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SEND(2)                     BSD System Calls Manual                    SEND(2)

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

SYNOPSIS
     #include <sys/socket.h>

     ssize_t
     send(int socket, const void *buffer, size_t length, int flags);

     ssize_t
     sendmsg(int socket, const struct msghdr *message, int flags);

     ssize_t
     sendto(int socket, const void *buffer, size_t length, int flags, const struct sockaddr *dest_addr,
         socklen_t dest_len);

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 dest_addr with dest_len specifying its size.  The length of the
     message is given by length.  If the message is too long to pass atomically through the underlying pro-tocol, protocol,
     tocol, 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() nor-mally normally
     mally blocks, unless the socket has been placed in non-blocking I/O mode.  The select(2) call may be
     used to determine 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 also support ``out-of-band'' data.  MSG_DONTROUTE is usually
     used only by diagnostic or routing programs.

     The sendmsg() system call uses a msghdr structure to minimize the number of directly supplied argu-ments. arguments.
     ments.  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 indi-cated indicated
     cated by msg_iov is sent in turn.  See recv(2) for a complete description of the msghdr structure.

RETURN VALUES
     Upon successful completion, the number of bytes which were sent is returned.  Otherwise, -1 is returned
     and the global variable errno is set to indicate the error.

ERRORS
     The send(), sendmsg(), and sendto() system calls will fail if:

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

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

     [EBADF]            An invalid descriptor is specified.

     [ECONNRESET]       A connection is forcibly closed by a peer.

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

     [EHOSTUNREACH]     The destination address specifies an unreachable host.

     [EINTR]            A signal interrupts the system call before any data is transmitted.

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

     [ENETDOWN]         The local network interface used to reach the destination is down.

     [ENETUNREACH]      No route to the network is present.

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

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

     [ENOTSOCK]         The argument socket is not a socket.

     [EOPNOTSUPP]       socket does not support (some of) the option(s) specified 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, the
                        SIGPIPE signal is generated to the calling thread.

     The sendmsg() and sendto() system calls will fail if:

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

     [EDESTADDRREQ]     The socket is not connection-mode and does not have its peer address set, and no
                        destination address is specified.

     [EISCONN]          A destination address was specified and the socket is already connected.

     [ENOENT]           A component of the pathname does not name an existing file or the path name is an
                        empty string.

     [ENOMEM]           Insufficient memory is available to fulfill the request.

     [ENOTCONN]         The socket is connection-mode, but is not connected.

     [ENOTDIR]          A component of the path prefix of the pathname in the socket address is not a direc-tory. directory.
                        tory.

     The send() system call will fail if:

     [EDESTADDRREQ]     The socket is not connection-mode and no peer address is set.

     [ENOTCONN]         The socket is not connected or otherwise has not had the peer pre-specified.

     The sendmsg() system call will fail if:

     [EINVAL]           The sum of the iov_len values overflows an ssize_t.

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

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

     The include file <sys/types.h> is necessary.

SEE ALSO
     fcntl(2), getsockopt(2), recv(2), select(2), socket(2), write(2), compat(5)

HISTORY
     The send() function call appeared in 4.2BSD.

4.2 Berkeley Distribution      February 21, 1994     4.2 Berkeley Distribution

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