ffi-rs

A module written in Rust and N-API provides interface (FFI) features for Node.js

Description

ffi-rs is a high-performance module written in Rust and N-API that provides FFI (Foreign Function Interface) features for Node.js. It allows developers to call functions written in other languages such as C++, C, and Rust directly from JavaScript without writing any C++ code.

This module aims to provide similar functionality to the node-ffi module but with a completely rewritten underlying codebase. The node-ffi module has been unmaintained for several years and is no longer usable, so ffi-rs was developed to fill that void.

features

• High performance ✨
• Simpler data description and API interface 💗
• Support more different data types between Node.js and c 😊
• Support modify data in place 🥸
• Provide many ways to handle pointer type directly 🐮
• Support run ffi task in a new thread 🤩️
• Support output errno info 🤔️

benchmark

$ node bench/bench.js
Running "ffi" suite...
Progress: 100%

  ffi-napi:
    2 028 ops/s, ±4.87%     | slowest, 99.24% slower

  ffi-rs:
    318 467 ops/s, ±0.17%   | fastest

Finished 2 cases!
  Fastest: ffi-rs
  Slowest: ffi-napi

install

$ npm i ffi-rs

Support type

Currently, ffi-rs only supports these types of parameters and return values. However, support for more types may be added in the future based on actual usage scenarios.

Basic Type

• string
• u8
• i32
• i64
• u64
• void(like js undefined)
• float(can only be used as paramsType instead of retType)
• double
• boolean

Reference Type

• pointer
• u8Array(buffer)
• i32Array
• stringArray
• doubleArray
• floatArray(can only be used as paramsType instead of retType)
• object(Nested object is also supported at the latest version)
• function

C++ Class

If you want to call C++ function whose argument type is class, you can use pointer type, see tutorial

Support Platform

Note: You need to make sure that the compilation environment of the dynamic library is the same as the installation and runtime environment of the ffi-rs call.

• darwin-x64
• darwin-arm64
• linux-x64-gnu
• linux-x64-musl
• win32-x64-msvc
• win32-ia32-msvc
• linux-arm64-gnu
• linux-arm64-musl

Usage

View test.ts get the latest usage

Here is an example of how to use ffi-rs:

For the following C++ code, we compile this file into a dynamic library

write foreign function code

Note: The return value type of a function must be of type c

#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>

extern "C" int sum(int a, int b) { return a + b; }

extern "C" double doubleSum(double a, double b) { return a + b; }

extern "C" const char *concatenateStrings(const char *str1, const char *str2) {
  std::string result = std::string(str1) + std::string(str2);
  char *cstr = new char[result.length() + 1];
  strcpy(cstr, result.c_str());
  return cstr;
}

extern "C" void noRet() { printf("%s", "hello world"); }
extern "C" bool return_opposite(bool input) { return !input; }

compile C code into a dynamic library

$ g++ -dynamiclib -o libsum.so cpp/sum.cpp # macos
$ g++ -shared -o libsum.so cpp/sum.cpp # linux
$ g++ -shared -o sum.dll cpp/sum.cpp # win

call dynamic library by ffi-rs

Then you can use ffi-rs to invoke the dynamic library file that contains functions.

Initialization

Suggested develop with typescript to get type hints

const { equal } = require('assert')
const { load, DataType, open, close, arrayConstructor, define } = require('ffi-rs')
const a = 1
const b = 100
const dynamicLib = platform === 'win32' ? './sum.dll' : "./libsum.so"
// first open dynamic library with key for close
// It only needs to be opened once.
open({
  library: 'libsum', // key
  path: dynamicLib // path
})
const r = load({
  library: "libsum", // path to the dynamic library file
  funcName: 'sum', // the name of the function to call
  retType: DataType.I32, // the return value type
  paramsType: [DataType.I32, DataType.I32], // the parameter types
  paramsValue: [a, b] // the actual parameter values
})
equal(r, a + b)
// release library memory when you're not using it.
close('libsum')

// use define function to define a function signature

const res = define({
  sum: {
    library: "libsum",
    retType: DataType.I32,
    paramsType: [DataType.I32, DataType.I32],
  },
  atoi: {
    library: "libnative",
    retType: DataType.I32,
    paramsType: [DataType.String],
    paramsValue: ["1000"],
  }
})
equal(res.sum([1, 2]), 3)
equal(res.atoi(["1000"]), 1000)

