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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 1.4 2004/08/27 21:23:32 asmodai 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 socket file descriptor is given by 71.Fa s . 72For 73.Fn send 74and 75.Fn sendto 76.Fa msg 77points to a buffer containing the message. 78For 79.Fn sendmsg 80.Fa msg 81points to a msghdr structure. 82The address of the target is given by 83.Fa to 84with 85.Fa tolen 86specifying its size. 87The length of the message is given by 88.Fa len . 89If the message is too long to pass atomically through the 90underlying protocol, the error 91.Er EMSGSIZE 92is returned, and 93the message is not transmitted. 94.Pp 95No indication of failure to deliver is implicit in a 96.Fn send . 97Locally detected errors are indicated by a return value of -1. 98.Pp 99If no messages space is available at the socket to hold 100the message to be transmitted, then 101.Fn send 102normally blocks, unless the socket has been placed in 103non-blocking I/O mode. 104The 105.Xr select 2 106call may be used to determine when it is possible to 107send more data. 108.Pp 109The 110.Fa flags 111parameter may include one or more of the following: 112.Bd -literal 113#define MSG_OOB 0x1 /* process out-of-band data */ 114#define MSG_PEEK 0x2 /* peek at incoming message */ 115#define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */ 116#define MSG_EOR 0x8 /* data completes record */ 117#define MSG_EOF 0x100 /* data completes transaction */ 118.Ed 119.Pp 120The flag 121.Dv MSG_OOB 122is used to send 123.Dq out-of-band 124data on sockets that support this notion (e.g.\& 125.Dv SOCK_STREAM ) ; 126the underlying protocol must also support 127.Dq out-of-band 128data. 129.Dv MSG_EOR 130is used to indicate a record mark for protocols which support the 131concept. 132.Dv MSG_EOF 133requests that the sender side of a socket be shut down, and that an 134appropriate indication be sent at the end of the specified data; 135this flag is only implemented for 136.Dv SOCK_STREAM 137sockets in the 138.Dv PF_INET 139protocol family, and is used to implement Transaction 140.Tn TCP 141(see 142.Xr ttcp 4 ) . 143.Dv MSG_DONTROUTE 144is usually used only by diagnostic or routing programs. 145.Pp 146See 147.Xr recv 2 148for a description of the 149.Fa msghdr 150structure. 151.Sh RETURN VALUES 152The call returns the number of characters sent, or -1 153if an error occurred. 154.Sh ERRORS 155.Fn Send , 156.Fn sendto , 157and 158.Fn sendmsg 159fail if: 160.Bl -tag -width Er 161.It Bq Er EBADF 162An invalid descriptor was specified. 163.It Bq Er EACCES 164The destination address is a broadcast address, and 165.Dv SO_BROADCAST 166has not been set on the socket. 167.It Bq Er ENOTSOCK 168The argument 169.Fa s 170is not a socket. 171.It Bq Er EFAULT 172An invalid user space address was specified for a parameter. 173.It Bq Er EMSGSIZE 174The socket requires that message be sent atomically, 175and the size of the message to be sent made this impossible. 176.It Bq Er EAGAIN 177The socket is marked non-blocking and the requested operation 178would block. 179.It Bq Er ENOBUFS 180The system was unable to allocate an internal buffer. 181The operation may succeed when buffers become available. 182.It Bq Er ENOBUFS 183The output queue for a network interface was full. 184This generally indicates that the interface has stopped sending, 185but may be caused by transient congestion. 186.It Bq Er EHOSTUNREACH 187The remote host was unreachable. 188.It Bq Er ECONNREFUSED 189The socket received an ICMP destination unreachable message 190from the last message sent. This typically means that the 191receiver is not listening on the remote port. 192.It Bq Er EHOSTDOWN 193The remote host was down. 194.It Bq Er EPIPE 195The socket is unable to send anymore data (SS_CANTSENDMORE has 196been set on the socket). This typically means that the socket 197is not connected. 198.El 199.Sh BUGS 200Because 201.Fn sendmsg 202doesn't necessarily block until the data has been transferred, it 203is possible to transfer an open file descriptor across an 204.Dv AF_UNIX 205domain socket 206(see 207.Xr recv 2 ) , 208then 209.Fn close 210it before it has actually been sent, the result being that the receiver 211gets a closed file descriptor. It is left to the application to 212implement an acknowlegment mechanism to prevent this from happening. 213.Sh SEE ALSO 214.Xr fcntl 2 , 215.Xr getsockopt 2 , 216.Xr recv 2 , 217.Xr select 2 , 218.Xr socket 2 , 219.Xr write 2 220.Sh HISTORY 221The 222.Fn send 223function call appeared in 224.Bx 4.2 . 225