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ref-napi

Turn Buffer instances into "pointers"

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This module is inspired by the old Pointer class from node-ffi, but with the intent of using Node's fast Buffer instances instead of a slow C++ Pointer class. These two concepts were previously very similar, but now this module brings over the functionality that Pointers had and Buffers are missing, so now Buffers are a lot more powerful.

Features:

  • Get the memory address of any Buffer instance
  • Read/write references to JavaScript Objects into Buffer instances
  • Read/write Buffer instances' memory addresses to other Buffer instances
  • Read/write int64_t and uint64_t data values (Numbers or Strings)
  • A "type" convention, so that you can specify a buffer as an int *, and reference/dereference at will.
  • Offers a buffer instance representing the NULL pointer

Installation

Install with npm:

$ npm install ref-napi

Examples

referencing and derefencing

var ref = require('ref-napi')

// so we can all agree that a buffer with the int value written
// to it could be represented as an "int *"
var buf = new Buffer(4)
buf.writeInt32LE(12345, 0)

// first, what is the memory address of the buffer?
console.log(buf.hexAddress())  // ← '7FA89D006FD8'

// using `ref`, you can set the "type", and gain magic abilities!
buf.type = ref.types.int

// now we can dereference to get the "meaningful" value
console.log(buf.deref())  // ← 12345


// you can also get references to the original buffer if you need it.
// this buffer could be thought of as an "int **"
var one = buf.ref()

// and you can dereference all the way back down to an int
console.log(one.deref().deref())  // ← 12345

See the full API Docs for more examples.

The "type" interface

You can easily define your own "type" objects at attach to Buffer instances. It just needs to be a regular JavaScript Object that contains the following properties:

Name Data Type Description
size Number The size in bytes required to hold this type.
indirection Number The current level of indirection of the buffer. Usually this would be 1, and gets incremented on Buffers from ref() calls. A value of less than or equal to 0 is invalid.
get Function (buffer, offset) The function to invoke when dereferencing this type when the indirection level is 1.
set Function (buffer, offset, value) The function to invoke when setting a value to a buffer instance.
name String (optional) The name to use during debugging for this type.
alignment Number (optional) The alignment of this type when placed in a struct. Defaults to the type's size.

Be sure to check out the Wiki page of "Known Types", for the list of built-in ref types, as well as known external type implementations.

For example, you could define a "bigint" type that dereferences into a bigint instance:

var ref = require('ref-napi')
var bigint = require('bigint')

// define the "type" instance according to the spec
var BigintType = {
    size: ref.sizeof.int64
  , indirection: 1
  , get: function (buffer, offset) {
      // return a bigint instance from the buffer
      return bigint.fromBuffer(buffer)
    }
  , set: function (buffer, offset, value) {
      // 'value' would be a bigint instance
      var val = value.toString()
      return ref.writeInt64(buffer, offset || 0, val)
    }
}

// now we can create instances of the type from existing buffers.
// "buf" is some Buffer instance returned from some external data
// source, which should contain "bigint" binary data.
buf.type = BigintType

// and now you can create "bigint" instances using this generic "types" API
var val = buf.deref()
            .add('1234')
            .sqrt()
            .shiftLeft(5)

Build the docs

Install the dev dependencies:

$ npm install

Generate the docs:

$ npm run docs

Incompatible packages

The ref-struct-napi and ref-array-napi packages have names that sound like they are compatible with this module.

They are not, and your application will experience crashes if you use them together with ref-napi. Use ref-struct-di or ref-array-di instead.

License

(The MIT License)

Copyright (c) 2012 Nathan Rajlich <nathan@tootallnate.net> Copyright (c) 2017 Anna Henningsen <anna@addaleax.net> (N-API port)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.