bsd/man/man2/socket.2

   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
  49 creates an endpoint for communication and returns a descriptor.
  50 .Pp
  51 The
  52 .Fa domain
  53 parameter specifies a communications domain within which
  54 communication will take place; this selects the protocol family
  55 which should be used.
  56 These families are defined in the include file
  57 .Ao Pa sys/socket.h Ac .
  58 The currently understood formats are
  59 .Pp
  60 .Bd -literal -offset indent -compact
  61 AF_UNIX         (UNIX internal protocols),
  62 AF_INET         (ARPA Internet protocols),
  63 AF_ISO          (ISO protocols),
  64 AF_NS           (Xerox Network Systems protocols), and
  65 AF_IMPLINK      (IMP \*(lqhost at IMP\*(rq link layer).
  66 .Ed
  67 .Pp
  68 The socket has the indicated
  69 .Fa type ,
  70 which specifies the semantics of communication.  Currently
  71 defined types are:
  72 .Pp
  73 .Bd -literal -offset indent -compact
  74 SOCK_STREAM
  75 SOCK_DGRAM
  76 SOCK_RAW
  77 SOCK_SEQPACKET
  78 SOCK_RDM
  79 .Ed
  80 .Pp
  81 A
  82 .Dv SOCK_STREAM
  83 type provides sequenced, reliable,
  84 two-way connection based byte streams.
  85 An out-of-band data transmission mechanism may be supported.
  86 A
  87 .Dv SOCK_DGRAM
  88 socket supports
  89 datagrams (connectionless, unreliable messages of
  90 a fixed (typically small) maximum length).
  91 A
  92 .Dv SOCK_SEQPACKET
  93 socket may provide a sequenced, reliable,
  94 two-way connection-based data transmission path for datagrams
  95 of fixed maximum length; a consumer may be required to read
  96 an entire packet with each read system call.
  97 This facility is protocol specific, and presently implemented
  98 only for
  99 .Dv PF_NS .
 100 .Dv SOCK_RAW
 101 sockets provide access to internal network protocols and interfaces.
 102 The types
 103 .Dv SOCK_RAW ,
 104 which is available only to the super-user, and
 105 .Dv SOCK_RDM ,
 106 which is planned,
 107 but not yet implemented, are not described here.
 108 .Pp
 109 The
 110 .Fa protocol
 111 specifies a particular protocol to be used with the socket.
 112 Normally only a single protocol exists to support a particular
 113 socket type within a given protocol family.  However, it is possible
 114 that many protocols may exist, in which case a particular protocol
 115 must be specified in this manner.  The protocol number to use is
 116 particular to the \*(lqcommunication domain\*(rq in which communication
 117 is to take place; see
 118 .Xr protocols 5 .
 119 .Pp
 120 Sockets of type
 121 .Dv SOCK_STREAM
 122 are full-duplex byte streams, similar
 123 to pipes.  A stream socket must be in a
 124 .Em connected
 125 state before any data may be sent or received
 126 on it.  A connection to another socket is created with a
 127 .Xr connect 2
 128 call.  Once connected, data may be transferred using
 129 .Xr read 2
 130 and
 131 .Xr write 2
 132 calls or some variant of the
 133 .Xr send 2
 134 and
 135 .Xr recv 2
 136 calls.  When a session has been completed a
 137 .Xr close 2
 138 may be performed.
 139 Out-of-band data may also be transmitted as described in
 140 .Xr send 2
 141 and received as described in
 142 .Xr recv 2 .
 143 .Pp
 144 The communications protocols used to implement a
 145 .Dv SOCK_STREAM
 146 insure that data
 147 is not lost or duplicated.  If a piece of data for which the
 148 peer protocol has buffer space cannot be successfully transmitted
 149 within a reasonable length of time, then
 150 the connection is considered broken and calls
 151 will indicate an error with
 152 -1 returns and with
 153 .Dv ETIMEDOUT
 154 as the specific code
 155 in the global variable
 156 .Va errno .
 157 The protocols optionally keep sockets
 158 .Dq warm
 159 by forcing transmissions
 160 roughly every minute in the absence of other activity.
 161 An error is then indicated if no response can be
 162 elicited on an otherwise
 163 idle connection for a extended period (e.g. 5 minutes).
 164 A
 165 .Dv SIGPIPE
 166 signal is raised if a process sends
 167 on a broken stream; this causes naive processes,
 168 which do not handle the signal, to exit.
 169 .Pp
 170 .Dv SOCK_SEQPACKET
 171 sockets employ the same system calls
 172 as
 173 .Dv SOCK_STREAM
 174 sockets.  The only difference
 175 is that
 176 .Xr read 2
 177 calls will return only the amount of data requested,
 178 and any remaining in the arriving packet will be discarded.
 179 .Pp
 180 .Dv SOCK_DGRAM
 181 and
 182 .Dv SOCK_RAW
 183 sockets allow sending of datagrams to correspondents
 184 named in
 185 .Xr send 2
 186 calls.  Datagrams are generally received with
 187 .Xr recvfrom 2 ,
 188 which returns the next datagram with its return address.
 189 .Pp
 190 An
 191 .Xr fcntl 2
 192 call can be used to specify a process group to receive
 193 a
 194 .Dv SIGURG
 195 signal when the out-of-band data arrives.
 196 It may also enable non-blocking I/O
 197 and asynchronous notification of I/O events
 198 via
 199 .Dv SIGIO .
 200 .Pp
 201 The operation of sockets is controlled by socket level
 202 .Em options .
 203 These options are defined in the file
 204 .Ao Pa sys/socket.h Ac .
 205 .Xr Setsockopt 2
 206 and
 207 .Xr getsockopt 2
 208 are used to set and get options, respectively.
 209 .Sh RETURN VALUES
 210 A -1 is returned if an error occurs, otherwise the return
 211 value is a descriptor referencing the socket.
 212 .Sh ERRORS
 213 The
 214 .Fn socket
 215 call fails if:
 216 .Bl -tag -width Er
 217 .It Bq Er EPROTONOSUPPORT
 218 The protocol type or the specified protocol is not supported
 219 within this domain.
 220 .It Bq Er EMFILE
 221 The per-process descriptor table is full.
 222 .It Bq Er ENFILE
 223 The system file table is full.
 224 .It Bq Er EACCES
 225 Permission to create a socket of the specified type and/or protocol
 226 is denied.
 227 .It Bq Er ENOBUFS
 228 Insufficient buffer space is available.
 229 The 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
 256 The
 257 .Fn socket
 258 function call appeared in
 259 .Bx 4.2 .