NAME

connect - connect a socket

SYNOPSIS

#include <sys/socket.h>

int connect(int socket, const struct sockaddr *address,
    socklen_t address_len);

DESCRIPTION

The connect() function requests a connection to be made on a socket. The function takes the following arguments:

socket

Specifies the file descriptor associated with the socket.

address

Points to a sockaddr structure containing the peer address. The length and format of the address depend on the address family of the socket.

address_len

Specifies the length of the sockaddr structure pointed to by the address argument.

If the socket has not already been bound to a local address, connect() will bind it to an address which, unless the socket's address family is AF_UNIX, is an unused local address.

If the initiating socket is not connection-mode, then connect() sets the socket's peer address, but no connection is made. For SOCK_DGRAM sockets, the peer address identifies where all datagrams are sent on subsequent send() calls, and limits the remote sender for subsequent recv() calls. If address is a null address for the protocol, the socket's peer address will be reset.

If the initiating socket is connection-mode, then connect() attempts to establish a connection to the address specified by the address argument.

If the connection cannot be established immediately and O_NONBLOCK is not set for the file descriptor for the socket, connect() will block for up to an unspecified timeout interval until the connection is established. If the timeout interval expires before the connection is established, connect() will fail and the connection attempt will be aborted. If connect() is interrupted by a signal that is caught while blocked waiting to establish a connection, connect() will fail and set errno to [EINTR], but the connection request will not be aborted, and the connection will be established asynchronously.

If the connection cannot be established immediately and O_NONBLOCK is set for the file descriptor for the socket, connect() will fail and set errno to [EINPROGRESS], but the connection request will not be aborted, and the connection will be established asynchronously. Subsequent calls to connect() for the same socket, before the connection is established, will fail and set errno to [EALREADY].

When the connection has been established asynchronously, select() and poll() will indicate that the file descriptor for the socket is ready for writing.

The socket in use may require the process to have appropriate privileges to use the connect() function.

RETURN VALUE

Upon successful completion, connect() returns 0. Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

The connect() function will fail if:

[EADDRNOTAVAIL]

The specified address is not available from the local machine.

[EAFNOSUPPORT]

The specified address is not a valid address for the address family of the specified socket.

[EALREADY]

A connection request is already in progress for the specified socket.

[EBADF]

The socket argument is not a valid file descriptor.

[ECONNREFUSED]

The target address was not listening for connections or refused the connection request.

[EFAULT]

The address parameter can not be accessed.

[EINPROGRESS]

O_NONBLOCK is set for the file descriptor for the socket and the connection cannot be immediately established; the connection will be established asynchronously.

[EINTR]

The attempt to establish a connection was interrupted by delivery of a signal that was caught; the connection will be established asynchronously.

[EISCONN]

The specified socket is connection-mode and is already connected.

[ENETUNREACH]

No route to the network is present.

[ENOTSOCK]

The socket argument does not refer to a socket.

[EPROTOTYPE]

The specified address has a different type than the socket bound to the specified peer address.

[ETIMEDOUT]

The attempt to connect timed out before a connection was made.

If the address family of the socket is AF_UNIX, then connect() will fail if:

[EIO]

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

[ELOOP]

Too many symbolic links were encountered in translating the pathname in address.

[ENAMETOOLONG]

A component of a pathname exceeded {NAME_MAX} characters, or an entire pathname exceeded {PATH_MAX} characters.

[ENOENT]

A component of the pathname does not name an existing file or the pathname is an empty string.

[ENOTDIR]

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

The connect() function may fail if:

[EACCES]

Search permission is denied for a component of the path prefix; or write access to the named socket is denied.

[EADDRINUSE]

Attempt to establish a connection that uses addresses that are already in use.

[ECONNRESET]

Remote host reset the connection request.

[EHOSTUNREACH]

The destination host cannot be reached (probably because the host is down or a remote router cannot reach it).

[EINVAL]

The address_len argument is not a valid length for the address family; or invalid address family in sockaddr structure.

[ENAMETOOLONG]

Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.

[ENETDOWN]

The local interface used to reach the destination is down.

[ENOBUFS]

No buffer space is available.

[ENOSR]

There were insufficient STREAMS resources available to complete the operation.

[EOPNOTSUPP]

The socket is listening and can not be connected.

APPLICATION USAGE

If connect() fails, the state of the socket is unspecified. Portable applications should close the file descriptor and create a new socket before attempting to reconnect.

SEE ALSO

accept(), bind(), close(), getsockname(), poll(), select(), send(), shutdown(), socket(), <sys/socket.h>.

CHANGE HISTORY

First released in Issue 4.