Introduction to ffi-napi

ffi-napi is a powerful Node.js package that provides a Foreign Function Interface (FFI) to call functions in compiled shared libraries directly from Node.js. This capability makes it easier to interact with native code, enabling high-performance integrations and system-level programming. In this article, we will explore the ffi-napi library, demonstrate its numerous APIs, and present an application example utilizing these APIs.

Overview of ffi-napi APIs

Below are several APIs provided by ffi-napi, along with their explanations and usage examples:

Loading a Shared Library

  const ffi = require('ffi-napi');
  const libm = ffi.Library('libm', {
    'cos': ['double', ['double']]
  });
  console.log(libm.cos(2)); // Outputs the cosine of 2

Defining Functions

  const ffi = require('ffi-napi');
  const libmath = ffi.Library('libmath', {
    'add': ['int', ['int', 'int']],
    'subtract': ['int', ['int', 'int']]
  });
  console.log(libmath.add(1, 2)); // 3
  console.log(libmath.subtract(5, 3)); // 2

Callback Functions

  const ffi = require('ffi-napi');
  const ref = require('ref-napi');
  const int = ref.types.int;
  const callback = ffi.Callback('void', [int], (result) => {
    console.log('Callback called with:', result);
  });
  const library = ffi.Library('library', {
    'functionWithCallback': ['void', [ffi.Function('void', [int])]]
  });
  library.functionWithCallback(callback); 

Structs in ffi-napi

  const ffi = require('ffi-napi');
  const ref = require('ref-napi');
  const StructType = require('ref-struct-di')(ref);
  const Point = StructType({
    'x': ref.types.int,
    'y': ref.types.int
  });
  const libgeo = ffi.Library('libgeo', {
    'movePoint': ['void', [Point]]
  });
  const point = new Point();
  point.x = 10;
  point.y = 20;
  libgeo.movePoint(point);

Union in ffi-napi

  const ffi = require('ffi-napi');
  const ref = require('ref-napi');
  const UnionType = require('ref-union-di')(ref);
  const Number = UnionType({
    'intVal': ref.types.int,
    'floatVal': ref.types.float
  });
  const libnum = ffi.Library('libnum', {
    'readNumber': ['void', [Number]]
  });
  const num = new Number();
  num.intVal = 42;
  libnum.readNumber(num);

Application Example Using ffi-napi

In this example, we will create a simple Node.js application that calls a native library to perform basic mathematical operations.

Creating the Shared Library (mathlib.c)

  #include <stdio.h>
  int add(int a, int b) {
    return a + b;
  }
  int subtract(int a, int b) {
    return a - b;
  }

Compiling the Shared Library

  gcc -shared -o libmath.so -fPIC mathlib.c

Node.js Application (app.js)

  const ffi = require('ffi-napi');
  const mathlib = ffi.Library('./libmath', {
    'add': ['int', ['int', 'int']],
    'subtract': ['int', ['int', 'int']]
  });
  console.log('Addition:', mathlib.add(10, 5)); // Addition: 15
  console.log('Subtraction:', mathlib.subtract(10, 5)); // Subtraction: 5

Conclusion

ffi-napi is an invaluable tool for developers looking to leverage existing native libraries within Node.js applications. Its comprehensive API, as demonstrated above, provides an intuitive and efficient method to bridge the gap between JavaScript and languages like C/C++. This can lead to performance improvements and expanded capabilities within your Node.js projects.

By understanding and utilizing ffi-napi, you can unlock a new level of integration and performance in your applications.

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