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@(#)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.
p 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.
p No indication of failure to deliver is implicit in a .Fn send . Locally detected errors are indicated by a return value of -1.
p 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.
p The .Fa flags parameter may include one or more of the following: d -literal #define MSG_OOB 0x1 /* process out-of-band data */ #define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */ .Ed
p 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.
p
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:
l -tag -width Er ===========
t Bq Er EACCES The SO_BROADCAST option is not set on the socket
and a broadcast address is given as the destination.
===========
t Bq Er EAGAIN The socket is marked non-blocking
and the requested operation would block.
===========
t Bq Er EBADF An invalid descriptor is specified.
===========
t Bq Er ECONNRESET A connection is forcibly closed by a peer.
===========
t Bq Er EFAULT An invalid user space address is specified for a parameter.
===========
t Bq Er EHOSTUNREACH The destination address specifies an unreachable host.
===========
t Bq Er EINTR A signal interrupts the system call
before any data is transmitted.
===========
t 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 .
===========
t Bq Er ENETDOWN The local network interface used to reach the destination is down.
===========
t Bq Er ENETUNREACH No route to the network is present.
===========
t Bq Er ENOBUFS The system is unable to allocate an internal buffer.
The operation may succeed when buffers become available.
===========
t 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.
===========
t Bq Er ENOTSOCK The argument
.Fa socket
is not a socket.
===========
t Bq Er EOPNOTSUPP .Fa socket
does not support (some of) the option(s) specified in
.Fa flags .
===========
t 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
p
The
.Fn sendmsg
and
.Fn sendto
system calls will fail if:
l -tag -width Er ===========
t Bq Er EAFNOSUPPORT Addresses in the specified address family cannot be used
with this socket.
===========
t Bq Er EDESTADDRREQ The socket is not connection-mode and does not have its peer address set,
and no destination address is specified.
===========
t Bq Er EISCONN A destination address was specified and the socket is already connected.
===========
t Bq Er ENOENT A component of the pathname does not name an existing file
or the path name is an empty string.
===========
t Bq Er ENOMEM Insufficient memory is available to fulfill the request.
===========
t Bq Er ENOTCONN The socket is connection-mode, but is not connected.
===========
t Bq Er ENOTDIR A component of the path prefix of the pathname in the socket address
is not a directory.
.El
p
The
.Fn send
system call will fail if:
l -tag -width Er ===========
t Bq Er EDESTADDRREQ The socket is not connection-mode and no peer address is set.
===========
t Bq Er ENOTCONN The socket is not connected or otherwise has not had the peer pre-specified.
.El
p
The
.Fn sendmsg
system call will fail if:
l -tag -width Er ===========
t Bq Er EINVAL The sum of the iov_len values overflows an ssize_t.
===========
t 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>
p The include file n 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 x 4.2 .