Import socket python что это

# Receiving data via UDP

UDP is a connectionless protocol. This means that peers sending messages do not require establishing a connection before sending messages. socket.recvfrom thus returns a tuple ( msg [the message the socket received], addr [the address of the sender])

A UDP server using solely the socket module:

Below is an alternative implementation using socketserver.UDPServer :

By default, sockets block. This means that execution of the script will wait until the socket receives data.

# Sending data via TCP

Sending data over the internet is made possible using multiple modules. The sockets module provides low-level access to the underlying Operating System operations responsible for sending or receiving data from other computers or processes.

The following code sends the byte string b’Hello’ to a TCP server listening on port 6667 on the host localhost and closes the connection when finished:

Socket output is blocking by default, that means that the program will wait in the connect and send calls until the action is ‘completed’. For connect that means the server actually accepting the connection. For send it only means that the operating system has enough buffer space to queue the data to be send later.

Sockets should always be closed after use.

# Multi-threaded TCP Socket Server

When run with no arguments, this program starts a TCP socket server that listens for connections to 127.0.0.1 on port 5000 . The server handles each connection in a separate thread.

When run with the -c argument, this program connects to the server, reads the client list, and prints it out. The client list is transferred as a JSON string. The client name may be specified by passing the -n argument. By passing different names, the effect on the client list may be observed.

client_list.py

Server Output

Client Output

The receive buffers are limited to 1024 bytes. If the JSON string representation of the client list exceeds this size, it will be truncated. This will cause the following exception to be raised:

What is a socket?

A socket is one endpoint of a two-way communication link between two programs running on ( a node in) a computer network. One socket (the server) listens on a particular port on and IP address, while another socket(the client) connects to the listening server to achieve communication.

Primarily, the way sockets send data is controlled by two properties — the address family, which determines the network layer protocol used and the socket type which determines the transport layer protocol used.

In this article, we will be learning how to use Python’s socket module ( socket ) — which is an interface to the Berkey sockets API, a low-level socket interface implemented by most modern operating systems. All examples and code samples in this article are written in Python 3.6.

Socket Types

Depending on the transport layer protocol used, sockets can either be:

1. SOCK_DGRAM for message-oriented datagram transport. These sockets are usually associated with the User Datagram Protocol (UDP) which provides an unreliable delivery of individual messages. Datagram sockets are commonly used when the order of messages is not important, such as when sending out the same data to multiple clients.
2. SOCK_STREAM for stream-oriented transport often associated with the Transmission Control Protocol (TCP). TCP provides a reliable and ordered delivery of byte between two host, with error handling and control, making it useful for implementing applications that involve transfer of large amounts of data.

An Overview of The Sockets Module

To use sockets in Python we will need to import the socket module.

The primary way of using the sockets module is through the sockets() function which returns a socket object with methods to implement various system socket calls. Python sockets supports a number of address families under the network layer protocol, mainly:

1. AF_INET — this is the most common, and uses IPv4 for network addressing. Most of the internet networking is presently done using IPv4.
2. AF_INET6 — this is the next generation of the internet protocol using IPv6 and provides a number of features not available under IPv4.
3. AF_UNIX — finally, this is the address family for Unix Domain Sockets (UDS), an inter-process communication protocol available on POSIX-compliant systems. This implementation allows passing of data between processes on an operating system without going through the network.

Network related services

In this section we will look at some socket functions and methods that provide access to network related tasks.

• gethostname() to get the official name of the current host.

• gethostbyname() converts the name of a server into its numerical address by consulting the operating system’s DNS configuration.

• gethostbyname_ex() to get more naming information about a server.

• gethostbyaddr() to perform a reverse lookup for a domain’s name.
• getfqdn() to convert a partial domain into a fully qualified domain name.

More network-related functions can be accessed from the python documentation referenced in the conclusion section below.

TCP/IP client-server communication

As we have established, sockets can either be configured to act as a server or client, to achieve bi-directional communication over TCP using the SOCK_STREAM family. In this example, we shall implement a simple echo application that receives all incoming data and sends them back to the sender. For that we will implement both client and server sockets. Furthermore, we will use the local loopback address 127.0.0.1 or localhost for our connections.

Echo Server

To set up a server, it must perform the sequence of methods socket() , bind() , listen() , and accept() .

• socket() creates a new socket given the address family and a socket type.
• bind() binds our socket object to a particular address composed of a host and port number.
• listen() allows the server to start accepting connections and takes in an argument, backlog , which is the number of unaccepted connections that the system can allow before refusing all new connections.
• accept() accepts incoming connections and returns a a tuple of (conn, address) where conn is a new socket that can be used to send and receive messages from the connection and address is the address bound to the socket on the other end of the connection.
• close() marks the socket as closed and can no longer accept connections.

We initialize a socket object, sock by passing in the address family ( socket.AF_INET ) and socket type ( socket.SOCK_STREAM ) to the socket.socket() function.

1. Next, we bind the socket object to an address of the form ('localhost',10000) — bind to localhost on port 10000 , using the bind() method.
2. Listen for incoming connections with a backlog of 1.
3. Continuously wait for and accept connections by calling sock.accept() and unpacking the return value into connection and client_address .
4. Call recv(16) on the returned connection to receive the data on chunks of 16.
5. If data as been received, then we transmit the received data back to the sender by calling the method sendall(data) on the connection, otherwise we print out a statement indicating no data has been received.
6. Finally when communication with the client is complete — all the chunks of the message have been transmitted, we call close() on the connection object. We use a try/finally block to ensure that close() is called even in the event of an error when transmitting messages.

Echo Client

Unlike a server, a client only needs to execute the sequence of socket() and connect() .

• connect() connects the socket to an address.

In this example:

1. We initialize a socket object as in the server.
2. Next we connect the socket to the same address that the server is listening on, in this case, ('localhost',10000) , using the connect(address) method.
3. In a try/finally block, we compose our message as a byte string and use sendall() method on the socket object with the message as an argument.
4. We then set up variables amount_received with an initial value of 0 and amount_expected which is just the length of our message, to keep track of the message chunks as we receive them.
5. Calling recv(16) on the socket object allows us to receive the message from our server in chunks of 16, and we keep receiving until amount_received is equal to amount_expected .
6. Finally we mark the socket as closed.

