Bug 796761 - Control characters can be pasted in register fields

If copied text includes control characters they are inserted when
pasted which can cause alignment issues. This commit filters the
clipboard text for control characters before it is pasted.

libgnucash/app-utils/gnc-ui-util.c

@@ -2663,3 +2663,67 @@ gnc_ui_util_remove_registered_prefs (void)
                                  GNC_PREF_AUTO_DECIMAL_PLACES,
                                  gnc_set_auto_decimal_places, NULL);
 }
+
+static gboolean
+unichar_is_cntrl (gunichar uc)
+{
+    if (uc < 0x20 || (uc > 0x7e && uc < 0xa0))
+        return TRUE;
+    else
+        return FALSE;
+}
+
+gchar *
+gnc_filter_text_for_control_chars (const gchar *text)
+{
+    gchar *normal_text, *nt;
+    GString *filtered;
+    gboolean cntrl = FALSE;
+    gboolean text_found = FALSE;
+
+    if (!text)
+        return NULL;
+
+    if (!g_utf8_validate (text, -1, NULL))
+        return NULL;
+
+    normal_text = g_utf8_normalize (text, -1, G_NORMALIZE_ALL_COMPOSE);
+
+    filtered = g_string_sized_new (strlen (normal_text) + 1);
+
+    nt = normal_text;
+
+    while (*nt)
+    {
+        gunichar uc = g_utf8_get_char (nt);
+
+        // check for starting with control characters
+        if (unichar_is_cntrl (uc) && !text_found)
+        {
+            nt = g_utf8_next_char (nt);
+            continue;
+        }
+        // check for alpha, num and punctuation
+        if (!unichar_is_cntrl (uc))
+        {
+            filtered = g_string_append_unichar (filtered, uc);
+            text_found = TRUE;
+        }
+        // check for control characters after text
+        if (unichar_is_cntrl (uc))
+            cntrl = TRUE;
+
+        nt = g_utf8_next_char (nt);
+
+        if (cntrl) // if control characters in text replace with space
+        {
+            gunichar uc2 = g_utf8_get_char (nt);
+
+            if (!unichar_is_cntrl (uc2))
+                filtered = g_string_append_unichar (filtered, ' ');
+        }
+        cntrl = FALSE;
+    }
+    g_free (normal_text);
+    return g_string_free (filtered, FALSE);
+}