GetSockName and Getpeername functions

These 2 functions either return the local protocol address (GETSOCKNAME) associated with a socket, or return the address of the foreign protocol associated with a socket (getpeername)

int getsockname (int sockfd, struct sockaddr* localaddr, socklen_t * addrlen);

int getpeername (int sockfd, struct sockaddr * peeraddr, socklen_t * addrlen);

The last parameter of these 2 functions is the value-result parameter, which means that all 2 functions are loaded with the socket address structure referred to by the LOCALADDR and peeraddr pointers

Reasons to need these 2 functions:

1) on a TCP client that does not call bind, when Connect returns successfully, GetSockName is used to return the local IP address and local port number that the connection was given by the kernel

2) After calling bind with port number 0, GetSockName is used to return the local port number given by the kernel

3) GetSockName can be used to obtain an address cluster for a socket

4) on a server that calls bind at a wildcard IP address, once the connection to a client is established, getsockname can be used to return the local IP address to which the connection was given by the kernel

In such a call, the socket descriptor parameter must be a connected local IP, not a descriptor of the listening socket

5) When a server is called by a process calling exec to execute a program, the only way it can acquire a client's identity is to call Getpeername

All clients and servers start with the calling socket, which returns a socket descriptor

The customer then calls Connect

The server calls bind, listen, accept

Sockets typically use the standard close function to close

Most TCP servers are concurrent

They call fork for each pending client connection to derive a child process

Most UDP servers are iterative

GetSockName and Getpeername functions