send

SEND(3P)                    POSIX Programmer's Manual                   SEND(3P)



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
       send — send a message on a socket

SYNOPSIS
       #include <sys/socket.h>

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

DESCRIPTION
       The send() function shall initiate transmission of a message from the
       specified socket to its peer. The send() function shall send a message
       only when the socket is connected. If the socket is a connectionless-mode
       socket, the message shall be sent to the pre-specified peer address.

       The send() function takes the following arguments:

       socket      Specifies the socket file descriptor.

       buffer      Points to the buffer containing the message to send.

       length      Specifies the length of the message in bytes.

       flags       Specifies the type of message transmission. Values of this
                   argument are formed by logically OR'ing zero or more of the
                   following flags:

                   MSG_EOR       Terminates a record (if supported by the
                                 protocol).

                   MSG_OOB       Sends out-of-band data on sockets that support
                                 out-of-band communications. 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 length of the message to be sent is specified by the length argument.
       If the message is too long to pass through the underlying protocol,
       send() shall fail and no data shall be transmitted.

       Successful completion of a call to send() 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,
       send() 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, send() shall fail. The select()
       and poll() functions can be used to determine when it is possible to send
       more data.

       The socket in use may require the process to have appropriate privileges
       to use the send() function.

RETURN VALUE
       Upon successful completion, send() shall return the number of bytes sent.
       Otherwise, -1 shall be returned and errno set to indicate the error.

ERRORS
       The send() function shall fail if:

       EAGAIN or EWOULDBLOCK
              The socket's file descriptor is marked O_NONBLOCK and the
              requested operation would block.

       EBADF  The socket argument is not a valid file descriptor.

       ECONNRESET
              A connection was forcibly closed by a peer.

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

       EINTR  A signal interrupted send() before any data was transmitted.

       EMSGSIZE
              The message is too large to be sent all at once, as the socket
              requires.

       ENOTCONN
              The socket 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.

       The send() function may fail if:

       EACCES The calling process does not have appropriate privileges.

       EIO    An I/O error occurred while reading from or writing to the file
              system.

       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.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       If the socket argument refers to a connection-mode socket, the send()
       function is equivalent to sendto() (with any value for the dest_addr and
       dest_len arguments, as they are ignored in this case). If the socket
       argument refers to a socket and the flags argument is 0, the send()
       function is equivalent to write().

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       connect(), getsockopt(), poll(), pselect(), recv(), recvfrom(),
       recvmsg(), sendmsg(), sendto(), setsockopt(), shutdown(), socket(),
       write()

       The Base Definitions volume of POSIX.1‐2017, <sys_socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute
       of Electrical and Electronics Engineers, Inc and The Open Group.  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.opengroup.org/unix/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                   2017                              SEND(3P)