1.0.4 • Public • Published


    A super-quick FFI for Node.js.

    dyncall is used to make dynamic calls to native functions. In order to avoid some cost of translating JavaScript values into raw C types, a shared buffer is used for both arguments and return values. Writing values to a buffer turns out to be quite a bit faster than unpacking them in native code.


    sbffi.getNativeFunction(pathToSharedLibrary, functionName, returnType, [argType1, argType2, ...])

    All the arguments are strings. The types must be standard C types. See the Types section below for details. When functions take 64-bit types, the parameters must be passed as BigInts. 64-bit return values will also be BigInts.

    // adder.c: some C library compiled to 
    uint32_t add(uint32_t a, uint32_t b) {
      return a + b;
    // index.js
    const { getNativeFunction } = require('sbffi');
    const libPath = '/path/to/';
    const add = getNativeFunction(libPath, 'add', 'uint32_t', ['uint32_t', 'uint32_t']);
    const result = add(23, 34);
    // 57

    To specify a callback, identify it in the arguments array as [cbReturnType, [cbArgTyp1, cbArgType2, ...]].


    The following types are supported:

    • (u)int[8|16|32|64]_t
    • bool
    • (unsigned) char
    • (unsigned) short
    • (unsigned) int
    • (unsigned) long
    • (unsigned) long long
    • float
    • double
    • size_t

    128-bit types are not yet supported, and while this list may grow over time, for now other types can be used if they're aliases of the above types.

    See the section below about pointers.


    Pointers are currently assumed to be 64-bit, and can be passed to native functions by specifying the type as pointer or referring to any other type with an asterisk in the string, for example: uint8_t *.

    You can put raw data into a Buffer, and then get a pointer to the start of that buffer with:

    const bufferPointer = sbffi.getBufferPointer(buffer);

    Arrays and strings must be passed as pointers.


    For now, sbfffi doesn't have any built-in support for structs. That being said, there are some helpful libraries like shared-structs and ref-napi (and its family of modules). As long as you can build up a C struct into a Buffer, you can pass pointers to them into C functions. Non-pointer struct arguments or return values are not supported.


    Using a non-release version of sbffi requires that cmake is installed in order to compile the native addon.


    A simple benchmark can be run with npm run bench. This will test calling a simple adding function from the test library using the following techniques:

    • ffi-napi: A successor to node-ffi compatible with modern versions of Node.js.
    • sbffi: This library.
    • napi-addon: A very simple/normal Node.js addon using NAPI in C.
    • napi-addon-sb: A NAPI addon using the same shared-buffer technique as sbffi, but with a hard-coded function call, rather than a dynamic/FFI call.
    • wasm: The adding function compiled to WebAssembly.
    • js: Re-implementing the function in plain JavaScript.

    Each function will be called 100000 times, in 5 repetitions, timed with console.time(). Here are the results on my machine (2019 Lenovo X1 Extreme, running Ubuntu, Node v12):

    ffi-napi: 1103.680ms
    sbffi: 39.981ms
    napi-addon: 8.214ms
    napi-addon-sb: 6.795ms
    wasm: 2.802ms
    js: 2.644ms
    ffi-napi: 1128.388ms
    sbffi: 97.446ms
    napi-addon: 3.631ms
    napi-addon-sb: 3.308ms
    wasm: 0.918ms
    js: 0.045ms
    ffi-napi: 1419.159ms
    sbffi: 29.797ms
    napi-addon: 3.946ms
    napi-addon-sb: 3.717ms
    wasm: 0.871ms
    js: 0.090ms
    ffi-napi: 1285.210ms
    sbffi: 73.335ms
    napi-addon: 4.618ms
    napi-addon-sb: 3.651ms
    wasm: 0.930ms
    js: 0.096ms
    ffi-napi: 772.013ms
    sbffi: 29.467ms
    napi-addon: 3.790ms
    napi-addon-sb: 3.352ms
    wasm: 0.847ms
    js: 0.087ms

    Of course, YMMV.


    Please see, and


    Please see LICENSE.txt.


    npm i sbffi

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