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10 .TH RECVFROM 3XNET "April 9, 2016"
11 .SH NAME
12 recvfrom \- receive a message from a socket
13 .SH SYNOPSIS
14 .LP
15 .nf
16 \fBcc\fR [ \fIflag\fR ... ] \fIfile\fR ... \fB-lxnet\fR [ \fIlibrary\fR ... ]
17 #include <sys/socket.h>
19 \fBssize_t\fR \fBrecvfrom\fR(\fBint\fR \fIsocket\fR, \fBvoid *restrict\fR \fIbuffer\fR, \fBsize_t\fR \fIlength\fR,
20 \fBint\fR \fIflags\fR, \fBstruct sockaddr *restrict\fR \fIaddress\fR,
21 \fBsocklen_t *restrict\fR \fIaddress_len\fR);
22 .fi
24 .SH DESCRIPTION
25 .LP
26 The \fBrecvfrom()\fR function receives a message from a connection-mode or
27 connectionless-mode socket. It is normally used with connectionless-mode
28 sockets because it permits the application to retrieve the source address of
29 received data.
30 .sp
31 .LP
32 The function takes the following arguments:
33 .sp
34 .ne 2
35 .na
36 \fB\fIsocket\fR\fR
37 .ad
38 .RS 15n
39 Specifies the socket file descriptor.
40 .RE
42 .sp
43 .ne 2
44 .na
45 \fB\fIbuffer\fR\fR
46 .ad
47 .RS 15n
48 Points to the buffer where the message should be stored.
49 .RE
51 .sp
52 .ne 2
53 .na
54 \fB\fIlength\fR\fR
55 .ad
56 .RS 15n
57 Specifies the length in bytes of the buffer pointed to by the \fIbuffer\fR
58 argument.
59 .RE
61 .sp
62 .ne 2
63 .na
64 \fB\fIflags\fR\fR
65 .ad
66 .RS 15n
67 Specifies the type of message reception. Values of this argument are formed by
68 logically OR'ing zero or more of the following values:
69 .sp
70 .ne 2
71 .na
72 \fBMSG_PEEK\fR
73 .ad
74 .RS 15n
75 Peeks at an incoming message. The data is treated as unread and the next
76 \fBrecvfrom()\fR or similar function will still return this data.
77 .RE
79 .sp
80 .ne 2
81 .na
82 \fBMSG_OOB\fR
83 .ad
84 .RS 15n
85 Requests out-of-band data. The significance and semantics of out-of-band data
86 are protocol-specific.
87 .RE
89 .sp
90 .ne 2
91 .na
92 \fBMSG_WAITALL\fR
93 .ad
94 .RS 15n
95 Requests that the function block until the full amount of data requested can be
96 returned. The function may return a smaller amount of data if a signal is
97 caught, if the connection is terminated, if MSG_PEEK was specified, or if an
98 error is pending for the socket.
99 .RE
101 .RE
103 .sp
104 .ne 2
105 .na
106 \fB\fIaddress\fR\fR
107 .ad
108 .RS 15n
109 A null pointer, or points to a \fBsockaddr\fR structure in which the sending
110 address is to be stored. The length and format of the address depend on the
111 address family of the socket.
112 .RE
114 .sp
115 .ne 2
116 .na
117 \fB\fIaddress_len\fR\fR
118 .ad
119 .RS 15n
120 Specifies the length of the \fBsockaddr\fR structure pointed to by the
121 \fIaddress\fR argument.
122 .RE
124 .sp
125 .LP
126 The \fBrecvfrom()\fR function returns the length of the message written to the
127 buffer pointed to by the \fIbuffer\fR argument. For message-based sockets such
128 as \fBSOCK_DGRAM\fR and \fBSOCK_SEQPACKET\fR, the entire message must be read
129 in a single operation. If a message is too long to fit in the supplied buffer,
130 and \fBMSG_PEEK\fR is not set in the \fIflags\fR argument, the excess bytes are
131 discarded. For stream-based sockets such as \fBSOCK_STREAM\fR, message
132 boundaries are ignored. In this case, data is returned to the user as soon as
133 it becomes available, and no data is discarded.
134 .sp
135 .LP
136 If the \fBMSG_WAITALL\fR flag is not set, data will be returned only up to the
137 end of the first message.
138 .sp
139 .LP
140 Not all protocols provide the source address for messages. If the
141 \fIaddress\fR argument is not a null pointer and the protocol provides the
142 source address of messages, the source address of the received message is
143 stored in the \fBsockaddr\fR structure pointed to by the \fIaddress\fR
144 argument, and the length of this address is stored in the object pointed to by
145 the \fIaddress_len\fR argument.
146 .sp
147 .LP
148 If the actual length of the address is greater than the length of the supplied
149 \fBsockaddr\fR structure, the stored address will be truncated.
150 .sp
151 .LP
152 If the \fIaddress\fR argument is not a null pointer and the protocol does not
153 provide the source address of messages, then the value stored in the object
154 pointed to by \fIaddress\fR is unspecified.
155 .sp
156 .LP
157 If no messages are available at the socket and \fBO_NONBLOCK\fR is not set on
158 the socket's file descriptor, \fBrecvfrom()\fR blocks until a message arrives.
