1sys_socket.h(0P) POSIX Programmer's Manual sys_socket.h(0P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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13 sys/socket.h — main sockets header
14
16 #include <sys/socket.h>
17
19 The <sys/socket.h> header shall define the socklen_t type, which is an
20 integer type of width of at least 32 bits; see APPLICATION USAGE.
21 The <sys/socket.h> header shall define the sa_family_t unsigned integer
23 type.
24 The <sys/socket.h> header shall define the sockaddr structure, which
26 shall include at least the following members:
27 sa_family_t sa_family Address family.
29 char sa_data[] Socket address (variable-length data).
30 The sockaddr structure is used to define a socket address which is used
32 in the bind(), connect(), getpeername(), getsockname(), recvfrom(), and
33 sendto() functions.
34 The <sys/socket.h> header shall define the sockaddr_storage structure,
36 which shall be:
37 * Large enough to accommodate all supported protocol-specific address
39 structures
40 * Aligned at an appropriate boundary so that pointers to it can be
42 cast as pointers to protocol-specific address structures and used
43 to access the fields of those structures without alignment problems
44 The sockaddr_storage structure shall include at least the following
46 members:
47 sa_family_t ss_family
49 When a pointer to a sockaddr_storage structure is cast as a pointer to
51 a sockaddr structure, the ss_family field of the sockaddr_storage
52 structure shall map onto the sa_family field of the sockaddr structure.
53 When a pointer to a sockaddr_storage structure is cast as a pointer to
54 a protocol-specific address structure, the ss_family field shall map
55 onto a field of that structure that is of type sa_family_t and that
56 identifies the protocol's address family.
57 The <sys/socket.h> header shall define the msghdr structure, which
59 shall include at least the following members:
60 void *msg_name Optional address.
62 socklen_t msg_namelen Size of address.
63 struct iovec *msg_iov Scatter/gather array.
64 int msg_iovlen Members in msg_iov.
65 void *msg_control Ancillary data; see below.
66 socklen_t msg_controllen Ancillary data buffer len.
67 int msg_flags Flags on received message.
68 The msghdr structure is used to minimize the number of directly sup‐
70 plied parameters to the recvmsg() and sendmsg() functions. This struc‐
71 ture is used as a value‐result parameter in the recvmsg() function and
72 value only for the sendmsg() function.
73 The <sys/socket.h> header shall define the iovec structure as described
75 in <sys/uio.h>.
76 The <sys/socket.h> header shall define the cmsghdr structure, which
78 shall include at least the following members:
79 socklen_t cmsg_len Data byte count, including the cmsghdr.
81 int cmsg_level Originating protocol.
82 int cmsg_type Protocol-specific type.
83 The cmsghdr structure is used for storage of ancillary data object
85 information.
86 Ancillary data consists of a sequence of pairs, each consisting of a
88 cmsghdr structure followed by a data array. The data array contains the
89 ancillary data message, and the cmsghdr structure contains descriptive
90 information that allows an application to correctly parse the data.
91 The values for cmsg_level shall be legal values for the level argument
93 to the getsockopt() and setsockopt() functions. The system documenta‐
94 tion shall specify the cmsg_type definitions for the supported proto‐
95 cols.
96 Ancillary data is also possible at the socket level. The <sys/socket.h>
98 header shall define the following symbolic constant for use as the
99 cmsg_type value when cmsg_level is SOL_SOCKET:
100 SCM_RIGHTS Indicates that the data array contains the access rights
102 to be sent or received.
103 The <sys/socket.h> header shall define the following macros to gain
105 access to the data arrays in the ancillary data associated with a mes‐
106 sage header:
107 CMSG_DATA(cmsg)
109 If the argument is a pointer to a cmsghdr structure, this macro
110 shall return an unsigned character pointer to the data array
111 associated with the cmsghdr structure.
112 CMSG_NXTHDR(mhdr,cmsg)
114 If the first argument is a pointer to a msghdr structure and the
115 second argument is a pointer to a cmsghdr structure in the ancil‐
116 lary data pointed to by the msg_control field of that msghdr
117 structure, this macro shall return a pointer to the next cmsghdr
118 structure, or a null pointer if this structure is the last cms‐
119 ghdr in the ancillary data.
120 CMSG_FIRSTHDR(mhdr)
122 If the argument is a pointer to a msghdr structure, this macro
123 shall return a pointer to the first cmsghdr structure in the
124 ancillary data associated with this msghdr structure, or a null
125 pointer if there is no ancillary data associated with the msghdr
126 structure.
