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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.\" $DragonFly: src/lib/libc/sys/send.2,v 1.2 2003/06/17 04:26:47 dillon Exp $ 35.\" 36.Dd February 15, 1995 37.Dt SEND 2 38.Os 39.Sh NAME 40.Nm send , 41.Nm sendto , 42.Nm sendmsg 43.Nd send a message from a socket 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In sys/types.h 48.In sys/socket.h 49.Ft ssize_t 50.Fn send "int s" "const void *msg" "size_t len" "int flags" 51.Ft ssize_t 52.Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "socklen_t tolen" 53.Ft ssize_t 54.Fn sendmsg "int s" "const struct msghdr *msg" "int flags" 55.Sh DESCRIPTION 56.Fn Send , 57.Fn sendto , 58and 59.Fn sendmsg 60are used to transmit a message to another socket. 61.Fn Send 62may be used only when the socket is in a 63.Em connected 64state, while 65.Fn sendto 66and 67.Fn sendmsg 68may be used at any time. 69.Pp 70The address of the target is given by 71.Fa to 72with 73.Fa tolen 74specifying its size. 75The length of the message is given by 76.Fa len . 77If the message is too long to pass atomically through the 78underlying protocol, the error 79.Er EMSGSIZE 80is returned, and 81the message is not transmitted. 82.Pp 83No indication of failure to deliver is implicit in a 84.Fn send . 85Locally detected errors are indicated by a return value of -1. 86.Pp 87If no messages space is available at the socket to hold 88the message to be transmitted, then 89.Fn send 90normally blocks, unless the socket has been placed in 91non-blocking I/O mode. 92The 93.Xr select 2 94call may be used to determine when it is possible to 95send more data. 96.Pp 97The 98.Fa flags 99parameter may include one or more of the following: 100.Bd -literal 101#define MSG_OOB 0x1 /* process out-of-band data */ 102#define MSG_PEEK 0x2 /* peek at incoming message */ 103#define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */ 104#define MSG_EOR 0x8 /* data completes record */ 105#define MSG_EOF 0x100 /* data completes transaction */ 106.Ed 107.Pp 108The flag 109.Dv MSG_OOB 110is used to send 111.Dq out-of-band 112data on sockets that support this notion (e.g.\& 113.Dv SOCK_STREAM ) ; 114the underlying protocol must also support 115.Dq out-of-band 116data. 117.Dv MSG_EOR 118is used to indicate a record mark for protocols which support the 119concept. 120.Dv MSG_EOF 121requests that the sender side of a socket be shut down, and that an 122appropriate indication be sent at the end of the specified data; 123this flag is only implemented for 124.Dv SOCK_STREAM 125sockets in the 126.Dv PF_INET 127protocol family, and is used to implement Transaction 128.Tn TCP 129(see 130.Xr ttcp 4 ) . 131.Dv MSG_DONTROUTE 132is usually used only by diagnostic or routing programs. 133.Pp 134See 135.Xr recv 2 136for a description of the 137.Fa msghdr 138structure. 139.Sh RETURN VALUES 140The call returns the number of characters sent, or -1 141if an error occurred. 142.Sh ERRORS 143.Fn Send , 144.Fn sendto , 145and 146.Fn sendmsg 147fail if: 148.Bl -tag -width Er 149.It Bq Er EBADF 150An invalid descriptor was specified. 151.It Bq Er EACCES 152The destination address is a broadcast address, and 153.Dv SO_BROADCAST 154has not been set on the socket. 155.It Bq Er ENOTSOCK 156The argument 157.Fa s 158is not a socket. 159.It Bq Er EFAULT 160An invalid user space address was specified for a parameter. 161.It Bq Er EMSGSIZE 162The socket requires that message be sent atomically, 163and the size of the message to be sent made this impossible. 164.It Bq Er EAGAIN 165The socket is marked non-blocking and the requested operation 166would block. 167.It Bq Er ENOBUFS 168The system was unable to allocate an internal buffer. 169The operation may succeed when buffers become available. 170.It Bq Er ENOBUFS 171The output queue for a network interface was full. 172This generally indicates that the interface has stopped sending, 173but may be caused by transient congestion. 174.It Bq Er EHOSTUNREACH 175The remote host was unreachable. 176.It Bq Er ECONNREFUSED 177The socket received an ICMP destination unreachable message 178from the last message sent. This typically means that the 179receiver is not listening on the remote port. 180.It Bq Er EHOSTDOWN 181The remote host was down. 182.El 183.Sh BUGS 184Because 185.Fn sendmsg 186doesn't necessarily block until the data has been transferred, it 187is possible to transfer an open file descriptor across an 188.Dv AF_UNIX 189domain socket 190(see 191.Xr recv 2 ) , 192then 193.Fn close 194it before it has actually been sent, the result being that the receiver 195gets a closed file descriptor. It is left to the application to 196implement an acknowlegment mechanism to prevent this from happening. 197.Sh SEE ALSO 198.Xr fcntl 2 , 199.Xr getsockopt 2 , 200.Xr recv 2 , 201.Xr select 2 , 202.Xr socket 2 , 203.Xr write 2 204.Sh HISTORY 205The 206.Fn send 207function call appeared in 208.Bx 4.2 . 209