaddr_in6` in C. For +:mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for +backward compatibility. Note, however, omission of *scopeid* can cause problems +in manipulating scoped IPv6 addresses. Other address families are currently not +supported. The address format required by a particular socket object is +automatically selected based on the address family specified when the socket +object was created. + +For IPv4 addresses, two special forms are accepted instead of a host address: +the empty string represents :const:`INADDR_ANY`, and the string +``''`` represents :const:`INADDR_BROADCAST`. The behavior is not +available for IPv6 for backward compatibility, therefore, you may want to avoid +these if you intend to support IPv6 with your Python programs. + +If you use a hostname in the *host* portion of IPv4/v6 socket address, the +program may show a nondeterministic behavior, as Python uses the first address +returned from the DNS resolution. The socket address will be resolved +differently into an actual IPv4/v6 address, depending on the results from DNS +resolution and/or the host configuration. For deterministic behavior use a +numeric address in *host* portion. + +.. versionadded:: 2.5 + AF_NETLINK sockets are represented as pairs ``pid, groups``. + +All errors raise exceptions. The normal exceptions for invalid argument types +and out-of-memory conditions can be raised; errors related to socket or address +semantics raise the error :exc:`socket.error`. + +Non-blocking mode is supported through :meth:`setblocking`. A generalization of +this based on timeouts is supported through :meth:`settimeout`. + +The module :mod:`socket` exports the following constants and functions: + + +.. exception:: error + + .. index:: module: errno + + This exception is raised for socket-related errors. The accompanying value is + either a string telling what went wrong or a pair ``(errno, string)`` + representing an error returned by a system call, similar to the value + accompanying :exc:`os.error`. See the module :mod:`errno`, which contains names + for the error codes defined by the underlying operating system. + + .. versionchanged:: 2.6 + :exc:`socket.error` is now a child class of :exc:`IOError`. + + +.. exception:: herror + + This exception is raised for address-related errors, i.e. for functions that use + *h_errno* in the C API, including :func:`gethostbyname_ex` and + :func:`gethostbyaddr`. + + The accompanying value is a pair ``(h_errno, string)`` representing an error + returned by a library call. *string* represents the description of *h_errno*, as + returned by the :cfunc:`hstrerror` C function. + + +.. exception:: gaierror + + This exception is raised for address-related errors, for :func:`getaddrinfo` and + :func:`getnameinfo`. The accompanying value is a pair ``(error, string)`` + representing an error returned by a library call. *string* represents the + description of *error*, as returned by the :cfunc:`gai_strerror` C function. The + *error* value will match one of the :const:`EAI_\*` constants defined in this + module. + + +.. exception:: timeout + + This exception is raised when a timeout occurs on a socket which has had + timeouts enabled via a prior call to :meth:`settimeout`. The accompanying value + is a string whose value is currently always "timed out". + + .. versionadded:: 2.3 + + +.. data:: AF_UNIX + AF_INET + AF_INET6 + + These constants represent the address (and protocol) families, used for the + first argument to :func:`socket`. If the :const:`AF_UNIX` constant is not + defined then this protocol is unsupported. + + +.. data:: SOCK_STREAM + SOCK_DGRAM + SOCK_RAW + SOCK_RDM + SOCK_SEQPACKET + + These constants represent the socket types, used for the second argument to + :func:`socket`. (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be + generally useful.) + + +.. data:: SO_* + SOMAXCONN + MSG_* + SOL_* + IPPROTO_* + IPPORT_* + INADDR_* + IP_* + IPV6_* + EAI_* + AI_* + NI_* + TCP_* + + Many constants of these forms, documented in the Unix documentation on sockets + and/or the IP protocol, are also defined in the socket module. They are + generally used in arguments to the :meth:`setsockopt` and :meth:`getsockopt` + methods of socket objects. In most cases, only those symbols that are defined + in the Unix header files are defined; for a few symbols, default values are + provided. + +.. data:: SIO_* + RCVALL_* + + Constants for Windows' WSAIoctl(). The constants are used as arguments to the + :meth:`ioctl` method of socket objects. + + .. versionadded:: 2.6 + + +.. data:: has_ipv6 + + This constant contains a boolean value which indicates if IPv6 is supported on + this platform. + + .. versionadded:: 2.3 + + +.. function:: create_connection(address[, timeout]) + + Connects to the *address* received (as usual, a ``(host, port)`` pair), with an + optional timeout for the connection. Especially useful for higher-level + protocols, it is not normally used directly from application-level code. + Passing the optional *timeout* parameter will set the timeout on the socket + instance (if it is not given or ``None``, the global default timeout setting is + used). + + .. versionadded:: 2.6 + + +.. function:: getaddrinfo(host, port[, family[, socktype[, proto[, flags]]]]) + + Resolves the *host*/*port* argument, into a sequence of 5-tuples that contain + all the necessary argument for the sockets manipulation. *host* is a domain + name, a string representation of IPv4/v6 address or ``None``. *port* is a string + service name (like ``'http'``), a numeric port number or ``None``. + + The rest of the arguments are optional and must be numeric if specified. For + *host* and *port*, by passing either an empty string or ``None``, you can pass + ``NULL`` to the C API. The :func:`getaddrinfo` function returns a list of + 5-tuples with the following structure: + + ``(family, socktype, proto, canonname, sockaddr)`` + + *family*, *socktype*, *proto* are all integer and are meant to be passed to the + :func:`socket` function. *canonname* is a string representing the canonical name + of the *host*. It can be a numeric IPv4/v6 address when :const:`AI_CANONNAME` is + specified for a numeric *host*. *sockaddr* is a tuple describing a socket + address, as described above. See the source for :mod:`socket` and other + library modules for a typical usage of the function. + + .. versionadded:: 2.2 + + +.. function:: getfqdn([name]) + + Return a fully qualified domain name for *name*. If *name* is omitted or empty, + it is interpreted as the local host. To find the fully qualified name, the + hostname returned by :func:`gethostbyaddr` is checked, then aliases for the + host, if available. The first name which includes a period is selected. In + case no fully qualified domain name is available, the hostname as returned by + :func:`gethostname` is returned. + + .. versionadded:: 2.0 + + +.. function:: gethostbyname(hostname) + + Translate a host name to IPv4 address format. The IPv4 address is returned as a + string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself + it is returned unchanged. See :func:`gethostbyname_ex` for a more complete + interface. :func:`gethostbyname` does not support IPv6 name resolution, and + :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support. + + +.. function:: gethostbyname_ex(hostname) + + Translate a host name to IPv4 address format, extended interface. Return a + triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary + host name responding to the given *ip_address*, *aliaslist* is a (possibly + empty) list of alternative host names for the same address, and *ipaddrlist* is + a list of IPv4 addresses for the same interface on the same host (often but not + always a single address). :func:`gethostbyname_ex` does not support IPv6 name + resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual + stack support. + + +.. function:: gethostname() + + Return a string containing the hostname of the machine where the Python + interpreter is currently executing. If you want to know the current machine's IP + address, you may want to use ``gethostbyname(gethostname())``. This operation + assumes that there is a valid address-to-host mapping for the host, and the + assumption does not always hold. Note: :func:`gethostname` doesn't always return + the fully qualified domain name; use ``getfqdn()`` (see above). + + +.. function:: gethostbyaddr(ip_address) + + Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the + primary host name responding to the given *ip_address*, *aliaslist* is a + (possibly empty) list of alternative host names for the same address, and + *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same + host (most likely containing only a single address). To find the fully qualified + domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports + both IPv4 and IPv6. + + +.. function:: getnameinfo(sockaddr, flags) + + Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending + on the settings of *flags*, the result can contain a fully-qualified domain name + or numeric address representation in *host*. Similarly, *port* can