sendmsg(2) - NetBSD Manual Pages

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SEND(2)                   NetBSD 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, int 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 de-
     tected 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) call may be used to de-
     termine when it is possible to send more data.

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

     #define MSG_OOB        0x1  /* process out-of-band data */
     #define MSG_DONTROUTE  0x4  /* bypass routing, use direct interface */

     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 al-
     so support ``out-of-band'' data.  MSG_DONTROUTE is usually used only by
     diagnostic or routing programs.

     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 oc-
     curred.


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 parame-
                   ter.

     [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 opera-
                   tion 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 for the message is unreachable.


SEE ALSO

     fcntl(2),  recv(2),  select(2),  getsockopt(2),  socket(2),  write(2)


HISTORY

     The send() function call appeared in 4.2BSD.

4.2 Berkeley Distribution      February 21, 1994                             2