Originální popis anglicky:
sendmsg - send a message on a socket using a message structure
Návod, kniha: POSIX Programmer's Manual
#include <sys/socket.h>
ssize_t sendmsg(int
socket, const struct msghdr
*message, int
flags );
The
sendmsg() function shall send a message through a connection-mode or
connectionless-mode socket. If the socket is connectionless-mode, the message
shall be sent to the address specified by
msghdr. If the socket is
connection-mode, the destination address in
msghdr shall be ignored.
The
sendmsg() function takes the following arguments:
- socket
- Specifies the socket file descriptor.
- message
- Points to a msghdr structure, containing both the
destination address and the buffers for the outgoing message. The length
and format of the address depend on the address family of the socket. The
msg_flags member is ignored.
- flags
- Specifies the type of message transmission. The application
may specify 0 or the following flag:
- MSG_EOR
Terminates a record (if supported by the
protocol).
- MSG_OOB
Sends out-of-band data on sockets that support
out-of-bound data. The significance and semantics of out-of-band data are
protocol-specific.
The
msg_iov and
msg_iovlen fields of
message specify zero
or more buffers containing the data to be sent.
msg_iov points to an
array of
iovec structures;
msg_iovlen shall be set to the
dimension of this array. In each
iovec structure, the
iov_base
field specifies a storage area and the
iov_len field gives its size in
bytes. Some of these sizes can be zero. The data from each storage area
indicated by
msg_iov is sent in turn.
Successful completion of a call to
sendmsg() does not guarantee delivery
of the message. A return value of -1 indicates only locally-detected errors.
If space is not available at the sending socket to hold the message to be
transmitted and the socket file descriptor does not have O_NONBLOCK set, the
sendmsg() function shall block until space is available. If space is
not available at the sending socket to hold the message to be transmitted and
the socket file descriptor does have O_NONBLOCK set, the
sendmsg()
function shall fail.
If the socket protocol supports broadcast and the specified address is a
broadcast address for the socket protocol,
sendmsg() shall fail if the
SO_BROADCAST option is not set for the socket.
The socket in use may require the process to have appropriate privileges to use
the
sendmsg() function.
Upon successful completion,
sendmsg() shall return the number of bytes
sent. Otherwise, -1 shall be returned and
errno set to indicate the
error.
The
sendmsg() function shall fail if:
- EAGAIN or EWOULDBLOCK
- The socket's file descriptor is marked O_NONBLOCK and the
requested operation would block.
- EAFNOSUPPORT
- Addresses in the specified address family cannot be used
with this socket.
- EBADF
- The socket argument is not a valid file
descriptor.
- ECONNRESET
- A connection was forcibly closed by a peer.
- EINTR
- A signal interrupted sendmsg() before any data was
transmitted.
- EINVAL
- The sum of the iov_len values overflows an
ssize_t.
- EMSGSIZE
- The message is too large to be sent all at once (as the
socket requires), or the msg_iovlen member of the msghdr
structure pointed to by message is less than or equal to 0 or is
greater than {IOV_MAX}.
- ENOTCONN
- The socket is connection-mode but is not connected.
- ENOTSOCK
- The socket argument does not refer to a socket.
- EOPNOTSUPP
- The socket argument is associated with a socket that
does not support one or more of the values set in flags.
- EPIPE
- The socket is shut down for writing, or the socket is
connection-mode and is no longer connected. In the latter case, and if the
socket is of type SOCK_STREAM, the SIGPIPE signal is generated to the
calling thread.
If the address family of the socket is AF_UNIX, then
sendmsg() shall fail
if:
- EIO
- An I/O error occurred while reading from or writing to the
file system.
- ELOOP
- A loop exists in symbolic links encountered during
resolution of the pathname in the socket address.
- ENAMETOOLONG
- A component of a pathname exceeded {NAME_MAX} characters,
or an entire pathname exceeded {PATH_MAX} characters.
- ENOENT
- A component of the pathname does not name an existing file
or the path name is an empty string.
- ENOTDIR
- A component of the path prefix of the pathname in the
socket address is not a directory.
The
sendmsg() function may fail if:
- EACCES
- Search permission is denied for a component of the path
prefix; or write access to the named socket is denied.
- EDESTADDRREQ
- The socket is not connection-mode and does not have its
peer address set, and no destination address was specified.
- EHOSTUNREACH
- The destination host cannot be reached (probably because
the host is down or a remote router cannot reach it).
- EIO
- An I/O error occurred while reading from or writing to the
file system.
- EISCONN
- A destination address was specified and the socket is
already connected.
- ENETDOWN
- The local network interface used to reach the destination
is down.
- ENETUNREACH
- No route to the network is present.
- ENOBUFS
- Insufficient resources were available in the system to
perform the operation.
- ENOMEM
- Insufficient memory was available to fulfill the request.
If the address family of the socket is AF_UNIX, then
sendmsg() may fail
if:
- ELOOP
- More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the pathname in the socket address.
- ENAMETOOLONG
- Pathname resolution of a symbolic link produced an
intermediate result whose length exceeds {PATH_MAX}.
The following sections are informative.
Done.
The
select() and
poll() functions can be used to determine when it
is possible to send more data.
None.
None.
getsockopt() ,
poll() ,
recv() ,
recvfrom() ,
recvmsg() ,
select() ,
send() ,
sendto() ,
setsockopt() ,
shutdown() ,
socket() , the Base
Definitions volume of IEEE Std 1003.1-2001,
<sys/socket.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
