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ffi-napi

A foreign function interface (FFI) for Node.js, N-API style

    4.0.3latest
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    npm

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node-ffi-napi

Node.js Foreign Function Interface for N-API

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node-ffi-napi is a Node.js addon for loading and calling dynamic libraries using pure JavaScript. It can be used to create bindings to native libraries without writing any C++ code.

It also simplifies the augmentation of node.js with C code as it takes care of handling the translation of types across JavaScript and C, which can add reams of boilerplate code to your otherwise simple C. See the example/factorial for an example of this use case.

WARNING: node-ffi-napi assumes you know what you're doing. You can pretty easily create situations where you will segfault the interpreter and unless you've got C debugger skills, you probably won't know what's going on.

WARNING: The original API of node-ffi is left mostly untouched in the N-API wrapper. However, the API did not have very well-defined properties in the context of garbage collection and multi-threaded execution. It is recommended to avoid any multi-threading usage of this library if possible.

Example

var ffi = require('ffi-napi');

var libm = ffi.Library('libm', {
  'ceil': [ 'double', [ 'double' ] ]
});
libm.ceil(1.5); // 2

// You can also access just functions in the current process by passing a null
var current = ffi.Library(null, {
  'atoi': [ 'int', [ 'string' ] ]
});
current.atoi('1234'); // 1234

For a more detailed introduction, see the node-ffi tutorial page.

Requirements

  • Linux, OS X, Windows, or Solaris.
  • libffi comes bundled with node-ffi-napi; it does not need to be installed on your system.
  • The current version is tested to run on Node 6 and above.

Installation

Make sure you've installed all the necessary build tools for your platform, then invoke:

$ npm install ffi-napi

Source Install / Manual Compilation

To compile from source it's easiest to use node-gyp:

$ npm install -g node-gyp

Now you can compile node-ffi-napi:

$ git clone git://github.com/node-ffi-napi/node-ffi-napi.git
$ cd node-ffi
$ node-gyp rebuild

Types

The types that you specify in function declarations correspond to ref's types system. So see its docs for a reference if you are unfamiliar.

V8 and 64-bit Types

Internally, V8 stores integers that will fit into a 32-bit space in a 32-bit integer, and those that fall outside of this get put into double-precision floating point numbers. This is problematic because FP numbers are imprecise. To get around this, the methods in node-ffi that deal with 64-bit integers return strings and can accept strings as parameters.

Call Overhead

There is non-trivial overhead associated with FFI calls. Comparing a hard-coded binding version of strtoul() to an FFI version of strtoul() shows that the native hard-coded binding is orders of magnitude faster. So don't just use the C version of a function just because it's faster. There's a significant cost in FFI calls, so make them worth it.

License

MIT License. See the LICENSE file.

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Last updated on 18 Mar 2021

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Socket installs a GitHub app to automatically flag issues on every pull request and report the health of your dependencies. Find out what is inside your node modules and prevent malicious activity before you update the dependencies.

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