rust/util: expose function to test strings for valid UTF-8

rs_check_utf8 will check that the provided string is valid
UTF-8 by converting it to a Rust string and returning true
or false.

rust/src/lib.rs

@@ -83,3 +83,4 @@ pub mod asn1;
 pub mod ssh;
 pub mod http2;
 pub mod plugin;
+pub mod util;

rust/src/util.rs

@@ -0,0 +1,24 @@
+/* Copyright (C) 2020 Open Information Security Foundation
+ *
+ * You can copy, redistribute or modify this Program under the terms of
+ * the GNU General Public License version 2 as published by the Free
+ * Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * version 2 along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+use std::ffi::CStr;
+use std::os::raw::c_char;
+
+#[no_mangle]
+pub unsafe extern "C" fn rs_check_utf8(val: *const c_char) -> bool {
+    CStr::from_ptr(val).to_str().is_ok()
+}