implement Filter; include "sys.m"; include "filter.m"; End: con byte 8r300;Esc: con byte 8r333;Eend: con byte 8r334;	# encoded End byteEesc: con byte 8r335;	# encoded Esc byte init(){} start(param: string): chan of ref Rq{	req := chan of ref Rq;	if(param == "encode")		spawn encode(req);	else		spawn decode(req);	return req;} encode(reqs: chan of ref Rq){	sys := load Sys Sys->PATH;	reqs <-= ref Rq.Start(sys->pctl(0, nil));	buf := array[8192] of byte;	rc := chan of int;	do{		reqs <-= ref Rq.Fill(buf, rc);		if((n := <-rc) <= 0){			if(n == 0)				reqs <-= ref Rq.Finished(nil);			break;		}		b := array[2*n + 2] of byte;	# optimise time not space		o := 1;		b[0] = End;		for(i := 0; i < n; i++){			if((c := buf[i]) == End || c == Esc){				b[o++] = Esc;				c = byte (Eend + (c& byte 1));			}			b[o++] = c;		}		b[o++] = End;		if(o != len b)			b = b[0:o];		reqs <-= ref Rq.Result(b, rc);	}while(<-rc != -1);} Slipesc, Slipend: con (1<<8) + iota;Slipsize: con 1006;	# rfc's suggestion slipin(c: byte, esc: int): int{	if(esc == Slipesc){	# last byte was Esc		if(c == Eend)			c = End;		else if(c == Eesc)			c = Esc;	}else{		if(c == Esc)			return Slipesc;		if(c == End)			return Slipend;	}	return int c;} decode(reqs: chan of ref Rq){	sys := load Sys Sys->PATH;	reqs <-= ref Rq.Start(sys->pctl(0, nil));	buf := array[8192] of byte;	b := array[Slipsize] of byte;	rc := chan of int;	c := 0;	o := 0;	for(;;){		reqs <-= ref Rq.Fill(buf, rc);		if((n := <-rc) <= 0){			if(n < 0)				exit;			break;		}		for(i := 0; i < n; i++){			c = slipin(buf[i], c);			if(c == Slipend){				if(o != 0){					reqs <-= ref Rq.Result(b[0:o], rc);					if(<-rc == -1)						exit;					b = array[Slipsize] of byte;					o = 0;				}			}else if(c != Slipesc){				if(o >= len b){					t := array[3*len b/2] of byte;					t[0:] = b;					b = t;				}				b[o++] = byte c;			}		}	}	# partial block discarded	reqs <-= ref Rq.Finished(nil);}