getpeername(2)                                          System Calls Manual                                          getpeername(2)

       getpeername - get name of connected peer socket

       Standard C library (libc, -lc)

       #include <sys/socket.h>

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

       getpeername() returns the address of the peer connected to the socket sockfd, in the buffer pointed to by addr.  The addrlen
       argument should be initialized to indicate the amount of space pointed to by addr.  On return it contains the actual size of
       the name returned (in bytes).  The name is truncated if the buffer provided is too small.

       The  returned  address  is  truncated if the buffer provided is too small; in this case, addrlen will return a value greater
       than was supplied to the call.

       On success, zero is returned.  On error, -1 is returned, and errno is set to indicate the error.

       EBADF  The argument sockfd is not a valid file descriptor.

       EFAULT The addr argument points to memory not in a valid part of the process address space.

       EINVAL addrlen is invalid (e.g., is negative).

              Insufficient resources were available in the system to perform the operation.

              The socket is not connected.

              The file descriptor sockfd does not refer to a socket.

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (getpeername() first appeared in 4.2BSD).

       For background on the socklen_t type, see accept(2).

       For stream sockets, once a connect(2) has been performed, either socket can call getpeername() to obtain the address of  the
       peer  socket.   On the other hand, datagram sockets are connectionless.  Calling connect(2) on a datagram socket merely sets
       the peer address for outgoing datagrams sent with write(2) or recv(2).  The caller of connect(2) can  use  getpeername()  to
       obtain  the  peer  address that it earlier set for the socket.  However, the peer socket is unaware of this information, and
       calling getpeername() on the peer socket will return no useful information (unless a connect(2) call was  also  executed  on
       the peer).  Note also that the receiver of a datagram can obtain the address of the sender when using recvfrom(2).

       accept(2), bind(2), getsockname(2), ip(7), socket(7), unix(7)

Linux man-pages 6.03                                         2022-10-30                                              getpeername(2)