.TH OPMUX 2
.SH NAME
Opmux, rpc \- RPC multiplexor for the Op file protocol
.SH SYNOPSIS
.EX
include "op.m";
include "opmux.m";
opmux := load Opmux Opmux->PATH;

init:	fn(ofd: ref Sys->FD, op: Op, endc: chan of string);
rpc:	fn(t: ref Op->Tmsg) : chan of ref Op->Rmsg;
term: fn();

recoverfn:	ref fn(): ref Sys->FD;
dump: fn();
debug: int;
.EE
.SH DESCRIPTION
.B Opmux
provides a multiplexor for Op connections. It permits issuing concurrent
requests through the same connection.
.PP
.B Init
initializes and prepares the module for operation. The other end of
the connection reached through
.I ofd
should be a server speaking Op. See
.IR intro (O).
An implementation for the
.IR op (2)
module must be supplied in the
.I op
argument. The channel
.I endc
can be used to terminate the multiplexor, by sending anything through it.
Usually, the error condition causing the termination is sent through.
.PP
The function
.B rpc
makes an Op RPC to the server reached through
.I ofd
(given to
.BR init ).
It must receive a valid
.B Tmsg
and returns a channel that can be used to obtain the reply as received
from the server. Errors are signaled by means of
.B Rmsg.Error
adts sent through this channel. The reply channel has enough
buffering to permit callers of
.B rpc
to ignore one reply message. But note that
.B Tget
requests asking to read data from a directory may receive a potentially
infinite number of replies, see
.IR get (O)
for details. 
.PP
The global
.B debug
may be set to a non-zero value to cause
.I Opmux
to print Op messages as they are sent/received. As an additional
aid,
.B dump
prints the internal state of the multiplexor (ie., messages sent with
pending replies) for debugging.
.PP
The function
.B term
terminates the operation of the module, aborting any outstanding RPC.
.PP
You may set the
pointer
.B recoverfn
to point to a function that returns a new descriptor open to reach the same server,
and
.I opmux
will try to recover by calling it, should it lose the connection. This feature is experimental
and not tested enough to be trusted.
.SH SOURCE
.B /usr/octopus/port/lib/opmux.b
.SH SEE ALSO
.IR intro (O),
.IR op (2),
and
.IR intro (5).