XDR, for Javascript

Read/write XDR encoded data structures (RFC 4506)


XDR is an open data format, specified in
RFC 4506. This library provides a way
to read and write XDR data from javascript. It can read/write all of the
primitive XDR types and also provides facilities to define readers for the
compound XDR types (enums, structs and unions)

Installation

via npm:

``shell
npm install --save @stellar/js-xdr
`

Usage

You can find some examples here.

First, let's import the library:

`javascript
var xdr = require('@stellar/js-xdr');
// or
import xdr from '@stellar/js-xdr';
`

Now, let's look at how to decode some primitive types:

`javascript
// booleans
xdr.Bool.fromXDR([0, 0, 0, 0]); // returns false
xdr.Bool.fromXDR([0, 0, 0, 1]); // returns true

// the inverse of fromXDR is toXDR, which returns a Buffer
xdr.Bool.toXDR(true); // returns Buffer.from([0,0,0,1])

// XDR ints and unsigned ints can be safely represented as
// a javascript number

xdr.Int.fromXDR([0xff, 0xff, 0xff, 0xff]); // returns -1
xdr.UnsignedInt.fromXDR([0xff, 0xff, 0xff, 0xff]); // returns 4294967295

// XDR Hypers, however, cannot be safely represented in the 53-bits
// of precision we get with a JavaScript Number, so we allow creation from big-endian arrays of numbers, strings, or bigints.
var result = xdr.Hyper.fromXDR([0, 0, 0, 0, 0, 0, 0, 0]); // returns an instance of xdr.Hyper
result = new xdr.Hyper(0); // equivalent

// convert the hyper to a string
result.toString(); // return '0'

// math!
var ten = result.toBigInt() + 10;
var minusone = result.toBigInt() - 1;

// construct a number from a string
var big = xdr.Hyper.fromString('1099511627776');

// encode the hyper back into xdr
big.toXDR(); //
`

Caveats

There are a couple of caveats to be aware of with this library:

1. We do not support quadruple precision floating point values. Attempting to
read or write these values will throw errors.
2. NaN is not handled perfectly for floats and doubles. There are several forms
of NaN as defined by IEEE754 and the browser polyfill for node's Buffer
class seems to handle them poorly.

Code generation

js-xdr by itself does not have any ability to parse XDR IDL files and produce
a parser for your custom data types. Instead, that is the responsibility of
xdrgen. xdrgen will take your .x files
and produce a javascript file that target this library to allow for your own
custom types.

See stellar-base for an example
(check out the src/generated directory)

Contributing

Please see CONTRIBUTING.md for details.

$3

1. Clone the repo

`shell
git clone https://github.com/stellar/js-xdr.git
`

2. Install dependencies inside js-xdr folder

`shell
cd js-xdr
npm i
`

3. Install Node 14

Because we support the oldest maintenance version of Node, please install and
develop on Node 14 so you don't get surprised when your code works locally but
breaks in CI.

Here's out to install nvm if you haven't: https://github.com/creationix/nvm

`shell
nvm install

if you've never installed 14.x before you'll want to re-install yarn


npm install -g yarn
`

If you work on several projects that use different Node versions, you might it
helpful to install this automatic version manager:
https://github.com/wbyoung/avn

4. Observe the project's code style

While you're making changes, make sure to run the linter periodically to catch any linting errors (in addition to making sure your text editor supports ESLint)

`shell
yarn fmt
``

If you're working on a file not in src`, limit your code to Node 14! See what's
supported here: https://node.green/ (The reason is that our npm library must
support earlier versions of Node, so the tests need to run on those versions.)