1RECVFROM(3P) POSIX Programmer's Manual RECVFROM(3P)
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 recvfrom — receive a message from a socket
13
15 #include <sys/socket.h>
16 ssize_t recvfrom(int socket, void *restrict buffer, size_t length,
18 int flags, struct sockaddr *restrict address,
19 socklen_t *restrict address_len);
20
22 The recvfrom() function shall receive a message from a connection-mode
23 or connectionless-mode socket. It is normally used with connectionless-
24 mode sockets because it permits the application to retrieve the source
25 address of received data.
26 The recvfrom() function takes the following arguments:
28 socket Specifies the socket file descriptor.
30 buffer Points to the buffer where the message should be stored.
32 length Specifies the length in bytes of the buffer pointed to by
34 the buffer argument.
35 flags Specifies the type of message reception. Values of this
37 argument are formed by logically OR'ing zero or more of the
38 following values:
39 MSG_PEEK Peeks at an incoming message. The data is
41 treated as unread and the next recvfrom() or
42 similar function shall still return this data.
43 MSG_OOB Requests out-of-band data. The significance and
45 semantics of out-of-band data are protocol-spe‐
46 cific.
47 MSG_WAITALL On SOCK_STREAM sockets this requests that the
49 function block until the full amount of data
50 can be returned. The function may return the
51 smaller amount of data if the socket is a mes‐
52 sage-based socket, if a signal is caught, if
53 the connection is terminated, if MSG_PEEK was
54 specified, or if an error is pending for the
55 socket.
56 address A null pointer, or points to a sockaddr structure in which
58 the sending address is to be stored. The length and format
59 of the address depend on the address family of the socket.
60 address_len Either a null pointer, if address is a null pointer, or a
62 pointer to a socklen_t object which on input specifies the
63 length of the supplied sockaddr structure, and on output
64 specifies the length of the stored address.
65 The recvfrom() function shall return the length of the message written
67 to the buffer pointed to by the buffer argument. For message-based
68 sockets, such as SOCK_RAW, SOCK_DGRAM, and SOCK_SEQPACKET, the entire
69 message shall be read in a single operation. If a message is too long
70 to fit in the supplied buffer, and MSG_PEEK is not set in the flags
71 argument, the excess bytes shall be discarded. For stream-based sock‐
72 ets, such as SOCK_STREAM, message boundaries shall be ignored. In this
73 case, data shall be returned to the user as soon as it becomes avail‐
74 able, and no data shall be discarded.
75 If the MSG_WAITALL flag is not set, data shall be returned only up to
77 the end of the first message.
78 Not all protocols provide the source address for messages. If the
80 address argument is not a null pointer and the protocol provides the
81 source address of messages, the source address of the received message
82 shall be stored in the sockaddr structure pointed to by the address
83 argument, and the length of this address shall be stored in the object
84 pointed to by the address_len argument.
85 If the actual length of the address is greater than the length of the
87 supplied sockaddr structure, the stored address shall be truncated.
88 If the address argument is not a null pointer and the protocol does not
90 provide the source address of messages, the value stored in the object
91 pointed to by address is unspecified.
92 If no messages are available at the socket and O_NONBLOCK is not set on
94 the socket's file descriptor, recvfrom() shall block until a message
95 arrives. If no messages are available at the socket and O_NONBLOCK is
96 set on the socket's file descriptor, recvfrom() shall fail and set
97 errno to [EAGAIN] or [EWOULDBLOCK].
98
100 Upon successful completion, recvfrom() shall return the length of the
101 message in bytes. If no messages are available to be received and the
102 peer has performed an orderly shutdown, recvfrom() shall return 0. Oth‐
103 erwise, the function shall return -1 and set errno to indicate the
104 error.
105
107 The recvfrom() function shall fail if:
108 EAGAIN or EWOULDBLOCK
110 The socket's file descriptor is marked O_NONBLOCK and no data is
111 waiting to be received; or MSG_OOB is set and no out-of-band
112 data is available and either the socket's file descriptor is
113 marked O_NONBLOCK or the socket does not support blocking to
114 await out-of-band data.
115 EBADF The socket argument is not a valid file descriptor.
117 ECONNRESET
119 A connection was forcibly closed by a peer.
120 EINTR A signal interrupted recvfrom() before any data was available.
122 EINVAL The MSG_OOB flag is set and no out-of-band data is available.
124 ENOTCONN
126 A receive is attempted on a connection-mode socket that is not
127 connected.
128 ENOTSOCK
130 The socket argument does not refer to a socket.
131 EOPNOTSUPP
133 The specified flags are not supported for this socket type.
134 ETIMEDOUT
136 The connection timed out during connection establishment, or due
137 to a transmission timeout on active connection.
138 The recvfrom() function may fail if:
140 EIO An I/O error occurred while reading from or writing to the file
142 system.
143 ENOBUFS
145 Insufficient resources were available in the system to perform
146 the operation.
147 ENOMEM Insufficient memory was available to fulfill the request.
149 The following sections are informative.
151
153 None.
154
156 The select() and poll() functions can be used to determine when data is
157 available to be received.
158
160 None.
161
163 None.
164
166 poll(), pselect(), read(), recv(), recvmsg(), send(), sendmsg(),
167 sendto(), shutdown(), socket(), write()
168 The Base Definitions volume of POSIX.1‐2017, <sys_socket.h>
170
172 Portions of this text are reprinted and reproduced in electronic form
173 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
174 table Operating System Interface (POSIX), The Open Group Base Specifi‐
175 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
176 Electrical and Electronics Engineers, Inc and The Open Group. In the
177 event of any discrepancy between this version and the original IEEE and
178 The Open Group Standard, the original IEEE and The Open Group Standard
179 is the referee document. The original Standard can be obtained online
180 at http://www.opengroup.org/unix/online.html .
181 Any typographical or formatting errors that appear in this page are
183 most likely to have been introduced during the conversion of the source
184 files to man page format. To report such errors, see https://www.ker‐
185 nel.org/doc/man-pages/reporting_bugs.html .
186IEEE/The Open Group 2017 RECVFROM(3P)