Load Main Program handle

You can alse pass emptry path string in open function like ffi-napi to get the main program handle refer dlopen

open({
  library: "libnative",
  path: "",
});
// In darwin/linux, you can call atoi function which is included in the basic c library
equal(
  load({
    library: "libnative",
    funcName: "atoi",
    retType: DataType.I32,
    paramsType: [DataType.String],
    paramsValue: ["1000"],
  }),
  1000,
);

Basic Types

number|string|boolean|double|void are basic types

const c = "foo"
const d = c.repeat(200)

equal(c + d, load({
  library: 'libsum',
  funcName: 'concatenateStrings',
  retType: DataType.String,
  paramsType: [DataType.String, DataType.String],
  paramsValue: [c, d]
}))

equal(undefined, load({
  library: 'libsum',
  funcName: 'noRet',
  retType: DataType.Void,
  paramsType: [],
  paramsValue: []
}))


equal(1.1 + 2.2, load({
  library: 'libsum',
  funcName: 'doubleSum',
  retType: DataType.Double,
  paramsType: [DataType.Double, DataType.Double],
  paramsValue: [1.1, 2.2]
}))
const bool_val = true
equal(!bool_val, load({
  library: 'libsum',
  funcName: 'return_opposite',
  retType: DataType.Boolean,
  paramsType: [DataType.Boolean],
  paramsValue: [bool_val],
}))

Buffer

In the latest version, ffi-rs supports modifying data in place.

The sample code is as follows

extern int modifyData(char* buffer) {
    // modify buffer data in place
}

const arr = Buffer.alloc(200) // create buffer
const res = load({
  library: "libsum",
  funcName: "modifyData",
  retType: DataType.I32,
  paramsType: [
    DataType.U8Array
  ],
  paramsValue: [arr]
})
console.log(arr) // buffer data can be updated

Array

When using array as retType, you should use arrayConstructor to specify the array type with a legal length which is important.

If the length is incorrect, the program may exit abnormally

extern "C" int *createArrayi32(const int *arr, int size) {
  int *vec = (int *)malloc((size) * sizeof(int));

  for (int i = 0; i < size; i++) {
    vec[i] = arr[i];
  }
  return vec;
}
extern "C" double *createArrayDouble(const double *arr, int size) {
  double *vec = (double *)malloc((size) * sizeof(double));
  for (int i = 0; i < size; i++) {
    vec[i] = arr[i];
  }
  return vec;
}

extern "C" char **createArrayString(char **arr, int size) {
  char **vec = (char **)malloc((size) * sizeof(char *));
  for (int i = 0; i < size; i++) {
    vec[i] = arr[i];
  }
  return vec;
}

let bigArr = new Array(100).fill(100)
deepStrictEqual(bigArr, load({
  library: 'libsum',
  funcName: 'createArrayi32',
  retType: arrayConstructor({ type: DataType.I32Array, length: bigArr.length }),
  paramsType: [DataType.I32Array, DataType.I32],
  paramsValue: [bigArr, bigArr.length],
}))

let bigDoubleArr = new Array(5).fill(1.1)
deepStrictEqual(bigDoubleArr, load({
  library: 'libsum',
  funcName: 'createArrayDouble',
  retType: arrayConstructor({ type: DataType.DoubleArray, length: bigDoubleArr.length }),
  paramsType: [DataType.DoubleArray, DataType.I32],
  paramsValue: [bigDoubleArr, bigDoubleArr.length],
}))
let stringArr = [c, c.repeat(20)]

deepStrictEqual(stringArr, load({
  library: 'libsum',
  funcName: 'createArrayString',
  retType: arrayConstructor({ type: DataType.StringArray, length: stringArr.length }),
  paramsType: [DataType.StringArray, DataType.I32],
  paramsValue: [stringArr, stringArr.length],
}))

Pointer

In ffi-rs, we use DataType.External for wrapping the pointer which enables it to be passed between Node.js and C.

Pointer is complicated and underlying, ffi-rs provide four functions to handle this pointer include createPointer, restorePointer, wrapPointer, unwrapPointer for different scene.

extern "C" const char *concatenateStrings(const char *str1, const char *str2) {
  std::string result = std::string(str1) + std::string(str2);
  char *cstr = new char[result.length() + 1];
  strcpy(cstr, result.c_str());
  return cstr;
}

extern "C" char *getStringFromPtr(void *ptr) { return (char *)ptr; };

// get pointer
const ptr = load({
  library: "libsum",
  funcName: "concatenateStrings",
  retType: DataType.External,
  paramsType: [DataType.String, DataType.String],
  paramsValue: [c, d],
})

// send pointer
const string = load({
  library: "libsum",
  funcName: "getStringFromPtr",
  retType: DataType.String,
  paramsType: [DataType.External],
  paramsValue: [ptr],
})

createPointer

createPointer function is used for create a pointer point to specify type. In order to avoid mistaks, developers have to understand what type this pointer is.

