GETPEERNAME(2) Linux Programmer's Manual GETPEERNAME(2)
getpeername - get name of connected peer socket
int getpeername(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
getpeername() returns the address of the peer connected to the socket sockfd, in the buf-
fer 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 getpeer-
name() 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 get-
peername() 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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Linux 2013-02-12 GETPEERNAME(2)