gno/usr.man/man2/send.2

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.\"     From: @(#)send.2	8.2 (Berkeley) 2/21/94
.\"	$Id: send.2,v 1.1 1997/02/27 07:32:15 gdr Exp $
.\"
.TH SEND 2 "16 January 1997" GNO "System Calls"
.SH NAME
.BR send ,
.BR sendto ,
.BR sendmsg
\- send a message from a socket
.SH SYNOPSIS
.br
#include <sys/types.h>
.br
#include <sys/socket.h>
.sp 1
int
\fBsend\fR (int \fIs\fR, const void *\fImsg\fR, size_t \fIlen\fR,
unsigned int \fIflags\fR);
.sp 1
int
\fBsendto\fR (int \fIs\fR, const void *\fImsg\fR, size_t \fIlen\fR,
int \fIflags\fR, const struct sockaddr *\fIto\fR, unsigned int \fItolen\fR);
.sp 1
int
\fBsendmsg\fR (int \fIs\fR, const struct msghdr *\fImsg\fR,
unsigned int \fIflags\fR);
.SH DESCRIPTION
.BR Send ,
.BR sendto ,
and
.BR sendmsg 
are used to transmit a message to another socket.
.BR Send 
may be used only when the socket is in a 
.IR connected 
state, while 
.BR sendto 
and
.BR sendmsg 
may be used at any time.
.LP
The address of the target is given by
.I to
with 
.I tolen
specifying its size.
The length of the message is given by
.RI ( 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.
.LP
No indication of failure to deliver is implicit in a
.BR send .
Locally detected errors are indicated by a return value of -1.
.LP
If no messages space is available at the socket to hold
the message to be transmitted, then
.BR send 
normally blocks, unless the socket has been placed in
non-blocking I/O mode.
The
.BR select (2)
call may be used to determine when it is possible to
send more data.
.LP
The
.I flags
parameter may include one or more of the following:
.nf

#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 */
.fi
.LP
The flag
.BR MSG_OOB
is used to send
.I out-of-band
data on sockets that support this notion (e.g.
.BR SOCK_STREAM ) ;
the underlying protocol must also support
.I out-of-band
data.
.BR MSG_EOR
is used to indicate a record mark for protocols which support the
concept.
.BR MSG_EOF
requests that the sender side of a socket be shut down, and that an
appropriate indication be sent at the end of the specified data;
this flag is only implemented for
.BR SOCK_STREAM
sockets in the
.BR PF_INET
protocol family, and is used to implement Transaction TCP (see
.BR ttcp (4)).
.BR MSG_DONTROUTE
is usually used only by diagnostic or routing programs.
.LP
See 
.BR recv (2)
for a description of the
.I msghdr
structure.
.SH RETURN VALUES
The call returns the number of characters sent, or -1
if an error occurred.
.SH ERRORS
.BR Send ,
.BR sendto ,
and
.BR sendmsg 
fail if:
.RS
.IP \fBEBADF\fR
An invalid descriptor was specified.
.IP \fBENOTSOCK\fR
The argument
.I s
is not a socket.
.IP \fBEFAULT\fR
An invalid user space address was specified for a parameter.
.IP \fBEMSGSIZE\fR
The socket requires that message be sent atomically,
and the size of the message to be sent made this impossible.
.IP \fBEAGAIN\fR
The socket is marked non-blocking and the requested operation
would block.
.IP \fBENOBUFS\fR
The system was unable to allocate an internal buffer.
The operation may succeed when buffers become available.
.IP \fBENOBUFS\fR
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.
.RE
.SH CONVORMANCE
The GNO prototypes of these routines differ slightly from that of
4.4BSD.
.SH SEE ALSO
.BR fcntl (2),
.BR recv (2),
.BR select (2),
.BR getsockopt (2),
.BR socket (2),
.BR write (2)
.SH HISTORY
The
.BR sendmsg
function call appeared in 4.2BSD.
The first appearance in GNO was in v2.0.5.