Tribblix: manual page: connect.3socket

CONNECT(3SOCKET) Sockets Library Functions CONNECT(3SOCKET)

NAME

connect - initiate a connection on a socket

SYNOPSIS

cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
#include <sys/types.h>
#include <sys/socket.h>

int connect(int s, const struct sockaddr *name, int namelen);

DESCRIPTION

The parameter s is a socket. If it is of type SOCK_DGRAM, connect()
specifies the peer with which the socket is to be associated. This
address is the address to which datagrams are to be sent if a
receiver is not explicitly designated. This address is the only
address from which datagrams are to be received. If the socket s is
of type SOCK_STREAM, connect() attempts to make a connection to
another socket. The other socket is specified by name. name is an
address in the communication space of the socket. Each communication
space interprets the name parameter in its own way. If s is not
bound, then s will be bound to an address selected by the underlying
transport provider. Generally, stream sockets can successfully
connect() only once. Datagram sockets can use connect() multiple
times to change their association. Datagram sockets can dissolve the
association by connecting to a null address.

Non-blocking Sockets
When a socket is created, it is by default a blocking socket. A
socket may be configured to be non-blocking either at socket creation
time or through the use of fcntl(2). When a socket is set to be non-
blocking, a call to connect initiates an asynchronous connection. If
the connection cannot be completed without blocking, such as when
making a TCP connection to a remote server, then the connection
attempt is made in the background and connect returns -1 and errno is
set to EINPROGRESS.

Applications can obtain the state of this connection attempt by
polling the socket's file descriptor for POLLOUT. The event ports
facility is the preferred means of polling on the file descriptor,
see port_create(3C) and port_get(3C) for more information on event
ports; however, applications may also use traditional portable
routines like poll(2) and select(3C).

When an asynchronous connection has completed, the application must
call getsockopt(3SOCKET) using the macro SOL_SOCKET as the level
argument and the macro SO_ERROR as the value of the option argument.
If the value of the SO_ERROR socket option is zero, then the connect
was successfully established. Otherwise, the connection could not be
established and the value is the corresponding error code that would
be commonly found in errno.

Even when a socket is in non-blocking mode, a call to connect may
fail synchronously. If any error other EINPROGRESS or EINTR occurs,
then there is no need for the application to poll for asynchronous
completion. Similarly, if a call to connect returns successfully,
then the socket connection will be established and there is no need
to poll for completion.

EXAMPLES

Example 1: Performing an asynchronous connection

The following sample C program shows how to create and connect to a
remote host using TCP. The program should be compiled and linked
against libnsl and libsocket. For example, if the contents of this
example where in a file called example.c, one would run cc example.c
-lnsl -lsocket.

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <inttypes.h>
#include <stdio.h>
#include <strings.h>
#include <stdlib.h>
#include <errno.h>
#include <port.h>
#include <unistd.h>
#include <assert.h>

int
main(int argc, char *argv[])
{
char *eptr;
long port;
int sock, ret, eport;
struct sockaddr_in6 sin6;

if (argc != 3) {
fprintf(stderr, "connect: <IP> <port>\n");
return (1);
}

bzero(&sin6, sizeof (struct sockaddr_in6));
sin6.sin6_family = AF_INET6;

/*
* Try to parse as an IPv6 address and then try v4.
*/
ret = inet_pton(AF_INET6, argv[1], &sin6.sin6_addr);
if (ret == -1) {
perror("inet_pton");
return (1);
} else if (ret == 0) {
struct in_addr v4;
ret = inet_pton(AF_INET, argv[1], &v4);
if (ret == -1) {
perror("inet_pton");
return (1);
} else if (ret == 0) {
fprintf(stderr, "connect: %s is not a valid "
"IPv4 or IPv6 address\n", argv[1]);
return (1);
}
/* N.B. Not a portable macro */
IN6_INADDR_TO_V4MAPPED(&v4, &sin6.sin6_addr);
}

