less: optionally query terminal size via "ESC [ 6 n". Closes bug 2659.

+7 bytes is not selected, +100 if selected.

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

2 files changed, 117 insertions, 81 deletions

diff --git a/miscutils/Config.src b/miscutils/Config.src
index 61529141d..b9fc196d8 100644
--- a/miscutils/Config.src
+++ b/miscutils/Config.src
@@ -360,72 +360,6 @@ config FEATURE_LAST_FANCY
           logged into the system (mimics sysvinit last). +900 bytes.
 endchoice
 
-config LESS
-        bool "less"
-        default y
-        help
-          'less' is a pager, meaning that it displays text files. It possesses
-          a wide array of features, and is an improvement over 'more'.
-
-config FEATURE_LESS_MAXLINES
-        int "Max number of input lines less will try to eat"
-        default 9999999
-        depends on LESS
-
-config FEATURE_LESS_BRACKETS
-        bool "Enable bracket searching"
-        default y
-        depends on LESS
-        help
-          This option adds the capability to search for matching left and right
-          brackets, facilitating programming.
-
-config FEATURE_LESS_FLAGS
-        bool "Enable extra flags"
-        default y
-        depends on LESS
-        help
-          The extra flags provided do the following:
-
-          The -M flag enables a more sophisticated status line.
-          The -m flag enables a simpler status line with a percentage.
-
-config FEATURE_LESS_MARKS
-        bool "Enable marks"
-        default y
-        depends on LESS
-        help
-          Marks enable positions in a file to be stored for easy reference.
-
-config FEATURE_LESS_REGEXP
-        bool "Enable regular expressions"
-        default y
-        depends on LESS
-        help
-          Enable regular expressions, allowing complex file searches.
-
-config FEATURE_LESS_WINCH
-        bool "Enable automatic resizing on window size changes"
-        default y
-        depends on LESS
-        help
-          Makes less track window size changes.
-
-config FEATURE_LESS_DASHCMD
-        bool "Enable flag changes ('-' command)"
-        default y
-        depends on LESS
-        help
-          This enables the ability to change command-line flags within
-          less itself ('-' keyboard command).
-
-config FEATURE_LESS_LINENUMS
-        bool "Enable dynamic switching of line numbers"
-        default y
-        depends on FEATURE_LESS_DASHCMD
-        help
-          Enables "-N" command.
-
 config HDPARM
         bool "hdparm"
         default y
diff --git a/miscutils/less.c b/miscutils/less.c
index 46024f9f7..16eb95d56 100644
--- a/miscutils/less.c
+++ b/miscutils/less.c
@@ -21,6 +21,85 @@
  *   redirected input has been read from stdin
  */
 
+//config:config LESS
+//config:       bool "less"
+//config:       default y
+//config:       help
+//config:         'less' is a pager, meaning that it displays text files. It possesses
+//config:         a wide array of features, and is an improvement over 'more'.
+//config:
+//config:config FEATURE_LESS_MAXLINES
+//config:       int "Max number of input lines less will try to eat"
+//config:       default 9999999
+//config:       depends on LESS
+//config:
+//config:config FEATURE_LESS_BRACKETS
+//config:       bool "Enable bracket searching"
+//config:       default y
+//config:       depends on LESS
+//config:       help
+//config:         This option adds the capability to search for matching left and right
+//config:         brackets, facilitating programming.
+//config:
+//config:config FEATURE_LESS_FLAGS
+//config:       bool "Enable extra flags"
+//config:       default y
+//config:       depends on LESS
+//config:       help
+//config:         The extra flags provided do the following:
+//config:
+//config:         The -M flag enables a more sophisticated status line.
+//config:         The -m flag enables a simpler status line with a percentage.
+//config:
+//config:config FEATURE_LESS_MARKS
+//config:       bool "Enable marks"
+//config:       default y
+//config:       depends on LESS
+//config:       help
+//config:         Marks enable positions in a file to be stored for easy reference.
+//config:
+//config:config FEATURE_LESS_REGEXP
+//config:       bool "Enable regular expressions"
+//config:       default y
+//config:       depends on LESS
+//config:       help
+//config:         Enable regular expressions, allowing complex file searches.
+//config:
+//config:config FEATURE_LESS_WINCH
+//config:       bool "Enable automatic resizing on window size changes"
+//config:       default y
+//config:       depends on LESS
+//config:       help
+//config:         Makes less track window size changes.
+//config:
+//config:config FEATURE_LESS_ASK_TERMINAL
+//config:       bool "Use 'tell me cursor position' ESC sequence to measure window"
+//config:       default y
+//config:       depends on FEATURE_LESS_WINCH
+//config:       help
+//config:         Makes less track window size changes.
+//config:         If terminal size can't be retrieved and $LINES/$COLUMNS are not set,
+//config:         this option makes less perform a last-ditch effort to find it:
+//config:         position cursor to 999,999 and ask terminal to report real
+//config:         cursor position using "ESC [ 6 n" escape sequence, then read stdin.
+//config:
+//config:         This is not clean but helps a lot on serial lines and such.
+//config:
+//config:config FEATURE_LESS_DASHCMD
+//config:       bool "Enable flag changes ('-' command)"
+//config:       default y
+//config:       depends on LESS
+//config:       help
+//config:         This enables the ability to change command-line flags within
+//config:         less itself ('-' keyboard command).
+//config:
+//config:config FEATURE_LESS_LINENUMS
+//config:       bool "Enable dynamic switching of line numbers"
+//config:       default y
+//config:       depends on FEATURE_LESS_DASHCMD
+//config:       help
+//config:         Enables "-N" command.
+
 //usage:#define less_trivial_usage
 //usage:       "[-EMNmh~I?] [FILE]..."
 //usage:#define less_full_usage "\n\n"
@@ -108,6 +187,9 @@ struct globals {
         regex_t pattern;
         smallint pattern_valid;
 #endif
+#if ENABLE_FEATURE_LESS_ASK_TERMINAL
+        smallint winsize_err;
+#endif
         smallint terminated;
         struct termios term_orig, term_less;
         char kbd_input[KEYCODE_BUFFER_SIZE];
@@ -815,12 +897,17 @@ static void reinitialize(void)
         cur_fline = 0;
         max_lineno = 0;
         open_file_and_read_lines();
+#if ENABLE_FEATURE_LESS_ASK_TERMINAL
+        if (G.winsize_err)
+                printf("\033[999;999H" "\033[6n");
+#endif
         buffer_fill_and_print();
 }
 
