From d493001feaf65d4bef1883fff3275ce1ebf415bc Mon Sep 17 00:00:00 2001
From: Junji Takakura <j.takakura@gmail.com>
Date: Sat, 21 Mar 2026 09:15:21 +0900
Subject: [PATCH 1/2] Add Rust FFI example using zwasm C API

---
 .gitignore                |  4 +++
 examples/rust/Cargo.toml  |  7 ++++
 examples/rust/build.rs    | 16 +++++++++
 examples/rust/src/main.rs | 68 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 95 insertions(+)
 create mode 100644 examples/rust/Cargo.toml
 create mode 100644 examples/rust/build.rs
 create mode 100644 examples/rust/src/main.rs

diff --git a/.gitignore b/.gitignore
index 861ae777..2ebe2ec8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,6 +12,10 @@ zig-cache/
 # Python
 __pycache__/
 
+# Rust
+target/
+Cargo.lock
+
 # Editor
 *.swp
 *~
diff --git a/examples/rust/Cargo.toml b/examples/rust/Cargo.toml
new file mode 100644
index 00000000..ba475ad5
--- /dev/null
+++ b/examples/rust/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "rust-example"
+version = "0.1.0"
+edition = "2024"
+build = "build.rs"
+
+[dependencies]
diff --git a/examples/rust/build.rs b/examples/rust/build.rs
new file mode 100644
index 00000000..41c1d2c8
--- /dev/null
+++ b/examples/rust/build.rs
@@ -0,0 +1,16 @@
+use std::{env, path::PathBuf};
+
+fn main() {
+    let manifest = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap());
+    let lib_dir = manifest
+        .join("..")
+        .join("..")
+        .join("zig-out")
+        .join("lib")
+        .canonicalize()
+        .expect("zig-out/lib not found — run `zig build lib` first");
+
+    println!("cargo:rustc-link-search=native={}", lib_dir.display());
+    println!("cargo:rustc-link-lib=zwasm");
+    println!("cargo:rustc-link-arg=-Wl,-rpath,{}", lib_dir.display());
+}
diff --git a/examples/rust/src/main.rs b/examples/rust/src/main.rs
new file mode 100644
index 00000000..4b53be5b
--- /dev/null
+++ b/examples/rust/src/main.rs
@@ -0,0 +1,68 @@
+//! main.rs — Minimal example using the zwasm C API via FFI
+//!
+//! Demonstrates: load module, invoke exported function, read result.
+//!
+//! Build: zig build lib && cargo build
+//! Run:   cargo run
+
+#[repr(C)]
+struct zwasm_module_t {
+    _private: [u8; 0],
+}
+
+#[link(name = "zwasm")]
+unsafe extern "C" {
+    fn zwasm_module_new(wasm_ptr: *const u8, len: usize) -> *mut zwasm_module_t;
+    fn zwasm_module_invoke(
+        module: *mut zwasm_module_t,
+        name: *const std::ffi::c_char,
+        args: *const u64,
+        nargs: u32,
+        results: *mut u64,
+        nresults: u32,
+    ) -> bool;
+    fn zwasm_module_delete(module: *mut zwasm_module_t);
+    fn zwasm_last_error_message() -> *const std::ffi::c_char;
+}
+
+/* Wasm module: export "f" () -> i32 { return 42 } */
+const WASM: &[u8] = &[
+    0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x05, 0x01, 0x60, 0x00, 0x01, 0x7f, 0x03,
+    0x02, 0x01, 0x00, 0x07, 0x05, 0x01, 0x01, 0x66, 0x00, 0x00, 0x0a, 0x06, 0x01, 0x04, 0x00, 0x41,
+    0x2a, 0x0b,
+];
+
+fn main() {
+    unsafe {
+        let module = zwasm_module_new(WASM.as_ptr(), WASM.len());
+
+        if module.is_null() {
+            let err_msg = zwasm_last_error_message();
+            let c_str = std::ffi::CStr::from_ptr(err_msg);
+            eprintln!("Failed to create module: {}", c_str.to_str().unwrap());
+            return;
+        }
+
+        let name = std::ffi::CString::new("f").unwrap();
+        let mut results = [0u64; 1];
+        let ok = zwasm_module_invoke(
+            module,
+            name.as_ptr(),
+            std::ptr::null(),
+            0,
+            results.as_mut_ptr(),
+            results.len() as u32,
+        );
+
+        if !ok {
+            let err_msg = zwasm_last_error_message();
+            let c_str = std::ffi::CStr::from_ptr(err_msg);
+            eprintln!("Invoke error: {}", c_str.to_str().unwrap());
+            zwasm_module_delete(module);
+            return;
+        }
+
+        println!("f() = {}", results[0]);
+        zwasm_module_delete(module);
+    }
+}

From 29614a0925b5c7b5423ed95d78201773b0bc3b21 Mon Sep 17 00:00:00 2001
From: Junji Takakura <j.takakura@gmail.com>
Date: Sat, 21 Mar 2026 09:19:31 +0900
Subject: [PATCH 2/2] Update README: add Rust example section

---
 README.md                 | 4 ++++
 examples/rust/src/main.rs | 4 ++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 1cda336b..c1840bf8 100644
--- a/README.md
+++ b/README.md
@@ -187,6 +187,10 @@ C example using `libzwasm`: load a module, invoke an export, read the result.
 
 Python ctypes example: same workflow as C, no compiled bindings needed.
 
+### Rust examples (`examples/rust/`)
+
+Rust FFI example: same workflow as C, using `extern "C"` bindings.
+
 ## Build
 
 Requires Zig 0.15.2.
diff --git a/examples/rust/src/main.rs b/examples/rust/src/main.rs
index 4b53be5b..1f9dcd74 100644
--- a/examples/rust/src/main.rs
+++ b/examples/rust/src/main.rs
@@ -16,7 +16,7 @@ unsafe extern "C" {
     fn zwasm_module_invoke(
         module: *mut zwasm_module_t,
         name: *const std::ffi::c_char,
-        args: *const u64,
+        args: *mut u64,
         nargs: u32,
         results: *mut u64,
         nresults: u32,
@@ -48,7 +48,7 @@ fn main() {
         let ok = zwasm_module_invoke(
             module,
             name.as_ptr(),
-            std::ptr::null(),
+            std::ptr::null_mut(),
             0,
             results.as_mut_ptr(),
             results.len() as u32,