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Diffstat (limited to 'Doc/library/socket.rst')
| -rw-r--r-- | Doc/library/socket.rst | 389 |
1 files changed, 356 insertions, 33 deletions
diff --git a/Doc/library/socket.rst b/Doc/library/socket.rst index f236d30f26..69fa378074 100644 --- a/Doc/library/socket.rst +++ b/Doc/library/socket.rst @@ -40,9 +40,23 @@ Socket families Depending on the system and the build options, various socket families are supported by this module. -Socket addresses are represented as follows: - -- A single string is used for the :const:`AF_UNIX` address family. +The address format required by a particular socket object is automatically +selected based on the address family specified when the socket object was +created. Socket addresses are represented as follows: + +- The address of an :const:`AF_UNIX` socket bound to a file system node + is represented as a string, using the file system encoding and the + ``'surrogateescape'`` error handler (see :pep:`383`). An address in + Linux's abstract namespace is returned as a :class:`bytes` object with + an initial null byte; note that sockets in this namespace can + communicate with normal file system sockets, so programs intended to + run on Linux may need to deal with both types of address. A string or + :class:`bytes` object can be used for either type of address when + passing it as an argument. + + .. versionchanged:: 3.3 + Previously, :const:`AF_UNIX` socket paths were assumed to use UTF-8 + encoding. - 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 @@ -80,6 +94,19 @@ Socket addresses are represented as follows: If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the reference, and *v3* should be set to 0. +- A tuple ``(interface, )`` is used for the :const:`AF_CAN` address family, + where *interface* is a string representing a network interface name like + ``'can0'``. The network interface name ``''`` can be used to receive packets + from all network interfaces of this family. + +- A string or a tuple ``(id, unit)`` is used for the :const:`SYSPROTO_CONTROL` + protocol of the :const:`PF_SYSTEM` family. The string is the name of a + kernel control using a dynamically-assigned ID. The tuple can be used if ID + and unit number of the kernel control are known or if a registered ID is + used. + + .. versionadded:: 3.3 + - Certain other address families (:const:`AF_BLUETOOTH`, :const:`AF_PACKET`) support specific representations. @@ -99,8 +126,9 @@ resolution and/or the host configuration. For deterministic behavior use a numeric address in *host* portion. 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 :exc:`socket.error` or one of its subclasses. +and out-of-memory conditions can be raised; starting from Python 3.3, errors +related to socket or address semantics raise :exc:`OSError` or one of its +subclasses (they used to raise :exc:`socket.error`). Non-blocking mode is supported through :meth:`~socket.setblocking`. A generalization of this based on timeouts is supported through @@ -115,20 +143,15 @@ The module :mod:`socket` exports the following constants and functions: .. exception:: error - .. index:: module: errno - - A subclass of :exc:`IOError`, this exception is raised for socket-related - errors. It is recommended that you inspect its ``errno`` attribute to - discriminate between different kinds of errors. + A deprecated alias of :exc:`OSError`. - .. seealso:: - The :mod:`errno` module contains symbolic names for the error codes - defined by the underlying operating system. + .. versionchanged:: 3.3 + Following :pep:`3151`, this class was made an alias of :exc:`OSError`. .. exception:: herror - A subclass of :exc:`socket.error`, this exception is raised for + A subclass of :exc:`OSError`, this exception is raised for address-related errors, i.e. for functions that use *h_errno* in the POSIX C API, including :func:`gethostbyname_ex` and :func:`gethostbyaddr`. The accompanying value is a pair ``(h_errno, string)`` representing an @@ -136,10 +159,12 @@ The module :mod:`socket` exports the following constants and functions: *string* represents the description of *h_errno*, as returned by the :c:func:`hstrerror` C function. + .. versionchanged:: 3.3 + This class was made a subclass of :exc:`OSError`. .. exception:: gaierror - A subclass of :exc:`socket.error`, this exception is raised for + A subclass of :exc:`OSError`, this exception is raised for address-related errors by :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 @@ -147,15 +172,19 @@ The module :mod:`socket` exports the following constants and functions: numeric *error* value will match one of the :const:`EAI_\*` constants defined in this module. + .. versionchanged:: 3.3 + This class was made a subclass of :exc:`OSError`. .. exception:: timeout - A subclass of :exc:`socket.error`, this exception is raised when a timeout + A subclass of :exc:`OSError`, this exception is raised when a timeout occurs on a socket which has had timeouts enabled via a prior call to :meth:`~socket.settimeout` (or implicitly through :func:`~socket.setdefaulttimeout`). The accompanying value is a string whose value is currently always "timed out". + .. versionchanged:: 3.3 + This class was