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ssh: add experimental mux mode

in mux mode, ssh relays raw MSG_CHANNEL_*
messages on standard input and output while
still handling authentication and key exchange
internally.

the intend is to use the mux mode to implement
something like the old sshnet ontop of ssh.

--- a/sys/src/cmd/ssh.c

+++ b/sys/src/cmd/ssh.c

@@ -80,7 +80,7 @@

 uchar sid[256];

 char thumb[2*SHA2_256dlen+1], *thumbfile;

-int fd, intr, raw, port, debug;

+int fd, intr, raw, port, mux, debug;

 char *user, *service, *status, *host, *remote, *cmd;

 Oneway recv, send;

@@ -987,6 +987,19 @@

 			break;

 		if(raw) write(2, s, n);

 		return;

+	case MSG_KEXINIT:

+		kex(1);

+		return;

+	}

+

+	if(mux){

+		n = recv.w - recv.r;

+		if(write(1, recv.r, n) != n)

+			sysfatal("write out: %r");

+		return;

+	}

+

+	switch(recv.r[0]){

 	case MSG_CHANNEL_DATA:

 		if(unpack(recv.r, recv.w-recv.r, "_us", &c, &s, &n) < 0)

 			break;

@@ -1051,9 +1064,6 @@

 	case MSG_CHANNEL_CLOSE:

 		shutdown();

 		return;

-	case MSG_KEXINIT:

-		kex(1);

-		return;

 	}

 	sysfatal("got: %.*H", (int)(recv.w - recv.r), recv.r);

 }

@@ -1147,7 +1157,7 @@

 void

 usage(void)

 {

-	fprint(2, "usage: %s [-dR] [-t thumbfile] [-T tries] [-u user] [-h] [user@]host [-W remote!port] [cmd args...]\n", argv0);

+	fprint(2, "usage: %s [-dRX] [-t thumbfile] [-T tries] [-u user] [-h] [user@]host [-W remote!port] [cmd args...]\n", argv0);

 	exits("usage");

 }

@@ -1203,6 +1213,10 @@

 		MaxPwTries = strtol(EARGF(usage()), &s, 0);

 		if(*s != 0) usage();

 		break;

+	case 'X':

+		mux = 1;

+		raw = 0;

+		break;

 	} ARGEND;

 	if(host == nil){

@@ -1269,50 +1283,51 @@

 	if(noneauth() < 0 && pubkeyauth() < 0 && passauth() < 0 && kbintauth() < 0)

 		sysfatal("auth: %r");

-	recv.pkt = MaxPacket;

-	recv.win = WinPackets*recv.pkt;

-	recv.chan = 0;

+	recv.pkt = send.pkt = MaxPacket;

+	recv.win = send.win =  WinPackets*recv.pkt;

+	recv.chan = send.win = 0;

-	/* open hailing frequencies */

-	if(remote != nil){

-		NetConnInfo *nci = getnetconninfo(nil, fd);

-		if(nci == nil)

-			sysfatal("can't get netconninfo: %r");

-		sendpkt("bsuuususu", MSG_CHANNEL_OPEN,

-			"direct-tcpip", 12,

-			recv.chan,

-			recv.win,

-			recv.pkt,

-			remote, strlen(remote),

-			port,

-			nci->laddr, strlen(nci->laddr),

-			atoi(nci->lserv));

-		free(nci);

-	} else {

-		sendpkt("bsuuu", MSG_CHANNEL_OPEN,

-			"session", 7,

-			recv.chan,

-			recv.win,

-			recv.pkt);

-	}

+	if(!mux){

+		/* open hailing frequencies */

+		if(remote != nil){

+			NetConnInfo *nci = getnetconninfo(nil, fd);

+			if(nci == nil)

+				sysfatal("can't get netconninfo: %r");

+			sendpkt("bsuuususu", MSG_CHANNEL_OPEN,

+				"direct-tcpip", 12,

+				recv.chan,

+				recv.win,

+				recv.pkt,

+				remote, strlen(remote),

+				port,

+				nci->laddr, strlen(nci->laddr),

+				atoi(nci->lserv));

+			free(nci);

+		} else {

+			sendpkt("bsuuu", MSG_CHANNEL_OPEN,

+				"session", 7,

+				recv.chan,

+				recv.win,

+				recv.pkt);

+		}

+Next1:		switch(recvpkt()){

+		default:

+			dispatch();

+			goto Next1;

+		case MSG_CHANNEL_OPEN_FAILURE:

+			if(unpack(recv.r, recv.w-recv.r, "_uus", &c, &b, &s, &n) < 0)

+				n = strlen(s = "???");

+			sysfatal("channel open failure: (%d) %.*s", b, utfnlen(s, n), s);

+		case MSG_CHANNEL_OPEN_CONFIRMATION:

+			break;

+		}

-Next1:	switch(recvpkt()){

-	default:

-		dispatch();

-		goto Next1;

-	case MSG_CHANNEL_OPEN_FAILURE:

-		if(unpack(recv.r, recv.w-recv.r, "_uus", &c, &b, &s, &n) < 0)

-			n = strlen(s = "???");

-		sysfatal("channel open failure: (%d) %.*s", b, utfnlen(s, n), s);

-	case MSG_CHANNEL_OPEN_CONFIRMATION:

-		break;

+		if(unpack(recv.r, recv.w-recv.r, "_uuuu", &recv.chan, &send.chan, &send.win, &send.pkt) < 0)

+			sysfatal("bad channel open confirmation");

+		if(send.pkt <= 0 || send.pkt > MaxPacket)

+			send.pkt = MaxPacket;

 	}

-	if(unpack(recv.r, recv.w-recv.r, "_uuuu", &recv.chan, &send.chan, &send.win, &send.pkt) < 0)

-		sysfatal("bad channel open confirmation");

-	if(send.pkt <= 0 || send.pkt > MaxPacket)

-		send.pkt = MaxPacket;

-

 	notify(catch);

 	atexit(shutdown);

@@ -1337,7 +1352,7 @@

 	/* child reads input and sends packets */

 	qlock(&sl);

-	if(remote == nil){

+	if(remote == nil && !mux){

 		if(raw) {

 			rawon();

 			sendpkt("busbsuuuus", MSG_CHANNEL_REQUEST,

@@ -1400,6 +1415,10 @@

 		}

 		if(n <= 0)

 			break;

+		if(mux){

+			sendpkt("[", buf, n);

+			continue;

+		}

 		send.win -= n;

 		while(send.win < 0)

 			rsleep(&send);

@@ -1407,8 +1426,10 @@

 			send.chan,

 			buf, n);

 	}

-	if(send.eof++ == 0)

+	if(send.eof++ == 0 && !mux)

 		sendpkt("bu", raw ? MSG_CHANNEL_CLOSE : MSG_CHANNEL_EOF, send.chan);

+	else if(recv.pid > 0 && mux)

+		postnote(PNPROC, recv.pid, "shutdown");

 	qunlock(&sl);

 	exits(nil);