Windows API Reference

Sockets API

The Windows Sockets API (Winsock) provides a network programming interface that supports a wide range of networking protocols, including TCP/IP. This section details the functions, structures, and constants used for socket-based network communication on Windows.

Core Concepts

Sockets: Endpoints for communication between processes on a network.
Address Families: Specify the protocol suite (e.g., AF_INET for IPv4, AF_INET6 for IPv6).
Socket Types: Define the communication semantics (e.g., SOCK_STREAM for reliable, connection-oriented communication; SOCK_DGRAM for unreliable, connectionless datagrams).
Protocols: Specific communication protocols within an address family (e.g., IPPROTO_TCP, IPPROTO_UDP).
Winsock DLL: The Dynamic Link Library (DLL) that implements the Winsock API.

Key Functions

Function	Description
`socket()`	Creates a socket that is an endpoint for communication.
`bind()`	Associates a local address with a socket.
`listen()`	Places a socket in a state where it can accept incoming connection requests.
`accept()`	Accepts a connection on a socket.
`connect()`	Establishes a connection to a remote socket.
`send()` / `sendto()`	Sends data over a socket.
`recv()` / `recvfrom()`	Receives data from a socket.
`closesocket()`	Closes an existing socket.
`getaddrinfo()`	Retrieves address information for a specified host and service.
`freeaddrinfo()`	Frees address information previously allocated by `getaddrinfo()`.

Important Structures

Structure	Description
`SOCKADDR`	A generic socket address structure.
`SOCKADDR_IN`	An IPv4 socket address structure.
`SOCKADDR_IN6`	An IPv6 socket address structure.
`WSADATA`	Contains information about the Winsock implementation.
`ADDRINFO`	Structure used by `getaddrinfo()` to store address information.

Common Constants

Address Family Constants: AF_UNSPEC, AF_INET, AF_INET6
Socket Type Constants: SOCK_STREAM, SOCK_DGRAM
Protocol Constants: IPPROTO_TCP, IPPROTO_UDP
Error Codes: Various constants starting with WSAE... (e.g., WSAECONNRESET, WSAETIMEDOUT)

Getting Started

A typical Winsock application follows these steps:

Call WSAStartup() to initialize the Winsock DLL.
Create a socket using socket().
(For server) Bind the socket to a local address and port using bind(), and then listen for connections using listen().
(For client) Connect to a remote server using connect().
Send and receive data using send()/sendto() and recv()/recvfrom().
Close the socket using closesocket().
Call WSACleanup() to release Winsock resources.