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.

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

EADDRINUSE

EADDRNOTAVAIL

EAFNOSUPPORT

EALREADY

EBADF

ECONNREFUSED

EINPROGRESS

EINTR

EINVAL

EIO

EISCONN

ELOOP

ENETUNREACH

EHOSTUNREACH

ENOENT

ENOENT

ENOSR

ENXIO

ETIMEDOUT

EWOULDBLOCK

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

ENOTSOCK

ENOTSOCK

EPROTOTYPE

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:

SEE ALSO

close(2), select(3C), socket.h(3HEAD), accept(3SOCKET), getsockname(3SOCKET), sockaddr(3SOCKET), socket(3SOCKET), attributes(7)