.\" $NetBSD: socket.2,v 1.5 1995/02/27 12:37:53 cgd Exp $ .\" .\" Copyright (c) 1983, 1991, 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. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. 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. .\" .\" @(#)socket.2 8.1 (Berkeley) 6/4/93 .\" .Dd June 4, 1993 .Dt SOCKET 2 .Os .Sh NAME .Nm socket .Nd create an endpoint for communication .Sh SYNOPSIS .Fd #include <sys/socket.h> .Ft int .Fo socket .Fa "int domain" .Fa "int type" .Fa "int protocol" .Fc .Sh DESCRIPTION .Fn Socket creates an endpoint for communication and returns a descriptor. .Pp The .Fa domain parameter specifies a communications domain within which communication will take place; this selects the protocol family which should be used. These families are defined in the include file .Ao Pa sys/socket.h Ac . The currently understood formats are .Pp .Bd -literal -offset indent -compact PF_LOCAL Host-internal protocols, formerly called PF_UNIX, PF_UNIX Host-internal protocols, deprecated, use PF_LOCAL, PF_INET Internet version 4 protocols, PF_ROUTE Internal Routing protocol, PF_KEY Internal key-management function, PF_INET6 Internet version 6 protocols, PF_SYSTEM System domain, PF_NDRV Raw access to network device .Ed .Pp The socket has the indicated .Fa type , which specifies the semantics of communication. Currently defined types are: .Pp .Bd -literal -offset indent -compact SOCK_STREAM SOCK_DGRAM SOCK_RAW SOCK_SEQPACKET SOCK_RDM .Ed .Pp A .Dv SOCK_STREAM type provides sequenced, reliable, two-way connection based byte streams. An out-of-band data transmission mechanism may be supported. A .Dv SOCK_DGRAM socket supports datagrams (connectionless, unreliable messages of a fixed (typically small) maximum length). A .Dv SOCK_SEQPACKET socket may provide a sequenced, reliable, two-way connection-based data transmission path for datagrams of fixed maximum length; a consumer may be required to read an entire packet with each read system call. This facility is protocol specific, and presently implemented only for .Dv PF_NS . .Dv SOCK_RAW sockets provide access to internal network protocols and interfaces. The types .Dv SOCK_RAW , which is available only to the super-user, and .Dv SOCK_RDM , which is planned, but not yet implemented, are not described here. .Pp The .Fa protocol specifies a particular protocol to be used with the socket. Normally only a single protocol exists to support a particular socket type within a given protocol family. However, it is possible that many protocols may exist, in which case a particular protocol must be specified in this manner. The protocol number to use is particular to the \*(lqcommunication domain\*(rq in which communication is to take place; see .Xr protocols 5 . .Pp Sockets of type .Dv SOCK_STREAM are full-duplex byte streams, similar to pipes. A stream socket must be in a .Em connected state before any data may be sent or received on it. A connection to another socket is created with a .Xr connect 2 call. Once connected, data may be transferred using .Xr read 2 and .Xr write 2 calls or some variant of the .Xr send 2 and .Xr recv 2 calls. When a session has been completed a .Xr close 2 may be performed. Out-of-band data may also be transmitted as described in .Xr send 2 and received as described in .Xr recv 2 . .Pp The communications protocols used to implement a .Dv SOCK_STREAM insure that data is not lost or duplicated. If a piece of data for which the peer protocol has buffer space cannot be successfully transmitted within a reasonable length of time, then the connection is considered broken and calls will indicate an error with -1 returns and with .Dv ETIMEDOUT as the specific code in the global variable .Va errno . The protocols optionally keep sockets .Dq warm by forcing transmissions roughly every minute in the absence of other activity. An error is then indicated if no response can be elicited on an otherwise idle connection for a extended period (e.g. 5 minutes). A .Dv SIGPIPE signal is raised if a process sends on a broken stream; this causes naive processes, which do not handle the signal, to exit. .Pp .Dv SOCK_SEQPACKET sockets employ the same system calls as .Dv SOCK_STREAM sockets. The only difference is that .Xr read 2 calls will return only the amount of data requested, and any remaining in the arriving packet will be discarded. .Pp .Dv SOCK_DGRAM and .Dv SOCK_RAW sockets allow sending of datagrams to correspondents named in .Xr send 2 calls. Datagrams are generally received with .Xr recvfrom 2 , which returns the next datagram with its return address. .Pp An .Xr fcntl 2 call can be used to specify a process group to receive a .Dv SIGURG signal when the out-of-band data arrives. It may also enable non-blocking I/O and asynchronous notification of I/O events via .Dv SIGIO . .Pp The operation of sockets is controlled by socket level .Em options . These options are defined in the file .Ao Pa sys/socket.h Ac . .Xr Setsockopt 2 and .Xr getsockopt 2 are used to set and get options, respectively. .Sh RETURN VALUES A -1 is returned if an error occurs, otherwise the return value is a descriptor referencing the socket. .Sh ERRORS The .Fn socket system call fails if: .Bl -tag -width Er .\" =========== .It Bq Er EACCES Permission to create a socket of the specified type and/or protocol is denied. .\" =========== .It Bq Er EAFNOSUPPORT The specified address family is not supported. .\" =========== .It Bq Er EISCONN The per-process descriptor table is full. .\" =========== .It Bq Er EMFILE The per-process descriptor table is full. .\" =========== .It Bq Er ENFILE The system file table is full. .\" =========== .It Bq Er ENOBUFS Insufficient buffer space is available. The socket cannot be created until sufficient resources are freed. .\" =========== .It Bq Er ENOMEM Insufficient memory was available to fulfill the request. .\" =========== .It Bq Er EPROTONOSUPPORT The protocol type or the specified protocol is not supported within this domain. .\" =========== .It Bq Er EPROTOTYPE The socket type is not supported by the protocol. .El .Pp If a new protocol family is defined, the socreate process is free to return any desired error code. The .Fn socket system call will pass this error code along (even if it is undefined). .Sh LEGACY SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/socket.h> .Pp The include file .In sys/types.h is necessary. .Sh SEE ALSO .Xr accept 2 , .Xr bind 2 , .Xr connect 2 , .Xr getsockname 2 , .Xr getsockopt 2 , .Xr ioctl 2 , .Xr listen 2 , .Xr read 2 , .Xr recv 2 , .Xr select 2 , .Xr send 2 , .Xr shutdown 2 , .Xr socketpair 2 , .Xr write 2 , .Xr getprotoent 3 , .Xr inet 4 , .Xr inet6 4 , .Xr unix 4 , .Xr compat 5 .Rs .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" .%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1" .Re .Rs .%T "BSD Interprocess Communication Tutorial" .%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1" .Re .Sh HISTORY The .Fn socket function call appeared in .Bx 4.2 .