send.2

早期freebsd实现

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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 sendto ,
.Nm sendmsg
.Nd send a message from a socket
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Ft ssize_t
.Fn send "int s" "const void *msg" "size_t len" "int flags"
.Ft ssize_t
.Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "int tolen"
.Ft ssize_t
.Fn sendmsg "int s" "const struct msghdr *msg" "int flags"
.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 to
with 
.Fa tolen
specifying its size.
The length of the message is given by
.Fa len .
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
See 
.Xr recv 2
for a description of the
.Fa msghdr
structure.
.Sh RETURN VALUES
The call returns the number of characters sent, or -1
if an error occurred.
.Sh ERRORS
.Fn Send ,
.Fn sendto ,
and
.Fn sendmsg
fail if:
.Bl -tag -width [EMSGSIZE]
.It Bq Er EBADF
An invalid descriptor was specified.
.It Bq Er ENOTSOCK
The argument
.Fa s
is not a socket.
.It Bq Er EFAULT
An invalid user space address was specified for a parameter.
.It Bq Er EMSGSIZE
The socket requires that message be sent atomically,
and the size of the message to be sent made this impossible.
.It Bq Er EAGAIN
The socket is marked non-blocking and the requested operation
would block.
.It Bq Er ENOBUFS
The system was 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 was full.
This generally indicates that the interface has stopped sending,
but may be caused by transient congestion.
.El
.Sh SEE ALSO
.Xr fcntl 2 ,
.Xr recv 2 ,
.Xr select 2 ,
.Xr getsockopt 2 ,
.Xr socket 2 ,
.Xr write 2
.Sh HISTORY
The
.Nm
function call appeared in
.Bx 4.2 .