sendmsg

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



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 a connectionless-mode
       socket, the message shall be sent to the address specified by msghdr if
       no pre-specified peer address has been set. If a peer address has been
       pre-specified, either the message shall be sent to the address
       specified in msghdr (overriding the pre-specified peer address), or the
       function shall return −1 and set errno to [EISCONN].  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.

                   MSG_NOSIGNAL  Requests not to send the SIGPIPE signal if an
                                 attempt to send is made on a stream-oriented
                                 socket that is no longer connected. The
                                 [EPIPE] error shall still be returned.

       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.

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
              connection-mode and is no longer connected. In the latter case,
              and if the socket is of type SOCK_STREAM or SOCK_SEQPACKET and
              the MSG_NOSIGNAL flag is not set, 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
              The length of a component of a pathname is longer than
              {NAME_MAX}.

       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 names an existing file that is neither a directory nor a
              symbolic link to a directory, or the pathname in the socket
              address contains at least one non-<slash> character and ends
              with one or more trailing <slash> characters and the last
              pathname component names an existing file that is neither a
              directory nor a symbolic link to 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
              The length of a pathname exceeds {PATH_MAX}, or pathname
              resolution of a symbolic link produced an intermediate result
              with a length that 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(), pselect(), recv(), recvfrom(), recvmsg(), send(),
       sendto(), setsockopt(), shutdown(), socket()

       The Base Definitions volume of POSIX.1‐2008, <sys_socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2013                      SENDMSG(3POSIX)