-static int getch_nowait(void)
+static int64_t getch_nowait(void)
 {
         int rd;
+        int64_t key64;
         struct pollfd pfd[2];
 
         pfd[0].fd = STDIN_FILENO;
@@ -868,8 +955,8 @@ static int getch_nowait(void)
 
         /* We have kbd_fd in O_NONBLOCK mode, read inside read_key()
          * would not block even if there is no input available */
-        rd = read_key(kbd_fd, kbd_input, /*timeout off:*/ -2);
-        if (rd == -1) {
+        key64 = read_key(kbd_fd, kbd_input, /*timeout off:*/ -2);
+        if ((int)key64 == -1) {
                 if (errno == EAGAIN) {
                         /* No keyboard input available. Since poll() did return,
                          * we should have input on stdin */
@@ -881,25 +968,29 @@ static int getch_nowait(void)
                 less_exit(0);
         }
         set_tty_cooked();
-        return rd;
+        return key64;
 }
 
 /* Grab a character from input without requiring the return key.
  * May return KEYCODE_xxx values.
  * Note that this function works best with raw input. */
-static int less_getch(int pos)
+static int64_t less_getch(int pos)
 {
-        int i;
+        int64_t key64;
+        int key;
 
  again:
         less_gets_pos = pos;
-        i = getch_nowait();
+        key = key64 = getch_nowait();
         less_gets_pos = -1;
 
-        /* Discard Ctrl-something chars */
-        if (i >= 0 && i < ' ' && i != 0x0d && i != 8)
+        /* Discard Ctrl-something chars.
+         * (checking only lower 32 bits is a size optimization:
+         * upper 32 bits are used only by KEYCODE_CURSOR_POS)
+         */
+        if (key >= 0 && key < ' ' && key != 0x0d && key != 8)
                 goto again;
-        return i;
+        return key;
 }
 
 static char* less_gets(int sz)
@@ -1514,8 +1605,6 @@ static void sigwinch_handler(int sig UNUSED_PARAM)
 int less_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int less_main(int argc, char **argv)
 {
-        int keypress;
-
         INIT_G();
 
         /* TODO: -x: do not interpret backspace, -xx: tab also */
@@ -1558,7 +1647,7 @@ int less_main(int argc, char **argv)
         term_less.c_cc[VMIN] = 1;
         term_less.c_cc[VTIME] = 0;
 
-        get_terminal_width_height(kbd_fd, &width, &max_displayed_line);
+        IF_FEATURE_LESS_ASK_TERMINAL(G.winsize_err =) get_terminal_width_height(kbd_fd, &width, &max_displayed_line);
         /* 20: two tabstops + 4 */
         if (width < 20 || max_displayed_line < 3)
                 return bb_cat(argv);
@@ -1573,11 +1662,14 @@ int less_main(int argc, char **argv)
         buffer = xmalloc((max_displayed_line+1) * sizeof(char *));
         reinitialize();
         while (1) {
+                int64_t keypress;
+
 #if ENABLE_FEATURE_LESS_WINCH
                 while (WINCH_COUNTER) {
  again:
                         winch_counter--;
-                        get_terminal_width_height(kbd_fd, &width, &max_displayed_line);
+                        IF_FEATURE_LESS_ASK_TERMINAL(G.winsize_err =) get_terminal_width_height(kbd_fd, &width, &max_displayed_line);
+ IF_FEATURE_LESS_ASK_TERMINAL(got_size:)
                         /* 20: two tabstops + 4 */
                         if (width < 20)
                                 width = 20;
@@ -1597,8 +1689,18 @@ int less_main(int argc, char **argv)
                         /* This took some time. Loop back and check,
                          * were there another SIGWINCH? */
                 }
-#endif
                 keypress = less_getch(-1); /* -1: do not position cursor */
+# if ENABLE_FEATURE_LESS_ASK_TERMINAL
+                if ((int32_t)keypress == KEYCODE_CURSOR_POS) {
+                        uint32_t rc = (keypress >> 32);
+                        width = (rc & 0x7fff);
+                        max_displayed_line = ((rc >> 16) & 0x7fff);
+                        goto got_size;
+                }
+# endif
+#else
+                keypress = less_getch(-1); /* -1: do not position cursor */
+#endif
                 keypress_process(keypress);
         }
 }