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.
10
12 sys/socket.h — main sockets header
13
15 #include <sys/socket.h>
16
18 The <sys/socket.h> header shall define the socklen_t type, which is an
19 integer type of width of at least 32 bits; see APPLICATION USAGE.
20 The <sys/socket.h> header shall define the sa_family_t unsigned integer
22 type.
23 The <sys/socket.h> header shall define the sockaddr structure, which
25 shall include at least the following members:
26 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
50 When a pointer to a sockaddr_storage structure is cast as a pointer to
52 a sockaddr structure, the ss_family field of the sockaddr_storage
53 structure shall map onto the sa_family field of the sockaddr structure.
54 When a pointer to a sockaddr_storage structure is cast as a pointer to
55 a protocol-specific address structure, the ss_family field shall map
56 onto a field of that structure that is of type sa_family_t and that
57 identifies the protocol's address family.
58 The <sys/socket.h> header shall define the msghdr structure, which
60 shall include at least the following members:
61 void *msg_name Optional address.
64 socklen_t msg_namelen Size of address.
65 struct iovec *msg_iov Scatter/gather array.
66 int msg_iovlen Members in msg_iov.
67 void *msg_control Ancillary data; see below.
68 socklen_t msg_controllen Ancillary data buffer len.
69 int msg_flags Flags on received message.
70 The msghdr structure is used to minimize the number of directly sup‐
72 plied parameters to the recvmsg() and sendmsg() functions. This struc‐
73 ture is used as a value‐result parameter in the recvmsg() function and
74 value only for the sendmsg() function.
75 The <sys/socket.h> header shall define the iovec structure as described
77 in <sys/uio.h>.
78 The <sys/socket.h> header shall define the cmsghdr structure, which
80 shall include at least the following members:
81 socklen_t cmsg_len Data byte count, including the cmsghdr.
84 int cmsg_level Originating protocol.
85 int cmsg_type Protocol-specific type.
86 The cmsghdr structure is used for storage of ancillary data object
88 information.
89 Ancillary data consists of a sequence of pairs, each consisting of a
91 cmsghdr structure followed by a data array. The data array contains the
92 ancillary data message, and the cmsghdr structure contains descriptive
93 information that allows an application to correctly parse the data.
94 The values for cmsg_level shall be legal values for the level argument
96 to the getsockopt() and setsockopt() functions. The system documenta‐
97 tion shall specify the cmsg_type definitions for the supported proto‐
98 cols.
99 Ancillary data is also possible at the socket level. The <sys/socket.h>
101 header shall define the following symbolic constant for use as the
102 cmsg_type value when cmsg_level is SOL_SOCKET:
103 SCM_RIGHTS Indicates that the data array contains the access rights
105 to be sent or received.
106 The <sys/socket.h> header shall define the following macros to gain
108 access to the data arrays in the ancillary data associated with a mes‐
109 sage header:
110 CMSG_DATA(cmsg)
112 If the argument is a pointer to a cmsghdr structure, this macro
113 shall return an unsigned character pointer to the data array
114 associated with the cmsghdr structure.
115 CMSG_NXTHDR(mhdr,cmsg)
117 If the first argument is a pointer to a msghdr structure and the
118 second argument is a pointer to a cmsghdr structure in the ancil‐
119 lary data pointed to by the msg_control field of that msghdr
120 structure, this macro shall return a pointer to the next cmsghdr
121 structure, or a null pointer if this structure is the last cms‐
122 ghdr in the ancillary data.
123 CMSG_FIRSTHDR(mhdr)
125 If the argument is a pointer to a msghdr structure, this macro
126 shall return a pointer to the first cmsghdr structure in the
127 ancillary data associated with this msghdr structure, or a null
128 pointer if there is no ancillary data associated with the msghdr
129 structure.
130 The <sys/socket.h> header shall define the linger structure, which
132 shall include at least the following members:
133 int l_onoff Indicates whether linger option is enabled.
136 int l_linger Linger time, in seconds.
137 The <sys/socket.h> header shall define the following symbolic constants
139 with distinct values:
140 SOCK_DGRAM Datagram socket.
142 SOCK_RAW Raw Protocol Interface.
144 SOCK_SEQPACKET
146 Sequenced-packet socket.
147 SOCK_STREAM Byte-stream socket.
149 The <sys/socket.h> header shall define the following symbolic constant
151 for use as the level argument of setsockopt() and getsockopt().
