SEND(2)                          System Calls                          SEND(2)

NAME

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

SYNOPSIS

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

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

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

       int sendmsg (int s, const struct msghdr *msg, unsigned 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_PEEK  0x2   /* peek at incoming message */
       #define   MSG_DONTROUTE  0x4   /* bypass routing, use direct interface */
       #define MSG_EOR          0x8   /* data completes record */
       #define   MSG_EOF        0x100 /* data completes transaction */

       The  flag MSG_OOB is used to send out-of-band data on sockets that sup‐
       port this notion (e.g.  SOCK_STREAM); the underlying protocol must also
       support  out-of-band  data.   MSG_EOR is used to indicate a record mark
       for protocols which support the concept.   MSG_EOF  requests  that  the
       sender  side  of a socket be shut down, and that an appropriate indica‐
       tion be sent at the end of the specified data; this flag is only imple‐
       mented  for  SOCK_STREAM sockets in the PF_INET protocol family, and is
       used to implement Transaction TCP (see ttcp(4)).  MSG_DONTROUTE is usu‐
       ally 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 oper‐
                     ation 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 send‐
                     ing, but may be caused by transient congestion.

CONVORMANCE

       The GNO prototypes of these  routines  differ  slightly  from  that  of
       4.4BSD.

SEE ALSO

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

HISTORY

       The  sendmsg function call appeared in 4.2BSD.  The first appearance in
       GNO was in v2.0.5.



GNO                             16 January 1997                        SEND(2)