For numeric type like i32|u8|i64|f64, createPointer will create a pointer like *mut i32 point to there number

For types that are originally pointer types like char * represent string type in c, createPointer will create a dual pointer like *mut *mut c_char point to *mut c_char.Developers can use unwrapPointer get the interal pointer *mut c_char

let bigDoubleArr = new Array(5).fill(1.1);
deepStrictEqual(
  bigDoubleArr,
  load({
    library: "libsum",
    funcName: "createArrayDouble",
    retType: arrayConstructor({
      type: DataType.DoubleArray,
      length: bigDoubleArr.length,
    }),
    paramsType: [DataType.DoubleArray, DataType.I32],
    paramsValue: [bigDoubleArr, bigDoubleArr.length],
  }),
);

For the code above, we can use createPointer function to wrap a pointer data and send it as paramsValue

const ptrArr: unknown[] = createPointer({
  paramsType: [DataType.DoubleArray],
  paramsValue: [[1.1,2.2]]
})

load({
  library: "libsum",
  funcName: "createArrayDouble",
  retType: arrayConstructor({
    type: DataType.DoubleArray,
    length: bigDoubleArr.length,
  }),
  paramsType: [DataType.External, DataType.I32],
  paramsValue: [unwrapPointer(ptrArr)[0], bigDoubleArr.length],
})

The two pieces of code above are equivalent

restorePointer

Similarly, you can use restorePointer to restore data from pointer which is wrapped by createPointer or as a return value of foreign function

const pointerArr = createPointer({
  paramsType: [DataType.DoubleArray],
  paramsValue: [[1.1, 2.2]]
})
const restoreData = restorePointer({
  retType: [arrayConstructor({
    type: DataType.DoubleArray,
    length: 2
  })],
  paramsValue: pointerArr
})
deepStrictEqual(restoreData, [[1.1, 2.2]])

wrapPointer

wrapPointer is used to create multiple pointer.

For example, developers can use wrapPointer to create a pointer point to other existing pointer.

const { wrapPointer } = require('ffi-rs')
// ptr type is *mut c_char
const ptr = load({
  library: "libsum",
  funcName: "concatenateStrings",
  retType: DataType.External,
  paramsType: [DataType.String, DataType.String],
  paramsValue: [c, d],
})

// wrapPtr type is *mut *mut c_char
const wrapPtr = wrapPointer([ptr])[0]

unwrapPointer

unwrapPointer is oppsite to wrapPointer which is used to get the internal pointer for multiple pointer

const { unwrapPointer, createPointer } = require('ffi-rs')
// ptr type is *mut *mut c_char
let ptr = createPointer({
  paramsType: [DataType.String],
  paramsValue: ["foo"]
})

// unwrapPtr type is *mut c_char
const unwrapPtr = unwrapPointer([ptr])[0]

Struct

To create a c struct or get a c struct as a return type, you need to define the types of the parameters strictly in the order in which the fields of the c structure are defined.

ffi-rs provide a c struct named Person with many types of field in sum.cpp

The example call method about how to call foreign function to create Person struct or use Person struct as a return value is here

Use array in struct

There are two types of array in c language like int* array and int array[100] yhat have some different usages.

The first type int* array is a pointer type store the first address of the array.

The second type int array[100] is a fixed length array and each element in array has continous address.

If you use a array as function parameter, this usually passes an array pointer regardless of which type you define.But if the array type is defined in struct, the two types of array define will cause different size and align of struct.

So, ffi-rs need to distinguish between the two types.

By default, ffi-rs use pointer array to calculate struct. If you confirm there should use static array, you can define it in the way

typedef struct Person {
  //...
  uint8_t staticBytes[16];
  //...
} Person;

// use arrayConstructor and set dynamicArray field to false
staticBytes: arrayConstructor({
  type: DataType.U8Array,
  length: parent.staticBytes.length,
  dynamicArray: false
}),