159 If no messages are available at the socket and \fBO_NONBLOCK\fR is set on the
160 socket's file descriptor, \fBrecvfrom()\fR fails and sets \fBerrno\fR to
161 \fBEAGAIN\fR or \fBEWOULDBLOCK\fR.
162 .SH USAGE
163 .LP
164 The \fBselect\fR(3C) and \fBpoll\fR(2) functions can be used to determine when
165 data is available to be received.
166 .SH RETURN VALUES
167 .LP
168 Upon successful completion, \fBrecvfrom()\fR returns the length of the message
169 in bytes. If no messages are available to be received and the peer has
170 performed an orderly shutdown, \fBrecvfrom()\fR returns 0. Otherwise the
171 function returns \(mi1 and sets \fBerrno\fR to indicate the error.
172 .SH ERRORS
173 .LP
174 The \fBrecvfrom()\fR function will fail if:
175 .sp
176 .ne 2
177 .na
178 \fB\fBEAGAIN\fR\fR
179 .ad
180 .br
181 .na
182 \fB\fBEWOULDBLOCK\fR\fR
183 .ad
184 .RS 15n
185 The socket's file descriptor is marked \fBO_NONBLOCK\fR and no data is waiting
186 to be received, or \fBMSG_OOB\fR is set and no out-of-band data is available
187 and either the socket's file descriptor is marked \fBO_NONBLOCK\fR or the
188 socket does not support blocking to await out-of-band data.
189 .RE
191 .sp
192 .ne 2
193 .na
194 \fB\fBEBADF\fR\fR
195 .ad
196 .RS 15n
197 The \fIsocket\fR argument is not a valid file descriptor.
198 .RE
200 .sp
201 .ne 2
202 .na
203 \fB\fBECONNRESET\fR\fR
204 .ad
205 .RS 15n
206 A connection was forcibly closed by a peer.
207 .RE
209 .sp
210 .ne 2
211 .na
212 \fB\fBEFAULT\fR\fR
213 .ad
214 .RS 15n
215 The \fIbuffer\fR, \fIaddress\fR or \fIaddress_len\fR parameter can not be
216 accessed or written.
217 .RE
219 .sp
220 .ne 2
221 .na
222 \fB\fBEINTR\fR\fR
223 .ad
224 .RS 15n
225 A signal interrupted \fBrecvfrom()\fR before any data was available.
226 .RE
228 .sp
229 .ne 2
230 .na
231 \fB\fBEINVAL\fR\fR
232 .ad
233 .RS 15n
234 The \fBMSG_OOB\fR flag is set and no out-of-band data is available.
235 .RE
237 .sp
238 .ne 2
239 .na
240 \fB\fBENOTCONN\fR\fR
241 .ad
242 .RS 15n
243 A receive is attempted on a connection-mode socket that is not connected.
244 .RE
246 .sp
247 .ne 2
248 .na
249 \fB\fBENOTSOCK\fR\fR
250 .ad
251 .RS 15n
252 The \fIsocket\fR argument does not refer to a socket.
253 .RE
255 .sp
256 .ne 2
257 .na
258 \fB\fBEOPNOTSUPP\fR\fR
259 .ad
260 .RS 15n
261 The specified flags are not supported for this socket type.
262 .RE
264 .sp
265 .ne 2
266 .na
267 \fB\fBETIMEDOUT\fR\fR
268 .ad
269 .RS 15n
270 The connection timed out during connection establishment, or due to a
271 transmission timeout on active connection.
272 .RE
274 .sp
275 .LP
276 The \fBrecvfrom()\fR function may fail if:
277 .sp
278 .ne 2
279 .na
280 \fB\fBEIO\fR\fR
281 .ad
282 .RS 11n
283 An I/O error occurred while reading from or writing to the file system.
284 .RE
286 .sp
287 .ne 2
288 .na
289 \fB\fBENOBUFS\fR\fR
290 .ad
291 .RS 11n
292 Insufficient resources were available in the system to perform the operation.
293 .RE
295 .sp
296 .ne 2
297 .na
298 \fB\fBENOMEM\fR\fR
299 .ad
300 .RS 11n
301 Insufficient memory was available to fulfill the request.
302 .RE
304 .sp
305 .ne 2
306 .na
307 \fB\fBENOSR\fR\fR
308 .ad
309 .RS 11n
310 There were insufficient STREAMS resources available for the operation to
311 complete.
312 .RE
314 .SH ATTRIBUTES
315 .LP
316 See \fBattributes\fR(5) for descriptions of the following attributes:
317 .sp
319 .sp
320 .TS
321 box;
322 c | c
323 l | l .
324 ATTRIBUTE TYPE ATTRIBUTE VALUE
325 _
326 Interface Stability Standard
327 _
328 MT-Level MT-Safe
329 .TE
331 .SH SEE ALSO
332 .LP
333 \fBpoll\fR(2), \fBsockaddr\fR(3SOCKET),
334 \fBrecv\fR(3XNET), \fBrecvmsg\fR(3XNET), \fBselect\fR(3C)
335 \fBsend\fR(3XNET), \fBsendmsg\fR(3XNET), \fBsendto\fR(3XNET),
336 \fBshutdown\fR(3XNET), \fBsocket\fR(3XNET), \fBattributes\fR(5),
337 \fBstandards\fR(5)