Implement the INCR ICCCM selection mechanism

xcb_get_property is now also called with a length that is a multiple
of four so that we advance the offset properly.

Some cleanup.

Selection code should work pretty well by now.  The amount of code
supporting it has more than doubled since GTK+.

src/sdtui.c

@@ -1833,8 +1833,13 @@ struct selection_watch
 
 	guint           watch;              ///< X11 connection watcher
 	xcb_window_t    wid;                ///< Withdrawn communications window
+	xcb_atom_t      atom_incr;          ///< INCR
 	xcb_atom_t      atom_utf8_string;   ///< UTF8_STRING
 	xcb_timestamp_t in_progress;        ///< Timestamp of last processed event
+	GString       * buffer;             ///< UTF-8 text buffer
+
+	gboolean        incr;               ///< INCR running
+	gboolean        incr_failure;       ///< INCR failure indicator
 };
 
 static gboolean
@@ -1877,57 +1882,48 @@ on_selection_text_received (SelectionWatch *self, const gchar *text)
 
 static gboolean
 read_utf8_property (SelectionWatch *self, xcb_window_t wid, xcb_atom_t property,
-	GString *buf)
+	gboolean *empty)
 {
 	guint32 offset = 0;
-	gboolean loop = TRUE, ok = TRUE;
+	gboolean more_data = TRUE, ok = TRUE;
-	while (ok && loop)
+	xcb_get_property_reply_t *gpr;
+	while (ok && more_data)
 	{
-		xcb_get_property_reply_t *gpr = xcb_get_property_reply (self->X,
+		if (!(gpr = xcb_get_property_reply (self->X,
 			xcb_get_property (self->X, FALSE /* delete */, wid,
-			property, XCB_GET_PROPERTY_TYPE_ANY, offset, 0x7fff), NULL);
+			property, XCB_GET_PROPERTY_TYPE_ANY, offset, 0x8000), NULL)))
+			return FALSE;
 
-		if (!gpr || gpr->type != self->atom_utf8_string || gpr->format != 8)
-			ok = FALSE;
-		else
-		{
 		int len = xcb_get_property_value_length (gpr);
-			g_string_append_len (buf, xcb_get_property_value (gpr), len);
+		if (offset == 0 && len == 0 && empty)
-			offset += len >> 2;
+			*empty = TRUE;
-			loop = gpr->bytes_after > 0;
-		}
 
+		ok = gpr->type == self->atom_utf8_string && gpr->format == 8;
+		more_data = gpr->bytes_after != 0;
+		if (ok)
+		{
+			offset += len >> 2;
+			g_string_append_len (self->buffer,
+				xcb_get_property_value (gpr), len);
+		}
 		free (gpr);
 	}
 	return ok;
 }
 
 static void
-process_x11_event (SelectionWatch *self, xcb_generic_event_t *event)
+on_x11_selection_change (SelectionWatch *self,
+	xcb_xfixes_selection_notify_event_t *e)
 {
-	xcb_generic_error_t *err = NULL;
-	int event_code = event->response_type & 0x7f;
-	if (event_code == 0)
-	{
-		err = (xcb_generic_error_t *) event;
-		g_warning (_("X11 request error (%d, major %d, minor %d)"),
-			err->error_code, err->major_code, err->minor_code);
-	}
-	else if (event_code ==
-		self->xfixes->first_event + XCB_XFIXES_SELECTION_NOTIFY)
-	{
-		xcb_xfixes_selection_notify_event_t *e =
-			(xcb_xfixes_selection_notify_event_t *) event;
-
 	// Not checking whether we should give up when this interrupts our
-		// current retrieval attempt--the timeout solves this
+	// current retrieval attempt--the timeout mostly solves this for all cases
 	if (e->owner == XCB_NONE)
 		return;
 
-		// Don't try to process two things at once.  Each request gets a few
+	// Don't try to process two things at once.  Each request gets a few seconds
-		// seconds to finish, then we move on, hoping that a property race
+	// to finish, then we move on, hoping that a property race doesn't commence.
-		// doesn't commence.  Ideally we'd set up a separate queue for these
+	// Ideally we'd set up a separate queue for these skipped requests and
-		// skipped requests and process them later.
+	// process them later.
 	if (self->in_progress != 0 && e->timestamp - self->in_progress < 5000)
 		return;
 
@@ -1936,26 +1932,95 @@ process_x11_event (SelectionWatch *self, xcb_generic_event_t *event)
 
 	(void) xcb_convert_selection (self->X, self->wid, e->selection,
 		self->atom_utf8_string, XCB_ATOM_PRIMARY, e->timestamp);
+
 	self->in_progress = e->timestamp;
-	}
+	self->incr = FALSE;
-	else if (event_code == XCB_SELECTION_NOTIFY)
+}
-	{
+
-		xcb_selection_notify_event_t *e =
+static void
-			(xcb_selection_notify_event_t *) event;
+on_x11_selection_receive (SelectionWatch *self,
-		if (e->time != self->in_progress)
+	xcb_selection_notify_event_t *e)
+{
+	if (e->requestor != self->wid
+	 || e->time != self->in_progress)
 		return;
 
 	self->in_progress = 0;
 	if (e->property == XCB_ATOM_NONE)
 		return;
 