made a subclass of :exc:`OSError`. .. data:: AF_UNIX AF_INET @@ -198,6 +227,7 @@ The module :mod:`socket` exports the following constants and functions: SOMAXCONN MSG_* SOL_* + SCM_* IPPROTO_* IPPORT_* INADDR_* @@ -215,6 +245,32 @@ The module :mod:`socket` exports the following constants and functions: in the Unix header files are defined; for a few symbols, default values are provided. +.. data:: AF_CAN + PF_CAN + SOL_CAN_* + CAN_* + + Many constants of these forms, documented in the Linux documentation, are + also defined in the socket module. + + Availability: Linux >= 2.6.25. + + .. versionadded:: 3.3 + + +.. data:: AF_RDS + PF_RDS + SOL_RDS + RDS_* + + Many constants of these forms, documented in the Linux documentation, are + also defined in the socket module. + + Availability: Linux >= 2.6.30. + + .. versionadded:: 3.3 + + .. data:: SIO_* RCVALL_* @@ -393,10 +449,15 @@ The module :mod:`socket` exports the following constants and functions: 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. + :const:`AF_INET6`, :const:`AF_UNIX`, :const:`AF_CAN` or :const:`AF_RDS`. The + socket type should be :const:`SOCK_STREAM` (the default), + :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other ``SOCK_`` + constants. The protocol number is usually zero and may be omitted in that + case or :const:`CAN_RAW` in case the address family is :const:`AF_CAN`. + + .. versionchanged:: 3.3 + The AF_CAN family was added. + The AF_RDS family was added. .. function:: socketpair([family[, type[, proto]]]) @@ -464,7 +525,7 @@ The module :mod:`socket` exports the following constants and functions: Unix manual page :manpage:`inet(3)` for details. 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 + :exc:`OSError` will be raised. Note that exactly what is valid depends on the underlying C implementation of :c:func:`inet_aton`. :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used @@ -481,7 +542,7 @@ The module :mod:`socket` exports the following constants and functions: argument. If the byte sequence passed to this function is not exactly 4 bytes in - length, :exc:`socket.error` will be raised. :func:`inet_ntoa` does not + length, :exc:`OSError` will be raised. :func:`inet_ntoa` does not support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual stack support. @@ -495,7 +556,7 @@ The module :mod:`socket` exports the following constants and functions: 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 + :exc:`OSError` will be raised. Note that exactly what is valid depends on both the value of *address_family* and the underlying implementation of :c:func:`inet_pton`. @@ -513,11 +574,54 @@ The module :mod:`socket` exports the following constants and functions: 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`. + :exc:`OSError` is raised for errors from the call to :func:`inet_ntop`. Availability: Unix (maybe not all platforms). +.. + XXX: Are sendmsg(), recvmsg() and CMSG_*() available on any + non-Unix platforms? The old (obsolete?) 4.2BSD form of the + interface, in which struct msghdr has no msg_control or + msg_controllen members, is not currently supported. + +.. function:: CMSG_LEN(length) + + Return the total length, without trailing padding, of an ancillary + data item with associated data of the given *length*. This value + can often be used as the buffer size for :meth:`~socket.recvmsg` to + receive a single item of ancillary data, but :rfc:`3542` requires + portable applications to use :func:`CMSG_SPACE` and thus include + space for padding, even when the item will be the last in the + buffer. Raises :exc:`OverflowError` if *length* is outside the + permissible range of values. + + Availability: most Unix platforms, possibly others. + + .. versionadded:: 3.3 + + +.. function:: CMSG_SPACE(length) + + Return the buffer size needed for :meth:`~socket.recvmsg` to + receive an ancillary data item with associated data of the given + *length*, along with any trailing padding. The buffer space needed + to receive multiple items is the sum of the :func:`CMSG_SPACE` + values for their associated data lengths. Raises + :exc:`OverflowError` if *length* is outside the permissible range + of values. + + Note that some systems might support ancillary data without + providing this function. Also note that setting the buffer size + using the results of this function may not precisely limit the + amount of ancillary data that can be received, since additional + data may be able to fit into the padding area. + + Availability: most Unix platforms, possibly others. + + .. versionadded:: 3.3 + + .. function:: getdefaulttimeout() Return the default timeout in seconds (float) for new socket objects. A value @@ -533,6 +637,49 @@ The module :mod:`socket` exports the following constants and functions: meanings. +.. function:: sethostname(name) + + Set the machine's hostname to *name*. This will raise a + :exc:`OSError` if you don't have enough rights. + + Availability: Unix. + + .. versionadded:: 3.3 + + +.. function:: if_nameindex() + + Return a list of network interface information + (index int, name string) tuples. + :exc:`OSError` if the system call fails. + + Availability: Unix. + + .. versionadded:: 3.3 + + +.. function:: if_nametoindex(if_name) + + Return