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 e4fdd0f38..5f9566f0a 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 f925984ba..d3a35e781 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 8422976c9..64557ab14 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 aec165f06..d93dd2af9 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)