vi: discover window size even on serial consoles. optional

function                                             old     new   delta
edit_file                                            671     761     +90
wh_helper                                              -      57     +57
query_screen_dimensions                               54      63      +9
ar_main                                              533     542      +9
refresh                                              767     773      +6
vi_main                                              242     243      +1
text_yank                                             56      54      -2
get_terminal_width_height                            180     135     -45
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 5/2 up/down: 172/-47)           Total: 125 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

4 files changed, 65 insertions, 26 deletions

diff --git a/editors/Config.in b/editors/Config.in
index e4fdd0f..5f9566f 100644
--- a/editors/Config.in
+++ b/editors/Config.in
@@ -168,6 +168,18 @@ config FEATURE_VI_WIN_RESIZE
 	help
 	  Make busybox vi behave nicely with terminals that get resized.
 
+config FEATURE_VI_ASK_TERMINAL
+	bool "Use 'tell me cursor position' ESC sequence to measure window"
+	default n
+	depends on VI
+	help
+	  If terminal size can't be retrieved and $LINES/$COLUMNS are not set,
+	  this option makes vi perform a last-ditch effort to find it:
+	  vi positions cursor to 999,999 and asks terminal to report real
+	  cursor position using "ESC [ 6 n" escape sequence, then reads stdin.
+
+	  This is not clean but helps a lot on serial lines and such.
+
 config FEATURE_VI_OPTIMIZE_CURSOR
 	bool "Optimize cursor movement"
 	default y
diff --git a/editors/vi.c b/editors/vi.c
index f925984..d3a35e7 100644
--- a/editors/vi.c
+++ b/editors/vi.c
@@ -138,6 +138,9 @@ struct globals {
 	int save_argc;           // how many file names on cmd line
 	int cmdcnt;              // repetition count
 	unsigned rows, columns;	 // the terminal screen is this size
+#if ENABLE_FEATURE_VI_ASK_TERMINAL
+	int get_rowcol_error;
+#endif
 	int crow, ccol;          // cursor is on Crow x Ccol
 	int offset;              // chars scrolled off the screen to the left
 	int have_status_msg;     // is default edit status needed?
@@ -503,7 +506,11 @@ static int init_text_buffer(char *fn)
 #if ENABLE_FEATURE_VI_WIN_RESIZE
 static void query_screen_dimensions(void)
 {
-	get_terminal_width_height(STDIN_FILENO, &columns, &rows);
+# if ENABLE_FEATURE_VI_ASK_TERMINAL
+	if (!G.get_rowcol_error)
+		G.get_rowcol_error =
+# endif
+			get_terminal_width_height(STDIN_FILENO, &columns, &rows);
 	if (rows > MAX_SCR_ROWS)
 		rows = MAX_SCR_ROWS;
 	if (columns > MAX_SCR_COLS)
@@ -530,6 +537,20 @@ static void edit_file(char *fn)
 	columns = 80;
 	size = 0;
 	query_screen_dimensions();
+#if ENABLE_FEATURE_VI_ASK_TERMINAL
+	if (G.get_rowcol_error /* TODO? && no input on stdin */) {
+		uint64_t k;
+		write1("\033[999;999H" "\033[6n");
+		fflush_all();
+		k = read_key(STDIN_FILENO, readbuffer, /*timeout_ms:*/ 100);
+		if ((int32_t)k == KEYCODE_CURSOR_POS) {
+			uint32_t rc = (k >> 32);
+			columns = (rc & 0x7fff);
+			rows = ((rc >> 16) & 0x7fff);
+		}
+		query_screen_dimensions();
+	}
+#endif
 	new_screen(rows, columns);	// get memory for virtual screen
 	init_text_buffer(fn);
 
diff --git a/libbb/read_key.c b/libbb/read_key.c
index 8422976..64557ab 100644
--- a/libbb/read_key.c
+++ b/libbb/read_key.c
@@ -214,7 +214,7 @@ int64_t FAST_FUNC read_key(int fd, char *buffer, int timeout)
 		}
 		n++;
 		/* Try to decipher "ESC [ NNN ; NNN R" sequence */
-		if (ENABLE_FEATURE_EDITING_ASK_TERMINAL
+		if ((ENABLE_FEATURE_EDITING_ASK_TERMINAL || ENABLE_FEATURE_VI_ASK_TERMINAL)
 		 && n >= 5
 		 && buffer[0] == '['
 		 && buffer[n-1] == 'R'
diff --git a/libbb/xfuncs.c b/libbb/xfuncs.c
index aec165f..d93dd2a 100644
--- a/libbb/xfuncs.c
+++ b/libbb/xfuncs.c
@@ -210,34 +210,40 @@ char* FAST_FUNC xmalloc_ttyname(int fd)
 	return buf;
 }
 
-/* It is perfectly ok to pass in a NULL for either width or for
- * height, in which case that value will not be set.  */
-int FAST_FUNC get_terminal_width_height(int fd, unsigned *width, unsigned *height)
+static int wh_helper(int value, int def_val, const char *env_name, int *err)
 {
-	struct winsize win = { 0, 0, 0, 0 };
-	int ret = ioctl(fd, TIOCGWINSZ, &win);
-
-	if (height) {
-		if (!win.ws_row) {
-			char *s = getenv("LINES");
-			if (s) win.ws_row = atoi(s);
-		}
-		if (win.ws_row <= 1 || win.ws_row >= 30000)
-			win.ws_row = 24;
-		*height = (int) win.ws_row;
-	}
-
-	if (width) {
-		if (!win.ws_col) {
-			char *s = getenv("COLUMNS");
-			if (s) win.ws_col = atoi(s);
+	if (value == 0) {
+		char *s = getenv(env_name);
+		if (s) {
+			value = atoi(s);
+			/* If LINES/COLUMNS are set, pretent that there is
+			 * no error getting w/h, this prevents some ugly
+			 * cursor tricks by our callers */
+			*err = 0;
 		}
-		if (win.ws_col <= 1 || win.ws_col >= 30000)
-			win.ws_col = 80;
-		*width = (int) win.ws_col;
 	}
+	if (value <= 1 || value >= 30000)
+		value = def_val;
+	return value;
+}
 
-	return ret;
+/* It is perfectly ok to pass in a NULL for either width or for
+ * height, in which case that value will not be set.  */
+int FAST_FUNC get_terminal_width_height(int fd, unsigned *width, unsigned *height)
+{
+	struct winsize win;
+	int err;
+
+	win.ws_row = 0;
+	win.ws_col = 0;
+	/* I've seen ioctl returning 0, but row/col is (still?) 0.
+	 * We treat that as an error too.  */
+	err = ioctl(fd, TIOCGWINSZ, &win) != 0 || win.ws_row == 0;
+	if (height)
+		*height = wh_helper(win.ws_row, 24, "LINES", &err);
+	if (width)
+		*width = wh_helper(win.ws_col, 80, "COLUMNS", &err);
+	return err;
 }
 
 int FAST_FUNC tcsetattr_stdin_TCSANOW(const struct termios *tp)