Running out server and client scripts on separate terminal windows, this is the output from the server;

UDP client-server communication

Unlike the case with TCP transmission which streams messages in an ordered manner, UDP is message oriented and does not require a long-lived connection. A message in this case has to fit within a single datagram and delivery is not assured.

Echo Server

Here, we’ll only execute the socket() and bind() sequence since, there isn’t really a connection to listen for. Instead we only need to bind the socket to a particular address and wait for incoming messages. We will then read the incoming messages using the recvfrom() method and send them back with sendto() .

• recvfrom() receives data from a socket and return a tuple of (bytes, address) where bytes is a bytes object containing the received data and address is the address of the sender.
• sendto(bytes,address) sends data(given by bytes ) to a socket bound to the address as defined by address .

In the example above:

1. We create a socket object using socket.socket(socket.AF_INET,socket.SOCK_DGRAM) . Please note that here we use the socket.socket_DGRAM socket type since we are using UDP.
2. Next we bind the socket to the ('localhost',10000) and wait for incoming messages.
3. When a message arrives, we proceed to read it with recvfrom(4096) , where 4096 is the number of bytes to be read, and unpack the return value in to data and address .At this point we can print out the length of data .
4. If some data has been received, we send it back to the sender using the sendto() method and print out the length of the return value — which is the sent data.

Echo Client

This client is similar to the server above, only that it doesn’t bind the socket to any address. Instead, the it uses sendto() to send messages to the server’s address.

1. We instantiate a sock object as in the server above.
2. We then compose a message as a byte string, and define a server_address as a tuple of the host and the port number bound to the server we wish to send messages to.
3. Inside a try/finally block, we send the message and wait for a response, printing the the data in both cases.
4. Finally we mark the socket as closed.

This is the output when the client and server scripts are run on the server:

Unix Domain Sockets

These are largely similar to TCP sockets with basically two exceptions:

1. The socket address in this case is a path on the file system such as ./socket_file unlike in the TCP sockets where the address was a tuple of a host name and a port number.
2. Since the node created to represent the socket is a file, it persists even after the socket is closed, and as such it’s supposed to be removed whenever the server starts up.

To implement a similar client-server communication setup with UDS, we would need to slightly modify the example of TCP above.

Echo Server

Here we alter the server_address variable in the script to a file system path, in this case ./socket_file .

Since we also need to make sure the node doesn’t already exist when starting the server, we use a try/except block to delete the file using os.unlink() if it exists.

Echo Client

In this case, we also replace the server_address variable to the file path that has been bound to the server.

Running the client and server results in an output almost similar to the TCP case. For the server we get:

Permissions

Since UDS sockets are represented by nodes on the the file system, this implies that standard file system permissions can be used to control access to the server. For instance, lets try to change the ownership of the existing node to a root user.

As we can see, connecting to the server as a regular user fails, meaning only a user with the correct permissions (in this case the root user), can access the server.

Dealing with Multiple connections — Multicast

When dealing with multiple clients, maintaining several point-to-point connections can be cumbersome for applications due to the increases bandwidth and processing needs. This is where multicast messages come in. With multicast, messages are delivered to multiple endpoints simultaneously. This method achieves increased efficiency since delivery of messages to all recipients is delegated to the network infrastructure.

Multicast messages are sent using UDP, since TCP assumes a pair of communicating endpoints. The addresses for multicast messages, identified as multicast groups, are a subset of IPv4 addresses, usually between the range of 224.0.0.0 to 239.255.255.255. Network routers and switches treat addresses in this range as special since they are reserved for multicast, ensuring messages sent to the group are distributed to all clients that join the group.

Send Multicast Messages

To send messages we use an ordinary sento() method with a multicast group as the address. Moreover, we also need to specify a Time To Live(TTL) value which determines how far the messages should be broadcast from the sender. The default TTL of 1, will result in messages being sent only to hosts within the local network. We shall use setsockopt() with the IP_MULTICAST_TTL option to set the TTL, which should be packed into a single byte.
We shall also set a timeout value on the socket, to prevent it from waiting indefinitely for responses, since we have no idea how many responses we expect to get from the network.

In this example:

1. We create a socket of type socket.SOCK_DGRAM , compose or message as a byte string and bind our socket to the multicast group address (‘224.10.10.10’, 10000) .
2. We then set a timeout of 0.2 using sock.settimeout(0.2) .
3. Using the struct module, we pack the number 1 into a byte and assign the byte to ttl .
4. Using setsockopt() we set the IP_MULTICAST_TTL option of the socket to the ttl we just created above and send the message using sendto() .
5. We then wait for responses from other hosts on the network, as long as the wait hasn’t timed out and print out the responses.

Receiving Multicast Messages

To receive messages, after creating our ordinary socket and binding it to a port, we would need to add it to the multicast group. This can be done by using the setsockopts() to set the IP_ADD_MEMBERSHIP option, which should be packed into an 8-byte representation of the multicast group, and the network interface on which the server should listen for connections. We shall use socket.inet_aton() to convert the multicast group IPv4 address from dotted-quad string format ( ‘224.10.10.10’ ) to 32-bit packed binary format.

In this example:

1. To add the socket to the multicast group, we use struct to pack the group address given by socket.inet_aton(multicast_group) and the network interface given by socket.INADDR_ANY into an 8-byte representation, which we then set to the socket’s IP_ADD_MEMBERSHIP .
2. As the socket receives messages, we use recvfrom(1024) to unpack the response into data and address , and send out an acknowlegement to the address using sendto() .

On running both scripts, on different hosts (A and B), this is the output of the multicast sender on Host A:

And receiver on Host B:

Sending Binary Data

So far we have been transmitting streams of text data encoded as bytes through our sockets. Sockets can also transmit binary data as streams of bytes. We can use struct to pack the binary data to prepare it for transmission. However, when sending multi-byte data, it is important that both sender and recipient know the order in which the bytes are. This is useful in reconstructing the bytes at the recipient’s end.

Binary Client

We shall now implement a binary client that sends an integer, a string and a floating point number by packaging the data into a series of bytes.