Function

ffi-rs supports passing js function to c, like this

typedef const void (*FunctionPointer)(int a, bool b, char *c, double d,
                                      char **e, int *f, Person *g);

extern "C" void callFunction(FunctionPointer func) {
  printf("callFunction\n");

  for (int i = 0; i < 2; i++) {
    int a = 100;
    bool b = false;
    double d = 100.11;
    char *c = (char *)malloc(14 * sizeof(char));
    strcpy(c, "Hello, World!");

    char **stringArray = (char **)malloc(sizeof(char *) * 2);
    stringArray[0] = strdup("Hello");
    stringArray[1] = strdup("world");

    int *i32Array = (int *)malloc(sizeof(int) * 3);
    i32Array[0] = 101;
    i32Array[1] = 202;
    i32Array[2] = 303;

    Person *p = createPerson();
    func(a, b, c, d, stringArray, i32Array, p);
  }
}

Corresponds to the code above，you can use ffi-rs like

let count = 0;
const func = (a, b, c, d, e, f, g) => {
  equal(a, 100);
  equal(b, false);
  equal(c, "Hello, World!");
  equal(d, "100.11");
  deepStrictEqual(e, ["Hello", "world"]);
  deepStrictEqual(f, [101, 202, 303]);
  deepStrictEqual(g, person);
  console.log("callback called");
  count++;
  if (count === 4) {
    logGreen("test succeed");
    process.exit(0);
  }
};
const funcExternal = createPointer({
  paramsType: [funcConstructor({
    paramsType: [
      DataType.I32,
      DataType.Boolean,
      DataType.String,
      DataType.Double,
      arrayConstructor({ type: DataType.StringArray, length: 2 }),
      arrayConstructor({ type: DataType.I32Array, length: 3 }),
      personType,
    ],
    retType: DataType.Void,
  })],
  paramsValue: [func]
})
load({
  library: "libsum",
  funcName: "callFunction",
  retType: DataType.Void,
  paramsType: [funcConstructor({
    paramsType: [
      DataType.I32,
      DataType.Boolean,
      DataType.String,
      DataType.Double,
      arrayConstructor({ type: DataType.StringArray, length: 2 }),
      arrayConstructor({ type: DataType.I32Array, length: 3 }),
      personType,
    ],
    retType: DataType.Void,
  })],
  paramsValue: [func]
});
load({
  library: "libsum",
  funcName: "callFunction",
  retType: DataType.Void,
  paramsType: [
    DataType.External,
  ],
  paramsValue: unwrapPointer(funcExternal),
});

The function parameters supports type are all in the example above

Attention，since the vast majority of scenarios developers pass js function to c as a callback, so ffi-rs will create threadsafe_function from jsfunction which means the jsfunction will be called asynchronous, and Node.js process will not be exited automatically

C++

We'll provide more examples from real-world scenarios, if you have any ideas, please submit an issue

class type

In C++ scene, we can use DataType.External to get a class type pointer

In the code below, we use C types to wrap C++ types such as convert char * to std::string and return class pointer

MyClass *createMyClass(std::string name, int age) {
  return new MyClass(name, age);
}

extern "C" MyClass *createMyClassFromC(const char *name, int age) {
  return createMyClass(std::string(name), age);
}

extern "C" void printMyClass(MyClass *instance) { instance->print(); }

And then, it can called by the following code

const classPointer = load({
  library: "libsum",
  funcName: "createMyClassFromC",
  retType: DataType.External,
  paramsType: [
    DataType.String,
    DataType.I32
  ],
  paramsValue: ["classString", 26],
});
load({
  library: "libsum",
  funcName: "printMyClass",
  retType: DataType.External,
  paramsType: [
    DataType.External,
  ],
  paramsValue: [classPointer],
})

errno

By default, ffi-rs will not output errno info, developers can get it by pass errno: true when call open method like

load({
   library: 'libnative',
   funcName: 'setsockopt',
   retType: DataType.I32,
   paramsType: [DataType.I32, DataType.I32, DataType.I32, DataType.External, DataType.I32],
   paramsValue: [socket._handle.fd, level, option, pointer[0], 4],
   errno: true // set errno as true
})

// The above code will return a object include three fields include errnoCode, errnoMessage, and the foreign function return value
// { errnoCode: 22, errnoMessage: 'Invalid argument (os error 22)', value: -1 }

runInNewThread

ffi-rs support run ffi task in a new thread without blocking the main thread which is useful for cpu intensive task.

To use the feature, you can pass runInNewThread option to load method

const testRunInNewThread = async () => {
  // will return a promise but the task will run in a new thread
  load({
    library: "libsum",
    funcName: "sum",
    retType: DataType.I32,
    paramsType: [DataType.I32, DataType.I32],
    paramsValue: [1, 2],
    runInNewThread: true,
  }).then(res => {
    equal(res, 3)
  })
}