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.\" $OpenBSD: connect.2,v 1.33 2017/10/05 12:30:16 bluhm Exp $
.\" $NetBSD: connect.2,v 1.8 1995/10/12 15:40:48 jtc Exp $
.\"
.\" Copyright (c) 1983, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)connect.2 8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: October 5 2017 $
.Dt CONNECT 2
.Os
.Sh NAME
.Nm connect
.Nd initiate a connection on a socket
.Sh SYNOPSIS
.In sys/socket.h
.Ft int
.Fn connect "int s" "const struct sockaddr *name" "socklen_t namelen"
.Sh DESCRIPTION
The parameter
.Fa s
is a socket.
If it is of type
.Dv SOCK_DGRAM ,
this call specifies the peer with which the socket is to be associated;
this address is that to which datagrams are to be sent,
and the only address from which datagrams are to be received.
If the socket is of type
.Dv SOCK_STREAM ,
this call attempts to make a connection to
another socket.
The other socket is specified by
.Fa name ,
which is an address in the communications space of the socket.
.Fa namelen
indicates the amount of space pointed to by
.Fa name ,
in bytes; the
.Fa sa_len
member of
.Fa name
is ignored.
Each communications space interprets the
.Fa name
parameter in its own way.
Generally, stream sockets may use
.Fn connect
only once; datagram sockets may use
.Fn connect
multiple times to change their association.
Datagram sockets may dissolve the association
by connecting to an invalid address, such as a null address.
.Pp
If the socket is in non-blocking mode and the connection cannot be
completed immediately, or if it is interrupted by a signal,
.Fn connect
will return an error and the connection attempt will proceed
asynchronously.
Subsequent calls to
.Fn connect
will fail with errno set to
.Er EALREADY .
It is possible to use
.Xr select 2
or
.Xr poll 2
to determine when the connect operation has completed by checking the
socket for writability.
The success or failure of the connection attempt may be determined by using
.Xr getsockopt 2
to check the socket error status with the
.Dv SO_ERROR
option at the
.Dv SOL_SOCKET
level.
If the connection was successful, the error value will be zero.
Otherwise, it will be one of the error values listed below.
.Sh RETURN VALUES
If the connection or binding succeeds, 0 is returned.
Otherwise a \-1 is returned, and a more specific error
code is stored in
.Va errno .
.Sh EXAMPLES
The following code connects to the host described by
.Fa name
and handles the case where
.Fn connect
is interrupted by a signal.
.Bd -literal -offset indent
#include <sys/socket.h>
#include <poll.h>
#include <errno.h>
#include <err.h>
int
connect_wait(int s)
{
struct pollfd pfd[1];
int error = 0;
socklen_t len = sizeof(error);
pfd[0].fd = s;
pfd[0].events = POLLOUT;
if (poll(pfd, 1, -1) == -1)
return -1;
if (getsockopt(s, SOL_SOCKET, SO_ERROR, &error, &len) < 0)
return -1;
if (error != 0) {
errno = error;
return -1;
}
return 0;
}
\&...
int retcode;
\&...
for (retcode = connect(s, name, namelen);
retcode != 0 && errno == EINTR;
retcode = connect_wait(s))
continue;
if (retcode == -1)
err(1, "connect");
.Ed
.Sh ERRORS
The
.Fn connect
call fails if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa s
is not a valid descriptor.
.It Bq Er ENOTSOCK
.Fa s
is not a socket.
.It Bq Er EADDRNOTAVAIL
No suitable address is available on the local machine.
.It Bq Er EAFNOSUPPORT
Addresses in the specified address family cannot be used with this socket.
.It Bq Er EISCONN
The socket is already connected.
.It Bq Er ETIMEDOUT
Connection establishment timed out without establishing a connection.
.It Bq Er EINVAL
A TCP connection with a local broadcast, the all-ones or a
multicast address as the peer was attempted.
.It Bq Er ECONNREFUSED
The attempt to connect was forcefully rejected.
.It Bq Er EHOSTUNREACH
The destination address specified an unreachable host.
.It Bq Er EINTR
The connection attempt was interrupted by a signal.
The attempt will continue asynchronously as if the socket was non-blocking.
.It Bq Er ENETUNREACH
The network isn't reachable from this host.
.It Bq Er EADDRINUSE
The address is already in use.
.It Bq Er EFAULT
The
.Fa name
parameter specifies an area outside
the process address space.
.It Bq Er EINPROGRESS
The socket is non-blocking and the connection cannot
be completed immediately.
.It Bq Er EALREADY
Either the socket is non-blocking or a previous call to
.Fn connect
was interrupted by a signal, and the connection attempt has not yet
been completed.
.It Bq Er EPERM
A TCP connection on a socket with socket option TCP_MD5SIG was
attempted without configuring the security parameters correctly.
.El
.Pp
The following errors are specific to connecting names in the
.Ux Ns -domain .
These errors may not apply in future versions of the
.Ux
IPC domain.
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Dv NAME_MAX
characters, or an entire pathname (including the terminating NUL)
exceeded
.Dv PATH_MAX
bytes.
.It Bq Er ENOENT
The named socket does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er EACCES
Write access to the named socket is denied.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EPROTOTYPE
The file described by
.Fa name
is of a different type than
.Fa s .
E.g.,
.Fa s
may be of type
.Dv SOCK_STREAM
whereas
.Fa name
may refer to a socket of type
.Dv SOCK_DGRAM .
.El
.Sh SEE ALSO
.Xr accept 2 ,
.Xr getsockname 2 ,
.Xr getsockopt 2 ,
.Xr poll 2 ,
.Xr select 2 ,
.Xr socket 2
.Sh STANDARDS
The
.Fn connect
function conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn connect
system call first appeared in
.Bx 4.1c .
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