Here we set up a socket of type socket.SOCK_STREAM and connect it to our server address. We then use a struct.Struct('I 2s f') specifier to pack the data before sending with sendall() .

Binary Server

On the other hand we have a server, that listens on the server address for incoming connections. After accepting a connection and receiving data we then proceed to unpack the data using a struct.Struct('I 2s f') specifier. Note that we use the same specifier on both ends of the communication so that the received bytes are interpreted in the same order they were packed.

The output we get from the client:

From the server output, the floating point numbers loses some precision as a result of packing and unpacking. Otherwise everything else is transmitted as is.

Blocking and Timeouts

By default, sockets operate in a blocking mode. This means that sending or receiving data pauses execution of the program until the the socket that’s receiving or sending data is ready. Sometimes, this mode of operation can result in a dreadlock whereby both endpoints are waiting for the other to send or receive data.

To try and overcome this challenge, sockets have an option to unset blocking, using the method socket.setblocking() , which has a default value of 1, i.e blocking is on. To disable blocking we call socket.setblocking(0) . However, this presents yet another challenge; if a socket is not ready for an operation with blocking disabled, then a socket.error is raised.

Another solution therefore, involves setting a timeout, using socket.settimeout(float) to a number( float ) of seconds during which blocking is on before evaluating whether the socket is ready or not. This timeout method is applicable in most cases since it acts as a compromise between blocking and not blocking.

Troubleshooting

As we can all attest to, some times things don’t work and more often than not, it’s never obvious why. It could be a issue with the code in which case looking at the errors and traceback could point us in the right direction. In such cases, referring to the official documentation would be the first option.

However, sometimes it could be configuration troubles on the client, server, or even the network infrastructure. To probe such issues we could use ping or netstat to identify the source of problems.

• ping — works directly with the TCP/IP stack, independent of any other application running on a host, to determine the status of the host, whether it’s up or not. ping works by sending ICMP echo request packets to the target host and waiting for an ICMP echo reply.
  Below is an example of ping running on Ubuntu:

• netstat —gives information sockets and their current states. Let’s fire up the TCP echo server and observe the output of netstat . From this we can tell that our server is presently using the tcp protocol, listening (state of LISTEN ) on port 10000 and host 127.0.0.1 .

Conclusion

We have covered quite a number of concepts in this article. However sockets and networking are very broad and it is not possible to cover everything in a single article. To have a better understanding of these concepts, it is imperative that we practise more. The socket module in particular has so many methods, functions and attributes that we haven’t covered, please feel free to refer to the official documentation. The internet also also a lot of information on socket programming and networking in general.

socket — Low-level networking interface¶

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

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

Availability : not Emscripten, not WASI.

This module does not work or is not available on WebAssembly platforms wasm32-emscripten and wasm32-wasi . See WebAssembly platforms for more information.

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.

Classes that simplify writing network servers.

A TLS/SSL wrapper for socket objects.

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.

Changed in version 3.3: Previously, AF_UNIX socket paths were assumed to use UTF-8 encoding.

Changed in version 3.5: 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, scope_id) is used, where flowinfo and scope_id represent the sin6_flowinfo and sin6_scope_id members in struct sockaddr_in6 in C. For socket module methods, flowinfo and scope_id can be omitted just for backward compatibility. Note, however, omission of scope_id can cause problems in manipulating scoped IPv6 addresses.

Changed in version 3.7: For multicast addresses (with scope_id meaningful) address may not contain %scope_id (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).

CAN_J1939 protocol require a tuple (interface, name, pgn, addr) where additional parameters are 64-bit unsigned integer representing the ECU name, a 32-bit unsigned integer representing the Parameter Group Number (PGN), and an 8-bit integer representing the address.

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.

New in version 3.3.

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.)

Changed in version 3.2: 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.

Some algorithm types require more recent Kernels.

New in version 3.6.

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.

New in version 3.7.

AF_PACKET is a low-level interface directly to network devices. The packets are represented by the tuple (ifname, proto[, pkttype[, hatype[, addr]]]) where:

ifname — String specifying the device name.

proto — An in network-byte-order integer specifying the Ethernet protocol number.

pkttype — Optional integer specifying the packet type:

PACKET_HOST (the default) — Packet addressed to the local host.

PACKET_BROADCAST — Physical-layer broadcast packet.

PACKET_MULTICAST — Packet sent to a physical-layer multicast address.

PACKET_OTHERHOST — Packet to some other host that has been caught by a device driver in promiscuous mode.

PACKET_OUTGOING — Packet originating from the local host that is looped back to a packet socket.

hatype — Optional integer specifying the ARP hardware address type.

addr — Optional bytes-like object specifying the hardware physical address, whose interpretation depends on the device.

AF_QIPCRTR is a Linux-only socket based interface for communicating with services running on co-processors in Qualcomm platforms. The address family is represented as a (node, port) tuple where the node and port are non-negative integers.

New in version 3.8.

IPPROTO_UDPLITE is a variant of UDP which allows you to specify what portion of a packet is covered with the checksum. It adds two socket options that you can change. self.setsockopt(IPPROTO_UDPLITE, UDPLITE_SEND_CSCOV, length) will change what portion of outgoing packets are covered by the checksum and self.setsockopt(IPPROTO_UDPLITE, UDPLITE_RECV_CSCOV, length) will filter out packets which cover too little of their data. In both cases length should be in range(8, 2**16, 8) .

Such a socket should be constructed with socket(AF_INET, SOCK_DGRAM, IPPROTO_UDPLITE) for IPv4 or socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDPLITE) for IPv6.

New in version 3.9.

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. Errors related to socket or address semantics raise OSError or one of its subclasses.

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

Module contents¶

The module socket exports the following elements.

Exceptions¶

A deprecated alias of OSError .

Changed in version 3.3: Following PEP 3151, this class was made an alias of OSError .

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.

Changed in version 3.3: This class was made a subclass of OSError .

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.

Changed in version 3.3: This class was made a subclass of OSError .

A deprecated alias of TimeoutError .

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”.

Changed in version 3.3: This class was made a subclass of OSError .

Changed in version 3.10: This class was made an alias of TimeoutError .

