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.
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13 recvfrom — receive a message from a socket
14
16 #include <sys/socket.h>
17 ssize_t recvfrom(int socket, void *restrict buffer, size_t length,
19 int flags, struct sockaddr *restrict address,
20 socklen_t *restrict address_len);
21
23 The recvfrom() function shall receive a message from a connection-mode
24 or connectionless-mode socket. It is normally used with connectionless-
25 mode sockets because it permits the application to retrieve the source
26 address of received data.
27 The recvfrom() function takes the following arguments:
29 socket Specifies the socket file descriptor.
31 buffer Points to the buffer where the message should be stored.
33 length Specifies the length in bytes of the buffer pointed to by
35 the buffer argument.
36 flags Specifies the type of message reception. Values of this
38 argument are formed by logically OR'ing zero or more of the
39 following values:
40 MSG_PEEK Peeks at an incoming message. The data is
42 treated as unread and the next recvfrom() or
43 similar function shall still return this data.
44 MSG_OOB Requests out-of-band data. The significance and
46 semantics of out-of-band data are protocol-spe‐
47 cific.
48 MSG_WAITALL On SOCK_STREAM sockets this requests that the
50 function block until the full amount of data
51 can be returned. The function may return the
52 smaller amount of data if the socket is a mes‐
53 sage-based socket, if a signal is caught, if
54 the connection is terminated, if MSG_PEEK was
55 specified, or if an error is pending for the
56 socket.
57 address A null pointer, or points to a sockaddr structure in which
59 the sending address is to be stored. The length and format
60 of the address depend on the address family of the socket.
61 address_len Either a null pointer, if address is a null pointer, or a
63 pointer to a socklen_t object which on input specifies the
64 length of the supplied sockaddr structure, and on output
65 specifies the length of the stored address.
66 The recvfrom() function shall return the length of the message written
68 to the buffer pointed to by the buffer argument. For message-based
69 sockets, such as SOCK_RAW, SOCK_DGRAM, and SOCK_SEQPACKET, the entire
70 message shall be read in a single operation. If a message is too long
71 to fit in the supplied buffer, and MSG_PEEK is not set in the flags
72 argument, the excess bytes shall be discarded. For stream-based sock‐
73 ets, such as SOCK_STREAM, message boundaries shall be ignored. In this
74 case, data shall be returned to the user as soon as it becomes avail‐
75 able, and no data shall be discarded.
76 If the MSG_WAITALL flag is not set, data shall be returned only up to
78 the end of the first message.
79 Not all protocols provide the source address for messages. If the
81 address argument is not a null pointer and the protocol provides the
82 source address of messages, the source address of the received message
83 shall be stored in the sockaddr structure pointed to by the address
84 argument, and the length of this address shall be stored in the object
85 pointed to by the address_len argument.
86 If the actual length of the address is greater than the length of the
88 supplied sockaddr structure, the stored address shall be truncated.
89 If the address argument is not a null pointer and the protocol does not
91 provide the source address of messages, the value stored in the object
92 pointed to by address is unspecified.
93 If no messages are available at the socket and O_NONBLOCK is not set on
95 the socket's file descriptor, recvfrom() shall block until a message
96 arrives. If no messages are available at the socket and O_NONBLOCK is
97 set on the socket's file descriptor, recvfrom() shall fail and set
98 errno to [EAGAIN] or [EWOULDBLOCK].
99
101 Upon successful completion, recvfrom() shall return the length of the
102 message in bytes. If no messages are available to be received and the
103 peer has performed an orderly shutdown, recvfrom() shall return 0. Oth‐
104 erwise, the function shall return −1 and set errno to indicate the
105 error.
106
108 The recvfrom() function shall fail if:
109 EAGAIN or EWOULDBLOCK
111 The socket's file descriptor is marked O_NONBLOCK and no data is
112 waiting to be received; or MSG_OOB is set and no out-of-band
113 data is available and either the socket's file descriptor is
114 marked O_NONBLOCK or the socket does not support blocking to
115 await out-of-band data.
116 EBADF The socket argument is not a valid file descriptor.
118 ECONNRESET
120 A connection was forcibly closed by a peer.
121 EINTR A signal interrupted recvfrom() before any data was available.
123 EINVAL The MSG_OOB flag is set and no out-of-band data is available.
125 ENOTCONN
127 A receive is attempted on a connection-mode socket that is not
128 connected.
129 ENOTSOCK
131 The socket argument does not refer to a socket.
132 EOPNOTSUPP
134 The specified flags are not supported for this socket type.
135 ETIMEDOUT
137 The connection timed out during connection establishment, or due
138 to a transmission timeout on active connection.
139 The recvfrom() function may fail if:
141 EIO An I/O error occurred while reading from or writing to the file
143 system.
144 ENOBUFS
146 Insufficient resources were available in the system to perform
147 the operation.
148 ENOMEM Insufficient memory was available to fulfill the request.
150 The following sections are informative.
152
154 None.
155
157 The select() and poll() functions can be used to determine when data is
158 available to be received.
159
161 None.
162
164 None.
165
167 poll(), pselect(), read(), recv(), recvmsg(), send(), sendmsg(),
168 sendto(), shutdown(), socket(), write()
169 The Base Definitions volume of POSIX.1‐2008, <sys_socket.h>
171
173 Portions of this text are reprinted and reproduced in electronic form
174 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
175 -- Portable Operating System Interface (POSIX), The Open Group Base
176 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
177 cal and Electronics Engineers, Inc and The Open Group. (This is
178 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
179 event of any discrepancy between this version and the original IEEE and
180 The Open Group Standard, the original IEEE and The Open Group Standard
181 is the referee document. The original Standard can be obtained online
182 at http://www.unix.org/online.html .
183 Any typographical or formatting errors that appear in this page are
185 most likely to have been introduced during the conversion of the source
186 files to man page format. To report such errors, see https://www.ker‐
187 nel.org/doc/man-pages/reporting_bugs.html .
188IEEE/The Open Group 2013 RECVFROM(3P)