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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 1.9 2007/06/30 19:03:52 swildner 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 *msgbuf" "size_t len" "int flags" 51.Ft ssize_t 52.Fn sendto "int s" "const void *msgbuf" "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 . 72.Fa msgbuf 73points to a buffer containing the message. 74.Fa msg 75points to a 76.Fa msghdr 77structure. 78The address of the target is given by 79.Fa to 80with 81.Fa tolen 82specifying its size. 83The length of the message is given by 84.Fa len . 85If the message is too long to pass atomically through the 86underlying protocol, the error 87.Er EMSGSIZE 88is returned, and 89the message is not transmitted. 90.Pp 91No indication of failure to deliver is implicit in a 92.Fn send . 93Locally detected errors are indicated by a return value of -1. 94.Pp 95If no messages space is available at the socket to hold 96the message to be transmitted, then 97.Fn send 98normally blocks, unless the socket has been placed in 99non-blocking I/O mode. 100The 101.Xr select 2 102call may be used to determine when it is possible to 103send more data. 104.Pp 105The 106.Fa flags 107parameter may include one or more of the following: 108.Bd -literal 109#define MSG_OOB 0x1 /* process out-of-band data */ 110#define MSG_PEEK 0x2 /* peek at incoming message */ 111#define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */ 112#define MSG_EOR 0x8 /* data completes record */ 113#define MSG_EOF 0x100 /* data completes transaction */ 114.Ed 115.Pp 116The flag 117.Dv MSG_OOB 118is used to send 119.Dq out-of-band 120data on sockets that support this notion (e.g.\& 121.Dv SOCK_STREAM ) ; 122the underlying protocol must also support 123.Dq out-of-band 124data. 125.Dv MSG_EOR 126is used to indicate a record mark for protocols which support the 127concept. 128.Dv MSG_EOF 129requests that the sender side of a socket be shut down, and that an 130appropriate indication be sent at the end of the specified data; 131this flag is only implemented for 132.Dv SOCK_STREAM 133sockets in the 134.Dv PF_INET 135protocol family. 136.Dv MSG_DONTROUTE 137is usually used only by diagnostic or routing programs. 138.Pp 139See 140.Xr recv 2 141for a description of the 142.Fa msghdr 143structure. 144.Sh RETURN VALUES 145Upon successful completion the number of characters which were sent is 146returned. Otherwise -1 is returned and the global variable 147.Va errno 148is set to indicate the error. 149.Sh ERRORS 150.Fn Send , 151.Fn sendto , 152and 153.Fn sendmsg 154fail if: 155.Bl -tag -width Er 156.It Bq Er EBADF 157An invalid descriptor was specified. 158.It Bq Er EACCES 159The destination address is a broadcast address, and 160.Dv SO_BROADCAST 161has not been set on the socket. 162.It Bq Er ENOTSOCK 163The argument 164.Fa s 165is not a socket. 166.It Bq Er EFAULT 167An invalid user space address was specified for a parameter. 168.It Bq Er EMSGSIZE 169The socket requires that message be sent atomically, 170and the size of the message to be sent made this impossible. 171.It Bq Er EAGAIN 172The socket is marked non-blocking and the requested operation 173would block. 174.It Bq Er ENOBUFS 175The system was unable to allocate an internal buffer. 176The operation may succeed when buffers become available. 177.It Bq Er ENOBUFS 178The output queue for a network interface was full. 179This generally indicates that the interface has stopped sending, 180but may be caused by transient congestion. 181.It Bq Er EHOSTUNREACH 182The remote host was unreachable. 183.It Bq Er ECONNREFUSED 184The socket received an ICMP destination unreachable message 185from the last message sent. This typically means that the 186receiver is not listening on the remote port. 187.It Bq Er EHOSTDOWN 188The remote host was down. 189.It Bq Er EPIPE 190The socket is unable to send anymore data (SS_CANTSENDMORE has 191been set on the socket). This typically means that the socket 192is not connected. 193.El 194.Sh SEE ALSO 195.Xr fcntl 2 , 196.Xr getsockopt 2 , 197.Xr recv 2 , 198.Xr select 2 , 199.Xr socket 2 , 200.Xr write 2 201.Sh HISTORY 202The 203.Fn send 204function call appeared in 205.Bx 4.2 . 206.Sh BUGS 207Because 208.Fn sendmsg 209doesn't necessarily block until the data has been transferred, it 210is possible to transfer an open file descriptor across an 211.Dv AF_UNIX 212domain socket 213(see 214.Xr recv 2 ) , 215then 216.Fn close 217it before it has actually been sent, the result being that the receiver 218gets a closed file descriptor. It is left to the application to 219implement an acknowledgment mechanism to prevent this from happening. 220