bsd/man/man2/socket.2

   1 .\"     $NetBSD: socket.2,v 1.5 1995/02/27 12:37:53 cgd Exp $
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  34 .\"     @(#)socket.2    8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd June 4, 1993
  37 .Dt SOCKET 2
  38 .Os
  39 .Sh NAME
  40 .Nm socket
  41 .Nd create an endpoint for communication
  42 .Sh SYNOPSIS
  43 .Fd #include <sys/socket.h>
  44 .Ft int
  45 .Fo socket
  46 .Fa "int domain"
  47 .Fa "int type"
  48 .Fa "int protocol"
  49 .Fc
  50 .Sh DESCRIPTION
  51 .Fn Socket
  52 creates an endpoint for communication and returns a descriptor.
  53 .Pp
  54 The
  55 .Fa domain
  56 parameter specifies a communications domain within which
  57 communication will take place; this selects the protocol family
  58 which should be used.
  59 These families are defined in the include file
  60 .Ao Pa sys/socket.h Ac .
  61 The currently understood formats are
  62 .Pp
  63 .Bd -literal -offset indent -compact
  64 PF_LOCAL        Host-internal protocols, formerly called PF_UNIX,
  65 PF_UNIX         Host-internal protocols, deprecated, use PF_LOCAL,
  66 PF_INET         Internet version 4 protocols,
  67 PF_ROUTE        Internal Routing protocol,
  68 PF_KEY          Internal key-management function,
  69 PF_INET6        Internet version 6 protocols,
  70 PF_SYSTEM       System domain,
  71 PF_NDRV         Raw access to network device
  72 .Ed
  73 .Pp
  74 The socket has the indicated
  75 .Fa type ,
  76 which specifies the semantics of communication.  Currently
  77 defined types are:
  78 .Pp
  79 .Bd -literal -offset indent -compact
  80 SOCK_STREAM
  81 SOCK_DGRAM
  82 SOCK_RAW
  83 SOCK_SEQPACKET
  84 SOCK_RDM
  85 .Ed
  86 .Pp
  87 A
  88 .Dv SOCK_STREAM
  89 type provides sequenced, reliable,
  90 two-way connection based byte streams.
  91 An out-of-band data transmission mechanism may be supported.
  92 A
  93 .Dv SOCK_DGRAM
  94 socket supports
  95 datagrams (connectionless, unreliable messages of
  96 a fixed (typically small) maximum length).
  97 A
  98 .Dv SOCK_SEQPACKET
  99 socket may provide a sequenced, reliable,
 100 two-way connection-based data transmission path for datagrams
 101 of fixed maximum length; a consumer may be required to read
 102 an entire packet with each read system call.
 103 This facility is protocol specific, and presently implemented
 104 only for
 105 .Dv PF_NS .
 106 .Dv SOCK_RAW
 107 sockets provide access to internal network protocols and interfaces.
 108 The types
 109 .Dv SOCK_RAW ,
 110 which is available only to the super-user, and
 111 .Dv SOCK_RDM ,
 112 which is planned,
 113 but not yet implemented, are not described here.
 114 .Pp
 115 The
 116 .Fa protocol
 117 specifies a particular protocol to be used with the socket.
 118 Normally only a single protocol exists to support a particular
 119 socket type within a given protocol family.  However, it is possible
 120 that many protocols may exist, in which case a particular protocol
 121 must be specified in this manner.  The protocol number to use is
 122 particular to the \*(lqcommunication domain\*(rq in which communication
 123 is to take place; see
 124 .Xr protocols 5 .
 125 .Pp
 126 Sockets of type
 127 .Dv SOCK_STREAM
 128 are full-duplex byte streams, similar
 129 to pipes.  A stream socket must be in a
 130 .Em connected
 131 state before any data may be sent or received
 132 on it.  A connection to another socket is created with a
 133 .Xr connect 2
 134 call.  Once connected, data may be transferred using
 135 .Xr read 2
 136 and
 137 .Xr write 2
 138 calls or some variant of the
 139 .Xr send 2
 140 and
 141 .Xr recv 2
 142 calls.  When a session has been completed a
 143 .Xr close 2
 144 may be performed.
 145 Out-of-band data may also be transmitted as described in
 146 .Xr send 2
 147 and received as described in
 148 .Xr recv 2 .
 149 .Pp
 150 The communications protocols used to implement a
 151 .Dv SOCK_STREAM
 152 insure that data
 153 is not lost or duplicated.  If a piece of data for which the
 154 peer protocol has buffer space cannot be successfully transmitted
 155 within a reasonable length of time, then
 156 the connection is considered broken and calls
 157 will indicate an error with
 158 -1 returns and with
 159 .Dv ETIMEDOUT
 160 as the specific code
 161 in the global variable
 162 .Va errno .
