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SENDMSG(3P)                POSIX Programmer's Manual               SENDMSG(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       sendmsg - send a message on a socket using a message structure
SYNOPSIS
       #include <sys/socket.h>
       ssize_t sendmsg(int socket, const struct msghdr *message, int flags);

DESCRIPTION
       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  buf-
       fers  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  deliv-
       ery  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 privi-
       leges to use the sendmsg() function.
RETURN VALUE
       Upon successful completion, sendmsg() shall return the number of  bytes
       sent.  Otherwise,  -1  shall  be returned and errno set to indicate the
       error.
ERRORS
       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  connec-
              tion-mode and is no longer connected. In the latter case, and if
              the socket is of type SOCK_STREAM, the SIGPIPE signal is  gener-
              ated 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.
EXAMPLES
       Done.
APPLICATION USAGE
       The  select()  and poll() functions can be used to determine when it is
       possible to send more data.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       getsockopt(), poll(), recv(), recvfrom(), recvmsg(), select(),  send(),
       sendto(), setsockopt(), shutdown(), socket(), the Base Definitions vol-
       ume of IEEE Std 1003.1-2001, <sys/socket.h>
COPYRIGHT
       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 .

IEEE/The Open Group                  2003                          SENDMSG(3P)