Winsock2

Winsock2, short for Windows Sockets 2, is the Windows API for network programming. It defines a standardized interface that allows Windows applications to perform socket-based communication over IP networks using protocols such as TCP and UDP. Winsock2 builds on the original Winsock 1.1 API and adds enhancements including a provider model, broader protocol support, and IPv6 capability.

The architecture of Winsock2 centers on enabling applications to access the Windows networking stack through a set of socket-based functions and an extensible provider interface. The Windows Sockets Service Provider Interface (SPI) allows multiple protocol stacks and providers to be plugged into the API. Typical application use involves creating sockets (via socket or WSASocket), and performing operations such as bind, listen, accept, connect, send, receive, sendto, and recvfrom. Modern applications also rely on name resolution functions like getaddrinfo and getnameinfo for protocol-independent addressing. Initialization and cleanup are performed with WSAStartup and WSACleanup, and errors are retrieved with WSAGetLastError.

Key features include support for both IPv4 and IPv6, including dual-stack sockets that can handle both address families. Winsock2 also provides support for asynchronous I/O through overlapped operations and I/O completion mechanisms, integrating with Windows event and notification models. Additional utilities such as WSAIoctl enable provider- and device-specific controls, while getaddrinfo/getnameinfo facilitate robust name resolution and translation.

Winsock2 remains the standard Windows Sockets API across Windows NT-based systems and desktop Windows editions, continuing to evolve with the platform. It enables legacy and modern network applications to operate within a unified, extensible framework, though some features related to older layered service providers have been deprecated or phased out in newer environments.