1.\" $NetBSD: socket.2,v 1.5 1995/02/27 12:37:53 cgd Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)socket.2 8.1 (Berkeley) 6/4/93 35.\" 36.Dd June 4, 1993 37.Dt SOCKET 2 38.Os BSD 4.2 39.Sh NAME 40.Nm socket 41.Nd create an endpoint for communication 42.Sh SYNOPSIS 43.Fd #include <sys/types.h> 44.Fd #include <sys/socket.h> 45.Ft int 46.Fn socket "int domain" "int type" "int protocol" 47.Sh DESCRIPTION 48.Fn Socket 49creates an endpoint for communication and returns a descriptor. 50.Pp 51The 52.Fa domain 53parameter specifies a communications domain within which 54communication will take place; this selects the protocol family 55which should be used. 56These families are defined in the include file 57.Ao Pa sys/socket.h Ac . 58The currently understood formats are 59.Pp 60.Bd -literal -offset indent -compact 61AF_UNIX (UNIX internal protocols), 62AF_INET (ARPA Internet protocols), 63AF_ISO (ISO protocols), 64AF_NS (Xerox Network Systems protocols), and 65AF_IMPLINK (IMP \*(lqhost at IMP\*(rq link layer). 66.Ed 67.Pp 68The socket has the indicated 69.Fa type , 70which specifies the semantics of communication. Currently 71defined types are: 72.Pp 73.Bd -literal -offset indent -compact 74SOCK_STREAM 75SOCK_DGRAM 76SOCK_RAW 77SOCK_SEQPACKET 78SOCK_RDM 79.Ed 80.Pp 81A 82.Dv SOCK_STREAM 83type provides sequenced, reliable, 84two-way connection based byte streams. 85An out-of-band data transmission mechanism may be supported. 86A 87.Dv SOCK_DGRAM 88socket supports 89datagrams (connectionless, unreliable messages of 90a fixed (typically small) maximum length). 91A 92.Dv SOCK_SEQPACKET 93socket may provide a sequenced, reliable, 94two-way connection-based data transmission path for datagrams 95of fixed maximum length; a consumer may be required to read 96an entire packet with each read system call. 97This facility is protocol specific, and presently implemented 98only for 99.Dv PF_NS . 100.Dv SOCK_RAW 101sockets provide access to internal network protocols and interfaces. 102The types 103.Dv SOCK_RAW , 104which is available only to the super-user, and 105.Dv SOCK_RDM , 106which is planned, 107but not yet implemented, are not described here. 108.Pp 109The 110.Fa protocol 111specifies a particular protocol to be used with the socket. 112Normally only a single protocol exists to support a particular 113socket type within a given protocol family. However, it is possible 114that many protocols may exist, in which case a particular protocol 115must be specified in this manner. The protocol number to use is 116particular to the \*(lqcommunication domain\*(rq in which communication 117is to take place; see 118.Xr protocols 5 . 119.Pp 120Sockets of type 121.Dv SOCK_STREAM 122are full-duplex byte streams, similar 123to pipes. A stream socket must be in a 124.Em connected 125state before any data may be sent or received 126on it. A connection to another socket is created with a 127.Xr connect 2 128call. Once connected, data may be transferred using 129.Xr read 2 130and 131.Xr write 2 132calls or some variant of the 133.Xr send 2 134and 135.Xr recv 2 136calls. When a session has been completed a 137.Xr close 2 138may be performed. 139Out-of-band data may also be transmitted as described in 140.Xr send 2 141and received as described in 142.Xr recv 2 . 143.Pp 144The communications protocols used to implement a 145.Dv SOCK_STREAM 146insure that data 147is not lost or duplicated. If a piece of data for which the 148peer protocol has buffer space cannot be successfully transmitted 149within a reasonable length of time, then 150the connection is considered broken and calls 151will indicate an error with 152-1 returns and with 153.Dv ETIMEDOUT 154as the specific code 155in the global variable 156.Va errno . 157The protocols optionally keep sockets 158.Dq warm 159by forcing transmissions 160roughly every minute in the absence of other activity. 161An error is then indicated if no response can be 162elicited on an otherwise 163idle connection for a extended period (e.g. 5 minutes). 164A 165.Dv SIGPIPE 166signal is raised if a process sends 167on a broken stream; this causes naive processes, 168which do not handle the signal, to exit. 169.Pp 170.Dv SOCK_SEQPACKET 171sockets employ the same system calls 172as 173.Dv SOCK_STREAM 174sockets. The only difference 175is that 176.Xr read 2 177calls will return only the amount of data requested, 178and any remaining in the arriving packet will be discarded. 179.Pp 180.Dv SOCK_DGRAM 181and 182.Dv SOCK_RAW 183sockets allow sending of datagrams to correspondents 184named in 185.Xr send 2 186calls. Datagrams are generally received with 187.Xr recvfrom 2 , 188which returns the next datagram with its return address. 189.Pp 190An 191.Xr fcntl 2 192call can be used to specify a process group to receive 193a 194.Dv SIGURG 195signal when the out-of-band data arrives. 196It may also enable non-blocking I/O 197and asynchronous notification of I/O events 198via 199.Dv SIGIO . 200.Pp 201The operation of sockets is controlled by socket level 202.Em options . 203These options are defined in the file 204.Ao Pa sys/socket.h Ac . 205.Xr Setsockopt 2 206and 207.Xr getsockopt 2 208are used to set and get options, respectively. 209.Sh RETURN VALUES 210A -1 is returned if an error occurs, otherwise the return 211value is a descriptor referencing the socket. 212.Sh ERRORS 213The 214.Fn socket 215call fails if: 216.Bl -tag -width Er 217.It Bq Er EPROTONOSUPPORT 218The protocol type or the specified protocol is not supported 219within this domain. 220.It Bq Er EMFILE 221The per-process descriptor table is full. 222.It Bq Er ENFILE 223The system file table is full. 224.It Bq Er EACCESS 225Permission to create a socket of the specified type and/or protocol 226is denied. 227.It Bq Er ENOBUFS 228Insufficient buffer space is available. 229The socket cannot be created until sufficient resources are freed. 230.El 231.Sh SEE ALSO 232.Xr accept 2 , 233.Xr bind 2 , 234.Xr connect 2 , 235.Xr getprotoent 3 , 236.Xr getsockname 2 , 237.Xr getsockopt 2 , 238.Xr ioctl 2 , 239.Xr listen 2 , 240.Xr read 2 , 241.Xr recv 2 , 242.Xr select 2 , 243.Xr send 2 , 244.Xr shutdown 2 , 245.Xr socketpair 2 , 246.Xr write 2 247.Rs 248.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 249.%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1" 250.Re 251.Rs 252.%T "BSD Interprocess Communication Tutorial" 253.%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1" 254.Re 255.Sh HISTORY 256The 257.Fn socket 258function call appeared in 259.Bx 4.2 . 260