FILTER(2)FILTER(2)NAMEfilter - data processing interface
SYNOPSIS
include "filter.m";
filter := load Filter filterpath;
Rq: adt {
pick {
Start =>
pid: int;
Fill or Result =>
buf: array of byte;
reply: chan of int;
Finished =>
buf: array of byte;
Info =>
msg: string;
Error =>
e: string;
}
};
init: fn();
start: fn(param: string): chan of ref Rq;
DESCRIPTION
Filter defines a general module interface for byte-stream processing.
This manual page documents how to use the interface, and by implication
how a Filter module should behave. There is a different implementation
module for each filter type and algorithm (eg, for compression or line
encoding). All implementations are instances of type Filter, loaded
from the Dis file filterpath, given in the manual page for each stan‐
dard filter (or you can write your own to match this specification).
For details of each existing filter module, see filter-deflate(2) and
following manual pages.
Init must be called before any other operation of a filter module.
Start sets the filter going; param can be used to pass any filter-spe‐
cific information to the processor. Start spawns a new thread to do
the processing; it returns a channel that is used to receive requests
from the filter. The first message sent is always Rq.Start; pid is the
process id of the new process spawned.
Subsequent messages are:
Rq.Fill
A request by the filter to fill buf with data. The number of
bytes that have actually been placed in the buffer should be
sent on reply. If -1 is sent, the filter will terminate. If
the value is 0, the filter will terminate once it has processed
all its input.
Rq.Result
Buf contains data from the filter. Receipt of the the data must
be acknowledged by sending a value on reply. If the value is
-1, the filter will terminate.
Rq.Finished
The filter has finished processing. Buf contains any data that
was not consumed by the filter. The filter terminates after
sending this message.
Rq.Info
This message is used to send a string of arbitrary information
from the filter during the course of its processing.
Rq.Error
The filter has encountered an error when processing. E is a
string describing the error. The filter terminates after sending
this message.
SOURCE
/module/filter.m
SEE ALSOgzip(1), filter-deflate(2), filter-slip(2)FILTER(2)
