1.\" $NetBSD: send.2,v 1.27 2008/05/09 15:52:50 christos Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)send.2 8.2 (Berkeley) 2/21/94 31.\" 32.Dd May 9, 2008 33.Dt SEND 2 34.Os 35.Sh NAME 36.Nm send , 37.Nm sendto , 38.Nm sendmsg 39.Nd send a message from a socket 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In 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 91call 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 0x0001 /* process out-of-band data */ 99#define MSG_PEEK 0x0002 /* peek at incoming message */ 100#define MSG_DONTROUTE 0x0004 /* bypass routing, use direct interface */ 101#define MSG_EOR 0x0008 /* data completes record */ 102#define MSG_NOSIGNAL 0x0400 /* do not generate SIGPIPE on EOF */ 103.Ed 104.Pp 105The flag 106.Dv MSG_OOB 107is used to send 108.Dq out-of-band 109data on sockets that support this notion (e.g. 110.Dv SOCK_STREAM ) ; 111the underlying protocol must also support 112.Dq out-of-band 113data. 114.Dv MSG_EOR 115is used to indicate a record mark for protocols which support the 116concept. 117.\" .Dv MSG_EOF 118.\" requests that the sender side of a socket be shut down, and that an 119.\" appropriate indication be sent at the end of the specified data; 120.\" this flag is only implemented for 121.\" .Dv SOCK_STREAM 122.\" sockets in the 123.\" .Dv PF_INET 124.\" protocol family, and is used to implement Transaction 125.\" .Tn TCP 126.\" (see 127.\" .Xr ttcp 4 ) . 128.Dv MSG_DONTROUTE 129is usually used only by diagnostic or routing programs. 130.Pp 131See 132.Xr recv 2 133for a description of the 134.Fa msghdr 135structure. 136.Dv MSG_NOSIGNAL 137is used to prevent 138.Dv SIGPIPE 139generation when writing a socket that 140may be closed. 141.Sh RETURN VALUES 142The call returns the number of characters sent, or \-1 143if an error occurred. 144.Sh ERRORS 145.Fn send , 146.Fn sendto , 147and 148.Fn sendmsg 149fail if: 150.Bl -tag -width Er 151.It Bq Er EBADF 152An invalid descriptor was specified. 153.It Bq Er ENOTSOCK 154The argument 155.Fa s 156is not a socket. 157.It Bq Er EFAULT 158An invalid user space address was specified for a parameter. 159.It Bq Er EMSGSIZE 160The socket requires that message be sent atomically, 161and the size of the message to be sent made this impossible. 162.It Bq Er EPIPE 163In a connected socket the connection has been broken. 164.It Bq Er EDSTADDRREQ 165In a non-connected socket a destination address has not been specified. 166.It Bq Er EAGAIN|EWOULDBLOCK 167The socket is marked non-blocking and the requested operation 168would block. 169.It Bq Er ENOBUFS 170The system was unable to allocate an internal buffer. 171The operation may succeed when buffers become available. 172.It Bq Er ENOBUFS 173The output queue for a network interface was full. 174This generally indicates that the interface has stopped sending, 175but may be caused by transient congestion. 176.It Bq Er EACCES 177The SO_BROADCAST option is not set on the socket, and a broadcast address 178was given as the destination. 179.It Bq Er EHOSTUNREACH 180The destination for the message is unreachable. 181.It Bq Er EHOSTDOWN 182The destination is a host on the local subnet and does not respond to 183.Xr arp 4 . 184.It Bq Er EINVAL 185The total length of the I/O is more than can be expressed by the ssize_t 186return value. 187.It Bq Er EAFNOSUPPORT 188Addresses in the specified address family cannot be used with this socket. 189.El 190.Pp 191.Fn sendto 192will also fail if: 193.Bl -tag -width Er 194.It Bq Er EISCONN 195A destination address was specified and the socket is already connected. 196.El 197.Pp 198.Fn sendmsg 199will also fail if: 200.Bl -tag -width Er 201.It Bq Er EMSGSIZE 202The 203.Fa msg_iovlen 204member of the 205.Fa msg 206structure is less than or equal to 0 207or is greater than 208.Dv {IOV_MAX} . 209.El 210.Sh SEE ALSO 211.Xr fcntl 2 , 212.Xr getsockopt 2 , 213.Xr recv 2 , 214.Xr select 2 , 215.Xr socket 2 , 216.Xr write 2 217.Sh HISTORY 218The 219.Fn send 220function call appeared in 221.Bx 4.2 . 222