Node-ffi NPM | npm.io

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("node-ffi");

var libm = new 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 = new ffi.Library(null, { "atoi": [ "int32", [ "string" ] ] });
current.atoi("1234"); // 1234

REQUIREMENTS

Linux, OS X, Windows, or Solaris.
libffi comes bundled with node-ffi, it does not need to be installed on your system.
The current version is tested to run on node 0.6.x.
If you need node 0.4.x support, use the 0.4 branch of node-ffi.

NPM INSTALL

$ npm install node-ffi

Most popular operating systems have a pre-compiled binary that comes along with node-ffi, so most of the time you will not need to compile anything! (Unless of course you want to, then see below).

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/rbranson/node-ffi.git
$ cd node-ffi
$ node-gyp configure build

TYPES

int8        Signed 8-bit Integer
uint8       Unsigned 8-bit Integer
int16       Signed 16-bit Integer
uint16      Unsigned 16-bit Integer
int32       Signed 32-bit Integer
uint32      Unsigned 32-bit Integer
int64       Signed 64-bit Integer
uint64      Unsigned 64-bit Integer
float       Single Precision Floating Point Number (float)
double      Double Precision Floating Point Number (double)
pointer     Pointer Type
string      Null-Terminated String (char *)

In addition to the basic types, there are type aliases for common C types.

byte        unsigned char
char        char
uchar       unsigned char
short       short
ushort      unsigned short
int         int
uint        unsigned int
long        long
ulong       unsigned long
longlong    long
ulonglong   unsigned long long
size_t      platform-dependent, usually pointer size

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 5x 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.