libbb/lineedit: try to make FEATURE_EDITING_ASK_TERMINAL less ugly

function                                             old     new   delta
read_line_input                                     4809    4829     +20
lineedit_read_key                                    207     223     +16
put_prompt                                           110     117      +7
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/0 up/down: 43/0)               Total: 43 bytes

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

1 files changed, 35 insertions, 10 deletions

diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index 2e1bc5d2e..b4c3fd35c 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -140,6 +140,9 @@ struct lineedit_statics {
         smallint newdelflag;     /* whether delbuf should be reused yet */
         CHAR_T delbuf[DELBUFSIZ];  /* a place to store deleted characters */
 #endif
+#if ENABLE_FEATURE_EDITING_ASK_TERMINAL
+        smallint sent_ESC_br_n6;
+#endif
 
         /* Formerly these were big buffers on stack: */
 #if ENABLE_FEATURE_TAB_COMPLETION
@@ -371,7 +374,8 @@ static void put_prompt(void)
 {
         out1str(cmdedit_prompt);
         fflush(NULL);
-        if (ENABLE_FEATURE_EDITING_ASK_TERMINAL) {
+#if ENABLE_FEATURE_EDITING_ASK_TERMINAL
+        {
                 /* Ask terminal where is the cursor now.
                  * lineedit_read_key handles response and corrects
                  * our idea of current cursor position.
@@ -405,10 +409,12 @@ static void put_prompt(void)
                 pfd.fd = STDIN_FILENO;
                 pfd.events = POLLIN;
                 if (safe_poll(&pfd, 1, 0) == 0) {
+                        S.sent_ESC_br_n6 = 1;
                         out1str("\033" "[6n");
                         fflush(NULL); /* make terminal see it ASAP! */
                 }
         }
+#endif
         cursor = 0;
         {
                 unsigned w = cmdedit_termw; /* volatile var */
@@ -1666,20 +1672,24 @@ static int lineedit_read_key(char *read_key_buffer)
                 /* Note: read_key sets errno to 0 on success: */
                 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
+#if ENABLE_FEATURE_EDITING_ASK_TERMINAL
+                if ((int32_t)ic == KEYCODE_CURSOR_POS
+                 && S.sent_ESC_br_n6
                 ) {
-                        int col = ((ic >> 32) & 0x7fff) - 1;
-                        if (col > cmdedit_prmt_len) {
-                                cmdedit_x += (col - cmdedit_prmt_len);
-                                while (cmdedit_x >= cmdedit_termw) {
-                                        cmdedit_x -= cmdedit_termw;
-                                        cmdedit_y++;
+                        S.sent_ESC_br_n6 = 0;
+                        if (cursor == 0) { /* otherwise it may be bogus */
+                                int col = ((ic >> 32) & 0x7fff) - 1;
+                                if (col > cmdedit_prmt_len) {
+                                        cmdedit_x += (col - cmdedit_prmt_len);
+                                        while (cmdedit_x >= cmdedit_termw) {
+                                                cmdedit_x -= cmdedit_termw;
+                                                cmdedit_y++;
+                                        }
                                 }
                         }
                         goto poll_again;
                 }
+#endif
 
 #if ENABLE_FEATURE_ASSUME_UNICODE
                 {
@@ -2192,6 +2202,21 @@ int FAST_FUNC read_line_input(const char *prompt, char *command, int maxsize, li
 #endif
         } /* while (1) */
 
+#if ENABLE_FEATURE_EDITING_ASK_TERMINAL
+        if (S.sent_ESC_br_n6) {
+                /* "sleep 1; busybox ash" + hold [Enter] to trigger.
+                 * We sent "ESC [ 6 n", but got '\n' first, and
+                 * KEYCODE_CURSOR_POS response is now buffered from terminal.
+                 * It's bad already and not much can be done with it
+                 * (it _will_ be visible for the next process to read stdin),
+                 * but without this delay it even shows up on the screen
+                 * as garbage because we restore echo settings with tcsetattr
+                 * before it comes in. UGLY!
+                 */
+                usleep(20*1000);
+        }
+#endif
+
 /* Stop bug catching using "command_must_not_be_used" trick */
 #undef command