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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 ✨
• Better type hints 🧐
• Simpler data description and API interface 💗
• Support more different data types between Node.js and C 😊
• Support modifying data in place 🥸
• Provide many ways to handle pointer type directly 🐮
• Support running ffi task in a new thread 🤩️
• Support output errno info 🤔️
• No need to use ref to handle pointer 🤫

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

Changelog

See CHANGELOG.md

Ecosystem

abstract-socket-rs

Install

$ npm i ffi-rs

Supported Types

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 Types

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

Reference Types

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

C++ Class

If you want to call a C++ function whose argument type is a class, you can use the pointer type. See tutorial

Supported Platforms

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
• win32-arm64-msvc
• linux-arm64-gnu
• linux-arm64-musl
• linux-arm-gnueabihf

Usage

View test.ts for 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 # Windows

Call Dynamic Library Using ffi-rs

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

Initialization

It's suggested to 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
  // freeResultMemory: true, // whether or not need to free the result of return value memory automatically, default is false
})
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],
  }
})
equal(res.sum([1, 2]), 3)
equal(res.atoi(["1000"]), 1000)

Load Main Program Handle

You can also pass an empty path string in the open function like ffi-napi to get the main program handle. Refer to dlopen

open({
  library: "libnative",
  path: "",
});
// In Darwin/Linux, you can call the 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 provides four functions to handle this pointer including createPointer, restorePointer, unwrapPointer, wrapPointer, freePointer, isNullPointer for different scenes.

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 creating a pointer pointing to a specified type. In order to avoid mistakes, developers have to understand what type this pointer is.

For numeric types like i32|u8|i64|f64, createPointer will create a pointer like *mut i32 pointing to these numbers.

For types that are originally pointer types like char * representing string type in C, createPointer will create a dual pointer like *mut *mut c_char pointing to *mut c_char. Developers can use unwrapPointer to get the internal 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 a pointer which is wrapped by createPointer or as a return value of a 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]])

freePointer

freePointer is used to free memory which is not freed automatically.

By default, ffi-rs will free data memory for ffi call args and return result to prevent memory leaks. Except in the following cases:

• set freeResultMemory: false when calling load method

If you set freeResultMemory to false, ffi-rs will not release the return result memory which was allocated in the C environment

• Use DataType.External as paramsType or retType

If developers use DataType.External as paramsType or retType, please use freePointer to release the memory of the pointer. ref test.ts

wrapPointer

wrapPointer is used to create multiple pointers.

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

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 opposite to wrapPointer which is used to get the internal pointer for multiple pointers

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 provides a C struct named Person with many types of fields in sum.cpp

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

Use array in struct

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

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

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

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

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

By default, ffi-rs uses pointer arrays to calculate struct. If you confirm there should be a static array, you can define it in this 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 pointers to C functions, 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);
  }
}

Corresponding to the code above, you can use ffi-rs like this:

const testFunction = () => {
  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);
    logGreen("test function succeed");
    // free function memory when it is not in use
    freePointer({
      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: funcExternal
    })
    if (!process.env.MEMORY) {
      close("libsum");
    }
  };
  // suggest using createPointer to create a function pointer for manual memory management
  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: [
      DataType.External,
    ],
    paramsValue: unwrapPointer(funcExternal),
  });
}

The function parameters support all types in the example above.

Attention: since the vast majority of scenarios developers pass JS functions to C as callbacks, ffi-rs will create threadsafe_function from JS functions which means the JS function will be called asynchronously, and the Node.js process will not exit automatically.

C++

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

Class type

In C++ scenarios, 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 converting char * to std::string and returning a 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 be 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],
})
freePointer({
  paramsType: [DataType.External],
  paramsValue: [classPointer],
  pointerType: PointerType.CPointer
})

errno

By default, ffi-rs will not output errno info. Developers can get it by passing errno: true when calling the 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 an object including three fields: errnoCode, errnoMessage, and the foreign function return value
// { errnoCode: 22, errnoMessage: 'Invalid argument (os error 22)', value: -1 }

Memory Management

It's important to free the memory allocations during a single ffi call to prevent memory leaks.

What kinds of data memory are allocated in this?

• Call parameters in the Rust environment which are allocated in the heap like String
• Return value which in the C environment which are allocated in the heap like char*

By default, ffi-rs will free call parameters memory which are allocated in Rust.

But it will not free the return value from the C side since some C dynamic libraries will manage their memory automatically (when ffi-rs >= 1.0.79)

There are two ways to prevent ffi-rs from releasing memory:

• Set freeResultMemory: false when calling load method, the default value is false

If you set freeResultMemory to false, ffi-rs will not release the return result memory which was allocated in the C environment

• Use DataType.External as paramsType or retType

If developers use DataType.External as paramsType or retType, please use freePointer to release the memory of the pointer when this memory is no longer in use. ref test.ts

runInNewThread

ffi-rs supports running ffi tasks in a new thread without blocking the main thread, which is useful for CPU-intensive tasks.

To use this feature, you can pass the runInNewThread option to the 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)
  })
}