GUACAMOLE-352: Add utility function for checking whether a keysym exists within the current RDP keyboard layout.

src/protocols/rdp/keyboard.c

@@ -244,6 +244,21 @@ void guac_rdp_keyboard_free(guac_rdp_keyboard* keyboard) {
     free(keyboard);
 }
 
+int guac_rdp_keyboard_is_defined(guac_rdp_keyboard* keyboard, int keysym) {
+
+    /* Verify keysym can actually be stored within keymap */
+    if (!GUAC_RDP_KEYSYM_STORABLE(keysym))
+        return 0;
+
+    /* Look up scancode mapping */
+    const guac_rdp_keysym_desc* keysym_desc =
+        &GUAC_RDP_KEYSYM_LOOKUP(keyboard->keymap, keysym);
+
+    /* Return whether the mapping actually exists */
+    return keysym_desc->scancode != 0;
+
+}
+
 int guac_rdp_keyboard_send_event(guac_rdp_keyboard* keyboard,
         int keysym, int pressed) {
 

src/protocols/rdp/keyboard.h

@@ -95,6 +95,23 @@ guac_rdp_keyboard* guac_rdp_keyboard_alloc(guac_client* client,
  */
 void guac_rdp_keyboard_free(guac_rdp_keyboard* keyboard);
 
+/**
+ * Returns whether the given keysym is defined for the keyboard layout
+ * associated with the given keyboard.
+ *
+ * @param keyboard
+ *     The guac_rdp_keyboard instance to check.
+ *
+ * @param keysym
+ *     The keysym of the key being checked against the keyboard layout of the
+ *     given keyboard.
+ *
+ * @return
+ *     Non-zero if the key is explicitly defined within the keyboard layout of
+ *     the given keyboard, zero otherwise.
+ */
+int guac_rdp_keyboard_is_defined(guac_rdp_keyboard* keyboard, int keysym);
+
 /**
  * Sends one or more RDP key events, effectively pressing or releasing the
  * given keysym on the remote side. The key events sent will depend on the