152 SOL_SOCKET Options to be accessed at socket level, not protocol
154 level.
155 The <sys/socket.h> header shall define the following symbolic constants
157 with distinct values for use as the option_name argument in getsock‐
158 opt() or setsockopt() calls (see the System Interfaces volume of
159 POSIX.1‐2017, Section 2.10.16, Use of Options):
160 SO_ACCEPTCONN Socket is accepting connections.
162 SO_BROADCAST Transmission of broadcast messages is supported.
164 SO_DEBUG Debugging information is being recorded.
166 SO_DONTROUTE Bypass normal routing.
168 SO_ERROR Socket error status.
170 SO_KEEPALIVE Connections are kept alive with periodic messages.
172 SO_LINGER Socket lingers on close.
174 SO_OOBINLINE Out-of-band data is transmitted in line.
176 SO_RCVBUF Receive buffer size.
178 SO_RCVLOWAT Receive ``low water mark''.
180 SO_RCVTIMEO Receive timeout.
182 SO_REUSEADDR Reuse of local addresses is supported.
184 SO_SNDBUF Send buffer size.
186 SO_SNDLOWAT Send ``low water mark''.
188 SO_SNDTIMEO Send timeout.
190 SO_TYPE Socket type.
192 The <sys/socket.h> header shall define the following symbolic constant
194 for use as the maximum backlog queue length which may be specified by
195 the backlog field of the listen() function:
196 SOMAXCONN The maximum backlog queue length.
198 The <sys/socket.h> header shall define the following symbolic constants
200 with distinct values for use as the valid values for the msg_flags
201 field in the msghdr structure, or the flags parameter in recv(),
202 recvfrom(), recvmsg(), send(), sendmsg(), or sendto() calls:
203 MSG_CTRUNC Control data truncated.
205 MSG_DONTROUTE Send without using routing tables.
207 MSG_EOR Terminates a record (if supported by the protocol).
209 MSG_OOB Out-of-band data.
211 MSG_NOSIGNAL No SIGPIPE generated when an attempt to send is made on a
213 stream-oriented socket that is no longer connected.
214 MSG_PEEK Leave received data in queue.
216 MSG_TRUNC Normal data truncated.
218 MSG_WAITALL Attempt to fill the read buffer.
220 The <sys/socket.h> header shall define the following symbolic constants
222 with distinct values:
223 AF_INET Internet domain sockets for use with IPv4 addresses.
225 AF_INET6 Internet domain sockets for use with IPv6 addresses.
227 AF_UNIX UNIX domain sockets.
229 AF_UNSPEC Unspecified.
231 The value of AF_UNSPEC shall be 0.
233 The <sys/socket.h> header shall define the following symbolic constants
235 with distinct values:
236 SHUT_RD Disables further receive operations.
238 SHUT_RDWR Disables further send and receive operations.
240 SHUT_WR Disables further send operations.
242 The <sys/socket.h> header shall define the size_t and ssize_t types as
244 described in <sys/types.h>.
245 The following shall be declared as functions and may also be defined as
247 macros. Function prototypes shall be provided.
248 int accept(int, struct sockaddr *restrict, socklen_t *restrict);
251 int bind(int, const struct sockaddr *, socklen_t);
252 int connect(int, const struct sockaddr *, socklen_t);
253 int getpeername(int, struct sockaddr *restrict, socklen_t *restrict);
254 int getsockname(int, struct sockaddr *restrict, socklen_t *restrict);
255 int getsockopt(int, int, int, void *restrict, socklen_t *restrict);
256 int listen(int, int);
257 ssize_t recv(int, void *, size_t, int);
258 ssize_t recvfrom(int, void *restrict, size_t, int,
259 struct sockaddr *restrict, socklen_t *restrict);
260 ssize_t recvmsg(int, struct msghdr *, int);
261 ssize_t send(int, const void *, size_t, int);
262 ssize_t sendmsg(int, const struct msghdr *, int);
263 ssize_t sendto(int, const void *, size_t, int, const struct sockaddr *,
264 socklen_t);
265 int setsockopt(int, int, int, const void *, socklen_t);
266 int shutdown(int, int);
267 int sockatmark(int);
268 int socket(int, int, int);
269 int socketpair(int, int, int, int [2]);
270 Inclusion of <sys/socket.h> may also make visible all symbols from
272 <sys/uio.h>.
