[PATCH] Cygwin: console: Fix handling of surrogate pairs

[Takashi Yano]

The commit 782aac590af7 introduced surrogate-pair handling. However,
it does not work as expected in the legacy console. This is because
a KeyDown event for ALT key with UnicodeChar == 0 is inserted the
between surrogate pair. The current code reads the next key event
unconditionally for the second UnicodeChar, but it is not correct.
This patch searches the next appropriate key event with a valid
UnicodeChar, ensuring that the second code unit is valid.

Fixes: 782aac590af7 ("Cygwin: console: Handle Unicode surrogate pairs.")
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
Reviewed-by:
---
 winsup/cygwin/fhandler/console.cc | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/winsup/cygwin/fhandler/console.cc b/winsup/cygwin/fhandler/console.cc
index 6fd4cd965..45eff6efe 100644
--- a/winsup/cygwin/fhandler/console.cc
+++ b/winsup/cygwin/fhandler/console.cc
@@ -1452,9 +1452,21 @@ fhandler_console::process_input_message (void)
 	    }
 	  else
 	    {
-	      WCHAR second = unicode_char >= 0xd800 && unicode_char <= 0xdbff
-		  && i + 1 < total_read ?
-		  input_rec[i + 1].Event.KeyEvent.uChar.UnicodeChar : 0;
+	      WCHAR second = 0;
+	      DWORD second_pos = i;
+	      if (unicode_char >= 0xd800 && unicode_char <= 0xdbff)
+		for (DWORD j = i + 1; j < total_read; j++)
+		  {
+		    /* Do not check bKeyDown. bKeyDown is 0 for surrogate
+		       pair in legacy console */
+		    if (input_rec[j].EventType == KEY_EVENT &&
+			input_rec[j].Event.KeyEvent.uChar.UnicodeChar)
+		      {
+			second = input_rec[j].Event.KeyEvent.uChar.UnicodeChar;
+			second_pos = j;
+			break;
+		      }
+		  }
 
 	      if (second < 0xdc00 || second > 0xdfff)
 		{
@@ -1465,7 +1477,7 @@ fhandler_console::process_input_message (void)
 		  /* handle surrogate pairs */
 		  WCHAR pair[2] = { unicode_char, second };
 		  nread = sys_wcstombs (tmp + 1, 59, pair, 2);
-		  i++;
+		  i = second_pos;
 		}
 
 	      /* Determine if the keystroke is modified by META.  The tricky
-- 
2.51.0