make ping func to be able to call inside the C code

Cargo.toml

@@ -24,6 +24,7 @@ tokio = { version = "1.24.0", features = ["full"] }
 safer-ffi = "0.0.10"
 sha1 = "0.10.5"
 swift-bridge = "0.1"
+libc = "0.2"
 
 
 [build-dependencies]

include/engine.h

@@ -22,6 +22,8 @@ void ovry_warning(const char *msg);
 
 void ovry_error(const char *msg);
 
+void overlay_ping(const char *listen_on);
+
 void c_exec_wasm_text_module(const char *wasm_text, const char *main_fn);
 
 void c_exec_wasm_native_module(const unsigned char *data, uintptr_t data_length);

src/pingpong.rs

@@ -1,3 +1,5 @@
-pub fn overlay_ping(listen_on: String) {
-    println!("OVERLAY_PING: {}", listen_on)
+#[no_mangle]
+pub extern "C" fn overlay_ping(listen_on: *const libc::c_char) {
+    let listen_on = unsafe { std::ffi::CStr::from_ptr(listen_on).to_string_lossy().into_owned() };
+    println!("OVERLAY_PING: {}", listen_on);
 }