diff --git a/ChangeLog b/ChangeLog
index 451f1b323..3c522ea36 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,6 +3,10 @@
    - stevesk@cvs.openbsd.org 2005/12/28 22:46:06
      [canohost.c channels.c clientloop.c]
      use 'break-in' for consistency; ok deraadt@ ok and input jmc@
+   - reyk@cvs.openbsd.org 2005/12/30 15:56:37
+     [channels.c channels.h clientloop.c]
+     add channel output filter interface.
+     ok djm@, suggested by markus@
 
 20051229
  - (tim) [buildpkg.sh.in] grep for $SSHDUID instead of $SSHDGID on /etc/passwd
@@ -3558,4 +3562,4 @@
    - (djm) Trim deprecated options from INSTALL. Mention UsePAM
    - (djm) Fix quote handling in sftp; Patch from admorten AT umich.edu
 
-$Id: ChangeLog,v 1.4053 2005/12/31 05:19:53 djm Exp $
+$Id: ChangeLog,v 1.4054 2005/12/31 05:22:32 djm Exp $
diff --git a/channels.c b/channels.c
index b431532a3..ed5903f6f 100644
--- a/channels.c
+++ b/channels.c
@@ -39,7 +39,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: channels.c,v 1.230 2005/12/28 22:46:06 stevesk Exp $");
+RCSID("$OpenBSD: channels.c,v 1.231 2005/12/30 15:56:36 reyk Exp $");
 
 #include "ssh.h"
 #include "ssh1.h"
@@ -58,8 +58,6 @@ RCSID("$OpenBSD: channels.c,v 1.230 2005/12/28 22:46:06 stevesk Exp $");
 
 /* -- channel core */
 
-#define CHAN_RBUF	16*1024
-
 /*
  * Pointer to an array containing all allocated channels.  The array is
  * dynamically extended as needed.
@@ -301,6 +299,7 @@ channel_new(char *ctype, int type, int rfd, int wfd, int efd,
 	c->confirm = NULL;
 	c->confirm_ctx = NULL;
 	c->input_filter = NULL;
+	c->output_filter = NULL;
 	debug("channel %d: new [%s]", found, remote_name);
 	return c;
 }
@@ -681,7 +680,8 @@ channel_cancel_cleanup(int id)
 	c->detach_close = 0;
 }
 void
-channel_register_filter(int id, channel_filter_fn *fn)
+channel_register_filter(int id, channel_infilter_fn *ifn,
+    channel_outfilter_fn *ofn)
 {
 	Channel *c = channel_lookup(id);
 
@@ -689,7 +689,8 @@ channel_register_filter(int id, channel_filter_fn *fn)
 		logit("channel_register_filter: %d: bad id", id);
 		return;
 	}
-	c->input_filter = fn;
+	c->input_filter = ifn;
+	c->output_filter = ofn;
 }
 
 void
@@ -1454,7 +1455,7 @@ static int
 channel_handle_wfd(Channel *c, fd_set * readset, fd_set * writeset)
 {
 	struct termios tio;
-	u_char *data;
+	u_char *data = NULL, *buf;
 	u_int dlen;
 	int len;
 
