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GETPEERNAME(2) System Calls Manual GETPEERNAME(2)

getpeername — get name of connected peer

#include <sys/socket.h>

int
getpeername(int s, struct sockaddr *name, socklen_t *namelen);

() returns the address information of the peer connected to socket s. One common use occurs when a process inherits an open socket, such as TCP servers forked from inetd(8). In this scenario, getpeername() is used to determine the connecting client's IP address.

() takes three parameters:

s contains the file descriptor of the socket whose peer should be looked up.

name points to a sockaddr structure that will hold the address information for the connected peer. Normal use requires one to use a structure specific to the protocol family in use, such as sockaddr_in (IPv4) or sockaddr_in6 (IPv6), cast to a (struct sockaddr *).

For greater portability, especially with the newer protocol families, the new struct sockaddr_storage should be used. sockaddr_storage is large enough to hold any of the other sockaddr_* variants. On return, it can be cast to the correct sockaddr type, based on the protocol family contained in its ss_family field.

namelen indicates the amount of space pointed to by name, in bytes.

If address information for the local end of the socket is required, the getsockname(2) function should be used instead.

If name does not point to enough space to hold the entire socket address, the result will be truncated to namelen bytes.

If the call succeeds, a 0 is returned and namelen is set to the actual size of the socket address returned in name. Otherwise, errno is set and a value of -1 is returned.

On failure, errno is set to one of the following:

[]
The argument s is not a valid descriptor.
[]
The argument s is a file, not a socket.
[]
The socket is not connected.
[]
Insufficient resources were available in the system to perform the operation.
[]
The name or namelen parameter points to memory not in a valid part of the process address space.

accept(2), bind(2), getsockname(2), socket(2), getpeereid(3)

The getpeername() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”).

The getpeername() function call appeared in 4.2BSD.

September 11, 2022 openbsd