19.1. socket — Low-level networking interface

Source code: Lib/socket.py

---

This module provides access to the BSD socket interface. It is available on all modern Unix systems, Windows, MacOS, and probably additional platforms.

備註

Some behavior may be platform dependent, since calls are made to the operating system socket APIs.

The Python interface is a straightforward transliteration of the Unix system call and library interface for sockets to Python’s object-oriented style: the socket() function returns a socket object whose methods implement the various socket system calls. Parameter types are somewhat higher-level than in the C interface: as with read() and write() operations on Python files, buffer allocation on receive operations is automatic, and buffer length is implicit on send operations.

也參考

Module socketserver

Classes that simplify writing network servers.

Module ssl

A TLS/SSL wrapper for socket objects.

19.1.1. Socket families

Depending on the system and the build options, various socket families are supported by this module.

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 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 bytes-like 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 bytes-like object can be used for either type of address when passing it as an argument.

  3.3 版更變: Previously, AF_UNIX socket paths were assumed to use UTF-8 encoding.

  3.5 版更變: Writable bytes-like object is now accepted.

• A pair (host, port) is used for the 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 integer.

  • For IPv4 addresses, two special forms are accepted instead of a host address: '' represents INADDR_ANY, which is used to bind to all interfaces, and the string '<broadcast>' represents INADDR_BROADCAST. This behavior is not compatible with IPv6, therefore, you may want to avoid these if you intend to support IPv6 with your Python programs.

• For AF_INET6 address family, a four-tuple (host, port, flowinfo, scopeid) is used, where flowinfo and scopeid represent the sin6_flowinfo and sin6_scope_id members in struct sockaddr_in6 in C. For 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.

  3.7 版更變: For multicast addresses (with scopeid meaningful) address may not contain %scope (or zone id) part. This information is superfluous and may be safely omitted (recommended).

• AF_NETLINK sockets are represented as pairs (pid, groups).

• Linux-only support for TIPC is available using the 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.

• A tuple (interface, ) is used for the 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.

  • CAN_ISOTP protocol require a tuple (interface, rx_addr, tx_addr) where both additional parameters are unsigned long integer that represent a CAN identifier (standard or extended).

• A string or a tuple (id, unit) is used for the SYSPROTO_CONTROL protocol of the 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.

  3.3 版新加入.

• AF_BLUETOOTH supports the following protocols and address formats:

  • BTPROTO_L2CAP accepts (bdaddr, psm) where bdaddr is the Bluetooth address as a string and psm is an integer.

  • BTPROTO_RFCOMM accepts (bdaddr, channel) where bdaddr is the Bluetooth address as a string and channel is an integer.

  • BTPROTO_HCI accepts (device_id,) where device_id is either an integer or a string with the Bluetooth address of the interface. (This depends on your OS; NetBSD and DragonFlyBSD expect a Bluetooth address while everything else expects an integer.)

    3.2 版更變: NetBSD and DragonFlyBSD support added.

  • BTPROTO_SCO accepts bdaddr where bdaddr is a bytes object containing the Bluetooth address in a string format. (ex. b'12:23:34:45:56:67') This protocol is not supported under FreeBSD.

• AF_ALG is a Linux-only socket based interface to Kernel cryptography. An algorithm socket is configured with a tuple of two to four elements (type, name [, feat [, mask]]), where:

  • type is the algorithm type as string, e.g. aead, hash, skcipher or rng.
  • name is the algorithm name and operation mode as string, e.g. sha256, hmac(sha256), cbc(aes) or drbg_nopr_ctr_aes256.
  • feat and mask are unsigned 32bit integers.

  Availability Linux 2.6.38, some algorithm types require more recent Kernels.

  3.6 版新加入.

• AF_VSOCK allows communication between virtual machines and their hosts. The sockets are represented as a (CID, port) tuple where the context ID or CID and port are integers.

  Availability: Linux >= 4.8 QEMU >= 2.8 ESX >= 4.0 ESX Workstation >= 6.5

  3.7 版新加入.

