bsd/man/man2/socket.2

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