contain a + string port name or a numeric port number. + + .. versionadded:: 2.2 + + +.. function:: getprotobyname(protocolname) + + Translate an Internet protocol name (for example, ``'icmp'``) to a constant + suitable for passing as the (optional) third argument to the :func:`socket` + function. This is usually only needed for sockets opened in "raw" mode + (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen + automatically if the protocol is omitted or zero. + + +.. function:: getservbyname(servicename[, protocolname]) + + Translate an Internet service name and protocol name to a port number for that + service. The optional protocol name, if given, should be ``'tcp'`` or + ``'udp'``, otherwise any protocol will match. + + +.. function:: getservbyport(port[, protocolname]) + + Translate an Internet port number and protocol name to a service name for that + service. The optional protocol name, if given, should be ``'tcp'`` or + ``'udp'``, otherwise any protocol will match. + + +.. function:: socket([family[, type[, proto]]]) + + Create a new socket using the given address family, socket type and protocol + number. The address family should be :const:`AF_INET` (the default), + :const:`AF_INET6` or :const:`AF_UNIX`. The socket type should be + :const:`SOCK_STREAM` (the default), :const:`SOCK_DGRAM` or perhaps one of the + other ``SOCK_`` constants. The protocol number is usually zero and may be + omitted in that case. + + +.. function:: socketpair([family[, type[, proto]]]) + + Build a pair of connected socket objects using the given address family, socket + type, and protocol number. Address family, socket type, and protocol number are + as for the :func:`socket` function above. The default family is :const:`AF_UNIX` + if defined on the platform; otherwise, the default is :const:`AF_INET`. + Availability: Unix. + + .. versionadded:: 2.4 + + +.. function:: fromfd(fd, family, type[, proto]) + + Duplicate the file descriptor *fd* (an integer as returned by a file object's + :meth:`fileno` method) and build a socket object from the result. Address + family, socket type and protocol number are as for the :func:`socket` function + above. The file descriptor should refer to a socket, but this is not checked --- + subsequent operations on the object may fail if the file descriptor is invalid. + This function is rarely needed, but can be used to get or set socket options on + a socket passed to a program as standard input or output (such as a server + started by the Unix inet daemon). The socket is assumed to be in blocking mode. + Availability: Unix. + + +.. function:: ntohl(x) + + Convert 32-bit positive integers from network to host byte order. On machines + where the host byte order is the same as network byte order, this is a no-op; + otherwise, it performs a 4-byte swap operation. + + +.. function:: ntohs(x) + + Convert 16-bit positive integers from network to host byte order. On machines + where the host byte order is the same as network byte order, this is a no-op; + otherwise, it performs a 2-byte swap operation. + + +.. function:: htonl(x) + + Convert 32-bit positive integers from host to network byte order. On machines + where the host byte order is the same as network byte order, this is a no-op; + otherwise, it performs a 4-byte swap operation. + + +.. function:: htons(x) + + Convert 16-bit positive integers from host to network byte order. On machines + where the host byte order is the same as network byte order, this is a no-op; + otherwise, it performs a 2-byte swap operation. + + +.. function:: inet_aton(ip_string) + + Convert an IPv4 address from dotted-quad string format (for example, + '123.45.67.89') to 32-bit packed binary format, as a string four characters in + length. This is useful when conversing with a program that uses the standard C + library and needs objects of type :ctype:`struct in_addr`, which is the C type + for the 32-bit packed binary this function returns. + + If the IPv4 address string passed to this function is invalid, + :exc:`socket.error` will be raised. Note that exactly what is valid depends on + the underlying C implementation of :cfunc:`inet_aton`. + + :func:`inet_aton` does not support IPv6, and :func:`getnameinfo` should be used + instead for IPv4/v6 dual stack support. + + +.. function:: inet_ntoa(packed_ip) + + Convert a 32-bit packed IPv4 address (a string four characters in length) to its + standard dotted-quad string representation (for example, '123.45.67.89'). This + is useful when conversing with a program that uses the standard C library and + needs objects of type :ctype:`struct in_addr`, which is the C type for the + 32-bit packed binary data this function takes as an argument. + + If the string passed to this function is not exactly 4 bytes in length, + :exc:`socket.error` will be raised. :func:`inet_ntoa` does not support IPv6, and + :func:`getnameinfo` should be used instead for IPv4/v6 dual stack support. + + +.. function:: inet_pton(address_family, ip_string) + + Convert an IP address from its family-specific string format to a packed, binary + format. :func:`inet_pton` is useful when a library or network protocol calls for + an object of type :ctype:`struct in_addr` (similar to :func:`inet_aton`) or + :ctype:`struct in6_addr`. + + Supported values for *address_family* are currently :const:`AF_INET` and + :const:`AF_INET6`. If the IP address string *ip_string* is invalid, + :exc:`socket.error` will be raised. Note that exactly what is valid depends on + both the value of *address_family* and the underlying implementation of + :cfunc:`inet_pton`. + + Availability: Unix (maybe not all platforms). + + .. versionadded:: 2.3 + + +.. function:: inet_ntop(address_family, packed_ip) + + Convert a packed IP address (a string of some number of characters) to its + standard, family-specific string representation (for example, ``'7.10.0.5'`` or + ``'5aef:2b::8'``) :func:`inet_ntop` is useful when a library or network protocol + returns an object of type :ctype:`struct in_addr` (similar to :func:`inet_ntoa`) + or :ctype:`struct in6_addr`. + + Supported values for *address_family* are currently :const:`AF_INET` and + :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the + specified address family, :exc:`ValueError` will be raised. A + :exc:`socket.error` is raised for errors from the call to :func:`inet_ntop`. + + Availability: Unix (maybe not all platforms). + + .. versionadded:: 2.3 + + +.. function:: getdefaulttimeout() + + Return the default timeout in floating seconds for new socket objects. A value + of ``None`` indicates that new socket objects have no timeout. When the socket + module is first imported, the default is ``None``. + + .. versionadded:: 2.3 + + +.. function:: setdefaulttimeout(timeout) + + Set the default timeout in floating seconds for new socket objects. A value of + ``None`` indicates that new socket objects have no timeout. When the socket + module is first imported, the default is ``None``. + + .. versionadded:: 2.3 + + +.. data:: SocketType + + This is a Python type object that represents the socket object type. It is the + same as ``type(socket(...))``. + + +.. seealso:: + + Module :mod:`SocketServer` + Classes that simplify writing network servers. + + +.. _socket-objects: + +Socket Objects +-------------- + +Socket objects have the following methods. Except for :meth:`makefile` these +correspond to Unix system calls applicable to sockets. + + +.. method:: socket.accept() + + Accept a connection. The socket must be bound to an address and listening for + connections. The return value is a pair ``(conn, address)`` where *conn* is a + *new* socket object usable to send and receive data on the connection, and + *address* is the address bound to the socket on the other end of the connection. + + +.. method:: socket.bind(address) + + Bind the socket to *address*. The socket must not already be bound. (The format + of *address* depends on the address family --- see above.) + + .. note:: + + This method has historically accepted a pair of parameters for :const:`AF_INET` + addresses instead of only a tuple. This was never intentional and is no longer + available in Python 2.0 and later. + + +.. method:: socket.close() + + Close the socket. All future operations on the socket object will fail. The + remote end will receive no more data (after queued data is flushed). Sockets are + automatically closed when they are garbage-collected. + + +.. method:: socket.connect(address) + + Connect to a remote socket at *address*. (The format of *address* depends on the + address family --- see above.) + + .. note:: + + This method has historically accepted a pair of parameters for :const:`AF_INET` + addresses instead of only a tuple. This was never intentional and is no longer + available in Python 2.0 and later. + + +.. method:: socket.connect_ex(address) + + Like ``connect(address)``, but return an error indicator instead of raising an + exception for errors returned by the C-level :cfunc:`connect` call (other + problems, such as "host not found," can still raise exceptions). The error + indicator is ``0`` if the operation