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diff --git a/Doc/library/socket.rst b/Doc/library/socket.rst new file mode 100644 index 0000000..0ec4461 --- /dev/null +++ b/Doc/library/socket.rst @@ -0,0 +1,941 @@ + +: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, MacOS, 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 +``'<broadcast>'`` 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. + + +.. 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:: 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. Specially 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 the :mod:`httplib` 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:: ssl(sock[, keyfile, certfile]) + + Initiate a SSL connection over the socket *sock*. *keyfile* is the name of a PEM + formatted file that contains your private key. *certfile* is a PEM formatted + certificate chain file. On success, a new :class:`SSLObject` is returned. + + .. warning:: + + This does not do any certificate verification! + + +.. 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.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; see :ref:`built-in-funcs` for more information. + + +.. 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 + + +.. _ssl-objects: + +SSL Objects +----------- + +SSL objects have the following methods. + + +.. method:: SSL.write(s) + + Writes the string *s* to the on the object's SSL connection. The return value is + the number of bytes written. + + +.. method:: SSL.read([n]) + + If *n* is provided, read *n* bytes from the SSL connection, otherwise read until + EOF. The return value is a string of the bytes read. + + +.. method:: SSL.server() + + Returns a string describing the server's certificate. Useful for debugging + purposes; do not parse the content of this string because its format can't be + parsed unambiguously. + + +.. method:: SSL.issuer() + + Returns a string describing the issuer of the server's certificate. Useful for + debugging purposes; do not parse the content of this string because its format + can't be parsed unambiguously. + + +.. _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 as msg: + s = None + continue + try: + s.bind(sa) + s.listen(1) + except socket.error as 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 as msg: + s = None + continue + try: + s.connect(sa) + except socket.error as 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) + +This example connects to an SSL server, prints the server and issuer's +distinguished names, sends some bytes, and reads part of the response:: + + import socket + + s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) + s.connect(('www.verisign.com', 443)) + + ssl_sock = socket.ssl(s) + + print repr(ssl_sock.server()) + print repr(ssl_sock.issuer()) + + # Set a simple HTTP request -- use httplib in actual code. + ssl_sock.write("""GET / HTTP/1.0\r + Host: www.verisign.com\r\n\r\n""") + + # Read a chunk of data. Will not necessarily + # read all the data returned by the server. + data = ssl_sock.read() + + # Note that you need to close the underlying socket, not the SSL object. + del ssl_sock + s.close() + +At this writing, this SSL example prints the following output (line breaks +inserted for readability):: + + '/C=US/ST=California/L=Mountain View/ + O=VeriSign, Inc./OU=Production Services/ + OU=Terms of use at www.verisign.com/rpa (c)00/ + CN=www.verisign.com' + '/O=VeriSign Trust Network/OU=VeriSign, Inc./ + OU=VeriSign International Server CA - Class 3/ + OU=www.verisign.com/CPS Incorp.by Ref. LIABILITY LTD.(c)97 VeriSign' + |