Constants¶

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

New in version 3.4.

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).

New in version 3.2.

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.

Changed in version 3.6: SO_DOMAIN , SO_PROTOCOL , SO_PEERSEC , SO_PASSSEC , TCP_USER_TIMEOUT , TCP_CONGESTION were added.

Changed in version 3.6.5: On Windows, TCP_FASTOPEN , TCP_KEEPCNT appear if run-time Windows supports.

Changed in version 3.7: TCP_NOTSENT_LOWAT was added.

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

Changed in version 3.10: IP_RECVTOS was added. Added TCP_KEEPALIVE . On MacOS this constant can be used in the same way that TCP_KEEPIDLE is used on Linux.

Changed in version 3.11: Added TCP_CONNECTION_INFO . On MacOS this constant can be used in the same way that TCP_INFO is used on Linux and BSD.

Many constants of these forms, documented in the Linux documentation, are also defined in the socket module.

New in version 3.3.

Changed in version 3.11: NetBSD support was added.

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.

The CAN_BCM_CAN_FD_FRAME flag is only available on Linux >= 4.8.

New in version 3.4.

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 must accept both CAN and CAN FD frames when reading from the socket.

This constant is documented in the Linux documentation.

New in version 3.5.

Joins the applied CAN filters such that only CAN frames that match all given CAN filters are passed to user space.

This constant is documented in the Linux documentation.

New in version 3.9.

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

New in version 3.7.

CAN_J1939, in the CAN protocol family, is the SAE J1939 protocol. J1939 constants, documented in the Linux documentation.

New in version 3.9.

Many constants of these forms, documented in the Linux documentation, are also defined in the socket module.

Many constants of these forms, documented in the Linux documentation, are also defined in the socket module.

New in version 3.3.

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

Changed in version 3.6: SIO_LOOPBACK_FAST_PATH was added.

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.

New in version 3.6.

Constants for Linux host/guest communication.

New in version 3.7.

New in version 3.4.

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.

Constant for Qualcomm’s IPC router protocol, used to communicate with service providing remote processors.

LOCAL_CREDS and LOCAL_CREDS_PERSISTENT can be used with SOCK_DGRAM, SOCK_STREAM sockets, equivalent to Linux/DragonFlyBSD SO_PASSCRED, while LOCAL_CREDS sends the credentials at first read, LOCAL_CREDS_PERSISTENT sends for each read, SCM_CREDS2 must be then used for the latter for the message type.

New in version 3.11.

Constant to optimize CPU locality, to be used in conjunction with SO_REUSEPORT .

New in version 3.11.

Functions¶

Creating sockets¶

The following functions all create socket objects .

class 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 , AF_PACKET , 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 , CAN_ISOTP or CAN_J1939 .

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 .

Raises an auditing event socket.__new__ with arguments self , family , type , protocol .

Changed in version 3.3: The AF_CAN family was added. The AF_RDS family was added.

Changed in version 3.4: The CAN_BCM protocol was added.

Changed in version 3.4: The returned socket is now non-inheritable.

Changed in version 3.7: The CAN_ISOTP protocol was added.

Changed in version 3.7: 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,

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

Changed in version 3.9: The CAN_J1939 protocol was added.

Changed in version 3.10: The IPPROTO_MPTCP protocol was added.

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 .

Changed in version 3.2: The returned socket objects now support the whole socket API, rather than a subset.

Changed in version 3.4: The returned sockets are now non-inheritable.

Changed in version 3.5: Windows support added.

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.

When a connection cannot be created, an exception is raised. By default, it is the exception from the last address in the list. If all_errors is True , it is an ExceptionGroup containing the errors of all attempts.

Changed in version 3.2: source_address was added.

Changed in version 3.11: all_errors was added.

Convenience function which creates a TCP socket bound to address (a 2-tuple (host, port) ) and return the socket object.

family should be either AF_INET or AF_INET6 . backlog is the queue size passed to socket.listen() ; if not specified , a default reasonable value is chosen. reuse_port dictates whether to set the SO_REUSEPORT socket option.

If dualstack_ipv6 is true and the platform supports it the socket will be able to accept both IPv4 and IPv6 connections, else it will raise ValueError . Most POSIX platforms and Windows are supposed to support this functionality. When this functionality is enabled the address returned by socket.getpeername() when an IPv4 connection occurs will be an IPv6 address represented as an IPv4-mapped IPv6 address. If dualstack_ipv6 is false it will explicitly disable this functionality on platforms that enable it by default (e.g. Linux). This parameter can be used in conjunction with has_dualstack_ipv6() :

On POSIX platforms the SO_REUSEADDR socket option is set in order to immediately reuse previous sockets which were bound on the same address and remained in TIME_WAIT state.

New in version 3.8.

Return True if the platform supports creating a TCP socket which can handle both IPv4 and IPv6 connections.

New in version 3.8.

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 .

Changed in version 3.4: The returned socket is now non-inheritable.

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

New in version 3.3.

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

Other functions¶

The socket module also offers various network-related services:

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.

New in version 3.7.

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, flowinfo, scope_id) 4-tuple for AF_INET6 ), and is meant to be passed to the socket.connect() method.

Raises an auditing event socket.getaddrinfo with arguments host , port , family , type , protocol .

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):

Changed in version 3.2: parameters can now be passed using keyword arguments.

Changed in version 3.7: for IPv6 multicast addresses, string representing an address will not contain %scope_id part.

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 gethostbyaddr() is checked, followed by aliases for the host, if available. The first name which includes a period is selected. In case no fully qualified domain name is available and name was provided, it is returned unchanged. If name was empty or equal to ‘0.0.0.0’ , the hostname from gethostname() is returned.

socket. 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 gethostbyname_ex() for a more complete interface. gethostbyname() does not support IPv6 name resolution, and getaddrinfo() should be used instead for IPv4/v6 dual stack support.

Raises an auditing event socket.gethostbyname with argument hostname .

Translate a host name to IPv4 address format, extended interface. Return a triple (hostname, aliaslist, ipaddrlist) where hostname is the host’s primary host name, 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). gethostbyname_ex() does not support IPv6 name resolution, and getaddrinfo() should be used instead for IPv4/v6 dual stack support.

