.\" $NetBSD: send.2,v 1.6 1996/01/15 01:17:18 thorpej Exp $ .\" .\" Copyright (c) 1983, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)send.2 8.2 (Berkeley) 2/21/94 .\" .Dd February 21, 1994 .Dt SEND 2 .Os BSD 4.2 .Sh NAME .Nm send , .Nm sendmsg , .Nm sendto .Nd send a message from a socket .Sh SYNOPSIS .Fd #include <sys/socket.h> .Ft ssize_t .Fo send .Fa "int socket" .Fa "const void *buffer" .Fa "size_t length" .Fa "int flags" .Fc .Ft ssize_t .Fo sendmsg .Fa "int socket" .Fa "const struct msghdr *message" .Fa "int flags" .Fc .Ft ssize_t .Fo sendto .Fa "int socket" .Fa "const void *buffer" .Fa "size_t length" .Fa "int flags" .Fa "const struct sockaddr *dest_addr" .Fa "socklen_t dest_len" .Fc .Sh DESCRIPTION .Fn Send , .Fn sendto , and .Fn sendmsg are used to transmit a message to another socket. .Fn Send may be used only when the socket is in a .Em connected state, while .Fn sendto and .Fn sendmsg may be used at any time. .Pp The address of the target is given by .Fa dest_addr with .Fa dest_len specifying its size. The length of the message is given by .Fa length . If the message is too long to pass atomically through the underlying protocol, the error .Er EMSGSIZE is returned, and the message is not transmitted. .Pp No indication of failure to deliver is implicit in a .Fn send . Locally detected errors are indicated by a return value of -1. .Pp If no messages space is available at the socket to hold the message to be transmitted, then .Fn send normally blocks, unless the socket has been placed in non-blocking I/O mode. The .Xr select 2 call may be used to determine when it is possible to send more data. .Pp The .Fa flags parameter may include one or more of the following: .Bd -literal #define MSG_OOB 0x1 /* process out-of-band data */ #define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */ .Ed .Pp The flag .Dv MSG_OOB is used to send .Dq out-of-band data on sockets that support this notion (e.g. .Dv SOCK_STREAM ) ; the underlying protocol must also support .Dq out-of-band data. .Dv MSG_DONTROUTE is usually used only by diagnostic or routing programs. .Pp The .Fn sendmsg system call uses a .Fa msghdr structure to minimize the number of directly supplied arguments. The .Fa msg_iov and .Fa msg_iovlen fields of message specify zero or more buffers containing the data to be sent. .Fa msg_iov points to an array of iovec structures; .Fa msg_iovlen shall be set to the dimension of this array. In each iovec structure, the .Fa iov_base field specifies a storage area and the .Fa iov_len field gives its size in bytes. Some of these sizes can be zero. The data from each storage area indicated by .Fa msg_iov is sent in turn. See .Xr recv 2 for a complete description of the .Fa msghdr structure. .Sh RETURN VALUES Upon successful completion, the number of bytes which were sent is returned. Otherwise, -1 is returned and the global variable .Va errno is set to indicate the error. .Sh ERRORS The .Fn send , .Fn sendmsg , and .Fn sendto system calls will fail if: .Bl -tag -width Er .\" =========== .It Bq Er EACCES The SO_BROADCAST option is not set on the socket and a broadcast address is given as the destination. .\" =========== .It Bq Er EAGAIN The socket is marked non-blocking and the requested operation would block. .\" =========== .It Bq Er EBADF An invalid descriptor is specified. .\" =========== .It Bq Er ECONNRESET A connection is forcibly closed by a peer. .\" =========== .It Bq Er EFAULT An invalid user space address is specified for a parameter. .\" =========== .It Bq Er EHOSTUNREACH The destination address specifies an unreachable host. .\" =========== .It Bq Er EINTR A signal interrupts the system call before any data is transmitted. .\" =========== .It Bq Er EMSGSIZE The socket requires that message be sent atomically, and the size of the message to be sent makes this impossible. .Dv IOV_MAX . .\" =========== .It Bq Er ENETDOWN The local network interface used to reach the destination is down. .\" =========== .It Bq Er ENETUNREACH No route to the network is present. .\" =========== .It Bq Er ENOBUFS The system is unable to allocate an internal buffer. The operation may succeed when buffers become available. .\" =========== .It Bq Er ENOBUFS The output queue for a network interface is full. This generally indicates that the interface has stopped sending, but may be caused by transient congestion. .\" =========== .It Bq Er ENOTSOCK The argument .Fa socket is not a socket. .\" =========== .It Bq Er EOPNOTSUPP .Fa socket does not support (some of) the option(s) specified in .Fa flags . .\" =========== .It Bq Er EPIPE The socket is shut down for writing or the socket is connection-mode and is no longer connected. In the latter case, and if the socket is of type SOCK_STREAM, the SIGPIPE signal is generated to the calling thread. .El .Pp The .Fn sendmsg and .Fn sendto system calls will fail if: .Bl -tag -width Er .\" =========== .It Bq Er EAFNOSUPPORT Addresses in the specified address family cannot be used with this socket. .\" =========== .It Bq Er EDESTADDRREQ The socket is not connection-mode and does not have its peer address set, and no destination address is specified. .\" =========== .It Bq Er EISCONN A destination address was specified and the socket is already connected. .\" =========== .It Bq Er ENOENT A component of the pathname does not name an existing file or the path name is an empty string. .\" =========== .It Bq Er ENOMEM Insufficient memory is available to fulfill the request. .\" =========== .It Bq Er ENOTCONN The socket is connection-mode, but is not connected. .\" =========== .It Bq Er ENOTDIR A component of the path prefix of the pathname in the socket address is not a directory. .El .Pp The .Fn send system call will fail if: .Bl -tag -width Er .\" =========== .It Bq Er EDESTADDRREQ The socket is not connection-mode and no peer address is set. .\" =========== .It Bq Er ENOTCONN The socket is not connected or otherwise has not had the peer pre-specified. .El .Pp The .Fn sendmsg system call will fail if: .Bl -tag -width Er .\" =========== .It Bq Er EINVAL The sum of the iov_len values overflows an ssize_t. .\" =========== .It Bq Er EMSGSIZE The socket requires that message be sent atomically, and the size of the message to be sent makes this impossible, or the msg_iovlen member of the msghdr structure pointed to by message is less than or equal to 0 or is greater than .Dv IOV_MAX . .El .Sh LEGACY SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/socket.h> .Pp The include file .In sys/types.h is necessary. .Sh SEE ALSO .Xr fcntl 2 , .Xr getsockopt 2 , .Xr recv 2 , .Xr select 2 , .Xr socket 2 , .Xr write 2 , .Xr compat 5 .Sh HISTORY The .Fn send function call appeared in .Bx 4.2 .