Manpage of GETPEERNAME
GETPEERNAMESection: Linux Programmer's Manual (2)
NAMEgetpeername - get name of connected peer socket
DESCRIPTIONgetpeername() returns the address of the peer connected to the socket sockfd, in the buffer pointed to by addr. The addrlenargument 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.
RETURN VALUEOn success, zero is returned. On error, -1 is returned, and errnois set appropriately.
- The argument sockfdis not a valid file descriptor.
- The addrargument points to memory not in a valid part of the process address space.
- addrlenis invalid (e.g., is negative).
- Insufficient resources were available in the system to perform the operation.
- The socket is not connected.
- The file descriptor sockfddoes not refer to a socket.
CONFORMING TOPOSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (getpeername() first appeared in 4.2BSD).
NOTESThe 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).
SEE ALSOaccept(2), bind(2), getsockname(2), ip(7), socket(7), unix(7)
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