From 95a60b7fddf3aeb0d5aa8f7f1714bc7d10d4ceb9 Mon Sep 17 00:00:00 2001
From: Takashi Yano <takashi.yano@nifty.ne.jp>
Date: Fri, 25 Feb 2022 17:10:03 +0900
Subject: [PATCH] Cygwin: console: Prevent the order of typeahead input from
 swapped.

- If a lot of keys are typed very quickly in the app which does
  not read console, the order of input keys in console input buffer
  occasionally swapped. Although this extremely rarely happens,
  is obviously a bug of cons_master_thread. This patch fixes the
  issue.
---
 winsup/cygwin/fhandler_console.cc | 53 +++++++++++++++++++++++++++++--
 1 file changed, 51 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/fhandler_console.cc b/winsup/cygwin/fhandler_console.cc
index aa0f26450..88c0f894b 100644
--- a/winsup/cygwin/fhandler_console.cc
+++ b/winsup/cygwin/fhandler_console.cc
@@ -208,6 +208,20 @@ fhandler_console::cons_master_thread (handle_set_t *p, tty *ttyp)
 	case WAIT_OBJECT_0:
 	  ReadConsoleInputW (p->input_handle,
 			     input_rec, INREC_SIZE, &total_read);
+	  if (total_read == INREC_SIZE /* Working space full */
+	      && cygwait (p->input_handle, (DWORD) 0) == WAIT_OBJECT_0)
+	    {
+	      const int incr = 1;
+	      size_t bytes = sizeof (INPUT_RECORD) * (total_read - incr);
+	      /* Discard oldest incr events. */
+	      memmove (input_rec, input_rec + incr, bytes);
+	      total_read -= incr;
+	      processed_up_to =
+		(processed_up_to + 1 >= incr) ? processed_up_to - incr : -1;
+	      ReadConsoleInputW (p->input_handle,
+				 input_rec + total_read, incr, &n);
+	      total_read += n;
+	    }
 	  break;
 	case WAIT_TIMEOUT:
 	  processed_up_to = -1;
@@ -291,8 +305,43 @@ remove_record:
 	}
       processed_up_to = total_read - 1;
       if (total_read)
-	/* Writeback input records other than interrupt. */
-	WriteConsoleInputW (p->input_handle, input_rec, total_read, &n);
+	{
+	  /* Writeback input records other than interrupt. */
+	  WriteConsoleInputW (p->input_handle, input_rec, total_read, &n);
+	  size_t bytes = sizeof (INPUT_RECORD) * total_read;
+	  do
+	    {
+	      const int additional_size = 128; /* Possible max number of
+						  incoming events during
+						  above process. */
+	      const int new_size = INREC_SIZE + additional_size;
+	      INPUT_RECORD tmp[new_size];
+	      /* Check if writeback was successfull. */
+	      PeekConsoleInputW (p->input_handle, tmp, new_size, &n);
+	      if (memcmp (input_rec, tmp, bytes) == 0)
+		break; /* OK */
+	      /* Try to fix */
+	      DWORD incr = n - total_read;
+	      DWORD ofst;
+	      for (ofst = 1; ofst <= incr; ofst++)
+		if (memcmp (input_rec, tmp + ofst, bytes) == 0)
+		  {
+		    ReadConsoleInputW (p->input_handle, tmp, new_size, &n);
+		    DWORD m;
+		    WriteConsoleInputW (p->input_handle, tmp + ofst,
+					total_read, &m);
+		    WriteConsoleInputW (p->input_handle, tmp, ofst, &m);
+		    if ( n > ofst + total_read)
+		      WriteConsoleInputW (p->input_handle,
+					  tmp + ofst + total_read,
+					  n - (ofst + total_read), &m);
+		    break;
+		  }
+	      if (ofst > incr) /* Hard to fix */
+		break; /* Giving up */
+	    }
+	  while (true);
+	}
 skip_writeback:
       ReleaseMutex (p->input_mutex);
       cygwait (40);