3 files changed, 94 insertions, 17 deletions

diff --git a/libbb/Config.in b/libbb/Config.in
index f5b804ff8..7ced387a9 100644
--- a/libbb/Config.in
+++ b/libbb/Config.in
@@ -102,6 +102,18 @@ config FEATURE_EDITING_FANCY_PROMPT
           Setting this option allows for prompts to use things like \w and
           \$ and escape codes.
 
+config FEATURE_EDITING_ASK_TERMINAL
+        bool "Query cursor position from terminal"
+        default n
+        depends on FEATURE_EDITING
+        help
+          Allow usage of "ESC [ 6 n" sequence. Terminal answers back with
+          current cursor position. This information is used to make line
+          editing more robust in some cases.
+          If you are not sure whether your terminals respond to this code
+          correctly, or want to save on code size (about 300 bytes),
+          then do not turn this option on.
+
 config FEATURE_VERBOSE_CP_MESSAGE
         bool "Give more precise messages when copy fails (cp, mv etc)"
         default n
diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index ccf3e0dc8..e1404fb68 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -86,8 +86,8 @@ struct lineedit_statics {
         volatile unsigned cmdedit_termw; /* = 80; */ /* actual terminal width */
         sighandler_t previous_SIGWINCH_handler;
 
-        unsigned cmdedit_x;        /* real x terminal position */
-        unsigned cmdedit_y;        /* pseudoreal y terminal position */
+        unsigned cmdedit_x;        /* real x (col) terminal position */
+        unsigned cmdedit_y;        /* pseudoreal y (row) terminal position */
         unsigned cmdedit_prmt_len; /* length of prompt (without colors etc) */
 
         unsigned cursor;
@@ -299,6 +299,16 @@ static void input_backward(unsigned num)
 
 static void put_prompt(void)
 {
+#if ENABLE_FEATURE_EDITING_ASK_TERMINAL
+        /* Ask terminal where is cursor now.
+         * lineedit_read_key handles response and corrects
+         * our idea of current cursor position.
+         * Testcase: run "echo -n long_line_long_line_long_line",
+         * then type in a long, wrapping command and try to
+         * delete it using backspace key.
+         */
+        out1str("\033" "[6n");
+#endif
         out1str(cmdedit_prompt);
         cursor = 0;
         {
@@ -1430,18 +1440,33 @@ static void win_changed(int nsig)
                 signal(SIGWINCH, win_changed); /* rearm ourself */
 }
 
-static int lineedit_read_key(smalluint *read_key_bufsize, char *read_key_buffer)
+static int lineedit_read_key(char *read_key_buffer)
 {
-        int ic;
+        int64_t ic;
         struct pollfd pfd;
+
         pfd.fd = STDIN_FILENO;
         pfd.events = POLLIN;
         do {
+ poll_again:
                 /* Wait for input. Can't just call read_key, it will return
                  * at once if stdin is in non-blocking mode. */
                 safe_poll(&pfd, 1, -1);
                 /* note: read_key sets errno to 0 on success: */
-                ic = read_key(STDIN_FILENO, read_key_bufsize, read_key_buffer);
+                ic = read_key(STDIN_FILENO, read_key_buffer);
+                if (ENABLE_FEATURE_EDITING_ASK_TERMINAL
+                 && (int32_t)ic == KEYCODE_CURSOR_POS
+                ) {
+                        int col = ((ic >> 32) & 0x7fff) - 1;
+                        if (col > 0) {
+                                cmdedit_x += col;
+                                while (cmdedit_x >= cmdedit_termw) {
+                                        cmdedit_x -= cmdedit_termw;
+                                        cmdedit_y++;
+                                }
+                        }
+                        goto poll_again;
+                }
         } while (errno == EAGAIN);
         return ic;
 }
@@ -1482,7 +1507,6 @@ int FAST_FUNC read_line_input(const char *prompt, char *command, int maxsize, li
 #endif
         struct termios initial_settings;
         struct termios new_settings;
-        smalluint read_key_bufsize;
         char read_key_buffer[KEYCODE_BUFFER_SIZE];
 