errno = 0;
port = strtol(argv[2], &eptr, 10);
if (errno != 0 || *eptr != '\0') {
fprintf(stderr, "failed to parse port %s\n", argv[2]);
return (1);
}
if (port <= 0 || port > UINT16_MAX) {
fprintf(stderr, "invalid port: %ld\n", port);
return (1);
}
sin6.sin6_port = htons(port);

sock = socket(AF_INET6, SOCK_STREAM | SOCK_NONBLOCK, 0);
if (sock < 0) {
perror("socket");
return (1);
}

eport = port_create();
if (eport < 0) {
perror("port_create");
(void) close(sock);
return (1);
}

ret = connect(sock, (struct sockaddr *)&sin6,
sizeof (struct sockaddr_in6));
if (ret != 0 && errno != EINPROGRESS && errno != EINTR) {
perror("connect");
(void) close(sock);
(void) close(eport);
return (1);
}

if (ret != 0) {
port_event_t pe;
int err;
socklen_t sz = sizeof (err);
if (port_associate(eport, PORT_SOURCE_FD, sock, POLLOUT,
NULL) != 0) {
perror("port_associate");
(void) close(sock);
(void) close(eport);
return (1);
}
if (port_get(eport, &pe, NULL) != 0) {
perror("port_get");
(void) close(sock);
(void) close(eport);
return (1);
}
assert(pe.portev_source == PORT_SOURCE_FD);
assert(pe.portev_object == (uintptr_t)sock);
if (getsockopt(sock, SOL_SOCKET, SO_ERROR, &err, &sz) != 0) {
perror("getsockopt");
(void) close(sock);
(void) close(eport);
return (1);
}
if (err != 0) {
/* Asynch connect failed */
fprintf(stderr, "asynchronous connect: %s\n",
strerror(err));
(void) close(sock);
(void) close(eport);
return (1);
}
}

/* Read and write to the socket and then clean up */

return (0);
}

RETURN VALUES

If the connection or binding succeeds, 0 is returned. Otherwise, -1
is returned and sets errno to indicate the error.

ERRORS

The call fails if:

EACCES
Search permission is denied for a component of the
path prefix of the pathname in name.

EADDRINUSE
The address is already in use.

EADDRNOTAVAIL
The specified address is not available on the remote
machine.

EAFNOSUPPORT
Addresses in the specified address family cannot be
used with this socket.

EALREADY
The socket is non-blocking, and a previous
connection attempt has not yet been completed.

EBADF
s is not a valid descriptor.

ECONNREFUSED
The attempt to connect was forcefully rejected. The
calling program should close(2) the socket
descriptor, and issue another socket(3SOCKET) call
to obtain a new descriptor before attempting another
connect() call.

EINPROGRESS
The socket is non-blocking, and the connection
cannot be completed immediately. See the section on
Non-blocking Sockets for more information.

EINTR
The connection attempt was interrupted before any
data arrived by the delivery of a signal. The
connection, however, will be established
asynchronously.

EINVAL
namelen is not the size of a valid address for the
specified address family.

EIO
An I/O error occurred while reading from or writing
to the file system.

EISCONN
The socket is already connected.

ELOOP
Too many symbolic links were encountered in
translating the pathname in name.

ENETUNREACH
The network is not reachable from this host.

EHOSTUNREACH
The remote host is not reachable from this host.

ENOENT
A component of the path prefix of the pathname in
name does not exist.

ENOENT
The socket referred to by the pathname in name does
not exist.

ENOSR
There were insufficient STREAMS resources available
to complete the operation.

ENXIO
The server exited before the connection was
complete.

ETIMEDOUT
Connection establishment timed out without
establishing a connection.

EWOULDBLOCK
The socket is marked as non-blocking, and the
requested operation would block.

The following errors are specific to connecting names in the UNIX
domain. These errors might not apply in future versions of the UNIX
IPC domain.

ENOTDIR
A component of the path prefix of the pathname in name
is not a directory.

ENOTSOCK
s is not a socket.

ENOTSOCK
name is not a socket.

EPROTOTYPE
The file that is referred to by name is a socket of a
type other than type s. For example, s is a SOCK_DGRAM
socket, while name refers to a SOCK_STREAM socket.

ATTRIBUTES