succeeded, otherwise the value of the + :cdata:`errno` variable. This is useful to support, for example, asynchronous + connects. + + .. note:: + + This method has historically accepted a pair of parameters for :const:`AF_INET` + addresses instead of only a tuple. This was never intentional and is no longer + available in Python 2.0 and later. + + +.. method:: socket.fileno() + + Return the socket's file descriptor (a small integer). This is useful with + :func:`select.select`. + + Under Windows the small integer returned by this method cannot be used where a + file descriptor can be used (such as :func:`os.fdopen`). Unix does not have + this limitation. + + +.. method:: socket.getpeername() + + Return the remote address to which the socket is connected. This is useful to + find out the port number of a remote IPv4/v6 socket, for instance. (The format + of the address returned depends on the address family --- see above.) On some + systems this function is not supported. + + +.. method:: socket.getsockname() + + Return the socket's own address. This is useful to find out the port number of + an IPv4/v6 socket, for instance. (The format of the address returned depends on + the address family --- see above.) + + +.. method:: socket.getsockopt(level, optname[, buflen]) + + Return the value of the given socket option (see the Unix man page + :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.) + are defined in this module. If *buflen* is absent, an integer option is assumed + and its integer value is returned by the function. If *buflen* is present, it + specifies the maximum length of the buffer used to receive the option in, and + this buffer is returned as a string. It is up to the caller to decode the + contents of the buffer (see the optional built-in module :mod:`struct` for a way + to decode C structures encoded as strings). + + +.. method:: socket.ioctl(control, option) + + :platform: Windows + + The `meth:ioctl` method is a limited interface to the WSAIoctl system + interface. Please refer to the MSDN documentation for more information. + + .. versionadded:: 2.6 + + +.. method:: socket.listen(backlog) + + Listen for connections made to the socket. The *backlog* argument specifies the + maximum number of queued connections and should be at least 1; the maximum value + is system-dependent (usually 5). + + +.. method:: socket.makefile([mode[, bufsize]]) + + .. index:: single: I/O control; buffering + + Return a :dfn:`file object` associated with the socket. (File objects are + described in :ref:`bltin-file-objects`.) The file object + references a :cfunc:`dup`\ ped version of the socket file descriptor, so the + file object and socket object may be closed or garbage-collected independently. + The socket must be in blocking mode (it can not have a timeout). The optional + *mode* and *bufsize* arguments are interpreted the same way as by the built-in + :func:`file` function. + + +.. method:: socket.recv(bufsize[, flags]) + + Receive data from the socket. The return value is a string representing the + data received. The maximum amount of data to be received at once is specified + by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of + the optional argument *flags*; it defaults to zero. + + .. note:: + + For best match with hardware and network realities, the value of *bufsize* + should be a relatively small power of 2, for example, 4096. + + +.. method:: socket.recvfrom(bufsize[, flags]) + + Receive data from the socket. The return value is a pair ``(string, address)`` + where *string* is a string representing the data received and *address* is the + address of the socket sending the data. See the Unix manual page + :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults + to zero. (The format of *address* depends on the address family --- see above.) + + +.. method:: socket.recvfrom_into(buffer[, nbytes[, flags]]) + + Receive data from the socket, writing it into *buffer* instead of creating a + new string. The return value is a pair ``(nbytes, address)`` where *nbytes* is + the number of bytes received and *address* is the address of the socket sending + the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the + optional argument *flags*; it defaults to zero. (The format of *address* + depends on the address family --- see above.) + + .. versionadded:: 2.5 + + +.. method:: socket.recv_into(buffer[, nbytes[, flags]]) + + Receive up to *nbytes* bytes from the socket, storing the data into a buffer + rather than creating a new string. If *nbytes* is not specified (or 0), + receive