a network interface index number corresponding to an + interface name. + :exc:`OSError` if no interface with the given name exists. + + Availability: Unix. + + .. versionadded:: 3.3 + + +.. function:: if_indextoname(if_index) + + Return a network interface name corresponding to a + interface index number. + :exc:`OSError` if no interface with the given index exists. + + Availability: Unix. + + .. versionadded:: 3.3 + + .. data:: SocketType This is a Python type object that represents the socket object type. It is the @@ -706,6 +853,109 @@ correspond to Unix system calls applicable to sockets. to zero. (The format of *address* depends on the address family --- see above.) +.. method:: socket.recvmsg(bufsize[, ancbufsize[, flags]]) + + Receive normal data (up to *bufsize* bytes) and ancillary data from + the socket. The *ancbufsize* argument sets the size in bytes of + the internal buffer used to receive the ancillary data; it defaults + to 0, meaning that no ancillary data will be received. Appropriate + buffer sizes for ancillary data can be calculated using + :func:`CMSG_SPACE` or :func:`CMSG_LEN`, and items which do not fit + into the buffer might be truncated or discarded. The *flags* + argument defaults to 0 and has the same meaning as for + :meth:`recv`. + + The return value is a 4-tuple: ``(data, ancdata, msg_flags, + address)``. The *data* item is a :class:`bytes` object holding the + non-ancillary data received. The *ancdata* item is a list of zero + or more tuples ``(cmsg_level, cmsg_type, cmsg_data)`` representing + the ancillary data (control messages) received: *cmsg_level* and + *cmsg_type* are integers specifying the protocol level and + protocol-specific type respectively, and *cmsg_data* is a + :class:`bytes` object holding the associated data. The *msg_flags* + item is the bitwise OR of various flags indicating conditions on + the received message; see your system documentation for details. + If the receiving socket is unconnected, *address* is the address of + the sending socket, if available; otherwise, its value is + unspecified. + + On some systems, :meth:`sendmsg` and :meth:`recvmsg` can be used to + pass file descriptors between processes over an :const:`AF_UNIX` + socket. When this facility is used (it is often restricted to + :const:`SOCK_STREAM` sockets), :meth:`recvmsg` will return, in its + ancillary data, items of the form ``(socket.SOL_SOCKET, + socket.SCM_RIGHTS, fds)``, where *fds* is a :class:`bytes` object + representing the new file descriptors as a binary array of the + native C :c:type:`int` type. If :meth:`recvmsg` raises an + exception after the system call returns, it will first attempt to + close any file descriptors received via this mechanism. + + Some systems do not indicate the truncated length of ancillary data + items which have been only partially received. If an item appears + to extend beyond the end of the buffer, :meth:`recvmsg` will issue + a :exc:`RuntimeWarning`, and will return the part of it which is + inside the buffer provided it has not been truncated before the + start of its associated data. + + On systems which support the :const:`SCM_RIGHTS` mechanism, the + following function will receive up to *maxfds* file descriptors, + returning the message data and a list containing the descriptors + (while ignoring unexpected conditions such as unrelated control + messages being received). See also :meth:`sendmsg`. :: + + import socket, array + + def recv_fds(sock, msglen, maxfds): + fds = array.array("i") # Array of ints + msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize)) + for cmsg_level, cmsg_type, cmsg_data in ancdata: + if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS): + # Append data, ignoring any truncated integers at the end. + fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)]) + return msg, list(fds) + + Availability: most Unix platforms, possibly others. + + .. versionadded:: 3.3 + + +.. method:: socket.recvmsg_into(buffers[, ancbufsize[, flags]]) + + Receive normal data and ancillary data from the socket, behaving as + :meth:`recvmsg` would, but scatter the non-ancillary data into a + series of buffers instead of returning a new bytes object. The + *buffers* argument must be an iterable of objects that export + writable buffers (e.g. :class:`bytearray` objects); these will be + filled with successive chunks of the non-ancillary data until it + has all been written or there are no more buffers. The operating + system may set a limit (:func:`~os.sysconf` value ``SC_IOV_MAX``) + on the number of buffers that can be used. The *ancbufsize* and + *flags* arguments have the same meaning as for :meth:`recvmsg`. + + The return value is a 4-tuple: ``(nbytes, ancdata, msg_flags, + address)``, where *nbytes* is the total number of bytes of + non-ancillary data written into the buffers, and *ancdata*, + *msg_flags* and *address* are the same as for :meth:`recvmsg`. + + Example:: + + >>> import socket + >>> s1, s2 = socket.socketpair() + >>> b1 = bytearray(b'----') + >>> b2 = bytearray(b'0123456789') + >>> b3 = bytearray(b'--------------') + >>> s1.send(b'Mary had a little lamb') + 22 + >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3]) + (22, [], 