Raises an auditing event socket.gethostbyname with argument hostname .

Return a string containing the hostname of the machine where the Python interpreter is currently executing.

Raises an auditing event socket.gethostname with no arguments.

Note: gethostname() doesn’t always return the fully qualified domain name; use getfqdn() for that.

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 getfqdn() . gethostbyaddr() supports both IPv4 and IPv6.

Raises an auditing event socket.gethostbyaddr with argument ip_address .

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.

For IPv6 addresses, %scope_id is appended to the host part if sockaddr contains meaningful scope_id. Usually this happens for multicast addresses.

For more information about flags you can consult getnameinfo(3).

Raises an auditing event socket.getnameinfo with argument sockaddr .

Translate an internet protocol name (for example, ‘icmp’ ) to a constant suitable for passing as the (optional) third argument to the socket() function. This is usually only needed for sockets opened in “raw” mode ( SOCK_RAW ); for the normal socket modes, the correct protocol is chosen automatically if the protocol is omitted or zero.

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.

Raises an auditing event socket.getservbyname with arguments servicename , 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.

Raises an auditing event socket.getservbyport with arguments port , protocolname .

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.

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.

Changed in version 3.10: Raises OverflowError if x does not fit in a 16-bit unsigned integer.

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.

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.

Changed in version 3.10: Raises OverflowError if x does not fit in a 16-bit unsigned integer.

Convert an IPv4 address from dotted-quad string format (for example, ‘123.45.67.89’) to 32-bit packed binary format, as a bytes object four characters in length. This is useful when conversing with a program that uses the standard C library and needs objects of type in_addr , which is the C type for the 32-bit packed binary this function returns.

inet_aton() also accepts strings with less than three dots; see the Unix manual page inet(3) for details.

If the IPv4 address string passed to this function is invalid, OSError will be raised. Note that exactly what is valid depends on the underlying C implementation of inet_aton() .

inet_aton() does not support IPv6, and inet_pton() should be used instead for IPv4/v6 dual stack support.

socket. inet_ntoa ( packed_ip ) ¶

Convert a 32-bit packed IPv4 address (a bytes-like object four bytes 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 in_addr , which is the C type for the 32-bit packed binary data this function takes as an argument.

If the byte sequence passed to this function is not exactly 4 bytes in length, OSError will be raised. inet_ntoa() does not support IPv6, and inet_ntop() should be used instead for IPv4/v6 dual stack support.

Changed in version 3.5: Writable bytes-like object is now accepted.

Convert an IP address from its family-specific string format to a packed, binary format. inet_pton() is useful when a library or network protocol calls for an object of type in_addr (similar to inet_aton() ) or in6_addr .

Supported values for address_family are currently AF_INET and AF_INET6 . If the IP address string ip_string is invalid, OSError will be raised. Note that exactly what is valid depends on both the value of address_family and the underlying implementation of inet_pton() .

Changed in version 3.4: Windows support added

Convert a packed IP address (a bytes-like object of some number of bytes) to its standard, family-specific string representation (for example, ‘7.10.0.5’ or ‘5aef:2b::8’ ). inet_ntop() is useful when a library or network protocol returns an object of type in_addr (similar to inet_ntoa() ) or in6_addr .

Supported values for address_family are currently AF_INET and AF_INET6 . If the bytes object packed_ip is not the correct length for the specified address family, ValueError will be raised. OSError is raised for errors from the call to inet_ntop() .

Changed in version 3.4: Windows support added

Changed in version 3.5: Writable bytes-like object is now accepted.

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 recvmsg() to receive a single item of ancillary data, but RFC 3542 requires portable applications to use CMSG_SPACE() and thus include space for padding, even when the item will be the last in the buffer. Raises OverflowError if length is outside the permissible range of values.

Availability : Unix, not Emscripten, not WASI.

Most Unix platforms.

New in version 3.3.

Return the buffer size needed for 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 CMSG_SPACE() values for their associated data lengths. Raises 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 : Unix, not Emscripten, not WASI.

most Unix platforms.

New in version 3.3.

Return the default timeout in seconds (float) 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 .

socket. setdefaulttimeout ( timeout ) ¶

Set the default timeout in seconds (float) for new socket objects. When the socket module is first imported, the default is None . See settimeout() for possible values and their respective meanings.

socket. sethostname ( name ) ¶

Set the machine’s hostname to name. This will raise an OSError if you don’t have enough rights.

Raises an auditing event socket.sethostname with argument name .

New in version 3.3.

Return a list of network interface information (index int, name string) tuples. OSError if the system call fails.

Availability : Unix, Windows, not Emscripten, not WASI.

New in version 3.3.

Changed in version 3.8: Windows support was added.

On Windows network interfaces have different names in different contexts (all names are examples):

friendly name: vEthernet (nat)

description: Hyper-V Virtual Ethernet Adapter

This function returns names of the second form from the list, ethernet_32770 in this example case.

Return a network interface index number corresponding to an interface name. OSError if no interface with the given name exists.

Availability : Unix, Windows, not Emscripten, not WASI.

New in version 3.3.

Changed in version 3.8: Windows support was added.

“Interface name” is a name as documented in if_nameindex() .

Return a network interface name corresponding to an interface index number. OSError if no interface with the given index exists.

Availability : Unix, Windows, not Emscripten, not WASI.

New in version 3.3.

Changed in version 3.8: Windows support was added.

“Interface name” is a name as documented in if_nameindex() .

Send the list of file descriptors fds over an AF_UNIX socket sock. The fds parameter is a sequence of file descriptors. Consult sendmsg() for the documentation of these parameters.

Availability : Unix, Windows, not Emscripten, not WASI.

Unix platforms supporting sendmsg() and SCM_RIGHTS mechanism.

New in version 3.9.

Receive up to maxfds file descriptors from an AF_UNIX socket sock. Return (msg, list(fds), flags, addr) . Consult recvmsg() for the documentation of these parameters.

Availability : Unix, Windows, not Emscripten, not WASI.

Unix platforms supporting sendmsg() and SCM_RIGHTS mechanism.

New in version 3.9.

Any truncated integers at the end of the list of file descriptors.