• Certain other address families (AF_PACKET, AF_CAN) support specific representations.

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.

All errors raise exceptions. The normal exceptions for invalid argument types and out-of-memory conditions can be raised; starting from Python 3.3, errors related to socket or address semantics raise OSError or one of its subclasses (they used to raise socket.error).

Non-blocking mode is supported through setblocking(). A generalization of this based on timeouts is supported through settimeout().

19.1.2. Module contents

The module socket exports the following elements.

19.1.2.1. Exceptions

exception socket.error

A deprecated alias of OSError.

3.3 版更變: Following PEP 3151, this class was made an alias of OSError.

exception socket.herror

A subclass of OSError, this exception is raised for address-related errors, i.e. for functions that use h_errno in the POSIX C API, including gethostbyname_ex() and gethostbyaddr(). The accompanying value is a pair (h_errno, string) representing an error returned by a library call. h_errno is a numeric value, while string represents the description of h_errno, as returned by the hstrerror() C function.

3.3 版更變: This class was made a subclass of OSError.

exception socket.gaierror

A subclass of OSError, this exception is raised for address-related errors by getaddrinfo() and 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 gai_strerror() C function. The numeric error value will match one of the EAI_* constants defined in this module.

3.3 版更變: This class was made a subclass of OSError.

exception socket.timeout

A subclass of OSError, this exception is raised when a timeout occurs on a socket which has had timeouts enabled via a prior call to settimeout() (or implicitly through setdefaulttimeout()). The accompanying value is a string whose value is currently always 「timed out」.

3.3 版更變: This class was made a subclass of OSError.

19.1.2.2. Constants

The AF_* and SOCK_* constants are now AddressFamily and SocketKind IntEnum collections.

3.4 版新加入.

socket.AF_UNIX

socket.AF_INET

socket.AF_INET6

These constants represent the address (and protocol) families, used for the first argument to socket(). If the AF_UNIX constant is not defined then this protocol is unsupported. More constants may be available depending on the system.

socket.SOCK_STREAM

socket.SOCK_DGRAM

socket.SOCK_RAW

socket.SOCK_RDM

socket.SOCK_SEQPACKET

These constants represent the socket types, used for the second argument to socket(). More constants may be available depending on the system. (Only SOCK_STREAM and SOCK_DGRAM appear to be generally useful.)

socket.SOCK_CLOEXEC

socket.SOCK_NONBLOCK

These two constants, if defined, can be combined with the socket types and allow you to set some flags atomically (thus avoiding possible race conditions and the need for separate calls).

也參考

Secure File Descriptor Handling for a more thorough explanation.

Availability: Linux >= 2.6.27.

3.2 版新加入.

SO_*

socket.SOMAXCONN

MSG_*

SOL_*

SCM_*

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 setsockopt() and 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.

3.6 版更變: SO_DOMAIN, SO_PROTOCOL, SO_PEERSEC, SO_PASSSEC, TCP_USER_TIMEOUT, TCP_CONGESTION were added.

3.6.5 版更變: On Windows, TCP_FASTOPEN, TCP_KEEPCNT appear if run-time Windows supports.

3.7 版更變: TCP_NOTSENT_LOWAT was added.

On Windows, TCP_KEEPIDLE, TCP_KEEPINTVL appear if run-time Windows supports.

socket.AF_CAN

socket.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.

3.3 版新加入.

socket.CAN_BCM

CAN_BCM_*

CAN_BCM, in the CAN protocol family, is the broadcast manager (BCM) protocol. Broadcast manager constants, documented in the Linux documentation, are also defined in the socket module.

Availability: Linux >= 2.6.25.

3.4 版新加入.

socket.CAN_RAW_FD_FRAMES

Enables CAN FD support in a CAN_RAW socket. This is disabled by default. This allows your application to send both CAN and CAN FD frames; however, you one must accept both CAN and CAN FD frames when reading from the socket.