up to the size available in the given buffer. See the Unix manual page + :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults + to zero. + + .. versionadded:: 2.5 + + +.. method:: socket.send(string[, flags]) + + Send data to the socket. The socket must be connected to a remote socket. The + optional *flags* argument has the same meaning as for :meth:`recv` above. + Returns the number of bytes sent. Applications are responsible for checking that + all data has been sent; if only some of the data was transmitted, the + application needs to attempt delivery of the remaining data. + + +.. method:: socket.sendall(string[, flags]) + + Send data to the socket. The socket must be connected to a remote socket. The + optional *flags* argument has the same meaning as for :meth:`recv` above. + Unlike :meth:`send`, this method continues to send data from *string* until + either all data has been sent or an error occurs. ``None`` is returned on + success. On error, an exception is raised, and there is no way to determine how + much data, if any, was successfully sent. + + +.. method:: socket.sendto(string[, flags], address) + + Send data to the socket. The socket should not be connected to a remote socket, + since the destination socket is specified by *address*. The optional *flags* + argument has the same meaning as for :meth:`recv` above. Return the number of + bytes sent. (The format of *address* depends on the address family --- see + above.) + + +.. method:: socket.setblocking(flag) + + Set blocking or non-blocking mode of the socket: if *flag* is 0, the socket is + set to non-blocking, else to blocking mode. Initially all sockets are in + blocking mode. In non-blocking mode, if a :meth:`recv` call doesn't find any + data, or if a :meth:`send` call can't immediately dispose of the data, a + :exc:`error` exception is raised; in blocking mode, the calls block until they + can proceed. ``s.setblocking(0)`` is equivalent to ``s.settimeout(0)``; + ``s.setblocking(1)`` is equivalent to ``s.settimeout(None)``. + + +.. method:: socket.settimeout(value) + + Set a timeout on blocking socket operations. The *value* argument can be a + nonnegative float expressing seconds, or ``None``. If a float is given, + subsequent socket operations will raise an :exc:`timeout` exception if the + timeout period *value* has elapsed before the operation has completed. Setting + a timeout of ``None`` disables timeouts on socket operations. + ``s.settimeout(0.0)`` is equivalent to ``s.setblocking(0)``; + ``s.settimeout(None)`` is equivalent to ``s.setblocking(1)``. + + .. versionadded:: 2.3 + + +.. method:: socket.gettimeout() + + Return the timeout in floating seconds associated with socket operations, or + ``None`` if no timeout is set. This reflects the last call to + :meth:`setblocking` or :meth:`settimeout`. + + .. versionadded:: 2.3 + +Some notes on socket blocking and timeouts: A socket object can be in one of +three modes: blocking, non-blocking, or timeout. Sockets are always created in +blocking mode. In blocking mode, operations block until complete. In +non-blocking mode, operations fail (with an error that is unfortunately +system-dependent) if they cannot be completed immediately. In timeout mode, +operations fail if they cannot be completed within the timeout specified for the +socket. The :meth:`setblocking` method is simply a shorthand for certain +:meth:`settimeout` calls. + +Timeout mode internally sets the socket in non-blocking mode. The blocking and +timeout modes are shared between file descriptors and socket objects that refer +to the same network endpoint. A consequence of this is that file objects +returned by the :meth:`makefile` method must only be used when the socket is in +blocking mode; in timeout or non-blocking mode file operations that cannot be +completed immediately will fail. + +Note that the :meth:`connect` operation is subject to the timeout setting, and +in general it is recommended to call :meth:`settimeout` before calling +:meth:`connect`. + + +.. method:: socket.setsockopt(level, optname, value) + + .. index:: module: struct + + Set the value of the given socket option (see the Unix manual page + :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the + :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a + string representing a buffer. In the latter case it is up to the caller to + ensure that the string contains the proper bits (see the optional built-in + module :mod:`struct` for a way to encode C structures as