Socket Objects¶

Socket objects have the following methods. Except for makefile() , these correspond to Unix system calls applicable to sockets.

Changed in version 3.2: Support for the context manager protocol was added. Exiting the context manager is equivalent to calling close() .

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.

The newly created socket is non-inheritable .

Changed in version 3.4: The socket is now non-inheritable.

Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the method now retries the system call instead of raising an InterruptedError exception (see PEP 475 for the rationale).

Bind the socket to address. The socket must not already be bound. (The format of address depends on the address family — see above.)

Raises an auditing event socket.bind with arguments self , address .

Mark the socket closed. The underlying system resource (e.g. a file descriptor) is also closed when all file objects from makefile() are closed. Once that happens, 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, but it is recommended to close() them explicitly, or to use a with statement around them.

Changed in version 3.6: OSError is now raised if an error occurs when the underlying close() call is made.

close() releases the resource associated with a connection but does not necessarily close the connection immediately. If you want to close the connection in a timely fashion, call shutdown() before close() .

Connect to a remote socket at address. (The format of address depends on the address family — see above.)

If the connection is interrupted by a signal, the method waits until the connection completes, or raise a TimeoutError on timeout, if the signal handler doesn’t raise an exception and the socket is blocking or has a timeout. For non-blocking sockets, the method raises an InterruptedError exception if the connection is interrupted by a signal (or the exception raised by the signal handler).

Raises an auditing event socket.connect with arguments self , address .

Changed in version 3.5: The method now waits until the connection completes instead of raising an InterruptedError exception if the connection is interrupted by a signal, the signal handler doesn’t raise an exception and the socket is blocking or has a timeout (see the PEP 475 for the rationale).

Like connect(address) , but return an error indicator instead of raising an exception for errors returned by the C-level 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 errno variable. This is useful to support, for example, asynchronous connects.

Raises an auditing event socket.connect with arguments self , address .

Put the socket object into closed state without actually closing the underlying file descriptor. The file descriptor is returned, and can be reused for other purposes.

New in version 3.2.

Duplicate the socket.

The newly created socket is non-inheritable .

Changed in version 3.4: The socket is now non-inheritable.

Return the socket’s file descriptor (a small integer), or -1 on failure. This is useful with select.select() .

Under Windows the small integer returned by this method cannot be used where a file descriptor can be used (such as os.fdopen() ). Unix does not have this limitation.

Get the inheritable flag of the socket’s file descriptor or socket’s handle: True if the socket can be inherited in child processes, False if it cannot.

New in version 3.4.

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.

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.)

socket. getsockopt ( level , optname [ , buflen ] ) ¶

Return the value of the given socket option (see the Unix man page getsockopt(2)). The needed symbolic constants ( 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 bytes object. It is up to the caller to decode the contents of the buffer (see the optional built-in module struct for a way to decode C structures encoded as byte strings).

Return True if socket is in blocking mode, False if in non-blocking.

This is equivalent to checking socket.gettimeout() != 0 .

New in version 3.7.

Return the timeout in seconds (float) associated with socket operations, or None if no timeout is set. This reflects the last call to setblocking() or settimeout() .

socket. ioctl ( control , option ) ¶ Platform

The ioctl() method is a limited interface to the WSAIoctl system interface. Please refer to the Win32 documentation for more information.

On other platforms, the generic fcntl.fcntl() and fcntl.ioctl() functions may be used; they accept a socket object as their first argument.

Currently only the following control codes are supported: SIO_RCVALL , SIO_KEEPALIVE_VALS , and SIO_LOOPBACK_FAST_PATH .

Changed in version 3.6: SIO_LOOPBACK_FAST_PATH was added.

Enable a server to accept connections. If backlog is specified, it must be at least 0 (if it is lower, it is set to 0); it specifies the number of unaccepted connections that the system will allow before refusing new connections. If not specified, a default reasonable value is chosen.

Changed in version 3.5: The backlog parameter is now optional.

Return a file object associated with the socket. The exact returned type depends on the arguments given to makefile() . These arguments are interpreted the same way as by the built-in open() function, except the only supported mode values are ‘r’ (default), ‘w’ and ‘b’ .

The socket must be in blocking mode; it can have a timeout, but the file object’s internal buffer may end up in an inconsistent state if a timeout occurs.

Closing the file object returned by makefile() won’t close the original socket unless all other file objects have been closed and socket.close() has been called on the socket object.

On Windows, the file-like object created by makefile() cannot be used where a file object with a file descriptor is expected, such as the stream arguments of subprocess.Popen() .

Receive data from the socket. The return value is a bytes object representing the data received. The maximum amount of data to be received at once is specified by bufsize. See the Unix manual page recv(2) for the meaning of the optional argument flags; it defaults to zero.

For best match with hardware and network realities, the value of bufsize should be a relatively small power of 2, for example, 4096.

Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the method now retries the system call instead of raising an InterruptedError exception (see PEP 475 for the rationale).

Receive data from the socket. The return value is a pair (bytes, address) where bytes is a bytes object representing the data received and address is the address of the socket sending the data. See the Unix manual page 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.)

Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the method now retries the system call instead of raising an InterruptedError exception (see PEP 475 for the rationale).

Changed in version 3.7: For multicast IPv6 address, first item of address does not contain %scope_id part anymore. In order to get full IPv6 address use getnameinfo() .

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 CMSG_SPACE() or 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 recv() .

The return value is a 4-tuple: (data, ancdata, msg_flags, address) . The data item is a 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 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, sendmsg() and recvmsg() can be used to pass file descriptors between processes over an AF_UNIX socket. When this facility is used (it is often restricted to SOCK_STREAM sockets), recvmsg() will return, in its ancillary data, items of the form (socket.SOL_SOCKET, socket.SCM_RIGHTS, fds) , where fds is a bytes object representing the new file descriptors as a binary array of the native C int type. If 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, recvmsg() will issue a 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 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 sendmsg() .

Most Unix platforms.

New in version 3.3.

Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the method now retries the system call instead of raising an InterruptedError exception (see PEP 475 for the rationale).

Receive normal data and ancillary data from the socket, behaving as 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. 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 ( 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 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 recvmsg() .

Most Unix platforms.

