connect(2) [opendarwin man page]
CONNECT(2) BSD System Calls Manual CONNECT(2) NAME
connect -- initiate a connection on a socket SYNOPSIS
#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, 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 SOCK_STREAM, this call attempts to make a connection to another socket. The other socket is specified by name, which is an address in the communications space of the socket. Each communications space interprets the name parameter in its own way. Generally, stream sockets may successfully connect() only once; datagram sockets may use connect() multiple times to change their association. Datagram sockets may dis- solve the association by connecting to an invalid address, such as a null address or an address with the address family set to AF_UNPSEC (the error EAFNOSUPPORT will be harmlessly returned). 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 errno. ERRORS
The connect() call fails if: [EBADF] S is not a valid descriptor. [ENOTSOCK] S is a descriptor for a file, not a socket. [EADDRNOTAVAIL] The specified address is not available on this machine. [EAFNOSUPPORT] Addresses in the specified address family cannot be used with this socket. [EISCONN] The socket is already connected. [ETIMEDOUT] Connection establishment timed out without establishing a connection. [ECONNREFUSED] The attempt to connect was forcefully rejected. [ENETUNREACH] The network isn't reachable from this host. [EADDRINUSE] The address is already in use. [EFAULT] The name parameter specifies an area outside the process address space. [EINPROGRESS] The socket is non-blocking and the connection cannot be completed immediately. It is possible to select(2) for completion by selecting the socket for writing. [EALREADY] The socket is non-blocking and a previous connection attempt has not yet been completed. The following errors are specific to connecting names in the UNIX domain. These errors may not apply in future versions of the UNIX IPC domain. [ENOTDIR] A component of the path prefix is not a directory. [ENAMETOOLONG] A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters. [ENOENT] The named socket does not exist. [EACCES] Search permission is denied for a component of the path prefix. [EACCES] Write access to the named socket is denied. [ELOOP] Too many symbolic links were encountered in translating the pathname. SEE ALSO
accept(2), select(2), socket(2), getsockname(2) HISTORY
The connect() function call appeared in 4.2BSD. 4.2 Berkeley Distribution June 4, 1993 4.2 Berkeley Distribution
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CONNECT(2) Linux Programmer's Manual CONNECT(2) NAME
connect - initiate a connection on a socket SYNOPSIS
#include <sys/types.h> #include <sys/socket.h> int connect(int sockfd, const struct sockaddr *serv_addr, socklen_t addrlen); DESCRIPTION
The file descriptor sockfd must refer to a socket. If the socket is of type SOCK_DGRAM then the serv_addr address is the address to which datagrams are sent by default, and the only address from which datagrams are received. If the socket is of type SOCK_STREAM or SOCK_SEQ- PACKET, this call attempts to make a connection to another socket. The other socket is specified by serv_addr, which is an address (of length addrlen) in the communications space of the socket. Each communications space interprets the serv_addr parameter in its own way. Generally, connection-based protocol sockets may successfully connect only once; connectionless protocol sockets may use connect multiple times to change their association. Connectionless sockets may dissolve the association by connecting to an address with the sa_family mem- ber of sockaddr set to AF_UNSPEC. RETURN VALUE
If the connection or binding succeeds, zero is returned. On error, -1 is returned, and errno is set appropriately. ERRORS
The following are general socket errors only. There may be other domain-specific error codes. EBADF The file descriptor is not a valid index in the descriptor table. EFAULT The socket structure address is outside the user's address space. ENOTSOCK The file descriptor is not associated with a socket. EISCONN The socket is already connected. ECONNREFUSED No one listening on the remote address. ETIMEDOUT Timeout while attempting connection. The server may be too busy to accept new connections. Note that for IP sockets the timeout may be very long when syncookies are enabled on the server. ENETUNREACH Network is unreachable. EADDRINUSE Local address is already in use. EINPROGRESS The socket is non-blocking and the connection cannot be completed immediately. It is possible to select(2) or poll(2) for comple- tion by selecting the socket for writing. After select indicates writability, use getsockopt(2) to read the SO_ERROR option at level SOL_SOCKET to determine whether connect completed successfully (SO_ERROR is zero) or unsuccessfully (SO_ERROR is one of the usual error codes listed here, explaining the reason for the failure). EALREADY The socket is non-blocking and a previous connection attempt has not yet been completed. EAGAIN No more free local ports or insufficient entries in the routing cache. For PF_INET see the net.ipv4.ip_local_port_range sysctl in ip(7) on how to increase the number of local ports. EAFNOSUPPORT The passed address didn't have the correct address family in its sa_family field. EACCES, EPERM The user tried to connect to a broadcast address without having the socket broadcast flag enabled or the connection request failed because of a local firewall rule. CONFORMING TO
SVr4, 4.4BSD (the connect function first appeared in BSD 4.2). SVr4 documents the additional general error codes EADDRNOTAVAIL, EINVAL, EAFNOSUPPORT, EALREADY, EINTR, EPROTOTYPE, and ENOSR. It also documents many additional error conditions not described here. NOTE
The third argument of connect is in reality an int (and this is what BSD 4.* and libc4 and libc5 have). Some POSIX confusion resulted in the present socklen_t. The draft standard has not been adopted yet, but glibc2 already follows it and also has socklen_t. See also accept(2). BUGS
Unconnecting a socket by calling connect with a AF_UNSPEC address is not yet implemented. SEE ALSO
accept(2), bind(2), listen(2), socket(2), getsockname(2) Linux 2.2 1998-10-03 CONNECT(2)