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1.1 root 1: .TH SOCKET 2 "18 July 1983"
2: .UC 4
3: .SH NAME
4: socket \- create an endpoint for communication
5: .SH SYNOPSIS
6: .nf
7: .ft B
8: #include <sys/types.h>
9: #include <sys/socket.h>
10: .PP
11: .ft B
12: s = socket(af, type, protocol)
13: int s, af, type, protocol;
14: .fi
15: .SH DESCRIPTION
16: .I Socket
17: creates an endpoint for communication and returns a descriptor.
18: .PP
19: The
20: .I af
21: parameter specifies an address format with which addresses specified
22: in later operations using the socket should be interpreted. These
23: formats are defined in the include file
24: .IR <sys/socket.h> .
25: The currently understood formats are
26: .PP
27: .RS
28: .nf
29: .ta 1.25i 1.75i
30: AF_UNIX (UNIX path names),
31: AF_INET (ARPA Internet addresses),
32: AF_PUP (Xerox PUP-I Internet addresses), and
33: AF_IMPLINK (IMP \*(lqhost at IMP\*(rq addresses).
34: .fi
35: .RE
36: .PP
37: The socket has the indicated
38: .I type
39: which specifies the semantics of communication. Currently
40: defined types are:
41: .PP
42: .RS
43: .nf
44: SOCK_STREAM
45: SOCK_DGRAM
46: SOCK_RAW
47: SOCK_SEQPACKET
48: SOCK_RDM
49: .fi
50: .RE
51: .PP
52: A SOCK_STREAM type provides sequenced, reliable,
53: two-way connection based byte streams with an out-of-band data
54: transmission mechanism.
55: A SOCK_DGRAM socket supports
56: datagrams (connectionless, unreliable messages of
57: a fixed (typically small) maximum length).
58: SOCK_RAW sockets provide access to internal network interfaces.
59: The types SOCK_RAW,
60: which is available only to the super-user, and
61: SOCK_SEQPACKET and SOCK_RDM, which are planned,
62: but not yet implemented, are not described here.
63: .PP
64: The
65: .I protocol
66: specifies a particular protocol to be used with the socket.
67: Normally only a single protocol exists to support a particular
68: socket type using a given address format. However, it is possible
69: that many protocols may exist in which case a particular protocol
70: must be specified in this manner. The protocol number to use is
71: particular to the \*(lqcommunication domain\*(rq in which communication
72: is to take place; see
73: .IR services (3N)
74: and
75: .IR protocols (3N).
76: .PP
77: Sockets of type SOCK_STREAM
78: are full-duplex byte streams, similar
79: to pipes. A stream socket must be in a
80: .I connected
81: state before any data may be sent or received
82: on it. A connection to another socket is created with a
83: .IR connect (2)
84: call. Once connected, data may be transferred using
85: .IR read (2)
86: and
87: .IR write (2)
88: calls or some variant of the
89: .IR send (2)
90: and
91: .IR recv (2)
92: calls. When a session has been completed a
93: .IR close (2)
94: may be performed.
95: Out-of-band data may also be transmitted as described in
96: .IR send (2)
97: and received as described in
98: .IR recv (2).
99: .PP
100: The communications protocols used to implement a
101: SOCK_STREAM insure that data
102: is not lost or duplicated. If a piece of data for which the
103: peer protocol has buffer space cannot be successfully transmitted
104: within a reasonable length of time, then
105: the connection is considered broken and calls
106: will indicate an error with
107: \-1 returns and with ETIMEDOUT as the specific code
108: in the global variable errno.
109: The protocols optionally keep sockets \*(lqwarm\*(rq by
110: forcing transmissions
111: roughly every minute in the absence of other activity.
112: An error is then indicated if no response can be
113: elicited on an otherwise
114: idle connection for a extended period (e.g. 5 minutes).
115: A SIGPIPE signal is raised if a process sends
116: on a broken stream; this causes naive processes,
117: which do not handle the signal, to exit.
118: .PP
119: SOCK_DGRAM and SOCK_RAW
120: sockets allow sending of datagrams to correspondents
121: named in
122: .IR send (2)
123: calls. It is also possible to receive datagrams at
124: such a socket with
125: .IR recv (2).
126: .PP
127: An
128: .IR fcntl (2)
129: call can be used to specify a process group to receive
130: a SIGURG signal when the out-of-band data arrives.
131: .PP
132: The operation of sockets is controlled by socket level
133: .IR options .
134: These options are defined in the file
135: .RI < sys/socket.h >
136: and explained below.
137: .I Setsockopt
138: and
139: .IR getsockopt (2)
140: are used to set and get options, respectively.
141: .PP
142: .RS
143: .DT
144: .nf
145: SO_DEBUG turn on recording of debugging information
146: SO_REUSEADDR allow local address reuse
147: SO_KEEPALIVE keep connections alive
148: SO_DONTROUTE do no apply routing on outgoing messages
149: SO_LINGER linger on close if data present
150: SO_DONTLINGER do not linger on close
151: .fi
152: .RE
153: .PP
154: SO_DEBUG enables debugging in the underlying protocol modules.
155: SO_REUSEADDR indicates the rules used in validating addresses supplied
156: in a
157: .IR bind (2)
158: call should allow reuse of local addresses. SO_KEEPALIVE enables the
159: periodic transmission of messages on a connected socket. Should the
160: connected party fail to respond to these messages, the connection is
161: considered broken and processes using the socket are notified via a
162: SIGPIPE signal. SO_DONTROUTE indicates that outgoing messages should
163: bypass the standard routing facilities. Instead, messages are directed
164: to the appropriate network interface according to the network portion
165: of the destination address. SO_LINGER
166: and SO_DONTLINGER control the actions taken when unsent messags
167: are queued on socket and a
168: .IR close (2)
169: is performed.
170: If the socket promises reliable delivery of data and SO_LINGER is set,
171: the system will block the process on the
172: .I close
173: attempt until it is able to transmit the data or until it decides it
174: is unable to deliver the information (a timeout period, termed the
175: linger interval, is specified in the
176: .IR setsockopt
177: call when SO_LINGER is requested).
178: If SO_DONTLINGER is specified and a
179: .I close
180: is issued, the system will process the close in a manner which allows
181: the process to continue as quickly as possible.
182: .SH "RETURN VALUE
183: A \-1 is returned if an error occurs, otherwise the return
184: value is a descriptor referencing the socket.
185: .SH "ERRORS
186: The \fIsocket\fP call fails if:
187: .TP 20
188: [EAFNOSUPPORT]
189: The specified address family is not supported in this version
190: of the system.
191: .TP 20
192: [ESOCKTNOSUPPORT]
193: The specified socket type is not supported in this address family.
194: .TP 20
195: [EPROTONOSUPPORT]
196: The specified protocol is not supported.
197: .TP 20
198: [EMFILE]
199: The per-process descriptor table is full.
200: .TP 20
201: [ENOBUFS]
202: No buffer space is available. The socket cannot be created.
203: .SH SEE ALSO
204: accept(2), bind(2), connect(2), getsockname(2), getsockopt(2),
205: ioctl(2), listen(2), recv(2),
206: select(2), send(2), shutdown(2), socketpair(2)
207: .br
208: ``A 4.2BSD Interprocess Communication Primer''.
209: .SH BUGS
210: The use of keepalives is a questionable feature for this layer.
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