From 4be4da65efbfb7656cdcab2bfcaff1d7b068a8c6 Mon Sep 17 00:00:00 2001
From: Takashi Yano <takashi.yano@nifty.ne.jp>
Date: Fri, 18 Mar 2022 21:35:07 +0900
Subject: [PATCH] Cygwin: console: Fix typeahead key swapping which still
 occurs.

- The commit "Cygwin: console: Improve the code to avoid typeahead
  key swapping." did not solve the problem enough. Two unexpected
  things happen.
  (1) wVirtualKeyCode and wVirtualScanCode of readback key event may
      be null'ed even if they are not zero on WriteConsoleInputW().
      Therefore, memcmp() may report the event sequence is not equal.
  (2) WriteConsoleInputW() may not be atomic. The event sequence
      which is written by WriteConsoleInputW() may be inserted by
      key input in the middle of the sequence. Current code gives
      up to fix in this situation.
  This patch should fix that issue.
---
 winsup/cygwin/fhandler_console.cc | 58 ++++++++++++++++++++-----------
 1 file changed, 38 insertions(+), 20 deletions(-)

diff --git a/winsup/cygwin/fhandler_console.cc b/winsup/cygwin/fhandler_console.cc
index e43d2ac14..b52ecfca6 100644
--- a/winsup/cygwin/fhandler_console.cc
+++ b/winsup/cygwin/fhandler_console.cc
@@ -180,6 +180,29 @@ cons_master_thread (VOID *arg)
   return 0;
 }
 
+/* Compare two INPUT_RECORD sequences */
+static inline bool
+inrec_eq (const INPUT_RECORD *a, const INPUT_RECORD *b, DWORD n)
+{
+  for (DWORD i = 0; i < n; i++)
+    {
+      if (a[i].EventType == KEY_EVENT && b[i].EventType == KEY_EVENT)
+	{ /* wVirtualKeyCode and wVirtualScanCode of the readback
+	     key event may be different from that of written event. */
+	  const KEY_EVENT_RECORD *ak = &a[i].Event.KeyEvent;
+	  const KEY_EVENT_RECORD *bk = &b[i].Event.KeyEvent;
+	  if (ak->bKeyDown != bk->bKeyDown
+	      || ak->uChar.UnicodeChar != bk->uChar.UnicodeChar
+	      || ak->dwControlKeyState != bk->dwControlKeyState
+	      || ak->wRepeatCount != bk->wRepeatCount)
+	    return false;
+	}
+      else if (memcmp (a + i, b + i, sizeof (INPUT_RECORD)) != 0)
+	return false;
+    }
+  return true;
+}
+
 /* This thread processes signals derived from input messages.
    Without this thread, those signals can be handled only when
    the process calls read() or select(). This thread reads input
@@ -327,30 +350,25 @@ remove_record:
 	      if (n < total_read)
 		break; /* Someone has read input without acquiring
 			  input_mutex. ConEmu cygwin-connector? */
-	      if (memcmp (input_rec, tmp, m.bytes (total_read)) == 0)
+	      if (inrec_eq (input_rec, tmp, total_read))
 		break; /* OK */
 	      /* Try to fix */
-	      DWORD incr = n - total_read;
-	      DWORD ofst;
-	      for (ofst = 1; ofst <= incr; ofst++)
-		if (memcmp (input_rec, tmp + ofst, m.bytes (total_read)) == 0)
+	      acquire_attach_mutex (mutex_timeout);
+	      ReadConsoleInputW (p->input_handle, tmp, inrec_size, &n);
+	      release_attach_mutex ();
+	      for (DWORD i = 0, j = 0; j < n; j++)
+		if (i == total_read || !inrec_eq (input_rec + i, tmp + j, 1))
 		  {
-		    acquire_attach_mutex (mutex_timeout);
-		    ReadConsoleInputW (p->input_handle, tmp, inrec_size, &n);
-		    release_attach_mutex ();
-		    memcpy (input_rec, tmp + ofst, m.bytes (total_read));
-		    memcpy (input_rec + total_read, tmp, m.bytes (ofst));
-		    if (n > ofst + total_read)
-		      memcpy (input_rec + total_read + ofst,
-			      tmp + ofst + total_read,
-			      m.bytes (n - (ofst + total_read)));
-		    total_read = n;
-		    break;
+		    if (total_read + j - i >= n)
+		      { /* Something is wrong. Giving up. */
+			WriteConsoleInputW (p->input_handle, tmp, n, &n);
+			goto skip_writeback;
+		      }
+		    input_rec[total_read + j - i] = tmp[j];
 		  }
-	      if (ofst > incr)
-		break; /* Writeback was not atomic. Or someone has read
-			  input without acquiring input_mutex.
-			  Giving up because hard to fix. */
+		else
+		  i++;
+	      total_read = n;
 	    }
 	  while (true);
 	}