Use mutable char to pass signature in ffi

.github/workflows/qaci.yml

@@ -113,7 +113,7 @@ jobs:
           python-version: "3.11"
 
       - name: Smoke test
-        run: pip install wheel && pip install web3 cffi && python ffi/rings.py
+        run: pip install wheel && pip install web3 cffi && python examples/ffi/rings.py
 
   rustfmt_and_clippy:
     name: Check rustfmt style && run clippy

ffi/rings.py → examples/ffi/rings.py

@@ -9,7 +9,7 @@
 acc = w3.eth.account.create()
 
 ffi = cffi.FFI()
-c_header = open("./ffi/rings.h", "r").read()
+c_header = open("./target/include/rings.h", "r").read()
 c_header = re.sub(r"#define .*", "", c_header)
 ffi.cdef(c_header)
 
@@ -22,22 +22,25 @@
     extension = "so"
 
 
-@ffi.callback("char*(*)(char *)")
-def signer(msg):
+@ffi.callback("void (*)(const char *, char *)")
+def signer(msg, output):
     c_input = ffi.string(msg)
     decoded = encode_defunct(c_input)
     sig = acc.sign_message(decoded)
-    ret = bytes(sig.signature)
-    return ffi.new("char[]", ret)
+    print("signature", sig.signature)
+    print("signature len", len(sig.signature))
+    ffi.memmove(output, sig.signature, len(sig.signature))
+    print("output", ffi.string(output))
+    return
 
 
-@ffi.callback("void(*)(char *, char *)")
+@ffi.callback("void(*)(const char *, const char *)")
 def custom_msg_callback(msg):
     print(msg)
     return
 
 
-@ffi.callback("void(*)(char *)")
+@ffi.callback("void(*)(const char *)")
 def builtin_msg_callback(msg):
     print(msg)
     return

node/build.rs

@@ -10,11 +10,11 @@ fn gen_cbinding() {
         .with_language(cbindgen::Language::C)
         .with_no_includes()
         .with_documentation(true)
-        .with_crate(crate_dir)
+        .with_crate(&crate_dir)
         .generate()
     {
         Ok(g) => {
-            g.write_to_file("../ffi/rings.h");
+            g.write_to_file(crate_dir + "/../target/include/rings.h");
         }
         Err(e) => println!("Unable to generate bindings, {:?}", e),
     };

node/src/client/ffi.rs

@@ -317,18 +317,25 @@ pub unsafe extern "C" fn new_client_with_callback(
     stabilize_timeout: u32,
     account: *const c_char,
     account_type: *const c_char,
-    signer: extern "C" fn(*const c_char) -> *const c_char,
+    signer: extern "C" fn(*const c_char, *mut c_char) -> (),
     callback_ptr: *const MessageCallbackInstanceFFI,
 ) -> ClientPtr {
     fn wrapped_signer(
-        signer: extern "C" fn(*const c_char) -> *const c_char,
+        signer: extern "C" fn(*const c_char, *mut c_char) -> (),
     ) -> impl Fn(String) -> Vec<u8> {
         move |data: String| -> Vec<u8> {
             let c_data = CString::new(data).expect("Failed to convert String to CString");
-            let sig = signer(c_data.as_ptr());
-            let c_ret = c_char_to_bytes(sig).expect("Failed to convert c char to [u8]");
+
+            let mut sig = Vec::<u8>::with_capacity(65);
+            let sig_ptr = sig.as_mut_ptr() as *mut c_char;
+            signer(c_data.as_ptr(), sig_ptr);
+
+            let c_ret = c_char_to_bytes(sig_ptr).expect("Failed to convert c char to [u8]");
             let c_ret_len = c_ret.len();
-            assert!(c_ret.len() >= 64, "sig length({c_ret_len} < 64) is invalid");
+            assert!(
+                c_ret.len() >= 64,
+                "sig length({c_ret_len} < 64) is invalid: {c_ret:?}"
+            );
             c_ret
         }
     }