1 files changed, 56 insertions, 0 deletions
diff --git a/src/rust/tor_util/ffi.rs b/src/rust/tor_util/ffi.rs
new file mode 100644
index 0000000000..af4bfc41af
--- /dev/null
+++ b/src/rust/tor_util/ffi.rs
@@ -0,0 +1,56 @@
+//! FFI functions, only to be called from C.
+//!
+//! Equivalent C versions of these live in `src/common/compat_rust.c`
+
+use std::mem::forget;
+use std::ffi::CString;
+
+use libc;
+use rust_string::RustString;
+
+/// Free the passed `RustString` (`rust_str_t` in C), to be used in place of
+/// `tor_free`().
+///
+/// # Examples
+/// ```c
+/// rust_str_t r_s = rust_welcome_string();
+/// rust_str_free(r_s);
+/// ```
+#[no_mangle]
+#[cfg_attr(feature = "cargo-clippy", allow(needless_pass_by_value))]
+pub unsafe extern "C" fn rust_str_free(_str: RustString) {
+    // Empty body: Just drop _str and we're done (Drop takes care of it).
+}
+
+/// Lends an immutable, NUL-terminated C String.
+///
+/// # Examples
+/// ```c
+/// rust_str_t r_s = rust_welcome_string();
+/// const char *s = rust_str_get(r_s);
+/// printf("%s", s);
+/// rust_str_free(r_s);
+/// ```
+#[no_mangle]
+pub unsafe extern "C" fn rust_str_get(str: RustString) -> *const libc::c_char {
+    let res = str.as_ptr();
+    forget(str);
+    res
+}
+
+/// Returns a short string to announce Rust support during startup.
+///
+/// # Examples
+/// ```c
+/// rust_str_t r_s = rust_welcome_string();
+/// const char *s = rust_str_get(r_s);
+/// printf("%s", s);
+/// rust_str_free(r_s);
+/// ```
+#[no_mangle]
+pub extern "C" fn rust_welcome_string() -> RustString {
+    let s = CString::new("Tor is running with Rust integration. Please report \
+                          any bugs you encouter.")
+            .unwrap();
+    RustString::from(s)
+}