| |
| :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, 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:`3493` 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. |
| |
| AF_NETLINK sockets are represented as pairs ``pid, groups``. |
| |
| |
| Linux-only support for TIPC is also available using the :const:`AF_TIPC` |
| address family. TIPC is an open, non-IP based networked protocol designed |
| for use in clustered computer environments. Addresses are represented by a |
| tuple, and the fields depend on the address type. The general tuple form is |
| ``(addr_type, v1, v2, v3 [, scope])``, where: |
| |
| - *addr_type* is one of TIPC_ADDR_NAMESEQ, TIPC_ADDR_NAME, or |
| TIPC_ADDR_ID. |
| - *scope* is one of TIPC_ZONE_SCOPE, TIPC_CLUSTER_SCOPE, and |
| TIPC_NODE_SCOPE. |
| - If *addr_type* is TIPC_ADDR_NAME, then *v1* is the server type, *v2* is |
| the port identifier, and *v3* should be 0. |
| |
| If *addr_type* is TIPC_ADDR_NAMESEQ, then *v1* is the server type, *v2* |
| is the lower port number, and *v3* is the upper port number. |
| |
| If *addr_type* is TIPC_ADDR_ID, then *v1* is the node, *v2* is the |
| reference, and *v3* should be set to 0. |
| |
| |
| 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". |
| |
| |
| .. 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. |
| |
| |
| .. data:: TIPC_* |
| |
| TIPC related constants, matching the ones exported by the C socket API. See |
| the TIPC documentation for more information. |
| |
| |
| .. data:: has_ipv6 |
| |
| This constant contains a boolean value which indicates if IPv6 is supported on |
| this platform. |
| |
| |
| .. 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). |
| |
| |
| .. 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 ``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. |
| |
| |
| .. 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. |
| |
| |
| .. 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. |
| |
| |
| .. 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. |
| |
| |
| .. 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). |
| |
| |
| .. 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). |
| |
| |
| .. 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``. |
| |
| |
| .. 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``. |
| |
| |
| .. 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.) |
| |
| |
| .. 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.) |
| |
| |
| .. 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. |
| |
| |
| .. 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. |
| |
| |
| .. 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.) |
| |
| |
| .. 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. |
| |
| |
| .. 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)``. |
| |
| |
| .. 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`. |
| |
| |
| 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. |
| |
| |
| .. attribute:: socket.type |
| |
| The socket type. |
| |
| |
| .. attribute:: socket.proto |
| |
| The socket protocol. |
| |
| |
| .. _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 all available interfaces |
| 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 True: |
| 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 = None # Symbolic name meaning all available interfaces |
| 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 True: |
| 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)) |
| |
| |
| The last example shows how to write a very simple network sniffer with raw |
| sockets on Windows. The example requires administrator privileges 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 promiscuous mode |
| s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF) |