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
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 the
35 buffer argument.
36 flags Specifies the type of message reception. Values of this argument
38 are formed by logically OR'ing zero or more of the following
39 values:
40 MSG_PEEK
42 Peeks at an incoming message. The data is treated as unread and
43 the next recvfrom() or similar function shall still return this
44 data.
45 MSG_OOB
47 Requests out-of-band data. The significance and semantics of
48 out-of-band data are protocol-specific.
49 MSG_WAITALL
51 On SOCK_STREAM sockets this requests that the function block
52 until the full amount of data can be returned. The function may
53 return the smaller amount of data if the socket is a message-
54 based socket, if a signal is caught, if the connection is termi‐
55 nated, if MSG_PEEK was specified, or if an error is pending for
56 the socket.
57 address
60 A null pointer, or points to a sockaddr structure in which the
61 sending address is to be stored. The length and format of the
62 address depend on the address family of the socket.
63 address_len
65 Specifies the length of the sockaddr structure pointed to by the
66 address argument.
67 The recvfrom() function shall return the length of the message written
70 to the buffer pointed to by the buffer argument. For message-based
71 sockets, such as SOCK_RAW, SOCK_DGRAM, and SOCK_SEQPACKET, the entire
72 message shall be read in a single operation. If a message is too long
73 to fit in the supplied buffer, and MSG_PEEK is not set in the flags
74 argument, the excess bytes shall be discarded. For stream-based sock‐
75 ets, such as SOCK_STREAM, message boundaries shall be ignored. In this
76 case, data shall be returned to the user as soon as it becomes avail‐
77 able, and no data shall be discarded.
78 If the MSG_WAITALL flag is not set, data shall be returned only up to
80 the end of the first message.
81 Not all protocols provide the source address for messages. If the
83 address argument is not a null pointer and the protocol provides the
84 source address of messages, the source address of the received message
85 shall be stored in the sockaddr structure pointed to by the address
86 argument, and the length of this address shall be stored in the object
87 pointed to by the address_len argument.
88 If the actual length of the address is greater than the length of the
90 supplied sockaddr structure, the stored address shall be truncated.
91 If the address argument is not a null pointer and the protocol does not
93 provide the source address of messages, the value stored in the object
94 pointed to by address is unspecified.
95 If no messages are available at the socket and O_NONBLOCK is not set on
97 the socket's file descriptor, recvfrom() shall block until a message
98 arrives. If no messages are available at the socket and O_NONBLOCK is
99 set on the socket's file descriptor, recvfrom() shall fail and set
100 errno to [EAGAIN] or [EWOULDBLOCK].
101
103 Upon successful completion, recvfrom() shall return the length of the
104 message in bytes. If no messages are available to be received and the
105 peer has performed an orderly shutdown, recvfrom() shall return 0. Oth‐
106 erwise, the function shall return -1 and set errno to indicate the
107 error.
108
110 The recvfrom() function shall fail if:
111 EAGAIN or EWOULDBLOCK
113 The socket's file descriptor is marked O_NONBLOCK and no data is
115 waiting to be received; or MSG_OOB is set and no out-of-band
116 data is available and either the socket's file descriptor is
117 marked O_NONBLOCK or the socket does not support blocking to
118 await out-of-band data.
119 EBADF The socket argument is not a valid file descriptor.
121 ECONNRESET
123 A connection was forcibly closed by a peer.
124 EINTR A signal interrupted recvfrom() before any data was available.
126 EINVAL The MSG_OOB flag is set and no out-of-band data is available.
128 ENOTCONN
130 A receive is attempted on a connection-mode socket that is not
131 connected.
132 ENOTSOCK
134 The socket argument does not refer to a socket.
135 EOPNOTSUPP
137 The specified flags are not supported for this socket type.
138 ETIMEDOUT
140 The connection timed out during connection establishment, or due
141 to a transmission timeout on active connection.
142 The recvfrom() function may fail if:
145 EIO An I/O error occurred while reading from or writing to the file
147 system.
148 ENOBUFS
150 Insufficient resources were available in the system to perform
151 the operation.
152 ENOMEM Insufficient memory was available to fulfill the request.
154 The following sections are informative.
157
159 None.
160
162 The select() and poll() functions can be used to determine when data is
163 available to be received.
164
166 None.
167
169 None.
170
172 poll(), read(), recv(), recvmsg(), select(), send(), sendmsg(),
173 sendto(), shutdown() , socket(), write(), the Base Definitions volume
174 of IEEE Std 1003.1-2001, <sys/socket.h>
175
177 Portions of this text are reprinted and reproduced in electronic form
178 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
179 -- Portable Operating System Interface (POSIX), The Open Group Base
180 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
181 Electrical and Electronics Engineers, Inc and The Open Group. In the
182 event of any discrepancy between this version and the original IEEE and
183 The Open Group Standard, the original IEEE and The Open Group Standard
184 is the referee document. The original Standard can be obtained online
185 at http://www.opengroup.org/unix/online.html .
186IEEE/The Open Group 2003 RECVFROM(3P)