Try to guess if the window is UTF-8 by outputting a three-byte UTF-8 wide character and seeing how much the cursor moves. Currently tries to figure out if this works by some stupid checks on the terminal, these need to be rethought. Also might be better using a width 1 character rather than width 2.

CHANGES

@@ -1,5 +1,9 @@
 19 May 2009
 
+* Try to guess if the window is UTF-8 by outputting a three-byte UTF-8 wide
+  character and seeing how much the cursor moves. Currently tries to figure out
+  if this works by some stupid checks on the terminal, these need to be
+  rethought. Also might be better using a width 1 character rather than width 2.
 * If LANG contains "UTF-8", assume the terminal supports UTF-8, on the grounds
   that anyone who configures it probably wants UTF-8. Not certain if this is
   a perfect idea but let's see if it causes any problems.
@@ -1278,7 +1282,7 @@
   (including mutt, emacs). No status bar yet and no key remapping or other
   customisation.
 
-$Id: CHANGES,v 1.294 2009-05-19 16:03:18 nicm Exp $
+$Id: CHANGES,v 1.295 2009-05-19 16:08:35 nicm Exp $
 
  LocalWords:  showw utf UTF fulvio ciriaco joshe OSC APC gettime abc DEF OA clr
  LocalWords:  rivo nurges lscm Erdely eol smysession mysession ek dstname RB ms

cmd-list-clients.c

@@ -1,4 +1,4 @@
-/* $Id: cmd-list-clients.c,v 1.13 2009-02-11 17:50:32 nicm Exp $ */
+/* $Id: cmd-list-clients.c,v 1.14 2009-05-19 16:08:35 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -47,14 +47,20 @@ cmd_list_clients_exec(unused struct cmd *self, struct cmd_ctx *ctx)
 {
 	struct client	*c;
 	u_int		 i;
+	const char	*s_utf8;
 
 	for (i = 0; i < ARRAY_LENGTH(&clients); i++) {
 		c = ARRAY_ITEM(&clients, i);
 		if (c == NULL || c->session == NULL)
 			continue;
 
-		ctx->print(ctx, "%s: %s [%ux%u %s]", c->tty.path,
+		if (c->tty.flags & TTY_UTF8)
-		    c->session->name, c->tty.sx, c->tty.sy, c->tty.termname);
+			s_utf8 = " (utf8)";
+		else
+			s_utf8 = "";
+		ctx->print(ctx, "%s: %s [%ux%u %s]%s", c->tty.path,
+			c->session->name, c->tty.sx, c->tty.sy, 
+			c->tty.termname, s_utf8);
 	}
 
 	return (0);

tmux.h

@@ -1,4 +1,4 @@
-/* $Id: tmux.h,v 1.324 2009-05-19 13:32:55 tcunha Exp $ */
+/* $Id: tmux.h,v 1.325 2009-05-19 16:08:35 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -1117,6 +1117,7 @@ void		 tty_putc(struct tty *, u_char);
 void		 tty_init(struct tty *, char *, char *);
 void		 tty_start_tty(struct tty *);
 void		 tty_stop_tty(struct tty *);
+void		 tty_detect_utf8(struct tty *);
 void		 tty_set_title(struct tty *, const char *);
 void		 tty_update_mode(struct tty *, int);
 void		 tty_draw_line(

tty.c

@@ -1,4 +1,4 @@
-/* $Id: tty.c,v 1.98 2009-05-14 16:21:55 nicm Exp $ */
+/* $Id: tty.c,v 1.99 2009-05-19 16:08:35 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -136,6 +136,8 @@ tty_start_tty(struct tty *tty)
 	int		 what;
 #endif
 
+	tty_detect_utf8(tty);
+
 	if (tcgetattr(tty->fd, &tty->tio) != 0)
 		fatal("tcgetattr failed");
 	memcpy(&tio, &tty->tio, sizeof tio);
@@ -197,15 +199,96 @@ tty_stop_tty(struct tty *tty)
 	tty_raw(tty, tty_term_string2(tty->term, TTYC_CSR, 0, ws.ws_row - 1));
 	tty_raw(tty, tty_term_string(tty->term, TTYC_RMACS));
 	tty_raw(tty, tty_term_string(tty->term, TTYC_SGR0));
-	tty_raw(tty, tty_term_string(tty->term, TTYC_CLEAR));
 	tty_raw(tty, tty_term_string(tty->term, TTYC_RMKX));
 	tty_raw(tty, tty_term_string(tty->term, TTYC_RMCUP));
-
+	tty_raw(tty, tty_term_string(tty->term, TTYC_CLEAR));
+	
 	tty_raw(tty, tty_term_string(tty->term, TTYC_CNORM));
 	if (tty_term_has(tty->term, TTYC_KMOUS))
 		tty_raw(tty, "\033[?1000l");
 }
 
+void
+tty_detect_utf8(struct tty *tty)
+{
+	struct pollfd	pfd;
+	char	      	buf[7];
+	size_t		len;
+	ssize_t		n;
+	int		nfds;
+	struct termios	tio, old_tio;
+#ifdef TIOCFLUSH
+	int		 what;
+#endif
+
+	if (tty->flags & TTY_UTF8)
+		return;
+
+	/*
+	 * If the terminal looks reasonably likely to support this, try to
+	 * write a three-byte UTF-8 wide character to the terminal, then read
+	 * the cursor position.
+	 *
+	 * XXX This entire function is a hack.
+	 */
+
+	/* Check if the terminal looks sort of vt100. */
+	if (strstr(tty_term_string(tty->term, TTYC_CLEAR), "[2J") == NULL ||
+	    strstr(tty_term_string(tty->term, TTYC_CUP), "H") == NULL)
+		return;
+
+	if (tcgetattr(tty->fd, &old_tio) != 0)
+		fatal("tcgetattr failed");
+	cfmakeraw(&tio);
+	if (tcsetattr(tty->fd, TCSANOW, &tio) != 0)
+		fatal("tcsetattr failed");
+
+#ifdef TIOCFLUSH
+	what = 0;
+	if (ioctl(tty->fd, TIOCFLUSH, &what) != 0)
+		fatal("ioctl(TIOCFLUSH)");
+#endif
+
+#define UTF8_TEST_DATA "\033[H\357\277\246\033[6n"
+	if (write(tty->fd, UTF8_TEST_DATA, (sizeof UTF8_TEST_DATA) - 1) == -1)
+		fatal("write failed");
+#undef UTF8_TEST_DATA
+
+	len = 0;
+	for (;;) {
+		pfd.fd = tty->fd;
+		pfd.events = POLLIN;
+
+		nfds = poll(&pfd, 1, 500);
+		if (nfds == -1) {
+			if (errno == EAGAIN || errno == EINTR)
+				continue;
+			fatal("poll failed");
+		}
+		if (nfds == 0)
+			break;
+#ifdef HAVE_POLL
+		if (pfd.revents & (POLLERR|POLLNVAL|POLLHUP))
+			break;
+#endif
+		if (!(pfd.revents & POLLIN))
+			continue;
+
+		if ((n = read(tty->fd, buf + len, 1)) != 1)
+			break;
+		buf[++len] = '\0';
+
+		if (len == (sizeof buf) - 1) {
+			if (strcmp(buf, "\033[1;3R") == 0)
+				tty->flags |= TTY_UTF8;
+			break;
+		}
+	}
+
+	if (tcsetattr(tty->fd, TCSANOW, &old_tio) != 0)
+		fatal("tcsetattr failed");
+}
+
 void
 tty_fill_acs(struct tty *tty)
 {