This constant is documented in the Linux documentation.

Availability: Linux >= 3.6.

3.5 版新加入.

socket.CAN_ISOTP

CAN_ISOTP, in the CAN protocol family, is the ISO-TP (ISO 15765-2) protocol. ISO-TP constants, documented in the Linux documentation.

Availability: Linux >= 2.6.25

3.7 版新加入.

socket.AF_RDS

socket.PF_RDS

socket.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.

3.3 版新加入.

socket.SIO_RCVALL

socket.SIO_KEEPALIVE_VALS

socket.SIO_LOOPBACK_FAST_PATH

RCVALL_*

Constants for Windows』 WSAIoctl(). The constants are used as arguments to the ioctl() method of socket objects.

3.6 版更變: SIO_LOOPBACK_FAST_PATH was added.

TIPC_*

TIPC related constants, matching the ones exported by the C socket API. See the TIPC documentation for more information.

socket.AF_ALG

socket.SOL_ALG

ALG_*

Constants for Linux Kernel cryptography.

Availability: Linux >= 2.6.38.

3.6 版新加入.

socket.AF_VSOCK

socket.IOCTL_VM_SOCKETS_GET_LOCAL_CID

VMADDR*

SO_VM*

Constants for Linux host/guest communication.

Availability: Linux >= 4.8.

3.7 版新加入.

socket.AF_LINK

Availability: BSD, OSX.

3.4 版新加入.

socket.has_ipv6

This constant contains a boolean value which indicates if IPv6 is supported on this platform.

socket.BDADDR_ANY

socket.BDADDR_LOCAL

These are string constants containing Bluetooth addresses with special meanings. For example, BDADDR_ANY can be used to indicate any address when specifying the binding socket with BTPROTO_RFCOMM.

socket.HCI_FILTER

socket.HCI_TIME_STAMP

socket.HCI_DATA_DIR

For use with BTPROTO_HCI. HCI_FILTER is not available for NetBSD or DragonFlyBSD. HCI_TIME_STAMP and HCI_DATA_DIR are not available for FreeBSD, NetBSD, or DragonFlyBSD.

19.1.2.3. Functions

19.1.2.3.1. Creating sockets

The following functions all create socket objects.

socket.socket(family=AF_INET, type=SOCK_STREAM, proto=0, fileno=None)

Create a new socket using the given address family, socket type and protocol number. The address family should be AF_INET (the default), AF_INET6, AF_UNIX, AF_CAN or AF_RDS. The socket type should be SOCK_STREAM (the default), SOCK_DGRAM, SOCK_RAW or perhaps one of the other SOCK_ constants. The protocol number is usually zero and may be omitted or in the case where the address family is AF_CAN the protocol should be one of CAN_RAW, CAN_BCM or CAN_ISOTP

If fileno is specified, the values for family, type, and proto are auto-detected from the specified file descriptor. Auto-detection can be overruled by calling the function with explicit family, type, or proto arguments. This only affects how Python represents e.g. the return value of socket.getpeername() but not the actual OS resource. Unlike socket.fromfd(), fileno will return the same socket and not a duplicate. This may help close a detached socket using socket.close().

The newly created socket is non-inheritable.

3.3 版更變: The AF_CAN family was added. The AF_RDS family was added.

3.4 版更變: The CAN_BCM protocol was added.

3.4 版更變: The returned socket is now non-inheritable.

3.7 版更變: The CAN_ISOTP protocol was added.

3.7 版更變: When SOCK_NONBLOCK or SOCK_CLOEXEC bit flags are applied to type they are cleared, and socket.type will not reflect them. They are still passed to the underlying system socket() call. Therefore::

sock = socket.socket(

socket.AF_INET, socket.SOCK_STREAM | socket.SOCK_NONBLOCK)

will still create a non-blocking socket on OSes that support SOCK_NONBLOCK, but sock.type will be set to socket.SOCK_STREAM.

socket.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 socket() function above. The default family is AF_UNIX if defined on the platform; otherwise, the default is AF_INET.