 163 The protocols optionally keep sockets
 164 .Dq warm
 165 by forcing transmissions
 166 roughly every minute in the absence of other activity.
 167 An error is then indicated if no response can be
 168 elicited on an otherwise
 169 idle connection for a extended period (e.g. 5 minutes).
 170 A
 171 .Dv SIGPIPE
 172 signal is raised if a process sends
 173 on a broken stream; this causes naive processes,
 174 which do not handle the signal, to exit.
 175 .Pp
 176 .Dv SOCK_SEQPACKET
 177 sockets employ the same system calls
 178 as
 179 .Dv SOCK_STREAM
 180 sockets.  The only difference
 181 is that
 182 .Xr read 2
 183 calls will return only the amount of data requested,
 184 and any remaining in the arriving packet will be discarded.
 185 .Pp
 186 .Dv SOCK_DGRAM
 187 and
 188 .Dv SOCK_RAW
 189 sockets allow sending of datagrams to correspondents
 190 named in
 191 .Xr send 2
 192 calls.  Datagrams are generally received with
 193 .Xr recvfrom 2 ,
 194 which returns the next datagram with its return address.
 195 .Pp
 196 An
 197 .Xr fcntl 2
 198 call can be used to specify a process group to receive
 199 a
 200 .Dv SIGURG
 201 signal when the out-of-band data arrives.
 202 It may also enable non-blocking I/O
 203 and asynchronous notification of I/O events
 204 via
 205 .Dv SIGIO .
 206 .Pp
 207 The operation of sockets is controlled by socket level
 208 .Em options .
 209 These options are defined in the file
 210 .Ao Pa sys/socket.h Ac .
 211 .Xr Setsockopt 2
 212 and
 213 .Xr getsockopt 2
 214 are used to set and get options, respectively.
 215 .Sh RETURN VALUES
 216 A -1 is returned if an error occurs, otherwise the return
 217 value is a descriptor referencing the socket.
 218 .Sh ERRORS
 219 The
 220 .Fn socket
 221 system call fails if:
 222 .Bl -tag -width Er
 223 .\" ===========
 224 .It Bq Er EACCES
 225 Permission to create a socket of the specified type and/or protocol
 226 is denied.
 227 .\" ===========
 228 .It Bq Er EAFNOSUPPORT
 229 The specified address family is not supported.
 230 .\" ===========
 231 .It Bq Er EISCONN
 232 The per-process descriptor table is full.
 233 .\" ===========
 234 .It Bq Er EMFILE
 235 The per-process descriptor table is full.
 236 .\" ===========
 237 .It Bq Er ENFILE
 238 The system file table is full.
 239 .\" ===========
 240 .It Bq Er ENOBUFS
 241 Insufficient buffer space is available.
 242 The socket cannot be created until sufficient resources are freed.
 243 .\" ===========
 244 .It Bq Er ENOMEM
 245 Insufficient memory was available to fulfill the request.
 246 .\" ===========
 247 .It Bq Er EPROTONOSUPPORT
 248 The protocol type or the specified protocol is not supported
 249 within this domain.
 250 .\" ===========
 251 .It Bq Er EPROTOTYPE
 252 The socket type is not supported by the protocol.
 253 .El
 254 .Pp
 255 If a new protocol family is defined,
 256 the socreate process is free to return any desired error code.
 257 The
 258 .Fn socket
 259 system call will pass this error code along
 260 (even if it is undefined).
 261 .Sh LEGACY SYNOPSIS
 262 .Fd #include <sys/types.h>
 263 .Fd #include <sys/socket.h>
 264 .Pp
 265 The include file
 266 .In sys/types.h
 267 is necessary.
 268 .Sh SEE ALSO
 269 .Xr accept 2 ,
 270 .Xr bind 2 ,
 271 .Xr connect 2 ,
 272 .Xr getsockname 2 ,
 273 .Xr getsockopt 2 ,
 274 .Xr ioctl 2 ,
 275 .Xr listen 2 ,
 276 .Xr read 2 ,
 277 .Xr recv 2 ,
 278 .Xr select 2 ,
 279 .Xr send 2 ,
 280 .Xr shutdown 2 ,
 281 .Xr socketpair 2 ,
 282 .Xr write 2 ,
 283 .Xr getprotoent 3 ,
 284 .Xr inet 4 ,
 285 .Xr inet6 4 ,
 286 .Xr unix 4 ,
 287 .Xr compat 5
 288 .Rs
 289 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
 290 .%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1"
 291 .Re
 292 .Rs
 293 .%T "BSD Interprocess Communication Tutorial"
 294 .%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1"
 295 .Re
 296 .Sh HISTORY
 297 The
 298 .Fn socket
 299 function call appeared in
 300 .Bx 4.2 .