-		GString *buf = g_string_new (NULL);
+	xcb_get_property_reply_t *gpr = xcb_get_property_reply (self->X,
-		if (read_utf8_property (self, e->requestor, e->property, buf))
+		xcb_get_property (self->X, FALSE /* delete */, e->requestor,
-			on_selection_text_received (self, buf->str);
+		e->property, XCB_GET_PROPERTY_TYPE_ANY, 0, 0), NULL);
-		g_string_free (buf, TRUE);
+	if (!gpr)
+		return;
 
-		(void) xcb_delete_property (self->X, self->wid, e->property);
+	// Garbage collection, GString only ever expands in size
+	g_string_free (self->buffer, TRUE);
+	self->buffer = g_string_new (NULL);
+
+	// When you select a lot of text in VIM, it starts the ICCCM INCR mechanism,
+	// from which there is no opt-out
+	if (gpr->type == self->atom_incr)
+	{
+		self->in_progress = e->time;
+		self->incr = TRUE;
+		self->incr_failure = FALSE;
 	}
+	else if (read_utf8_property (self, e->requestor, e->property, NULL))
+		on_selection_text_received (self, self->buffer->str);
+
+	free (gpr);
+	(void) xcb_delete_property (self->X, self->wid, e->property);
+}
+
+static void
+on_x11_property_notify (SelectionWatch *self, xcb_property_notify_event_t *e)
+{
+	if (!self->incr
+	 || e->window != self->wid
+	 || e->state != XCB_PROPERTY_NEW_VALUE
+	 || e->atom != XCB_ATOM_PRIMARY)
+		return;
+
+	gboolean empty = FALSE;
+	if (!read_utf8_property (self, e->window, e->atom, &empty))
+		// We need to keep deleting the property
+		self->incr_failure = TRUE;
+
+	// Once it's empty, we've consumed everything and can move on undisturbed
+	if (empty)
+	{
+		if (!self->incr_failure)
+			on_selection_text_received (self, self->buffer->str);
+
+		self->in_progress = 0;
+		self->incr = FALSE;
+	}
+
+	(void) xcb_delete_property (self->X, e->window, e->atom);
+}
+
+static void
+process_x11_event (SelectionWatch *self, xcb_generic_event_t *event)
+{
+	int event_code = event->response_type & 0x7f;
+	if (event_code == 0)
+	{
+		xcb_generic_error_t *err = (xcb_generic_error_t *) event;
+		g_warning (_("X11 request error (%d, major %d, minor %d)"),
+			err->error_code, err->major_code, err->minor_code);
+	}
+	else if (event_code ==
+		self->xfixes->first_event + XCB_XFIXES_SELECTION_NOTIFY)
+		on_x11_selection_change (self,
+			(xcb_xfixes_selection_notify_event_t *) event);
+	else if (event_code == XCB_SELECTION_NOTIFY)
+		on_x11_selection_receive (self,
+			(xcb_selection_notify_event_t *) event);
+	else if (event_code == XCB_PROPERTY_NOTIFY)
+		on_x11_property_notify (self,
+			(xcb_property_notify_event_t *) event);
 }
 
 static gboolean
@@ -1991,6 +2056,8 @@ selection_watch_init (SelectionWatch *self, Application *app)
 	// fallback might be good to add (COMPOUND_TEXT is complex)
 	g_return_if_fail
 		((self->atom_utf8_string = resolve_atom (self->X, "UTF8_STRING")));
+	g_return_if_fail
+		((self->atom_incr = resolve_atom (self->X, "INCR")));
 
 	self->xfixes = xcb_get_extension_data (self->X, &xcb_xfixes_id);
 	g_return_if_fail (self->xfixes->present);
@@ -2005,9 +2072,10 @@ selection_watch_init (SelectionWatch *self, Application *app)
 
 	xcb_screen_t *screen = setup_iter.data;
 	self->wid = xcb_generate_id (self->X);
+	const uint32_t values[] = {XCB_EVENT_MASK_PROPERTY_CHANGE};
 	(void) xcb_create_window (self->X, screen->root_depth, self->wid,
 		screen->root, 0, 0, 1, 1, 0, XCB_WINDOW_CLASS_INPUT_OUTPUT,
-		screen->root_visual, 0, NULL);
+		screen->root_visual, XCB_CW_EVENT_MASK, values);
 
 	(void) xcb_xfixes_select_selection_input (self->X, self->wid,
 		XCB_ATOM_PRIMARY, XCB_XFIXES_SELECTION_EVENT_MASK_SET_SELECTION_OWNER |
@@ -2017,6 +2085,9 @@ selection_watch_init (SelectionWatch *self, Application *app)
 	(void) xcb_flush (self->X);
 	self->watch = g_io_add_watch (g_io_channel_unix_new
 		(xcb_get_file_descriptor (self->X)), G_IO_IN, process_x11, self);
+
+	// Never NULL so that we don't need to care about pointer validity
+	self->buffer = g_string_new (NULL);
 }
 
 static void
@@ -2026,6 +2097,8 @@ selection_watch_destroy (SelectionWatch *self)
 		xcb_disconnect (self->X);
 	if (self->watch)
 		g_source_remove (self->watch);
+	if (self->buffer)
+		g_string_free (self->buffer, TRUE);
 }
 
 #endif  // WITH_X11