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       getpeername - get name of connected peer socket


       #include <sys/socket.h>

       int getpeername(int sockfd, struct sockaddr *addr, socklen_t *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 appropriately.


       EBADF  The argument sockfd is not a valid descriptor.

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

       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 argument sockfd is a file, not a socket.


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


       The third argument of getpeername() is in reality an int * (and this is what 4.x  BSD  and
       libc4  and libc5 have).  Some POSIX confusion resulted in the present socklen_t, also used
       by glibc.  See also 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)


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