127 The <sys/socket.h> header shall define the linger structure, which
129 shall include at least the following members:
130 int l_onoff Indicates whether linger option is enabled.
132 int l_linger Linger time, in seconds.
133 The <sys/socket.h> header shall define the following symbolic constants
135 with distinct values:
136 SOCK_DGRAM Datagram socket.
138 SOCK_RAW Raw Protocol Interface.
140 SOCK_SEQPACKET
142 Sequenced-packet socket.
143 SOCK_STREAM Byte-stream socket.
145 The <sys/socket.h> header shall define the following symbolic constant
147 for use as the level argument of setsockopt() and getsockopt().
148 SOL_SOCKET Options to be accessed at socket level, not protocol
150 level.
151 The <sys/socket.h> header shall define the following symbolic constants
153 with distinct values for use as the option_name argument in getsock‐
154 opt() or setsockopt() calls (see the System Interfaces volume of
155 POSIX.1‐2008, Section 2.10.16, Use of Options):
156 SO_ACCEPTCONN Socket is accepting connections.
158 SO_BROADCAST Transmission of broadcast messages is supported.
160 SO_DEBUG Debugging information is being recorded.
162 SO_DONTROUTE Bypass normal routing.
164 SO_ERROR Socket error status.
166 SO_KEEPALIVE Connections are kept alive with periodic messages.
168 SO_LINGER Socket lingers on close.
170 SO_OOBINLINE Out-of-band data is transmitted in line.
172 SO_RCVBUF Receive buffer size.
174 SO_RCVLOWAT Receive ``low water mark''.
176 SO_RCVTIMEO Receive timeout.
178 SO_REUSEADDR Reuse of local addresses is supported.
180 SO_SNDBUF Send buffer size.
182 SO_SNDLOWAT Send ``low water mark''.
184 SO_SNDTIMEO Send timeout.
186 SO_TYPE Socket type.
188 The <sys/socket.h> header shall define the following symbolic constant
190 for use as the maximum backlog queue length which may be specified by
191 the backlog field of the listen() function:
192 SOMAXCONN The maximum backlog queue length.
194 The <sys/socket.h> header shall define the following symbolic constants
196 with distinct values for use as the valid values for the msg_flags
197 field in the msghdr structure, or the flags parameter in recv(),
198 recvfrom(), recvmsg(), send(), sendmsg(), or sendto() calls:
199 MSG_CTRUNC Control data truncated.
201 MSG_DONTROUTE Send without using routing tables.
203 MSG_EOR Terminates a record (if supported by the protocol).
205 MSG_OOB Out-of-band data.
207 MSG_NOSIGNAL No SIGPIPE generated when an attempt to send is made on a
209 stream-oriented socket that is no longer connected.
210 MSG_PEEK Leave received data in queue.
212 MSG_TRUNC Normal data truncated.
214 MSG_WAITALL Attempt to fill the read buffer.
216 The <sys/socket.h> header shall define the following symbolic constants
218 with distinct values:
219 AF_INET Internet domain sockets for use with IPv4 addresses.
221 AF_INET6 Internet domain sockets for use with IPv6 addresses.
223 AF_UNIX UNIX domain sockets.
225 AF_UNSPEC Unspecified.
227 The <sys/socket.h> header shall define the following symbolic constants
229 with distinct values:
230 SHUT_RD Disables further receive operations.
232 SHUT_RDWR Disables further send and receive operations.
234 SHUT_WR Disables further send operations.
236 The <sys/socket.h> header shall define the size_t and ssize_t types as
238 described in <sys/types.h>.
239 The following shall be declared as functions and may also be defined as
241 macros. Function prototypes shall be provided.
242 int accept(int, struct sockaddr *restrict, socklen_t *restrict);
244 int bind(int, const struct sockaddr *, socklen_t);
245 int connect(int, const struct sockaddr *, socklen_t);
246 int getpeername(int, struct sockaddr *restrict, socklen_t *restrict);
247 int getsockname(int, struct sockaddr *restrict, socklen_t *restrict);
248 int getsockopt(int, int, int, void *restrict, socklen_t *restrict);
249 int listen(int, int);
250 ssize_t recv(int, void *, size_t, int);
251 ssize_t recvfrom(int, void *restrict, size_t, int,
252 struct sockaddr *restrict, socklen_t *restrict);
253 ssize_t recvmsg(int, struct msghdr *, int);
254 ssize_t send(int, const void *, size_t, int);
255 ssize_t sendmsg(int, const struct msghdr *, int);
256 ssize_t sendto(int, const void *, size_t, int, const struct sockaddr *,
257 socklen_t);
258 int setsockopt(int, int, int, const void *, socklen_t);
259 int shutdown(int, int);
260 int sockatmark(int);
261 int socket(int, int, int);
262 int socketpair(int, int, int, int [2]);
263 Inclusion of <sys/socket.h> may also make visible all symbols from
265 <sys/uio.h>.
