ximcp: Unmark to fabricate key events with XKeyEvent serial

_XimProtoKeypressFilter() and _XimProtoKeyreleaseFilter() can
receive XKeyEvent from both the typing on the keyboard and the
callback of XIM_FORWARD_EVENT.

If the filter functions unmark to fabricate XKeyEvent from the typing
on the keyboard during receiving XKeyEvent from the callback of
XIM_FORWARD_EVENT with typing keys very quickly likes an bar code
scanner (or evemu-play), XIM server cannot receive some key events and
it causes the key typing order to get scrambled.

Now XIM client saves the serial in XKeyEvent and the filter functions
unmark to fabricate XKeyEvent from the callback of XIM_FORWARD_EVENT
only.

This and 024d229f are same patches but the regression issues will be
fixed by the later patches.

Closes: #198
Fixes: 024d229f ("ximcp: Unmark to fabricate key events with XKeyEvent serial")
Part-of: <https://gitlab.freedesktop.org/xorg/lib/libx11/-/merge_requests/246>

3 files changed, 58 insertions, 9 deletions

diff --git a/modules/im/ximcp/imDefFlt.c b/modules/im/ximcp/imDefFlt.c
index 44cc6884..834b9db4 100644
--- a/modules/im/ximcp/imDefFlt.c
+++ b/modules/im/ximcp/imDefFlt.c
@@ -142,9 +142,9 @@ _XimProtoKeypressFilter(
 {
     Xim		im = (Xim)ic->core.im;
 
-    if (IS_FABRICATED(im)) {
+    if (_XimIsFabricatedSerial(im, ev->serial)) {
 	_XimPendingFilter(ic);
-	UNMARK_FABRICATED(im);
+	_XimUnfabricateSerial(im, ev->serial);
 	return NOTFILTERD;
     }
 
@@ -203,9 +203,9 @@ _XimProtoKeyreleaseFilter(
 {
     Xim		im = (Xim)ic->core.im;
 
-    if (IS_FABRICATED(im)) {
+    if (_XimIsFabricatedSerial(im, ev->serial)) {
 	_XimPendingFilter(ic);
-	UNMARK_FABRICATED(im);
+	_XimUnfabricateSerial(im, ev->serial);
 	return NOTFILTERD;
     }
 
diff --git a/modules/im/ximcp/imDefIm.c b/modules/im/ximcp/imDefIm.c
index fe4d18ba..ac7f1195 100644
--- a/modules/im/ximcp/imDefIm.c
+++ b/modules/im/ximcp/imDefIm.c
@@ -430,6 +430,7 @@ _XimPreConnect(
 	return False;
 
     im->private.proto.im_window = im_window;
+    im->private.proto.fabricated_serial = 0;
     return True;
 }
 
diff --git a/modules/im/ximcp/imDefLkup.c b/modules/im/ximcp/imDefLkup.c
index dd1adf53..5192e8c1 100644
--- a/modules/im/ximcp/imDefLkup.c
+++ b/modules/im/ximcp/imDefLkup.c
@@ -341,6 +341,54 @@ _XimForwardEvent(
     return _XimForwardEventCore(ic, ev, sync);
 }
 
+Bool
+_XimFabricateSerial(
+    Xim			 im,
+    unsigned long	 serial)
+{
+    if (!serial)
+	return False;
+    if (serial == im->private.proto.fabricated_serial) {
+	fprintf(stderr, "%s,%d: The key event is already fabricated.\n", __FILE__, __LINE__);
+	return False;
+    }
+    if (im->private.proto.fabricated_serial)
+	fprintf(stderr, "%s,%d: Tried to fabricate a wrong key event.\n", __FILE__, __LINE__);
+
+    MARK_FABRICATED(im);
+    im->private.proto.fabricated_serial = serial;
+    return True;
+}
+
+Bool
+_XimUnfabricateSerial(
+    Xim			 im,
+    unsigned long	 serial)
+{
+    if (!serial)
+	return False;
+    if (!im->private.proto.fabricated_serial) {
+	fprintf(stderr, "%s,%d: The key event is already unfabricated.\n", __FILE__, __LINE__);
+	return False;
+    }
+    if (serial != im->private.proto.fabricated_serial)
+	fprintf(stderr, "%s,%d: Tried to unfabricate a wrong key event.\n", __FILE__, __LINE__);
+
+    im->private.proto.fabricated_serial = 0;
+    UNMARK_FABRICATED(im);
+    return True;
+}
+
+Bool
+_XimIsFabricatedSerial(
+    Xim			 im,
+    unsigned long	 serial)
+{
+    if (!serial)
+	return False;
+    return (serial == im->private.proto.fabricated_serial);
+}
+
 static void
 _XimProcEvent(
     Display		*d,
@@ -355,7 +403,7 @@ _XimProcEvent(
     ev->xany.serial |= serial << 16;
     ev->xany.send_event = False;
     ev->xany.display = d;
-    MARK_FABRICATED(ic->core.im);
+    _XimFabricateSerial((Xim)ic->core.im, ev->xany.serial);
     return;
 }
 
@@ -704,10 +752,6 @@ _XimCommitRecv(
 
     (void)_XimRespSyncReply(ic, flag);
 
-    if (ic->private.proto.registed_filter_event
-	& (KEYPRESS_MASK | KEYRELEASE_MASK))
-	    MARK_FABRICATED(im);
-
     bzero(&ev, sizeof(ev));	/* uninitialized : found when running kterm under valgrind */
 
     ev.type = KeyPress;
@@ -719,6 +763,10 @@ _XimCommitRecv(
 
     ev.time = 0L;
     ev.serial = LastKnownRequestProcessed(im->core.display);
+
+    if (ic->private.proto.registed_filter_event
+	& (KEYPRESS_MASK | KEYRELEASE_MASK))
+	    _XimFabricateSerial(im, ev.serial);
     /* FIXME :
        I wish there were COMMENTs (!) about the data passed around.
     */