Some more Rusty Fun... :) (0.38.3)

src/rust/src/lib.rs

@@ -48,4 +48,46 @@ pub extern "C" fn fun_rust_print_string(msg: *const core::ffi::c_char) -> i32 {
     0
 }
 
+// Return a newly allocated duplicate of the given C string.
+// Caller (C side) must free using fun_rust_string_free.
+#[no_mangle]
+pub extern "C" fn fun_rust_echo_string(input: *const core::ffi::c_char) -> *mut core::ffi::c_char {
+    use core::ffi::CStr;
+    unsafe {
+        if input.is_null() {
+            // allocate empty string
+            let v = Vec::<u8>::from([0u8]);
+            return v.leak().as_mut_ptr() as *mut core::ffi::c_char;
+        }
+        match CStr::from_ptr(input).to_str() {
+            Ok(s) => {
+                let mut v = s.as_bytes().to_vec();
+                v.push(0); // NUL-terminate
+                v.leak().as_mut_ptr() as *mut core::ffi::c_char
+            }
+            Err(_) => {
+                // On invalid UTF-8, still duplicate bytes as-is
+                let c = CStr::from_ptr(input);
+                let mut v = c.to_bytes().to_vec();
+                v.push(0);
+                v.leak().as_mut_ptr() as *mut core::ffi::c_char
+            }
+        }
+    }
+}
+
+// Free a C string previously returned by fun_rust_echo_string
+#[no_mangle]
+pub extern "C" fn fun_rust_string_free(ptr: *mut core::ffi::c_char) {
+    if ptr.is_null() { return; }
+    unsafe {
+        // Reconstruct a Vec<u8> so Rust will free it when it drops
+        // Determine length by scanning for NUL
+        let mut len: usize = 0;
+        while *ptr.add(len) != 0 { len += 1; }
+        let slice = core::slice::from_raw_parts_mut(ptr as *mut u8, len + 1);
+        let _ = Vec::from_raw_parts(slice.as_mut_ptr(), len + 1, len + 1);
+    }
+}
+
 // No custom panic handler; use std default