Callback functions from Rust to Go

Question content

I'm trying to create the possibility to call a rust function from go and then said rust function calls back the function to go. I'm using cgo as the ffi interface between go and rust. The following is my go code (src/main.go):

package main

import (
    "c"
    "fmt"
    "unsafe"
)

/*
#cgo cflags: -i./../lib
#cgo ldflags: -l./../bin -lgo_move -wl,-rpath=./bin
#include "move.h"
*/

//export cosmoscallbackwrapper
func cosmoscallbackwrapper(data *c.uchar, datalen c.int) {
    // convert data to go slice
    godata := c.gobytes(unsafe.pointer(data), datalen)

    // call the actual callback function
    cosmoscallback(godata)
}

// setcosmoscallback sets the callback function to be called by the move vm.
func setcosmoscallback(callback func([]byte)) {
    cosmoscallback = callback
    c.set_cosmos_callback((c.cosmos_callback)(unsafe.pointer(c.cosmoscallbackwrapper)))
}

var cosmoscallback func([]byte)

func main() {
    // create a new move interpreter

    // set the callback function
    setcosmoscallback(func(data []byte) {
        fmt.println("received data from move vm:", data)
        // handle data and call cosmos sdk functions as needed
    })
}

This is my rust code (src/lib.rs)

use std::os::raw::{c_char, c_int};
use std::ffi::cstring;
use std::sync::mutex;
#[macro_use] extern crate lazy_static;
pub fn main() {
}
pub type cosmoscallback = extern "c" fn(*const c_char, c_int);

lazy_static! {
        static ref callback: mutex<option<cosmoscallback>> = mutex::new(none);
}

#[no_mangle]
pub extern "c" fn set_cosmos_callback(callback: cosmoscallback) {
        let mut cb = callback.lock().unwrap();
        *cb = some(callback);
}
#[no_mangle]
pub extern "c" fn cosmoscallbackwrapper(data: *const c_char, data_len: c_int) {
    let cb = callback.lock().unwrap();
    if let some(callback) = &*cb {
        callback(data, data_len);
    }
}

This is my cargo.toml file:

[package]
name = "go-move"
version = "0.1.0"
edition = "2021"

[lib]
crate-type = ["cdylib"]

[dependencies]
libc = "0.2"
lazy_static = "1.4.0"


[workspace]
members = [    ".",]

This is lib/move.h (header file of shared library):

#ifndef move_vm_lib_h
#define move_vm_lib_h

#include <stdint.h>
//typedef void (*cosmos_callback)(const unsigned char *data, int data_len);
//void set_cosmos_callback(cosmos_callback callback);

typedef void (*cosmos_callback)(const uint8_t* data, int32_t data_len);

void set_cosmos_callback(cosmos_callback callback);
#endif

This is my makefile:

shell := /bin/bash
.phony: build
os = $(shell uname)
clean:
        rm -rf bin
        rm -rf target
build:
        @echo the os is $(os)
        mkdir bin
        cargo build --release
ifeq ($(os),linux)
        cp target/release/libgo_move.so bin/
else
        cp target/release/libgo_move.dylib bin/
endif
        cp -a lib/. bin/
        go build --ldflags="-l./bin -lgo_move" -o bin/main src/main.go
run:
        export ld_library_path=./bin && ./main

The file structure is as follows:

src
    main.go
    main.rs
bin
    libgo_move.so (after cargo build)
lib
    move.h
cargo.toml
makefile

After running make clean build I get the following output:

cp target/release/libgo_move.so bin/
cp -a lib/. bin/
go build -o bin/main  src/main.go
# command-line-arguments
src/main.go:27:59: could not determine kind of name for C.cosmosCallbackWrapper
src/main.go:27:25: could not determine kind of name for C.cosmos_callback
src/main.go:27:2: could not determine kind of name for C.set_cosmos_callback

For some reason it can't find the ffi function.

Correct answer

This is a stupid mistake:

/*
#cgo CFLAGS: -I./../lib
#cgo LDFLAGS: -L./../bin -lgo_move -Wl,-rpath=./bin
#include "move.h"
*/

Must be done before importing. That's all.

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