         INIT_S();
@@ -1561,7 +1585,7 @@ int FAST_FUNC read_line_input(const char *prompt, char *command, int maxsize, li
 
         while (1) {
                 fflush(NULL);
-                ic = lineedit_read_key(&read_key_bufsize, read_key_buffer);
+                ic = lineedit_read_key(read_key_buffer);
 
 #if ENABLE_FEATURE_EDITING_VI
                 newdelflag = 1;
@@ -1738,7 +1762,7 @@ int FAST_FUNC read_line_input(const char *prompt, char *command, int maxsize, li
                         sc = cursor;
                         prev_ic = ic;
 
-                        ic = lineedit_read_key(&read_key_bufsize, read_key_buffer);
+                        ic = lineedit_read_key(read_key_buffer);
                         if (errno) /* error */
                                 goto prepare_to_die;
 
@@ -1801,7 +1825,7 @@ int FAST_FUNC read_line_input(const char *prompt, char *command, int maxsize, li
                         put();
                         break;
                 case 'r'|VI_CMDMODE_BIT:
-                        ic = lineedit_read_key(&read_key_bufsize, read_key_buffer);
+                        ic = lineedit_read_key(read_key_buffer);
                         if (errno) /* error */
                                 goto prepare_to_die;
                         if (ic < ' ' || ic > 255) {
diff --git a/libbb/read_key.c b/libbb/read_key.c
index fd100b0ec..3771045d2 100644
--- a/libbb/read_key.c
+++ b/libbb/read_key.c
@@ -9,7 +9,7 @@
  */
 #include "libbb.h"
 
-int FAST_FUNC read_key(int fd, smalluint *nbuffered, char *buffer)
+int64_t FAST_FUNC read_key(int fd, char *buffer)
 {
         struct pollfd pfd;
         const char *seq;
@@ -67,9 +67,7 @@ int FAST_FUNC read_key(int fd, smalluint *nbuffered, char *buffer)
         };
 
         errno = 0;
-        n = 0;
-        if (nbuffered)
-                n = *nbuffered;
+        n = (unsigned char) *buffer++;
         if (n == 0) {
                 /* If no data, block waiting for input. If we read more
                  * than the minimal ESC sequence size, the "n=0" below
@@ -148,11 +146,54 @@ int FAST_FUNC read_key(int fd, smalluint *nbuffered, char *buffer)
                 }
         }
         /* We did not find matching sequence, it was a bare ESC.
-         * We possibly read and stored more input in buffer[]
-         * by now. */
+         * We possibly read and stored more input in buffer[] by now. */
+
+        /* Try to decipher "ESC [ NNN ; NNN R" sequence */
+        if (ENABLE_FEATURE_EDITING_ASK_TERMINAL
+         && n != 0
+         && buffer[0] == '['
+        ) {
+                char *end;
+                unsigned long row, col;
+
+                while (n < KEYCODE_BUFFER_SIZE-1) { /* 1 for cnt */
+                        if (safe_poll(&pfd, 1, 50) == 0) {
+                                /* No more data! */
+                                break;
+                        }
+                        errno = 0;
+                        if (safe_read(fd, buffer + n, 1) <= 0) {
+                                /* If EAGAIN, then fd is O_NONBLOCK and poll lied:
+                                 * in fact, there is no data. */
+                                if (errno != EAGAIN)
+                                        c = -1; /* otherwise it's EOF/error */
+                                goto ret;
+                        }
+                        if (buffer[n++] == 'R')
+                                goto got_R;
+                }
+                goto ret;
+ got_R:
+                if (!isdigit(buffer[1]))
+                        goto ret;
+                row = strtoul(buffer + 1, &end, 10);
+                if (*end != ';' || !isdigit(end[1]))
+                        goto ret;
+                col = strtoul(end + 1, &end, 10);
+                if (*end != 'R')
+                        goto ret;
+                if (row < 1 || col < 1 || (row | col) > 0x7fff)
+                        goto ret;
+
+                buffer[-1] = 0;
+
+                /* Pack into "1 <row15bits> <col16bits>" 32-bit sequence */
+                c = (((-1 << 15) | row) << 16) | col;
+                /* Return it in high-order word */
+                return ((int64_t) c << 32) | (uint32_t)KEYCODE_CURSOR_POS;
+        }
 
  ret:
-        if (nbuffered)
-                *nbuffered = n;
+        buffer[-1] = n;
         return c;
 }