1SENDMSG(P) POSIX Programmer's Manual SENDMSG(P)
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6 sendmsg - send a message on a socket using a message structure
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9 #include <sys/socket.h>
10 ssize_t sendmsg(int socket, const struct msghdr *message, int flags);
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15 The sendmsg() function shall send a message through a connection-mode
16 or connectionless-mode socket. If the socket is connectionless-mode,
17 the message shall be sent to the address specified by msghdr. If the
18 socket is connection-mode, the destination address in msghdr shall be
19 ignored.
20 The sendmsg() function takes the following arguments:
22 socket Specifies the socket file descriptor.
24 message
26 Points to a msghdr structure, containing both the destination
27 address and the buffers for the outgoing message. The length and
28 format of the address depend on the address family of the
29 socket. The msg_flags member is ignored.
30 flags Specifies the type of message transmission. The application may
32 specify 0 or the following flag:
33 MSG_EOR
35 Terminates a record (if supported by the protocol).
36 MSG_OOB
38 Sends out-of-band data on sockets that support out-of-bound
39 data. The significance and semantics of out-of-band data are
40 protocol-specific.
41 The msg_iov and msg_iovlen fields of message specify zero or more buf‐
45 fers containing the data to be sent. msg_iov points to an array of
46 iovec structures; msg_iovlen shall be set to the dimension of this
47 array. In each iovec structure, the iov_base field specifies a storage
48 area and the iov_len field gives its size in bytes. Some of these sizes
49 can be zero. The data from each storage area indicated by msg_iov is
50 sent in turn.
51 Successful completion of a call to sendmsg() does not guarantee deliv‐
53 ery of the message. A return value of -1 indicates only locally-
54 detected errors.
55 If space is not available at the sending socket to hold the message to
57 be transmitted and the socket file descriptor does not have O_NONBLOCK
58 set, the sendmsg() function shall block until space is available. If
59 space is not available at the sending socket to hold the message to be
60 transmitted and the socket file descriptor does have O_NONBLOCK set,
61 the sendmsg() function shall fail.
62 If the socket protocol supports broadcast and the specified address is
64 a broadcast address for the socket protocol, sendmsg() shall fail if
65 the SO_BROADCAST option is not set for the socket.
66 The socket in use may require the process to have appropriate privi‐
68 leges to use the sendmsg() function.
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71 Upon successful completion, sendmsg() shall return the number of bytes
72 sent. Otherwise, -1 shall be returned and errno set to indicate the
73 error.
74
76 The sendmsg() function shall fail if:
77 EAGAIN or EWOULDBLOCK
79 The socket's file descriptor is marked O_NONBLOCK and the
80 requested operation would block.
81 EAFNOSUPPORT
83 Addresses in the specified address family cannot be used with
84 this socket.
85 EBADF The socket argument is not a valid file descriptor.
87 ECONNRESET
89 A connection was forcibly closed by a peer.
90 EINTR A signal interrupted sendmsg() before any data was transmitted.
92 EINVAL The sum of the iov_len values overflows an ssize_t.
94 EMSGSIZE
96 The message is too large to be sent all at once (as the socket
97 requires), or the msg_iovlen member of the msghdr structure
98 pointed to by message is less than or equal to 0 or is greater
99 than {IOV_MAX}.
100 ENOTCONN
102 The socket is connection-mode but is not connected.
103 ENOTSOCK
105 The socket argument does not refer to a socket.
106 EOPNOTSUPP
108 The socket argument is associated with a socket that does not
109 support one or more of the values set in flags.
110 EPIPE The socket is shut down for writing, or the socket is connec‐
112 tion-mode and is no longer connected. In the latter case, and if
113 the socket is of type SOCK_STREAM, the SIGPIPE signal is gener‐
114 ated to the calling thread.
115 If the address family of the socket is AF_UNIX, then sendmsg() shall
118 fail if:
119 EIO An I/O error occurred while reading from or writing to the file
121 system.
122 ELOOP A loop exists in symbolic links encountered during resolution of
124 the pathname in the socket address.
125 ENAMETOOLONG
127 A component of a pathname exceeded {NAME_MAX} characters, or an
128 entire pathname exceeded {PATH_MAX} characters.
129 ENOENT A component of the pathname does not name an existing file or
131 the path name is an empty string.
132 ENOTDIR
134 A component of the path prefix of the pathname in the socket
135 address is not a directory.
136 The sendmsg() function may fail if:
139 EACCES Search permission is denied for a component of the path prefix;
141 or write access to the named socket is denied.
142 EDESTADDRREQ
144 The socket is not connection-mode and does not have its peer
145 address set, and no destination address was specified.
146 EHOSTUNREACH
148 The destination host cannot be reached (probably because the
149 host is down or a remote router cannot reach it).
150 EIO An I/O error occurred while reading from or writing to the file
152 system.
153 EISCONN
155 A destination address was specified and the socket is already
156 connected.
157 ENETDOWN
159 The local network interface used to reach the destination is
160 down.
161 ENETUNREACH
163 No route to the network is present.
164 ENOBUFS
166 Insufficient resources were available in the system to perform
167 the operation.
168 ENOMEM Insufficient memory was available to fulfill the request.
170 If the address family of the socket is AF_UNIX, then sendmsg() may fail
173 if:
174 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
176 resolution of the pathname in the socket address.
177 ENAMETOOLONG
179 Pathname resolution of a symbolic link produced an intermediate
180 result whose length exceeds {PATH_MAX}.
181 The following sections are informative.
184
186 Done.
187
189 The select() and poll() functions can be used to determine when it is
190 possible to send more data.
191
193 None.
194
196 None.
197
199 getsockopt() , poll() , recv() , recvfrom() , recvmsg() , select() ,
200 send() , sendto() , setsockopt() , shutdown() , socket() , the Base
201 Definitions volume of IEEE Std 1003.1-2001, <sys/socket.h>
202
204 Portions of this text are reprinted and reproduced in electronic form
205 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
206 -- Portable Operating System Interface (POSIX), The Open Group Base
207 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
208 Electrical and Electronics Engineers, Inc and The Open Group. In the
209 event of any discrepancy between this version and the original IEEE and
210 The Open Group Standard, the original IEEE and The Open Group Standard
211 is the referee document. The original Standard can be obtained online
212 at http://www.opengroup.org/unix/online.html .
213IEEE/The Open Group 2003 SENDMSG(P)