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 (including when the peer of a
connectionless socket has been set via connect()).
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.
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 or otherwise has not had the peer
pre-specified.
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, the SIGPIPE signal is
generated to the calling thread.
The send() function may fail if:
EACCES The calling process does not have the 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
The send() function is equivalent to sendto() with a null pointer
dest_len argument, and to write() if no flags are used.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
connect() , getsockopt() , poll() , recv() , recvfrom() , recvmsg() ,
select() , sendmsg() , sendto() , setsockopt() , shutdown() , socket()
, the Base Definitions volume of IEEE Std 1003.1-2001, <sys/socket.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .