1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
231 lines
6.6 KiB
Groff
231 lines
6.6 KiB
Groff
.\" Copyright 1994, 1995 Massachusetts Institute of Technology
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.\"
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.\" Permission to use, copy, modify, and distribute this software and
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.\" its documentation for any purpose and without fee is hereby
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.\" granted, provided that both the above copyright notice and this
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.\" permission notice appear in all copies, that both the above
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.\" copyright notice and this permission notice appear in all
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.\" supporting documentation, and that the name of M.I.T. not be used
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.\" in advertising or publicity pertaining to distribution of the
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.\" software without specific, written prior permission. M.I.T. makes
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.\" no representations about the suitability of this software for any
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.\" purpose. It is provided "as is" without express or implied
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.\" warranty.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS
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.\" ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
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.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
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.\" SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 18, 1995
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.Dt TTCP 4
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.Os FreeBSD 2.1
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.Sh NAME
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.Nm ttcp
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.Nd Transmission Control Protocol Extensions for Transactions
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.Sh
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.Fd #include <sys/socket.h>
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.Fd #include <netinet/in.h>
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.Fd #include <netinet/tcp.h>
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.Ft int
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.Fn setsockopt sock IPPROTO_TCP TCP_NOPUSH &One "sizeof One"
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.br
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.Ft ssize_t
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.Fn sendto sock msg len MSG_EOF &sin "sizeof sin"
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.br
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.Ft ssize_t
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.Fn sendto sock msg len MSG_EOF 0 0
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.Sh DESCRIPTION
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.Tn T/TCP
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refers to a set of extensions to the
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.Tn TCP
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protocol (see
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.Xr tcp 4 )
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which permit hosts to reliably exchange a small amount of data in a
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two-packet exchange, thus eliminating the extra round-trip delays
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inherent in a standard
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.Tn TCP
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connection. The socket interface includes modifications to support
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.Tn T/TCP ,
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detailed here for the specific case, and in the
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.Xr socket 2
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and
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.Xr send 2
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manual pages for the protocol-independent support.
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.Tn T/TCP
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is defined in RFC 1644.
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.Pp
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The
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.Tn T/TCP
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extensions work by including certain options in all segments of a
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particular connection, which enable the implementation to avoid the
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three-way handshake for all but the first connection between a pair of
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hosts. These same options also make it possible to more reliably
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recognize old, duplicate packets, which in turn reduces the amount of
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time the
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.Tn TCP
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protocol must maintain state after a connection closes. The
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.Dq Li net.inet.tcp.rfc1644
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MIB variable can be used to disable
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.Tn T/TCP
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negotiation at run time; however, the protocol has been designed to
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ensure that attempts by non-T/TCP
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systems to communicate with T/TCP-enhanced
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ones automatically degenerate into standard
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.Tn TCP .
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.Sh TRANSACTION MODEL
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The expected model of a
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.Dq transaction
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as used by
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.Tn T/TCP
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is a fairly simple one:
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.Bl -enum
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.It
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A client program generates a request to be sent to the server, which
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is small enough to fit in a single
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.Tn TCP
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segment, and sends a SYN PUSH FIN segment with options and data to the
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server.
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.It
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The server program accepts the request in the same manner as for
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regular
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.Tn TCP
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connections, interprets it, and generates a reply which may be small
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enough to fit in a single segment. If it is, the reply is sent in a
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single SYN PUSH FIN ACK segment with (different) options and data back
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to the client. If not, then the connection degenerates into (almost)
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the usual case for
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.Tn TCP .
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The server then closes its socket.
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.It
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The client reads the reply and closes its socket.
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.El
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.Sh CLIENT SUPPORT
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Support on the client side is provided by extending the semantics of
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the
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.Xr sendto 2
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and
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.Xr sendmsg 2
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system calls to understand the notion of
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.Dq implied connect
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and
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.Dq send and shutdown.
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To send the request in a transaction, the
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.Xr sendto 2
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system call is typically used, as in the following example:
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.Bd -literal -offset indent
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char request[REQ_LEN];
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struct sockaddr_in sin;
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int sock, req_len;
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sock = socket(PF_INET, SOCK_STREAM, 0);
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/* prepare request[] and sin */
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err = sendto(sock, request, req_len, MSG_EOF,
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(struct sockaddr *)&sin, sin.sin_len);
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/* do something if error */
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req_len = read(sock, request, sizeof request);
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close(sock);
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/* do something with the reply */
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.Ed
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.Pp
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Note that, after the
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call to
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.Fn sendto ,
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the socket is now in the same state as if the
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.Xr connect 2
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and
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.Xr shutdown 2
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system calls had been used. That is to say, the only reasonable
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operations to perform on this socket are
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.Xr read 2
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and
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.Xr close 2 .
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(Because the client's
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.Tn TCP
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sender is already shut down, it is not possible to
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.Xr connect 2
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this socket to another destination.)
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.Sh SERVER SUPPORT
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There are two different options available for servers using
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.Tn T/TCP :
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.Bl -enum
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.It
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Set the
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.Dv TCP_NOPUSH
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socket option, and use normal
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.Xr write 2
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calls when formulating the response.
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.It
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Use
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.Xr sendto 2
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with the
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.Dv MSG_EOF
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flag, as in the client, but with the destination unspecified.
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.El
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.Pp
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The first option is generally the appropriate choice when converting
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existing servers to use
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.Tn T/TCP
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extensions; simply add a call to
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.Fn setsockopt sock IPPROTO_TCP TCP_NOPUSH &One "sizeof One"
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(where
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.Va One
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is an integer variable with a non-zero value). The server socket must
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be closed before any data is sent (unless the socket buffers fill up).
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.Pp
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The second option is preferable for new servers, and is sometimes easy
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enough to retrofit into older servers. In this case, where the reply
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phase would ordinarily have included a call to
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.Fn write ,
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one substitutes:
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.Pp
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.Dl "sendto(sock, buf, len, MSG_EOF, (struct sockaddr *)0, 0)"
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.Pp
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In this case, the reply is sent immediately, but as in the client
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case, the socket is no lnoger useful for anything and should be
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immediately closed.
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.Sh MIB VARIABLES
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The
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.Tn T/TCP
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extensions require the
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.Dq Li net.inet.tcp.rfc1644
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MIB variable to be true in order for the appropriate
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.Tn TCP
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options to be sent. See
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.Xr tcp 4
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for more information.
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.Sh SEE ALSO
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.Xr send 2 ,
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.Xr setsockopt 2 ,
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.Xr inet 4 ,
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.Xr tcp 4
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.Rs
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.%A R. Braden
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.%T "T/TCP \- TCP Extensions for Transactions"
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.%O RFC 1644
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.Re
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.Sh HISTORY
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Support for
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.Tn T/TCP
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first appeared in
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.Fx 2.1 ,
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based on code written by Bob Braden and Liming Wei at the
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University of Southern California, Information Sciences Institute, and
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ported by Andras Olah at the University of Twente.
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