fix(c-api) Trap's messages are always null terminated

lib/c-api/CHANGELOG.md

@@ -8,6 +8,11 @@ Looking for changes to the Wasmer CLI and the Rust API? See our [Primary Changel
 
 ## **[Unreleased]**
 
+### Fixed
+- [#2444](https://github.com/wasmerio/wasmer/pull/2444) Trap's messages are always null terminated.
+
+## 2.0.0 - 2020/06/16
+
 ## 2.0.0-rc1 - 2020/06/02
 
 ### Added

lib/c-api/src/wasm_c_api/instance.rs

@@ -87,7 +87,7 @@ pub unsafe extern "C" fn wasm_instance_new(
 ///
 /// # Example
 ///
-/// See `wasm_instance_new`.
+/// See [`wasm_instance_new`].
 #[no_mangle]
 pub unsafe extern "C" fn wasm_instance_delete(_instance: Option<Box<wasm_instance_t>>) {}
 

lib/c-api/src/wasm_c_api/mod.rs

@@ -224,6 +224,50 @@ pub mod module;
 /// cbindgen:ignore
 pub mod store;
 
+/// A trap represents an error which stores trace message with
+/// backtrace.
+///
+/// # Example
+///
+/// ```rust
+/// # use inline_c::assert_c;
+/// # fn main() {
+/// #    (assert_c! {
+/// # #include "tests/wasmer.h"
+/// #
+/// int main() {
+///     // Create an engine and a store.
+///     wasm_engine_t* engine = wasm_engine_new();
+///     wasm_store_t* store = wasm_store_new(engine);
+///
+///     // Create the trap message.
+///     wasm_message_t message;
+///     wasm_name_new_from_string_nt(&message, "foobar");
+///
+///     // Create the trap with its message.
+///     // The backtrace will be generated automatically.
+///     wasm_trap_t* trap = wasm_trap_new(store, &message);
+///     assert(trap);
+///
+///     wasm_name_delete(&message);
+///
+///     // Do something with the trap.
+///
+///     // Free everything.
+///     wasm_trap_delete(trap);
+///     wasm_store_delete(store);
+///     wasm_engine_delete(engine);
+///
+///     return 0;
+/// }
+/// #    })
+/// #    .success();
+/// # }
+/// ```
+///
+/// Usually, a trap is returned from a host function (an imported
+/// function).
+///
 /// cbindgen:ignore
 pub mod trap;
 

lib/c-api/src/wasm_c_api/trap.rs

@@ -1,6 +1,6 @@
 use super::store::wasm_store_t;
 use super::types::{wasm_byte_vec_t, wasm_frame_t, wasm_frame_vec_t, wasm_message_t};
-use std::str;
+use std::ffi::CString;
 use wasmer::RuntimeError;
 
 // opaque type which is a `RuntimeError`
@@ -15,22 +15,98 @@ impl From<RuntimeError> for wasm_trap_t {
     }
 }
 
+/// Create a new trap message.
+///
+/// Be careful, the message is typed with `wasm_message_t` which
+/// represents a null-terminated string.
+///
+/// # Example
+///
+/// See the module's documentation for a complete example.
 #[no_mangle]
 pub unsafe extern "C" fn wasm_trap_new(
     _store: &mut wasm_store_t,
     message: &wasm_message_t,
 ) -> Option<Box<wasm_trap_t>> {
     let message_bytes = message.into_slice()?;
-    let message_str = c_try!(str::from_utf8(message_bytes));
-    let runtime_error = RuntimeError::new(message_str);
+
+    // The trap message is typed with `wasm_message_t` which is a
+    // typeref to `wasm_name_t` with the exception that it's a
+    // null-terminated string. `RuntimeError` must contain a valid
+    // Rust `String` that doesn't contain a null byte. We must ensure
+    // this behavior.
+    let runtime_error = match CString::new(message_bytes) {
+        // The string is well-formed and doesn't contain a nul byte.
+        Ok(cstring) => RuntimeError::new(cstring.into_string().ok()?),
+
+        // The string is well-formed but is nul-terminated. Let's
+        // create a `String` which is null-terminated too.
+        Err(nul_error) if nul_error.nul_position() + 1 == message_bytes.len() => {
+            let mut vec = nul_error.into_vec();
+            vec.pop();
+
+            RuntimeError::new(String::from_utf8(vec).ok()?)
+        }
+
+        // The string not well-formed.
+        Err(_) => return None,
+    };
+
     let trap = runtime_error.into();
 
     Some(Box::new(trap))
 }
 
+/// Deletes a trap.
+///
+/// # Example
+///
+/// See the module's documentation for a complete example.
 #[no_mangle]
 pub unsafe extern "C" fn wasm_trap_delete(_trap: Option<Box<wasm_trap_t>>) {}
 