@@ -1462,11 +1463,22 @@ channel_handle_wfd(Channel *c, fd_set * readset, fd_set * writeset)
 	if (c->wfd != -1 &&
 	    FD_ISSET(c->wfd, writeset) &&
 	    buffer_len(&c->output) > 0) {
+		if (c->output_filter != NULL) {
+			if ((buf = c->output_filter(c, &data, &dlen)) == NULL) {
+				debug2("channel %d: filter stops", c->self);
+				chan_read_failed(c);
+			}
+		} else if (c->datagram) {
+			buf = data = buffer_get_string(&c->output, &dlen);
+		} else {
+			buf = data = buffer_ptr(&c->output);
+			dlen = buffer_len(&c->output);
+		}
+
 		if (c->datagram) {
-			data = buffer_get_string(&c->output, &dlen);
 			/* ignore truncated writes, datagrams might get lost */
 			c->local_consumed += dlen + 4;
-			len = write(c->wfd, data, dlen);
+			len = write(c->wfd, buf, dlen);
 			xfree(data);
 			if (len < 0 && (errno == EINTR || errno == EAGAIN))
 				return 1;
@@ -1486,7 +1498,8 @@ channel_handle_wfd(Channel *c, fd_set * readset, fd_set * writeset)
 		if (compat20 && c->wfd_isatty)
 			dlen = MIN(dlen, 8*1024);
 #endif
-		len = write(c->wfd, data, dlen);
+
+		len = write(c->wfd, buf, dlen);
 		if (len < 0 && (errno == EINTR || errno == EAGAIN))
 			return 1;
 		if (len <= 0) {
@@ -1503,14 +1516,14 @@ channel_handle_wfd(Channel *c, fd_set * readset, fd_set * writeset)
 			}
 			return -1;
 		}
-		if (compat20 && c->isatty && dlen >= 1 && data[0] != '\r') {
+		if (compat20 && c->isatty && dlen >= 1 && buf[0] != '\r') {
 			if (tcgetattr(c->wfd, &tio) == 0 &&
 			    !(tio.c_lflag & ECHO) && (tio.c_lflag & ICANON)) {
 				/*
 				 * Simulate echo to reduce the impact of
 				 * traffic analysis. We need to match the
 				 * size of a SSH2_MSG_CHANNEL_DATA message
-				 * (4 byte channel id + data)
+				 * (4 byte channel id + buf)
 				 */
 				packet_send_ignore(4 + len);
 				packet_send();
diff --git a/channels.h b/channels.h
index 7990fe147..a97dd9007 100644
--- a/channels.h
+++ b/channels.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: channels.h,v 1.82 2005/12/12 13:46:18 markus Exp $	*/
+/*	$OpenBSD: channels.h,v 1.83 2005/12/30 15:56:37 reyk Exp $	*/
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -63,7 +63,8 @@ struct Channel;
 typedef struct Channel Channel;
 
 typedef void channel_callback_fn(int, void *);
-typedef int channel_filter_fn(struct Channel *, char *, int);
+typedef int channel_infilter_fn(struct Channel *, char *, int);
+typedef u_char *channel_outfilter_fn(struct Channel *, u_char **, u_int *);
 
 struct Channel {
 	int     type;		/* channel type/state */
@@ -111,7 +112,8 @@ struct Channel {
 	int			detach_close;
 
 	/* filter */
-	channel_filter_fn	*input_filter;
+	channel_infilter_fn	*input_filter;
+	channel_outfilter_fn	*output_filter;
 
 	int     datagram;	/* keep boundaries */
 };
@@ -145,6 +147,8 @@ struct Channel {
 #define CHAN_EOF_SENT			0x04
 #define CHAN_EOF_RCVD			0x08
 
+#define CHAN_RBUF	16*1024
+
 /* check whether 'efd' is still in use */
 #define CHANNEL_EFD_INPUT_ACTIVE(c) \
 	(compat20 && c->extended_usage == CHAN_EXTENDED_READ && \
@@ -169,7 +173,7 @@ void	 channel_send_open(int);
 void	 channel_request_start(int, char *, int);
 void	 channel_register_cleanup(int, channel_callback_fn *, int);
 void	 channel_register_confirm(int, channel_callback_fn *, void *);
-void	 channel_register_filter(int, channel_filter_fn *);
+void	 channel_register_filter(int, channel_infilter_fn *, channel_outfilter_fn *);
 void	 channel_cancel_cleanup(int);
 int	 channel_close_fd(int *);
 void	 channel_send_window_changes(void);
diff --git a/clientloop.c b/clientloop.c
index a71552cad..b76f7cfe0 100644
--- a/clientloop.c
+++ b/clientloop.c
@@ -59,7 +59,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: clientloop.c,v 1.148 2005/12/28 22:46:06 stevesk Exp $");
+RCSID("$OpenBSD: clientloop.c,v 1.149 2005/12/30 15:56:37 reyk Exp $");
 
 #include "ssh.h"
 #include "ssh1.h"
@@ -1386,7 +1386,7 @@ client_loop(int have_pty, int escape_char_arg, int ssh2_chan_id)
 		session_ident = ssh2_chan_id;
 		if (escape_char != SSH_ESCAPECHAR_NONE)
 			channel_register_filter(session_ident,
-			    simple_escape_filter);
+			    simple_escape_filter, NULL);
 		if (session_ident != -1)
 			channel_register_cleanup(session_ident,
 			    client_channel_closed, 0);