getpeername(2)

1getpeername(2)                System Calls Manual               getpeername(2)
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NAME

6       getpeername - get name of connected peer socket
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <sys/socket.h>
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14       int getpeername(int sockfd, struct sockaddr *restrict addr,
15                       socklen_t *restrict addrlen);
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DESCRIPTION

18       getpeername()  returns  the address of the peer connected to the socket
19       sockfd, in the buffer pointed to by addr.  The addrlen argument  should
20       be  initialized to indicate the amount of space pointed to by addr.  On
21       return it contains the actual size of the  name  returned  (in  bytes).
22       The name is truncated if the buffer provided is too small.
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24       The  returned address is truncated if the buffer provided is too small;
25       in this case, addrlen will return a value greater than was supplied  to
26       the call.
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RETURN VALUE

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

33       EBADF  The argument sockfd is not a valid file descriptor.
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35       EFAULT The addr argument points to memory not in a valid  part  of  the
36              process address space.
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38       EINVAL addrlen is invalid (e.g., is negative).
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40       ENOBUFS
41              Insufficient  resources  were available in the system to perform
42              the operation.
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44       ENOTCONN
45              The socket is not connected.
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47       ENOTSOCK
48              The file descriptor sockfd does not refer to a socket.
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STANDARDS

51       POSIX.1-2008.
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HISTORY

54       POSIX.1-2001, SVr4, 4.4BSD (first appeared in 4.2BSD).
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NOTES

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