New in version 3.3.

Receive data from the socket, writing it into buffer instead of creating a new bytestring. 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 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.)

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 bytestring. If nbytes is not specified (or 0), receive up to the size available in the given buffer. Returns the number of bytes received. See the Unix manual page recv(2) for the meaning of the optional argument flags; it defaults to zero.

socket. send ( bytes [ , 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 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. For further information on this topic, consult the Socket Programming HOWTO .

Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the method now retries the system call instead of raising an InterruptedError exception (see PEP 475 for the rationale).

Send data to the socket. The socket must be connected to a remote socket. The optional flags argument has the same meaning as for recv() above. Unlike send() , this method continues to send data from bytes 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.

Changed in version 3.5: The socket timeout is no longer reset each time data is sent successfully. The socket timeout is now the maximum total duration to send all data.

Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the method now retries the system call instead of raising an InterruptedError exception (see PEP 475 for the rationale).

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 recv() above. Return the number of bytes sent. (The format of address depends on the address family — see above.)

Raises an auditing event socket.sendto with arguments self , address .

Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the method now retries the system call instead of raising an InterruptedError exception (see PEP 475 for the rationale).

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 bytes-like objects (e.g. bytes objects); the operating system may set a limit ( 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 bytes-like object holding the associated data. Note that some systems (in particular, systems without CMSG_SPACE() ) might support sending only one control message per call. The flags argument defaults to 0 and has the same meaning as for 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 AF_UNIX socket, on systems which support the SCM_RIGHTS mechanism. See also recvmsg() .

Most Unix platforms.

Raises an auditing event socket.sendmsg with arguments self , address .

New in version 3.3.

Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the method now retries the system call instead of raising an InterruptedError exception (see PEP 475 for the rationale).

Specialized version of sendmsg() for AF_ALG socket. Set mode, IV, AEAD associated data length and flags for AF_ALG socket.

New in version 3.6.

Send a file until EOF is reached by using high-performance os.sendfile and return the total number of bytes which were sent. file must be a regular file object opened in binary mode. If os.sendfile is not available (e.g. Windows) or file is not a regular file send() will be used instead. offset tells from where to start reading the file. If specified, count is the total number of bytes to transmit as opposed to sending the file until EOF is reached. File position is updated on return or also in case of error in which case file.tell() can be used to figure out the number of bytes which were sent. The socket must be of SOCK_STREAM type. Non-blocking sockets are not supported.

New in version 3.5.

Set the inheritable flag of the socket’s file descriptor or socket’s handle.

New in version 3.4.

Set blocking or non-blocking mode of the socket: if flag is false, the socket is set to non-blocking, else to blocking mode.

This method is a shorthand for certain settimeout() calls:

sock.setblocking(True) is equivalent to sock.settimeout(None)

sock.setblocking(False) is equivalent to sock.settimeout(0.0)

Changed in version 3.7: The method no longer applies SOCK_NONBLOCK flag on socket.type .

Set a timeout on blocking socket operations. The value argument can be a nonnegative floating point number expressing seconds, or None . If a non-zero value is given, subsequent socket operations will raise a timeout exception if the timeout period value has elapsed before the operation has completed. If zero is given, the socket is put in non-blocking mode. If None is given, the socket is put in blocking mode.

For further information, please consult the notes on socket timeouts .

Changed in version 3.7: The method no longer toggles SOCK_NONBLOCK flag on socket.type .

Set the value of the given socket option (see the Unix manual page setsockopt(2)). The needed symbolic constants are defined in the socket module ( SO_* etc.). The value can be an integer, None or a bytes-like object representing a buffer. In the later case it is up to the caller to ensure that the bytestring contains the proper bits (see the optional built-in module struct for a way to encode C structures as bytestrings). When value is set to None , optlen argument is required. It’s equivalent to call setsockopt() C function with optval=NULL and optlen=optlen .

Changed in version 3.5: Writable bytes-like object is now accepted.

Changed in version 3.6: setsockopt(level, optname, None, optlen: int) form added.

Shut down one or both halves of the connection. If how is SHUT_RD , further receives are disallowed. If how is SHUT_WR , further sends are disallowed. If how is SHUT_RDWR , further sends and receives are disallowed.

Duplicate a socket and prepare it for sharing with a target process. The target process must be provided with process_id. The resulting bytes object can then be passed to the target process using some form of interprocess communication and the socket can be recreated there using fromshare() . Once this method has been called, it is safe to close the socket since the operating system has already duplicated it for the target process.

New in version 3.3.

Note that there are no methods read() or write() ; use recv() and send() without flags argument instead.

Socket objects also have these (read-only) attributes that correspond to the values given to the socket constructor.

The socket family.

The socket type.

The socket protocol.

Notes on socket timeouts¶

A socket object can be in one of three modes: blocking, non-blocking, or timeout. Sockets are by default always created in blocking mode, but this can be changed by calling setdefaulttimeout() .

In blocking mode, operations block until complete or the system returns an error (such as connection timed out).

In non-blocking mode, operations fail (with an error that is unfortunately system-dependent) if they cannot be completed immediately: functions from the select module can be used to know when and whether a socket is available for reading or writing.

In timeout mode, operations fail if they cannot be completed within the timeout specified for the socket (they raise a timeout exception) or if the system returns an error.

At the operating system level, sockets in timeout mode are internally set in non-blocking mode. Also, the blocking and timeout modes are shared between file descriptors and socket objects that refer to the same network endpoint. This implementation detail can have visible consequences if e.g. you decide to use the fileno() of a socket.

Timeouts and the connect method¶

The connect() operation is also subject to the timeout setting, and in general it is recommended to call settimeout() before calling connect() or pass a timeout parameter to create_connection() . However, the system network stack may also return a connection timeout error of its own regardless of any Python socket timeout setting.

Timeouts and the accept method¶

If getdefaulttimeout() is not None , sockets returned by the accept() method inherit that timeout. Otherwise, the behaviour depends on settings of the listening socket:

if the listening socket is in blocking mode or in timeout mode, the socket returned by accept() is in blocking mode;

if the listening socket is in non-blocking mode, whether the socket returned by accept() is in blocking or non-blocking mode is operating system-dependent. If you want to ensure cross-platform behaviour, it is recommended you manually override this setting.

