1.\" $OpenBSD: send.2,v 1.23 2007/05/31 19:19:33 jmc Exp $ 2.\" $NetBSD: send.2,v 1.6 1996/01/15 01:17:18 thorpej Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)send.2 8.2 (Berkeley) 2/21/94 32.\" 33.Dd $Mdocdate: May 31 2007 $ 34.Dt SEND 2 35.Os 36.Sh NAME 37.Nm send , 38.Nm sendto , 39.Nm sendmsg 40.Nd send a message from a socket 41.Sh SYNOPSIS 42.Fd #include <sys/types.h> 43.Fd #include <sys/socket.h> 44.Ft ssize_t 45.Fn send "int s" "const void *msg" "size_t len" "int flags" 46.Ft ssize_t 47.Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "socklen_t tolen" 48.Ft ssize_t 49.Fn sendmsg "int s" "const struct msghdr *msg" "int flags" 50.Sh DESCRIPTION 51.Fn send , 52.Fn sendto , 53and 54.Fn sendmsg 55are used to transmit a message to another socket. 56.Fn send 57may be used only when the socket is in a 58.Em connected 59state, while 60.Fn sendto 61and 62.Fn sendmsg 63may be used at any time. 64.Pp 65The address of the target is given by 66.Fa to 67with 68.Fa tolen 69specifying its size. 70The length of the message is given by 71.Fa len . 72If the message is too long to pass atomically through the 73underlying protocol, the error 74.Er EMSGSIZE 75is returned, and 76the message is not transmitted. 77.Pp 78No indication of failure to deliver is implicit in a 79.Fn send . 80Locally detected errors are indicated by a return value of \-1. 81.Pp 82If no messages space is available at the socket to hold 83the message to be transmitted, then 84.Fn send 85normally blocks, unless the socket has been placed in 86non-blocking I/O mode. 87The 88.Xr select 2 89or 90.Xr poll 2 91system calls may be used to determine when it is possible to 92send more data. 93.Pp 94The 95.Fa flags 96parameter may include one or more of the following: 97.Bd -literal 98#define MSG_OOB 0x1 /* process out-of-band data */ 99#define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */ 100.Ed 101.Pp 102The flag 103.Dv MSG_OOB 104is used to send 105.Dq out-of-band 106data on sockets that support this notion (e.g., 107.Dv SOCK_STREAM ) ; 108the underlying protocol must also support 109.Dq out-of-band 110data. 111.Dv MSG_DONTROUTE 112is usually used only by diagnostic or routing programs. 113.Pp 114See 115.Xr recv 2 116for a description of the 117.Fa msghdr 118structure. 119.Sh RETURN VALUES 120The call returns the number of characters sent, or \-1 121if an error occurred. 122.Sh ERRORS 123.Fn send , 124.Fn sendto , 125and 126.Fn sendmsg 127fail if: 128.Bl -tag -width Er 129.It Bq Er EBADF 130An invalid descriptor was specified. 131.It Bq Er ENOTSOCK 132The argument 133.Fa s 134is not a socket. 135.It Bq Er EFAULT 136An invalid user space address was specified for a parameter. 137.It Bq Er EMSGSIZE 138The socket requires that message be sent atomically, 139and the size of the message to be sent made this impossible. 140.It Bq Er EAGAIN 141The socket is marked non-blocking and the requested operation 142would block. 143.It Bq Er ENOBUFS 144The system was unable to allocate an internal buffer. 145The operation may succeed when buffers become available. 146.It Bq Er ENOBUFS 147The output queue for a network interface was full. 148This generally indicates that the interface has stopped sending, 149but may be caused by transient congestion. 150.It Bq Er EACCES 151The 152.Dv SO_BROADCAST 153option is not set on the socket, and a broadcast address 154was given as the destination. 155.It Bq Er EHOSTUNREACH 156The destination address specified an unreachable host. 157.It Bq Er EINVAL 158The 159.Fa flags 160parameter is invalid. 161.It Bq Er EHOSTDOWN 162The destination address specified a host that is down. 163.It Bq Er ENETDOWN 164The destination address specified a network that is down. 165.It Bq Er ECONNREFUSED 166The destination host rejected the message (or a previous one). 167This error can only be returned by connected sockets. 168.It Bq Er ENOPROTOOPT 169There was a problem sending the message. 170This error can only be returned by connected sockets. 171.It Bq Er EDESTADDRREQ 172The socket is not connected, and no destination address was specified. 173.It Bq Er EISCONN 174The socket is already connected, and a destination address was specified. 175.El 176.Pp 177In addition, 178.Fn send 179and 180.Fn sendto 181may return the following error: 182.Bl -tag -width Er 183.It Bq Er EINVAL 184.Fa len 185was larger than 186.Dv SSIZE_MAX . 187.El 188.Pp 189Also, 190.Fn sendmsg 191may return the following errors: 192.Bl -tag -width Er 193.It Bq Er EINVAL 194The sum of the 195.Fa iov_len 196values in the 197.Fa msg_iov 198array overflowed an 199.Em ssize_t . 200.It Bq Er EMSGSIZE 201The 202.Fa msg_iovlen 203member of 204.Fa msg 205was less than 0 or larger than 206.Dv IOV_MAX . 207.It Bq Er EAFNOSUPPORT 208Addresses in the specified address family cannot be used with this socket. 209.El 210.Sh SEE ALSO 211.Xr fcntl 2 , 212.Xr getsockopt 2 , 213.Xr poll 2 , 214.Xr recv 2 , 215.Xr select 2 , 216.Xr socket 2 , 217.Xr write 2 , 218.Xr CMSG_DATA 3 219.Sh HISTORY 220The 221.Fn send 222function call appeared in 223.Bx 4.2 . 224