strings). + + +.. method:: socket.shutdown(how) + + Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`, + further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends + are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are + disallowed. + +Note that there are no methods :meth:`read` or :meth:`write`; use :meth:`recv` +and :meth:`send` without *flags* argument instead. + +Socket objects also have these (read-only) attributes that correspond to the +values given to the :class:`socket` constructor. + + +.. attribute:: socket.family + + The socket family. + + .. versionadded:: 2.5 + + +.. attribute:: socket.type + + The socket type. + + .. versionadded:: 2.5 + + +.. attribute:: socket.proto + + The socket protocol. + + .. versionadded:: 2.5 + + +.. _socket-example: + +Example +------- + +Here are four minimal example programs using the TCP/IP protocol: a server that +echoes all data that it receives back (servicing only one client), and a client +using it. Note that a server must perform the sequence :func:`socket`, +:meth:`bind`, :meth:`listen`, :meth:`accept` (possibly repeating the +:meth:`accept` to service more than one client), while a client only needs the +sequence :func:`socket`, :meth:`connect`. Also note that the server does not +:meth:`send`/:meth:`recv` on the socket it is listening on but on the new +socket returned by :meth:`accept`. + +The first two examples support IPv4 only. :: + + # Echo server program + import socket + + HOST = '' # Symbolic name meaning the local host + PORT = 50007 # Arbitrary non-privileged port + s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) + s.bind((HOST, PORT)) + s.listen(1) + conn, addr = s.accept() + print 'Connected by', addr + while 1: + data = conn.recv(1024) + if not data: break + conn.send(data) + conn.close() + +:: + + # Echo client program + import socket + + HOST = 'daring.cwi.nl' # The remote host + PORT = 50007 # The same port as used by the server + s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) + s.connect((HOST, PORT)) + s.send('Hello, world') + data = s.recv(1024) + s.close() + print 'Received', repr(data) + +The next two examples are identical to the above two, but support both IPv4 and +IPv6. The server side will listen to the first address family available (it +should listen to both instead). On most of IPv6-ready systems, IPv6 will take +precedence and the server may not accept IPv4 traffic. The client side will try +to connect to the all addresses returned as a result of the name resolution, and +sends traffic to the first one connected successfully. :: + + # Echo server program + import socket + import sys + + HOST = '' # Symbolic name meaning the local host + PORT = 50007 # Arbitrary non-privileged port + s = None + for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM, 0, socket.AI_PASSIVE): + af, socktype, proto, canonname, sa = res + try: + s = socket.socket(af, socktype, proto) + except socket.error, msg: + s = None + continue + try: + s.bind(sa) + s.listen(1) + except socket.error, msg: + s.close() + s = None + continue + break + if s is None: + print 'could not open socket' + sys.exit(1) + conn, addr = s.accept() + print 'Connected by', addr + while 1: + data = conn.recv(1024) + if not data: break + conn.send(data) + conn.close() + +:: + + # Echo client program + import socket + import sys + + HOST = 'daring.cwi.nl' # The remote host + PORT = 50007 # The same port as used by the server + s = None + for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM): + af, socktype, proto, canonname, sa = res + try: + s = socket.socket(af, socktype, proto) + except socket.error, msg: + s = None + continue + try: + s.connect(sa) + except socket.error, msg: + s.close() + s = None + continue + break + if s is None: + print 'could not open socket' + sys.exit(1) + s.send('Hello, world') + data = s.recv(1024) + s.close() + print 'Received', repr(data) + + +The last example shows how to write a very simple network sniffer with raw +sockets on Windows. The example requires administrator priviliges to modify +the interface:: + + import socket + + # the public network interface + HOST = socket.gethostbyname(socket.gethostname()) + + # create a raw socket and bind it to the public interface + s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP) + s.bind((HOST, 0)) + + # Include IP headers + s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1) + + # receive all packages + s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON) + + # receive a package + print s.recvfrom(65565) + + # disabled promiscous mode + s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)