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 socket() , bind() , listen() , accept() (possibly repeating the accept() to service more than one client), while a client only needs the sequence socket() , connect() . Also note that the server does not sendall() / recv() on the socket it is listening on but on the new socket returned by accept() .

The first two examples support IPv4 only.

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.

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:

The next example shows how to use the socket interface to communicate to a CAN network using the raw socket protocol. To use CAN with the broadcast manager protocol instead, open a socket with:

After binding ( CAN_RAW ) or connecting ( CAN_BCM ) the socket, you can use the socket.send() and socket.recv() operations (and their counterparts) on the socket object as usual.

This last example might require special privileges:

Running an example several times with too small delay between executions, could lead to this error:

This is because the previous execution has left the socket in a TIME_WAIT state, and can’t be immediately reused.

There is a socket flag to set, in order to prevent this, socket.SO_REUSEADDR :

the SO_REUSEADDR flag tells the kernel to reuse a local socket in TIME_WAIT state, without waiting for its natural timeout to expire.

For an introduction to socket programming (in C), see the following papers:

An Introductory 4.3BSD Interprocess Communication Tutorial, by Stuart Sechrest

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.

Сокеты в Python для начинающих

В далеком для меня 2010 году я писал статью для начинающих про сокеты в Python. Сейчас этот блог канул в небытие, но статья мне показалась довольно полезной. Статью нашел на флешке в либровском документе, так что это не кросспост, не копипаст — в интернете ее нигде нет.

Что это

Для начала нужно разобраться что такое вообще сокеты и зачем они нам нужны. Как говорит вики, сокет — это программный интерфейс для обеспечения информационного обмена между процессами. Но гораздо важнее не зазубрить определение, а понять суть. Поэтому я тут постараюсь рассказать все как можно подробнее и проще.

Существуют клиентские и серверные сокеты. Вполне легко догадаться что к чему. Серверный сокет прослушивает определенный порт, а клиентский подключается к серверу. После того, как было установлено соединение начинается обмен данными.

Рассмотрим это на простом примере. Представим себе большой зал с множеством небольших окошек, за которыми стоят девушки. Есть и пустые окна, за которыми никого нет. Те самые окна — это порты. Там, где стоит девушка — это открытый порт, за которым стоит какое-то приложение, которое его прослушивает. То есть, если, вы подойдете к окошку с номером 9090, то вас поприветствуют и спросят, чем могут помочь. Так же и с сокетами. Создается приложение, которое прослушивает свой порт. Когда клиент устанавливает соединение с сервером на этом порту именно данное приложение будет ответственно за работу этим клиентом. Вы же не подойдете к одному окошку, а кричать вам будут из соседнего 🙂

После успешной установки соединения сервер и клиент начинают обмениваться информацией. Например, сервер посылает приветствие и предложение ввести какую-либо команду. Клиент в свою очередь вводит команду, сервер ее анализирует, выполняет необходимые операции и отдает клиенту результат.

Сервер

Сейчас создайте два файла — один для сервера, а другой для клиента.

В Python для работы с сокетами используется модуль socket:

Прежде всего нам необходимо создать сокет:

Здесь ничего особенного нет и данная часть является общей и для клиентских и для серверных сокетов. Дальше мы будем писать код для сервера. Это вполне логично — зачем нам писать клиентское приложение, если некуда подключаться 🙂

Теперь нам нужно определиться с хостом и портом для нашего сервера. Насчет хоста — мы оставим строку пустой, чтобы наш сервер был доступен для всех интерфейсов. А порт возьмем любой от нуля до 65535. Следует отметить, что в большинстве операционных систем прослушивание портов с номерами 0 — 1023 требует особых привилегий. Я выбрал порт 9090. Теперь свяжем наш сокет с данными хостом и портом с помощью метода bind, которому передается кортеж, первый элемент (или нулевой, если считать от нуля) которого — хост, а второй — порт:

Теперь у нас все готово, чтобы принимать соединения. С помощью метода listen мы запустим для данного сокета режим прослушивания. Метод принимает один аргумент — максимальное количество подключений в очереди. Напряжем нашу бурную фантазию и вспомним про зал с окошками. Так вот этот параметр определяет размер очереди. Если он установлен в единицу, а кто-то, явно лишний, пытается еще подстроится сзади, то его пошлют 🙂 Установим его в единицу:

Ну вот, наконец-то, мы можем принять подключение с помощью метода accept, который возвращает кортеж с двумя элементами: новый сокет и адрес клиента. Именно этот сокет и будет использоваться для приема и посылке клиенту данных.

Вот и все. Теперь мы установили с клиентом связь и можем с ним «общаться». Т.к. мы не можем точно знать, что и в каких объемах клиент нам пошлет, то мы будем получать данные от него небольшими порциями. Чтобы получить данные нужно воспользоваться методом recv, который в качестве аргумента принимает количество байт для чтения. Мы будем читать порциями по 1024 байт (или 1 кб):

Как мы и говорили для общения с клиентом мы используем сокет, который получили в результате выполнения метода accept. Мы в бесконечном цикле принимаем 1024 байт данных с помощью метода recv. Если данных больше нет, то этот метод ничего не возвращает. Таким образом мы можем получать от клиента любое количество данных.

Дальше в нашем примере для наглядности мы что-то сделаем с полученными данными и отправим их обратно клиенту. Например, с помощью метода upper у строк вернем клиенту строку в верхнем регистре.

Теперь можно и закрыть соединение:

Собственно сервер готов. Он принимает соединение, принимает от клиента данные, возвращает их в виде строки в верхнем регистре и закрывает соединение. Все просто 🙂 В итоге у вас должно было получиться следующее:

Клиент

Думаю, что теперь будет легче. Да и само клиентское приложение проще — нам нужно создать сокет, подключиться к серверу послать ему данные, принять данные и закрыть соединение. Все это делается так:

Думаю, что все понятно, т.к. все уже разбиралось ранее. Единственное новое здесь — это метод connect, с помощью которого мы подключаемся к серверу. Дальше мы читаем 1024 байт данных и закрываем сокет.