1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" From: @(#)send.2 8.2 (Berkeley) 2/21/94 33.\" $FreeBSD: src/lib/libc/sys/send.2,v 1.10.2.6 2001/12/14 18:34:01 ru Exp $ 34.\" 35.Dd February 15, 1995 36.Dt SEND 2 37.Os 38.Sh NAME 39.Nm send , 40.Nm sendto , 41.Nm sendmsg 42.Nd send a message from a socket 43.Sh LIBRARY 44.Lb libc 45.Sh SYNOPSIS 46.In sys/types.h 47.In sys/socket.h 48.Ft ssize_t 49.Fn send "int s" "const void *msg" "size_t len" "int flags" 50.Ft ssize_t 51.Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "socklen_t tolen" 52.Ft ssize_t 53.Fn sendmsg "int s" "const struct msghdr *msg" "int flags" 54.Sh DESCRIPTION 55.Fn Send , 56.Fn sendto , 57and 58.Fn sendmsg 59are used to transmit a message to another socket. 60.Fn Send 61may be used only when the socket is in a 62.Em connected 63state, while 64.Fn sendto 65and 66.Fn sendmsg 67may be used at any time. 68.Pp 69The address of the target is given by 70.Fa to 71with 72.Fa tolen 73specifying its size. 74The length of the message is given by 75.Fa len . 76If the message is too long to pass atomically through the 77underlying protocol, the error 78.Er EMSGSIZE 79is returned, and 80the message is not transmitted. 81.Pp 82No indication of failure to deliver is implicit in a 83.Fn send . 84Locally detected errors are indicated by a return value of -1. 85.Pp 86If no messages space is available at the socket to hold 87the message to be transmitted, then 88.Fn send 89normally blocks, unless the socket has been placed in 90non-blocking I/O mode. 91The 92.Xr select 2 93call may be used to determine when it is possible to 94send more data. 95.Pp 96The 97.Fa flags 98parameter may include one or more of the following: 99.Bd -literal 100#define MSG_OOB 0x1 /* process out-of-band data */ 101#define MSG_PEEK 0x2 /* peek at incoming message */ 102#define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */ 103#define MSG_EOR 0x8 /* data completes record */ 104#define MSG_EOF 0x100 /* data completes transaction */ 105.Ed 106.Pp 107The flag 108.Dv MSG_OOB 109is used to send 110.Dq out-of-band 111data on sockets that support this notion (e.g.\& 112.Dv SOCK_STREAM ) ; 113the underlying protocol must also support 114.Dq out-of-band 115data. 116.Dv MSG_EOR 117is used to indicate a record mark for protocols which support the 118concept. 119.Dv MSG_EOF 120requests that the sender side of a socket be shut down, and that an 121appropriate indication be sent at the end of the specified data; 122this flag is only implemented for 123.Dv SOCK_STREAM 124sockets in the 125.Dv PF_INET 126protocol family, and is used to implement Transaction 127.Tn TCP 128(see 129.Xr ttcp 4 ) . 130.Dv MSG_DONTROUTE 131is usually used only by diagnostic or routing programs. 132.Pp 133See 134.Xr recv 2 135for a description of the 136.Fa msghdr 137structure. 138.Sh RETURN VALUES 139The call returns the number of characters sent, or -1 140if an error occurred. 141.Sh ERRORS 142.Fn Send , 143.Fn sendto , 144and 145.Fn sendmsg 146fail if: 147.Bl -tag -width Er 148.It Bq Er EBADF 149An invalid descriptor was specified. 150.It Bq Er EACCES 151The destination address is a broadcast address, and 152.Dv SO_BROADCAST 153has not been set on the socket. 154.It Bq Er ENOTSOCK 155The argument 156.Fa s 157is not a socket. 158.It Bq Er EFAULT 159An invalid user space address was specified for a parameter. 160.It Bq Er EMSGSIZE 161The socket requires that message be sent atomically, 162and the size of the message to be sent made this impossible. 163.It Bq Er EAGAIN 164The socket is marked non-blocking and the requested operation 165would block. 166.It Bq Er ENOBUFS 167The system was unable to allocate an internal buffer. 168The operation may succeed when buffers become available. 169.It Bq Er ENOBUFS 170The output queue for a network interface was full. 171This generally indicates that the interface has stopped sending, 172but may be caused by transient congestion. 173.It Bq Er EHOSTUNREACH 174The remote host was unreachable. 175.It Bq Er ECONNREFUSED 176The socket received an ICMP destination unreachable message 177from the last message sent. This typically means that the 178receiver is not listening on the remote port. 179.It Bq Er EHOSTDOWN 180The remote host was down. 181.El 182.Sh BUGS 183Because 184.Fn sendmsg 185doesn't necessarily block until the data has been transferred, it 186is possible to transfer an open file descriptor across an 187.Dv AF_UNIX 188domain socket 189(see 190.Xr recv 2 ) , 191then 192.Fn close 193it before it has actually been sent, the result being that the receiver 194gets a closed file descriptor. It is left to the application to 195implement an acknowlegment mechanism to prevent this from happening. 196.Sh SEE ALSO 197.Xr fcntl 2 , 198.Xr getsockopt 2 , 199.Xr recv 2 , 200.Xr select 2 , 201.Xr socket 2 , 202.Xr write 2 203.Sh HISTORY 204The 205.Fn send 206function call appeared in 207.Bx 4.2 . 208