1RECV(3P) POSIX Programmer's Manual RECV(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 recv - receive a message from a connected socket
13
15 #include <sys/socket.h>
16 ssize_t recv(int socket, void *buffer, size_t length, int flags);
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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 argument
36 are formed by logically OR'ing zero or more of the following
37 values:
38 MSG_PEEK
40 Peeks at an incoming message. The data is treated as unread and
41 the next recv() or similar function shall still return this
42 data.
43 MSG_OOB
45 Requests out-of-band data. The significance and semantics of
46 out-of-band data are protocol-specific.
47 MSG_WAITALL
49 On SOCK_STREAM sockets this requests that the function block
50 until the full amount of data can be returned. The function may
51 return the smaller amount of data if the socket is a message-
52 based socket, if a signal is caught, if the connection is termi‐
53 nated, if MSG_PEEK was specified, or if an error is pending for
54 the socket.
55 The recv() function shall return the length of the message written to
59 the buffer pointed to by the buffer argument. For message-based sock‐
60 ets, such as SOCK_DGRAM and SOCK_SEQPACKET, the entire message shall be
61 read in a single operation. If a message is too long to fit in the
62 supplied buffer, and MSG_PEEK is not set in the flags argument, the
63 excess bytes shall be discarded. For stream-based sockets, such as
64 SOCK_STREAM, message boundaries shall be ignored. In this case, data
65 shall be returned to the user as soon as it becomes available, and no
66 data shall be discarded.
67 If the MSG_WAITALL flag is not set, data shall be returned only up to
69 the end of the first message.
70 If no messages are available at the socket and O_NONBLOCK is not set on
72 the socket's file descriptor, recv() shall block until a message
73 arrives. If no messages are available at the socket and O_NONBLOCK is
74 set on the socket's file descriptor, recv() shall fail and set errno to
75 [EAGAIN] or [EWOULDBLOCK].
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78 Upon successful completion, recv() shall return the length of the mes‐
79 sage in bytes. If no messages are available to be received and the peer
80 has performed an orderly shutdown, recv() shall return 0. Otherwise, -1
81 shall be returned and errno set to indicate the error.
82
84 The recv() function shall fail if:
85 EAGAIN or EWOULDBLOCK
87 The socket's file descriptor is marked O_NONBLOCK and no data is
89 waiting to be received; or MSG_OOB is set and no out-of-band
90 data is available and either the socket's file descriptor is
91 marked O_NONBLOCK or the socket does not support blocking to
92 await out-of-band data.
93 EBADF The socket argument is not a valid file descriptor.
95 ECONNRESET
97 A connection was forcibly closed by a peer.
98 EINTR The recv() function was interrupted by a signal that was caught,
100 before any data was available.
101 EINVAL The MSG_OOB flag is set and no out-of-band data is available.
103 ENOTCONN
105 A receive is attempted on a connection-mode socket that is not
106 connected.
107 ENOTSOCK
109 The socket argument does not refer to a socket.
110 EOPNOTSUPP
112 The specified flags are not supported for this socket type or
113 protocol.
114 ETIMEDOUT
116 The connection timed out during connection establishment, or due
117 to a transmission timeout on active connection.
118 The recv() function may fail if:
121 EIO An I/O error occurred while reading from or writing to the file
123 system.
124 ENOBUFS
126 Insufficient resources were available in the system to perform
127 the operation.
128 ENOMEM Insufficient memory was available to fulfill the request.
130 The following sections are informative.
133
135 None.
136
138 The recv() function is equivalent to recvfrom() with a zero address_len
139 argument, and to read() if no flags are used.
140 The select() and poll() functions can be used to determine when data is
142 available to be received.
143
145 None.
146
148 None.
149
151 poll(), read(), recvmsg(), recvfrom(), select(), send(), sendmsg(),
152 sendto(), shutdown(), socket(), write(), the Base Definitions volume of
153 IEEE Std 1003.1-2001, <sys/socket.h>
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156 Portions of this text are reprinted and reproduced in electronic form
157 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
158 -- Portable Operating System Interface (POSIX), The Open Group Base
159 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
160 Electrical and Electronics Engineers, Inc and The Open Group. In the
161 event of any discrepancy between this version and the original IEEE and
162 The Open Group Standard, the original IEEE and The Open Group Standard
163 is the referee document. The original Standard can be obtained online
164 at http://www.opengroup.org/unix/online.html .
165IEEE/The Open Group 2003 RECV(3P)