273 The following sections are informative.
275
277 To forestall portability problems, it is recommended that applications
278 not use values larger than 231 -1 for the socklen_t type.
279 The sockaddr_storage structure solves the problem of declaring storage
281 for automatic variables which is both large enough and aligned enough
282 for storing the socket address data structure of any family. For exam‐
283 ple, code with a file descriptor and without the context of the address
284 family can pass a pointer to a variable of this type, where a pointer
285 to a socket address structure is expected in calls such as getpeer‐
286 name(), and determine the address family by accessing the received con‐
287 tent after the call.
288 The example below illustrates a data structure which aligns on a 64-bit
290 boundary. An implementation-defined field _ss_align following _ss_pad1
291 is used to force a 64-bit alignment which covers proper alignment good
292 enough for needs of at least sockaddr_in6 (IPv6) and sockaddr_in (IPv4)
293 address data structures. The size of padding field _ss_pad1 depends on
294 the chosen alignment boundary. The size of padding field _ss_pad2
295 depends on the value of overall size chosen for the total size of the
296 structure. This size and alignment are represented in the above example
297 by implementation-defined (not required) constants _SS_MAXSIZE (chosen
298 value 128) and _SS_ALIGNMENT (with chosen value 8). Constants
299 _SS_PAD1SIZE (derived value 6) and _SS_PAD2SIZE (derived value 112) are
300 also for illustration and not required. The implementation-defined def‐
301 initions and structure field names above start with an <underscore> to
302 denote implementation private name space. Portable code is not expected
303 to access or reference those fields or constants.
304 /*
307 * Desired design of maximum size and alignment.
308 */
309 #define _SS_MAXSIZE 128
310 /* Implementation-defined maximum size. */
311 #define _SS_ALIGNSIZE (sizeof(int64_t))
312 /* Implementation-defined desired alignment. */
313 /*
315 * Definitions used for sockaddr_storage structure paddings design.
316 */
317 #define _SS_PAD1SIZE (_SS_ALIGNSIZE - sizeof(sa_family_t))
318 #define _SS_PAD2SIZE (_SS_MAXSIZE - (sizeof(sa_family_t)+ \
319 _SS_PAD1SIZE + _SS_ALIGNSIZE))
320 struct sockaddr_storage {
321 sa_family_t ss_family; /* Address family. */
322 /*
323 * Following fields are implementation-defined.
324 */
325 char _ss_pad1[_SS_PAD1SIZE];
326 /* 6-byte pad; this is to make implementation-defined
327 pad up to alignment field that follows explicit in
328 the data structure. */
329 int64_t _ss_align; /* Field to force desired structure
330 storage alignment. */
331 char _ss_pad2[_SS_PAD2SIZE];
332 /* 112-byte pad to achieve desired size,
333 _SS_MAXSIZE value minus size of ss_family
334 __ss_pad1, __ss_align fields is 112. */
335 };
336
338 None.
339
341 None.
342
344 <sys_types.h>, <sys_uio.h>
345 The System Interfaces volume of POSIX.1‐2017, accept(), bind(), con‐
347 nect(), getpeername(), getsockname(), getsockopt(), listen(), recv(),
348 recvfrom(), recvmsg(), send(), sendmsg(), sendto(), setsockopt(), shut‐
349 down(), sockatmark(), socket(), socketpair()
350
352 Portions of this text are reprinted and reproduced in electronic form
353 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
354 table Operating System Interface (POSIX), The Open Group Base Specifi‐
355 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
356 Electrical and Electronics Engineers, Inc and The Open Group. In the
357 event of any discrepancy between this version and the original IEEE and
358 The Open Group Standard, the original IEEE and The Open Group Standard
359 is the referee document. The original Standard can be obtained online
360 at http://www.opengroup.org/unix/online.html .
361 Any typographical or formatting errors that appear in this page are
363 most likely to have been introduced during the conversion of the source
364 files to man page format. To report such errors, see https://www.ker‐
365 nel.org/doc/man-pages/reporting_bugs.html .
366IEEE/The Open Group 2017 sys_socket.h(0P)