+/// Gets the message attached to the trap.
+///
+/// # Example
+///
+/// ```rust
+/// # use inline_c::assert_c;
+/// # fn main() {
+/// #    (assert_c! {
+/// # #include "tests/wasmer.h"
+/// #
+/// int main() {
+///     // Create an engine and a store.
+///     wasm_engine_t* engine = wasm_engine_new();
+///     wasm_store_t* store = wasm_store_new(engine);
+///
+///     // Create the trap message.
+///     wasm_message_t message;
+///     wasm_name_new_from_string_nt(&message, "foobar");
+///
+///     // Create the trap with its message.
+///     // The backtrace will be generated automatically.
+///     wasm_trap_t* trap = wasm_trap_new(store, &message);
+///     assert(trap);
+///
+///     // Get the trap's message back.
+///     wasm_message_t retrieved_message;
+///     wasm_trap_message(trap, &retrieved_message);
+///     assert(retrieved_message.size == message.size);
+///
+///     // Free everything.
+///     wasm_name_delete(&message);
+///     wasm_name_delete(&retrieved_message);
+///     wasm_trap_delete(trap);
+///     wasm_store_delete(store);
+///     wasm_engine_delete(engine);
+///
+///     return 0;
+/// }
+/// #    })
+/// #    .success();
+/// # }
+/// ```
 #[no_mangle]
 pub unsafe extern "C" fn wasm_trap_message(
     trap: &wasm_trap_t,
@@ -39,18 +115,21 @@ pub unsafe extern "C" fn wasm_trap_message(
 ) {
     let message = trap.inner.message();
     let mut byte_vec = message.into_bytes();
-    byte_vec.push(0); // append NUL
+    byte_vec.push(0);
+
     let byte_vec: wasm_byte_vec_t = byte_vec.into();
 
     out.size = byte_vec.size;
     out.data = byte_vec.data;
 }
 
+/// Gets the origin frame attached to the trap.
 #[no_mangle]
 pub unsafe extern "C" fn wasm_trap_origin(trap: &wasm_trap_t) -> Option<Box<wasm_frame_t>> {
     trap.inner.trace().first().map(Into::into).map(Box::new)
 }
 
+/// Gets the trace (as a list of frames) attached to the trap.
 #[no_mangle]
 pub unsafe extern "C" fn wasm_trap_trace(
     trap: &wasm_trap_t,
@@ -63,3 +142,72 @@ pub unsafe extern "C" fn wasm_trap_trace(
     out.size = frame_vec.size;
     out.data = frame_vec.data;
 }
+
+#[cfg(test)]
+mod tests {
+    use inline_c::assert_c;
+
+    #[test]
+    fn test_trap_message_null_terminated() {
+        (assert_c! {
+            #include "tests/wasmer.h"
+
+            int main() {
+                wasm_engine_t* engine = wasm_engine_new();
+                wasm_store_t* store = wasm_store_new(engine);
+
+                wasm_message_t original_message;
+                wasm_name_new_from_string_nt(&original_message, "foobar");
+                assert(original_message.size == 7); // 6 for `foobar` + 1 for nul byte.
+
+                wasm_trap_t* trap = wasm_trap_new(store, &original_message);
+                assert(trap);
+
+                wasm_message_t retrieved_message;
+                wasm_trap_message(trap, &retrieved_message);
+                assert(retrieved_message.size == 7);
+
+                wasm_name_delete(&original_message);
+                wasm_name_delete(&retrieved_message);
+                wasm_trap_delete(trap);
+                wasm_store_delete(store);
+                wasm_engine_delete(engine);
+
+                return 0;
+            }
+        })
+        .success();
+    }
+
+    #[test]
+    fn test_trap_message_not_null_terminated() {
+        (assert_c! {
+            #include "tests/wasmer.h"
+
+            int main() {
+                wasm_engine_t* engine = wasm_engine_new();
+                wasm_store_t* store = wasm_store_new(engine);
+
+                wasm_message_t original_message;
+                wasm_name_new_from_string(&original_message, "foobar");
+                assert(original_message.size == 6); // 6 for `foobar` + 0 for nul byte.
+
+                wasm_trap_t* trap = wasm_trap_new(store, &original_message);
+                assert(trap);
+
+                wasm_message_t retrieved_message;
+                wasm_trap_message(trap, &retrieved_message);
+                assert(retrieved_message.size == 7);
+
+                wasm_name_delete(&original_message);
+                wasm_name_delete(&retrieved_message);
+                wasm_trap_delete(trap);
+                wasm_store_delete(store);
+                wasm_engine_delete(engine);
+
+                return 0;
+            }
+        })
+        .success();
+    }
+}

lib/engine/src/trap/error.rs

@@ -158,7 +158,7 @@ impl RuntimeError {
 
     /// Returns a reference the `message` stored in `Trap`.
     pub fn message(&self) -> String {
-        format!("{}", self.inner.source)
+        self.inner.source.to_string()
     }
 
     /// Returns a list of function frames in WebAssembly code that led to this