0, None) + >>> [b1, b2, b3] + [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')] + + Availability: most Unix platforms, possibly others. + + .. versionadded:: 3.3 + + .. method:: socket.recvfrom_into(buffer[, nbytes[, flags]]) Receive data from the socket, writing it into *buffer* instead of creating a @@ -754,6 +1004,41 @@ correspond to Unix system calls applicable to sockets. above.) +.. method:: socket.sendmsg(buffers[, ancdata[, flags[, address]]]) + + Send normal and ancillary data to the socket, gathering the + non-ancillary data from a series of buffers and concatenating it + into a single message. The *buffers* argument specifies the + non-ancillary data as an iterable of buffer-compatible objects + (e.g. :class:`bytes` objects); the operating system may set a limit + (:func:`~os.sysconf` value ``SC_IOV_MAX``) on the number of buffers + that can be used. The *ancdata* argument specifies the ancillary + data (control messages) as an iterable of zero or more tuples + ``(cmsg_level, cmsg_type, cmsg_data)``, where *cmsg_level* and + *cmsg_type* are integers specifying the protocol level and + protocol-specific type respectively, and *cmsg_data* is a + buffer-compatible object holding the associated data. Note that + some systems (in particular, systems without :func:`CMSG_SPACE`) + might support sending only one control message per call. The + *flags* argument defaults to 0 and has the same meaning as for + :meth:`send`. If *address* is supplied and not ``None``, it sets a + destination address for the message. The return value is the + number of bytes of non-ancillary data sent. + + The following function sends the list of file descriptors *fds* + over an :const:`AF_UNIX` socket, on systems which support the + :const:`SCM_RIGHTS` mechanism. See also :meth:`recvmsg`. :: + + import socket, array + + def send_fds(sock, msg, fds): + return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))]) + + Availability: most Unix platforms, possibly others. + + .. versionadded:: 3.3 + + .. method:: socket.setblocking(flag) Set blocking or non-blocking mode of the socket: if *flag* is false, the @@ -795,9 +1080,7 @@ correspond to Unix system calls applicable to sockets. 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. Depending on the platform, shutting down one half of the connection - can also close the opposite half (e.g. on Mac OS X, ``shutdown(SHUT_WR)`` does - not allow further reads on the other end of the connection). + disallowed. Note that there are no methods :meth:`read` or :meth:`write`; use :meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead. @@ -942,13 +1225,13 @@ sends traffic to the first one connected successfully. :: af, socktype, proto, canonname, sa = res try: s = socket.socket(af, socktype, proto) - except socket.error as msg: + except OSError as msg: s = None continue try: s.bind(sa) s.listen(1) - except socket.error as msg: + except OSError as msg: s.close() s = None continue @@ -977,12 +1260,12 @@ sends traffic to the first one connected successfully. :: af, socktype, proto, canonname, sa = res try: s = socket.socket(af, socktype, proto) - except socket.error as msg: + except OSError as msg: s = None continue try: s.connect(sa) - except socket.error as msg: + except OSError as msg: s.close() s = None continue @@ -996,7 +1279,7 @@ sends traffic to the first one connected successfully. :: print('Received', repr(data)) -The last example shows how to write a very simple network sniffer with raw +The next example shows how to write a very simple network sniffer with raw sockets on Windows. The example requires administrator privileges to modify the interface:: @@ -1021,11 +1304,51 @@ the interface:: # disabled promiscuous mode s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF) +The last example shows how to use the socket interface to communicate to a CAN +network. This example might require special priviledge:: + + import socket + import struct + + + # CAN frame packing/unpacking (see 'struct can_frame' in <linux/can.h>) + + can_frame_fmt = "=IB3x8s" + can_frame_size = struct.calcsize(can_frame_fmt) + + def build_can_frame(can_id, data): + can_dlc = len(data) + data = data.ljust(8, b'\x00') + return struct.pack(can_frame_fmt, can_id, can_dlc, data) + + def dissect_can_frame(frame): + can_id, can_dlc, data = struct.unpack(can_frame_fmt, frame) + return (can_id, can_dlc, data[:can_dlc]) + + + # create a raw socket and bind it to the 'vcan0' interface + s = socket.socket(socket.AF_CAN, socket.SOCK_RAW, socket.CAN_RAW) + s.bind(('vcan0',)) + + while True: + cf, addr = s.recvfrom(can_frame_size) + + print('Received: can_id=%x, can_dlc=%x, data=%s' % dissect_can_frame(cf)) + + try: + s.send(cf) + except OSError: + print('Error sending CAN frame') + + try: + s.send(build_can_frame(0x01, b'\x01\x02\x03')) + except OSError: + print('Error sending CAN frame') Running an example several times with too small delay between executions, could lead to this error:: - socket.error: [Errno 98] Address already in use + OSError: [Errno 98] Address already in use This is because the previous execution has left the socket in a ``TIME_WAIT`` state, and can't be immediately reused. |