Python Socket Library Overview

Introduction

• Provides access to BSD socket interface.
• Available on Unix, Windows, MacOS.
• Python interface mirrors Unix system call and library interface with an object-oriented style.

Socket Families

• AF_UNIX: Address bound to a file system node, represented as a string.
• AF_INET: Uses a pair (host, port), supports IPv4.
• AF_INET6: Uses a four-tuple (host, port, flowinfo, scope_id), supports IPv6.
• AF_NETLINK, AF_TIPC, AF_CAN, AF_ALG, AF_VSOCK, AF_PACKET: Various address families for specific use cases.
• AF_BLUETOOTH, AF_HYPERV: Specialized for Bluetooth and Hyper-V communication.
• IPPROTO_UDPLITE: Allows specification of packet coverage for checksum.

Error Handling

• Errors raise exceptions such as OSError or its subclasses.
• Non-blocking mode supported via setblocking(), timeouts via settimeout().

Key Constants

• Address Family Constants: e.g., socket.AF_INET, socket.AF_INET6.
• Socket Type Constants: e.g., socket.SOCK_STREAM, socket.SOCK_DGRAM.
• Miscellaneous Constants: Various constants like SO_REUSEADDR for socket options.

Functions

Creating Sockets

• socket.socket(): Creates a new socket with specified family, type, and protocol.
• socket.socketpair(): Builds a pair of connected socket objects.
• socket.create_connection(): Connects to a TCP service.
• socket.create_server(): Creates a TCP socket server.
• socket.fromfd() and socket.fromshare(): Create sockets from file descriptors or shared data.

Other Functions

• socket.getaddrinfo(): Translates address info.
• socket.gethostname(), socket.gethostbyname(): Resolves hostnames.
• socket.inet_pton() and socket.inet_ntop(): IP address conversions.
• socket.send() and socket.recv(): Sending and receiving data.

Socket Objects

• Methods correspond to Unix system calls.
• Key Methods: accept(), bind(), close(), connect(), listen(), recv(), send().
• Attributes: family, type, proto.

Examples

TCP Echo Server and Client

• Server: Uses socket(), bind(), listen(), accept().
• Client: Uses socket(), connect().

Advanced Examples

• Network sniffer on Windows with raw sockets.
• Communication with CAN network using raw socket protocol.

Notes

• Timeouts: Sockets can operate in blocking, non-blocking, or timeout modes.
• Security: Using SO_REUSEADDR to manage socket reuse in TIME_WAIT state.

References

• For more detailed study, refer to Unix Programmer’s Manual and specific RFCs for network programming.