socket-api

Applications need a way to access network services (TCP, UDP) without implementing protocol internals. An interface is needed to allow applications to send/receive data over the network.

An application programming interface that provides a set of functions for applications to use network services, acting as the Service Access Point between the application and transport layers.

1. Application calls socket() to create a socket endpoint
2. Calls bind() to assign local address/port (server) or connect() to initiate connection (client)
3. Uses send()/recv() (or write()/read()) to exchange data
4. Calls close() to terminate the connection
5. Server uses listen() and accept() to handle incoming connections

• Standardized interface across operating systems (Berkeley sockets, Winsock)
• Hides protocol details from applications
• Supports both connection-oriented (TCP) and connectionless (UDP) sockets
• File descriptor-based (sockets behave like files)

• Built from: Service Access Point — concrete implementation of SAP
• Built from: Service Primitives — API calls are primitives
• Related: TCP and UDP — accessed via socket API
• Related: Application Layer — applications use sockets

• Blocking vs non-blocking sockets: blocking waits, non-blocking returns immediately
• Socket descriptor leaks if close() isn’t called (resource exhaustion)
• Different socket types: stream (TCP), datagram (UDP), raw sockets