read_key,lineeedit: parse position answerback faster; sanitize its use

it's still not reliable, and probably cannot be made so...
added comment with explanation.

function                                             old     new   delta
put_prompt                                            52     110     +58
read_key                                             601     607      +6
lineedit_read_key                                    201     207      +6
win_changed                                          108     104      -4
read_line_input                                     4824    4809     -15
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/2 up/down: 70/-19)             Total: 51 bytes

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

diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index bfd0e3346131b9e5ffa79233f80fc7eeb985cd65..2e1bc5d2ef0a133d9f8a8a48a18b44faf58661e1 100644 (file)
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -370,6 +370,7 @@ static void input_backward(unsigned num)
 static void put_prompt(void)
 {
        out1str(cmdedit_prompt);
+       fflush(NULL);
        if (ENABLE_FEATURE_EDITING_ASK_TERMINAL) {
                /* Ask terminal where is the cursor now.
                 * lineedit_read_key handles response and corrects
@@ -380,7 +381,33 @@ static void put_prompt(void)
                 * Note: we print it _after_ prompt, because
                 * prompt may contain CR. Example: PS1='\[\r\n\]\w '
                 */
-               out1str("\033" "[6n");
+               /* Problem: if there is buffered input on stdin,
+                * the response will be delivered later,
+                * possibly to an unsuspecting application.
+                * Testcase: "sleep 1; busybox ash" + press and hold [Enter].
+                * Result:
+                * ~/srcdevel/bbox/fix/busybox.t4 #
+                * ~/srcdevel/bbox/fix/busybox.t4 #
+                * ^[[59;34~/srcdevel/bbox/fix/busybox.t4 #  <-- garbage
+                * ~/srcdevel/bbox/fix/busybox.t4 #
+                *
+                * Checking for input with poll only makes the race narrower,
+                * I still can trigger it. Strace:
+                *
+                * write(1, "~/srcdevel/bbox/fix/busybox.t4 # ", 33) = 33
+                * poll([{fd=0, events=POLLIN}], 1, 0) = 0 (Timeout)  <-- no input exists
+                * write(1, "\33[6n", 4) = 4  <-- send the ESC sequence, quick!
+                * poll([{fd=0, events=POLLIN}], 1, 4294967295) = 1 ([{fd=0, revents=POLLIN}])
+                * read(0, "\n", 1)      = 1  <-- oh crap, user's input got in first
+                */
+               struct pollfd pfd;
+
+               pfd.fd = STDIN_FILENO;
+               pfd.events = POLLIN;
+               if (safe_poll(&pfd, 1, 0) == 0) {
+                       out1str("\033" "[6n");
+                       fflush(NULL); /* make terminal see it ASAP! */
+               }
        }
        cursor = 0;
        {
@@ -1603,7 +1630,7 @@ static void cmdedit_setwidth(unsigned w, int redraw_flg)
                int new_y = (cursor + cmdedit_prmt_len) / w;
                /* redraw */
                redraw((new_y >= cmdedit_y ? new_y : cmdedit_y), command_len - cursor);
-               fflush(stdout);
+               fflush(NULL);
        }
 }
 
@@ -1640,6 +1667,7 @@ static int lineedit_read_key(char *read_key_buffer)
                ic = read_key(STDIN_FILENO, read_key_buffer);
 
                if (ENABLE_FEATURE_EDITING_ASK_TERMINAL
+                && cursor == 0 /* otherwise it may be bogus */
                 && (int32_t)ic == KEYCODE_CURSOR_POS
                ) {
                        int col = ((ic >> 32) & 0x7fff) - 1;
@@ -1708,7 +1736,7 @@ int FAST_FUNC read_line_input(const char *prompt, char *command, int maxsize, li
        ) {
                /* Happens when e.g. stty -echo was run before */
                parse_and_put_prompt(prompt);
-               fflush(stdout);
+               /* fflush(stdout); - done by parse_and_put_prompt */
                if (fgets(command, maxsize, stdin) == NULL)
                        len = -1; /* EOF or error */
                else
@@ -2190,7 +2218,7 @@ int FAST_FUNC read_line_input(const char *prompt, char *command, int maxsize, li
        tcsetattr_stdin_TCSANOW(&initial_settings);
        /* restore SIGWINCH handler */
        signal(SIGWINCH, previous_SIGWINCH_handler);
-       fflush(stdout);
+       fflush(NULL);
 
        len = command_len;
        DEINIT_S();
@@ -2204,7 +2232,7 @@ int FAST_FUNC read_line_input(const char *prompt, char *command, int maxsize, li
 int FAST_FUNC read_line_input(const char* prompt, char* command, int maxsize)
 {
        fputs(prompt, stdout);
-       fflush(stdout);
+       fflush(NULL);
        fgets(command, maxsize, stdin);
        return strlen(command);
 }

diff --git a/libbb/read_key.c b/libbb/read_key.c
index ec1b3a4a846b4c390312086682265bda2d1e6283..a2253ce3e8f3c6493dd0a939d857ea796fd7cd93 100644 (file)
--- a/libbb/read_key.c
+++ b/libbb/read_key.c
@@ -202,6 +202,31 @@ int64_t FAST_FUNC read_key(int fd, char *buffer)
                        break;
                }
                n++;
+               /* Try to decipher "ESC [ NNN ; NNN R" sequence */
+               if (ENABLE_FEATURE_EDITING_ASK_TERMINAL
+                && n >= 5
+                && buffer[0] == '['
+                && buffer[n-1] == 'R'
+                && isdigit(buffer[1])
+               ) {
+                       char *end;
+                       unsigned long row, col;
+
+                       row = strtoul(buffer + 1, &end, 10);
+                       if (*end != ';' || !isdigit(end[1]))
+                               continue;
+                       col = strtoul(end + 1, &end, 10);
+                       if (*end != 'R')
+                               continue;
+                       if (row < 1 || col < 1 || (row | col) > 0x7fff)
+                               continue;
+
+                       buffer[-1] = 0;
+                       /* Pack into "1 <row15bits> <col16bits>" 32-bit sequence */
+                       col |= (((-1 << 15) | row) << 16);
+                       /* Return it in high-order word */
+                       return ((int64_t) col << 32) | (uint32_t)KEYCODE_CURSOR_POS;
+               }
        }
  got_all:
 
@@ -213,34 +238,6 @@ int64_t FAST_FUNC read_key(int fd, char *buffer)
                return 27;
        }
 
-       /* Try to decipher "ESC [ NNN ; NNN R" sequence */
-       if (ENABLE_FEATURE_EDITING_ASK_TERMINAL
-        && n >= 5
-        && buffer[0] == '['
-        && isdigit(buffer[1])
-        && buffer[n-1] == 'R'
-       ) {
-               char *end;
-               unsigned long row, col;
-
-               row = strtoul(buffer + 1, &end, 10);
-               if (*end != ';' || !isdigit(end[1]))
-                       goto not_R;
-               col = strtoul(end + 1, &end, 10);
-               if (*end != 'R')
-                       goto not_R;
-               if (row < 1 || col < 1 || (row | col) > 0x7fff)
-                       goto not_R;
-
-               buffer[-1] = 0;
-
-               /* Pack into "1 <row15bits> <col16bits>" 32-bit sequence */
-               col |= (((-1 << 15) | row) << 16);
-               /* Return it in high-order word */
-               return ((int64_t) col << 32) | (uint32_t)KEYCODE_CURSOR_POS;
-       }
- not_R:
-
        /* We were doing "buffer[-1] = n; return c;" here, but this results
         * in unknown key sequences being interpreted as ESC + garbage.
         * This was not useful. Pretend there was no key pressed,