The newly created sockets are non-inheritable.

3.2 版更變: The returned socket objects now support the whole socket API, rather than a subset.

3.4 版更變: The returned sockets are now non-inheritable.

3.5 版更變: Windows support added.

socket.create_connection(address[, timeout[, source_address]])

Connect to a TCP service listening on the Internet address (a 2-tuple (host, port)), and return the socket object. This is a higher-level function than socket.connect(): if host is a non-numeric hostname, it will try to resolve it for both AF_INET and AF_INET6, and then try to connect to all possible addresses in turn until a connection succeeds. This makes it easy to write clients that are compatible to both IPv4 and IPv6.

Passing the optional timeout parameter will set the timeout on the socket instance before attempting to connect. If no timeout is supplied, the global default timeout setting returned by getdefaulttimeout() is used.

If supplied, source_address must be a 2-tuple (host, port) for the socket to bind to as its source address before connecting. If host or port are 『』 or 0 respectively the OS default behavior will be used.

3.2 版更變: source_address was added.

socket.fromfd(fd, family, type, proto=0)

Duplicate the file descriptor fd (an integer as returned by a file object’s fileno() method) and build a socket object from the result. Address family, socket type and protocol number are as for the 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.

The newly created socket is non-inheritable.

3.4 版更變: The returned socket is now non-inheritable.

socket.fromshare(data)

Instantiate a socket from data obtained from the socket.share() method. The socket is assumed to be in blocking mode.

Availability: Windows.

3.3 版新加入.

socket.SocketType

This is a Python type object that represents the socket object type. It is the same as type(socket(...)).

19.1.2.3.2. Other functions

The socket module also offers various network-related services:

socket.close(fd)

Close a socket file descriptor. This is like os.close(), but for sockets. On some platforms (most noticeable Windows) os.close() does not work for socket file descriptors.

3.7 版新加入.

socket.getaddrinfo(host, port, family=0, type=0, proto=0, flags=0)

Translate the host/port argument into a sequence of 5-tuples that contain all the necessary arguments for creating a socket connected to that service. host is a domain name, a string representation of an IPv4/v6 address or None. port is a string service name such as 'http', a numeric port number or None. By passing None as the value of host and port, you can pass NULL to the underlying C API.

The family, type and proto arguments can be optionally specified in order to narrow the list of addresses returned. Passing zero as a value for each of these arguments selects the full range of results. The flags argument can be one or several of the AI_* constants, and will influence how results are computed and returned. For example, AI_NUMERICHOST will disable domain name resolution and will raise an error if host is a domain name.

The function returns a list of 5-tuples with the following structure:

(family, type, proto, canonname, sockaddr)

In these tuples, family, type, proto are all integers and are meant to be passed to the socket() function. canonname will be a string representing the canonical name of the host if AI_CANONNAME is part of the flags argument; else canonname will be empty. sockaddr is a tuple describing a socket address, whose format depends on the returned family (a (address, port) 2-tuple for AF_INET, a (address, port, flow info, scope id) 4-tuple for AF_INET6), and is meant to be passed to the socket.connect() method.

The following example fetches address information for a hypothetical TCP connection to example.org on port 80 (results may differ on your system if IPv6 isn’t enabled):

>>> socket.getaddrinfo("example.org", 80, proto=socket.IPPROTO_TCP)
[(<AddressFamily.AF_INET6: 10>, <SocketType.SOCK_STREAM: 1>,
 6, '', ('2606:2800:220:1:248:1893:25c8:1946', 80, 0, 0)),
 (<AddressFamily.AF_INET: 2>, <SocketType.SOCK_STREAM: 1>,
 6, '', ('93.184.216.34', 80))]

3.2 版更變: parameters can now be passed using keyword arguments.

3.7 版更變: for IPv6 multicast addresses, string representing an address will not contain %scope part.