2 files changed, 34 insertions, 1 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);