GUACAMOLE-33: Restore guac_common_cursor_remove_user() (reverts commit af7968e).

src/common/guac_cursor.c

@@ -367,3 +367,12 @@ void guac_common_cursor_set_blank(guac_common_cursor* cursor) {
 
 }
 
+void guac_common_cursor_remove_user(guac_common_cursor* cursor,
+        guac_user* user) {
+
+    /* Disassociate from given user */
+    if (cursor->user == user)
+        cursor->user = NULL;
+
+}
+

src/common/guac_cursor.h

@@ -249,4 +249,19 @@ void guac_common_cursor_set_ibar(guac_common_cursor* cursor);
  */
 void guac_common_cursor_set_blank(guac_common_cursor* cursor);
 
+/**
+ * Removes the given user, such that future synchronization will not occur.
+ * This is necessary when a user leaves the connection. If a user leaves the
+ * connection and this is not called, the corresponding guac_user and socket
+ * may cease to be valid, and future synchronization attempts will segfault.
+ *
+ * @param cursor
+ *     The cursor to remove the user from.
+ *
+ * @param user
+ *     The user to remove.
+ */
+void guac_common_cursor_remove_user(guac_common_cursor* cursor,
+        guac_user* user);
+
 #endif

src/protocols/vnc/user.c

@@ -97,3 +97,12 @@ int guac_vnc_user_join_handler(guac_user* user, int argc, char** argv) {
 
 }
 
+int guac_vnc_user_leave_handler(guac_user* user) {
+
+    guac_vnc_client* vnc_client = (guac_vnc_client*) user->client->data;
+
+    guac_common_cursor_remove_user(vnc_client->display->cursor, user);
+
+    return 0;
+}
+

src/protocols/vnc/user.h

@@ -29,5 +29,10 @@
  */
 guac_user_join_handler guac_vnc_user_join_handler;
 
+/**
+ * Handler for leaving users.
+ */
+guac_user_leave_handler guac_vnc_user_leave_handler;
+
 #endif