node-ffi
Node.js Foreign Function Interface
node-ffi 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 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.
Example
var ffi = require('ffi');
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.
libfficomes bundled with node-ffi; it does not need to be installed on your system.- The current version is tested to run on node v0.6, v0.8, v0.9 and v0.10.
Installation
Make sure you've installed all the necessary build
tools for your platform,
then invoke:
$ npm install ffi
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:
$ git clone git://github.com/node-ffi/node-ffi.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 (FP) 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.