1RECV(3P) POSIX Programmer's Manual RECV(3P)
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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 recv — receive a message from a connected socket
14
16 #include <sys/socket.h>
17 ssize_t recv(int socket, void *buffer, size_t length, int flags);
19
21 The recv() function shall receive a message from a connection-mode or
22 connectionless-mode socket. It is normally used with connected sockets
23 because it does not permit the application to retrieve the source
24 address of received data.
25 The recv() function takes the following arguments:
27 socket Specifies the socket file descriptor.
29 buffer Points to a buffer where the message should be stored.
31 length Specifies the length in bytes of the buffer pointed to by the
33 buffer argument.
34 flags Specifies the type of message reception. Values of this argu‐
36 ment are formed by logically OR'ing zero or more of the fol‐
37 lowing values:
38 MSG_PEEK Peeks at an incoming message. The data is treated
40 as unread and the next recv() or similar function
41 shall still return this data.
42 MSG_OOB Requests out-of-band data. The significance and
44 semantics of out-of-band data are protocol-spe‐
45 cific.
46 MSG_WAITALL On SOCK_STREAM sockets this requests that the
48 function block until the full amount of data can
49 be returned. The function may return the smaller
50 amount of data if the socket is a message-based
51 socket, if a signal is caught, if the connection
52 is terminated, if MSG_PEEK was specified, or if
53 an error is pending for the socket.
54 The recv() function shall return the length of the message written to
56 the buffer pointed to by the buffer argument. For message-based sock‐
57 ets, such as SOCK_DGRAM and SOCK_SEQPACKET, the entire message shall be
58 read in a single operation. If a message is too long to fit in the
59 supplied buffer, and MSG_PEEK is not set in the flags argument, the
60 excess bytes shall be discarded. For stream-based sockets, such as
61 SOCK_STREAM, message boundaries shall be ignored. In this case, data
62 shall be returned to the user as soon as it becomes available, and no
63 data shall be discarded.
64 If the MSG_WAITALL flag is not set, data shall be returned only up to
66 the end of the first message.
67 If no messages are available at the socket and O_NONBLOCK is not set on
69 the socket's file descriptor, recv() shall block until a message
70 arrives. If no messages are available at the socket and O_NONBLOCK is
71 set on the socket's file descriptor, recv() shall fail and set errno to
72 [EAGAIN] or [EWOULDBLOCK].
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75 Upon successful completion, recv() shall return the length of the mes‐
76 sage in bytes. If no messages are available to be received and the peer
77 has performed an orderly shutdown, recv() shall return 0. Otherwise, −1
78 shall be returned and errno set to indicate the error.
79
81 The recv() function shall fail if:
82 EAGAIN or EWOULDBLOCK
84 The socket's file descriptor is marked O_NONBLOCK and no data is
85 waiting to be received; or MSG_OOB is set and no out-of-band
86 data is available and either the socket's file descriptor is
87 marked O_NONBLOCK or the socket does not support blocking to
88 await out-of-band data.
89 EBADF The socket argument is not a valid file descriptor.
91 ECONNRESET
93 A connection was forcibly closed by a peer.
94 EINTR The recv() function was interrupted by a signal that was caught,
96 before any data was available.
97 EINVAL The MSG_OOB flag is set and no out-of-band data is available.
99 ENOTCONN
101 A receive is attempted on a connection-mode socket that is not
102 connected.
103 ENOTSOCK
105 The socket argument does not refer to a socket.
106 EOPNOTSUPP
108 The specified flags are not supported for this socket type or
109 protocol.
110 ETIMEDOUT
112 The connection timed out during connection establishment, or due
113 to a transmission timeout on active connection.
114 The recv() function may fail if:
116 EIO An I/O error occurred while reading from or writing to the file
118 system.
119 ENOBUFS
121 Insufficient resources were available in the system to perform
122 the operation.
123 ENOMEM Insufficient memory was available to fulfill the request.
125 The following sections are informative.
127
129 None.
130
132 The recv() function is equivalent to recvfrom() with null pointer
133 address and address_len arguments, and to read() if the socket argument
134 refers to a socket and the flags argument is 0.
135 The select() and poll() functions can be used to determine when data is
137 available to be received.
138
140 None.
141
143 None.
144
146 poll(), pselect(), read(), recvmsg(), recvfrom(), send(), sendmsg(),
147 sendto(), shutdown(), socket(), write()
148 The Base Definitions volume of POSIX.1‐2008, <sys_socket.h>
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152 Portions of this text are reprinted and reproduced in electronic form
153 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
154 -- Portable Operating System Interface (POSIX), The Open Group Base
155 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
156 cal and Electronics Engineers, Inc and The Open Group. (This is
157 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
158 event of any discrepancy between this version and the original IEEE and
159 The Open Group Standard, the original IEEE and The Open Group Standard
160 is the referee document. The original Standard can be obtained online
161 at http://www.unix.org/online.html .
162 Any typographical or formatting errors that appear in this page are
164 most likely to have been introduced during the conversion of the source
165 files to man page format. To report such errors, see https://www.ker‐
166 nel.org/doc/man-pages/reporting_bugs.html .
167IEEE/The Open Group 2013 RECV(3P)