266 The following sections are informative.
268
270 To forestall portability problems, it is recommended that applications
271 not use values larger than 231 −1 for the socklen_t type.
272 The sockaddr_storage structure solves the problem of declaring storage
274 for automatic variables which is both large enough and aligned enough
275 for storing the socket address data structure of any family. For exam‐
276 ple, code with a file descriptor and without the context of the address
277 family can pass a pointer to a variable of this type, where a pointer
278 to a socket address structure is expected in calls such as getpeer‐
279 name(), and determine the address family by accessing the received con‐
280 tent after the call.
281 The example below illustrates a data structure which aligns on a 64-bit
283 boundary. An implementation-defined field _ss_align following _ss_pad1
284 is used to force a 64-bit alignment which covers proper alignment good
285 enough for needs of at least sockaddr_in6 (IPv6) and sockaddr_in (IPv4)
286 address data structures. The size of padding field _ss_pad1 depends on
287 the chosen alignment boundary. The size of padding field _ss_pad2
288 depends on the value of overall size chosen for the total size of the
289 structure. This size and alignment are represented in the above example
290 by implementation-defined (not required) constants _SS_MAXSIZE (chosen
291 value 128) and _SS_ALIGNMENT (with chosen value 8). Constants
292 _SS_PAD1SIZE (derived value 6) and _SS_PAD2SIZE (derived value 112) are
293 also for illustration and not required. The implementation-defined def‐
294 initions and structure field names above start with an <underscore> to
295 denote implementation private name space. Portable code is not expected
296 to access or reference those fields or constants.
297 /*
299 * Desired design of maximum size and alignment.
300 */
301 #define _SS_MAXSIZE 128
302 /* Implementation-defined maximum size. */
303 #define _SS_ALIGNSIZE (sizeof(int64_t))
304 /* Implementation-defined desired alignment. */
305 /*
307 * Definitions used for sockaddr_storage structure paddings design.
308 */
309 #define _SS_PAD1SIZE (_SS_ALIGNSIZE − sizeof(sa_family_t))
310 #define _SS_PAD2SIZE (_SS_MAXSIZE − (sizeof(sa_family_t)+ \
311 _SS_PAD1SIZE + _SS_ALIGNSIZE))
312 struct sockaddr_storage {
313 sa_family_t ss_family; /* Address family. */
314 /*
315 * Following fields are implementation-defined.
316 */
317 char _ss_pad1[_SS_PAD1SIZE];
318 /* 6-byte pad; this is to make implementation-defined
319 pad up to alignment field that follows explicit in
320 the data structure. */
321 int64_t _ss_align; /* Field to force desired structure
322 storage alignment. */
323 char _ss_pad2[_SS_PAD2SIZE];
324 /* 112-byte pad to achieve desired size,
325 _SS_MAXSIZE value minus size of ss_family
326 __ss_pad1, __ss_align fields is 112. */
327 };
328
330 None.
331
333 None.
334
336 <sys_types.h>, <sys_uio.h>
337 The System Interfaces volume of POSIX.1‐2008, accept(), bind(), con‐
339 nect(), getpeername(), getsockname(), getsockopt(), listen(), recv(),
340 recvfrom(), recvmsg(), send(), sendmsg(), sendto(), setsockopt(), shut‐
341 down(), sockatmark(), socket(), socketpair()
342
344 Portions of this text are reprinted and reproduced in electronic form
345 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
346 -- Portable Operating System Interface (POSIX), The Open Group Base
347 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
348 cal and Electronics Engineers, Inc and The Open Group. (This is
349 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
350 event of any discrepancy between this version and the original IEEE and
351 The Open Group Standard, the original IEEE and The Open Group Standard
352 is the referee document. The original Standard can be obtained online
353 at http://www.unix.org/online.html .
354 Any typographical or formatting errors that appear in this page are
356 most likely to have been introduced during the conversion of the source
357 files to man page format. To report such errors, see https://www.ker‐
358 nel.org/doc/man-pages/reporting_bugs.html .
359IEEE/The Open Group 2013 sys_socket.h(0P)