1RECVFROM(P) POSIX Programmer's Manual RECVFROM(P)
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6 recvfrom - receive a message from a socket
7
9 #include <sys/socket.h>
10 ssize_t recvfrom(int socket, void *restrict buffer, size_t length,
12 int flags, struct sockaddr *restrict address,
13 socklen_t *restrict address_len);
14
17 The recvfrom() function shall receive a message from a connection-mode
18 or connectionless-mode socket. It is normally used with connectionless-
19 mode sockets because it permits the application to retrieve the source
20 address of received data.
21 The recvfrom() function takes the following arguments:
23 socket Specifies the socket file descriptor.
25 buffer Points to the buffer where the message should be stored.
27 length Specifies the length in bytes of the buffer pointed to by the
29 buffer argument.
30 flags Specifies the type of message reception. Values of this argument
32 are formed by logically OR'ing zero or more of the following
33 values:
34 MSG_PEEK
36 Peeks at an incoming message. The data is treated as unread and
37 the next recvfrom() or similar function shall still return this
38 data.
39 MSG_OOB
41 Requests out-of-band data. The significance and semantics of
42 out-of-band data are protocol-specific.
43 MSG_WAITALL
45 On SOCK_STREAM sockets this requests that the function block
46 until the full amount of data can be returned. The function may
47 return the smaller amount of data if the socket is a message-
48 based socket, if a signal is caught, if the connection is termi‐
49 nated, if MSG_PEEK was specified, or if an error is pending for
50 the socket.
51 address
54 A null pointer, or points to a sockaddr structure in which the
55 sending address is to be stored. The length and format of the
56 address depend on the address family of the socket.
57 address_len
59 Specifies the length of the sockaddr structure pointed to by the
60 address argument.
61 The recvfrom() function shall return the length of the message written
64 to the buffer pointed to by the buffer argument. For message-based
65 sockets, such as SOCK_RAW, SOCK_DGRAM, and SOCK_SEQPACKET, the
66 entire message shall be read in a single operation. If a message is
67 too long to fit in the supplied buffer, and MSG_PEEK is not set in the
68 flags argument, the excess bytes shall be discarded. For stream-based
69 sockets, such as SOCK_STREAM, message boundaries shall be ignored. In
70 this case, data shall be returned to the user as soon as it becomes
71 available, and no data shall be discarded.
72 If the MSG_WAITALL flag is not set, data shall be returned only up to
74 the end of the first message.
75 Not all protocols provide the source address for messages. If the
77 address argument is not a null pointer and the protocol provides the
78 source address of messages, the source address of the received message
79 shall be stored in the sockaddr structure pointed to by the address
80 argument, and the length of this address shall be stored in the object
81 pointed to by the address_len argument.
82 If the actual length of the address is greater than the length of the
84 supplied sockaddr structure, the stored address shall be truncated.
85 If the address argument is not a null pointer and the protocol does not
87 provide the source address of messages, the value stored in the object
88 pointed to by address is unspecified.
89 If no messages are available at the socket and O_NONBLOCK is not set on
91 the socket's file descriptor, recvfrom() shall block until a message
92 arrives. If no messages are available at the socket and O_NONBLOCK is
93 set on the socket's file descriptor, recvfrom() shall fail and set
94 errno to [EAGAIN] or [EWOULDBLOCK].
95
97 Upon successful completion, recvfrom() shall return the length of the
98 message in bytes. If no messages are available to be received and the
99 peer has performed an orderly shutdown, recvfrom() shall return 0. Oth‐
100 erwise, the function shall return -1 and set errno to indicate the
101 error.
102
104 The recvfrom() function shall fail if:
105 EAGAIN or EWOULDBLOCK
107 The socket's file descriptor is marked O_NONBLOCK and no data is
109 waiting to be received; or MSG_OOB is set and no out-of-band
110 data is available and either the socket's file descriptor is
111 marked O_NONBLOCK or the socket does not support blocking to
112 await out-of-band data.
113 EBADF The socket argument is not a valid file descriptor.
115 ECONNRESET
117 A connection was forcibly closed by a peer.
118 EINTR A signal interrupted recvfrom() before any data was available.
120 EINVAL The MSG_OOB flag is set and no out-of-band data is available.
122 ENOTCONN
124 A receive is attempted on a connection-mode socket that is not
125 connected.
126 ENOTSOCK
128 The socket argument does not refer to a socket.
129 EOPNOTSUPP
131 The specified flags are not supported for this socket type.
132 ETIMEDOUT
134 The connection timed out during connection establishment, or due
135 to a transmission timeout on active connection.
136 The recvfrom() function may fail if:
139 EIO An I/O error occurred while reading from or writing to the file
141 system.
142 ENOBUFS
144 Insufficient resources were available in the system to perform
145 the operation.
146 ENOMEM Insufficient memory was available to fulfill the request.
148 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() , read() , recv() , recvmsg() , select() , send() , sendmsg() ,
167 sendto() , shutdown() , socket() , write() , the Base Definitions vol‐
168 ume of IEEE Std 1003.1-2001, <sys/socket.h>
169
171 Portions of this text are reprinted and reproduced in electronic form
172 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
173 -- Portable Operating System Interface (POSIX), The Open Group Base
174 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
175 Electrical and Electronics Engineers, Inc and The Open Group. In the
176 event of any discrepancy between this version and the original IEEE and
177 The Open Group Standard, the original IEEE and The Open Group Standard
178 is the referee document. The original Standard can be obtained online
179 at http://www.opengroup.org/unix/online.html .
180IEEE/The Open Group 2003 RECVFROM(P)