sendmsg



SEND(2)                   OpenBSD Programmer's Manual                  SEND(2)


NAME

     send, sendto, sendmsg - send a message from a socket


SYNOPSIS

     #include <sys/types.h>
     #include <sys/socket.h>

     ssize_t
     send(int s, const void *msg, size_t len, int flags);

     ssize_t
     sendto(int s, const void *msg, size_t len, int flags, const struct
     sockaddr *to, socklen_t tolen);

     ssize_t
     sendmsg(int s, const struct msghdr *msg, int flags);


DESCRIPTION

     send(), sendto(), and sendmsg() are used to transmit a message to another
     socket.  send() may be used only when the socket is in a connected state,
     while sendto() and sendmsg() may be used at any time.

     The address of the target is given by to with tolen specifying its size.
     The length of the message is given by len.  If the message is too long to
     pass atomically through the underlying protocol, the error EMSGSIZE is
     returned, and the message is not transmitted.

     No indication of failure to deliver is implicit in a send().  Locally
     detected errors are indicated by a return value of -1.

     If no messages space is available at the socket to hold the message to be
     transmitted, then send() normally blocks, unless the socket has been
     placed in non-blocking I/O mode.  The select(2) or poll(2) system calls
     may be used to determine when it is possible to send more data.

     The flags parameter may include one or more of the following:

           MSG_OOB          process out-of-band data
           MSG_DONTROUTE    bypass routing, use direct interface
           MSG_NOSIGNAL     don't send SIGPIPE
           MSG_DONTWAIT     don't block

     The flag MSG_OOB is used to send ``out-of-band'' data on sockets that
     support this notion (e.g., SOCK_STREAM); the underlying protocol must
     also support ``out-of-band'' data.  MSG_DONTROUTE is usually used only by
     diagnostic or routing programs.  MSG_NOSIGNAL is used to request not to
     send the SIGPIPE signal if an attempt to send is made on a socket that is
     shut down for writing or no longer connected.

     See recv(2) for a description of the msghdr structure.


RETURN VALUES

     The call returns the number of characters sent, or -1 if an error
     occurred.


ERRORS

     send(), sendto(), and sendmsg() fail if:

     [EBADF]            An invalid descriptor was specified.

     [ENOTSOCK]         The argument s is not a socket.

     [EFAULT]           An invalid user space address was specified for a
                        parameter.

     [EMSGSIZE]         The socket requires that message be sent atomically,
                        and the size of the message to be sent made this
                        impossible.

     [EAGAIN]           The socket is marked non-blocking and the requested
                        operation would block.

     [ENOBUFS]          The system was unable to allocate an internal buffer.
                        The operation may succeed when buffers become
                        available.

     [ENOBUFS]          The output queue for a network interface was full.
                        This generally indicates that the interface has
                        stopped sending, but may be caused by transient
                        congestion.

     [EACCES]           The SO_BROADCAST option is not set on the socket, and
                        a broadcast address was given as the destination.

     [EHOSTUNREACH]     The destination address specified an unreachable host.

     [EINVAL]           The flags parameter is invalid.

     [EHOSTDOWN]        The destination address specified a host that is down.

     [ENETDOWN]         The destination address specified a network that is
                        down.

     [ECONNREFUSED]     The destination host rejected the message (or a
                        previous one).  This error can only be returned by
                        connected sockets.

     [ENOPROTOOPT]      There was a problem sending the message.  This error
                        can only be returned by connected sockets.

     [EDESTADDRREQ]     The socket is not connected, and no destination
                        address was specified.

     [EISCONN]          The socket is already connected, and a destination
                        address was specified.

     [EPIPE]            The socket is shut down for writing or not longer
                        connected and the MSG_NOSIGNAL flag is set.

     In addition, send() and sendto() may return the following error:

     [EINVAL]           len was larger than SSIZE_MAX.

     Also, sendmsg() may return the following errors:

     [EINVAL]           The sum of the iov_len values in the msg_iov array
                        overflowed an ssize_t.

     [EMSGSIZE]         The msg_iovlen member of msg was less than 0 or larger
                        than IOV_MAX.

     [EAFNOSUPPORT]     Addresses in the specified address family cannot be
                        used with this socket.

     [EMFILE]           The message contains control information utilizing
                        CMSG_DATA(3) to pass file descriptors, but too many
                        file descriptors are already in-flight.


SEE ALSO

     fcntl(2), getsockopt(2), poll(2), recv(2), select(2), socket(2),
     write(2), CMSG_DATA(3)


HISTORY

     The send() function call appeared in 4.2BSD.

OpenBSD 5.4                     October 5, 2012                    OpenBSD 5.4

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